Android APIs
public class

NestedScrollView

extends FrameLayout
implements NestedScrollingParent NestedScrollingChild
java.lang.Object
   ↳ android.view.View
     ↳ android.view.ViewGroup
       ↳ android.widget.FrameLayout
         ↳ android.support.v4.widget.NestedScrollView

Class Overview

NestedScrollView is just like ScrollView, but it supports acting as both a nested scrolling parent and child on both new and old versions of Android. Nested scrolling is enabled by default.

Summary

XML Attributes
Attribute Name Related Method Description
android:fillViewport setFillViewport(boolean) Defines whether the scrollview should stretch its content to fill the viewport. 
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Inherited XML Attributes
From class android.widget.FrameLayout
From class android.view.ViewGroup
From class android.view.View
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Inherited Constants
From class android.view.ViewGroup
From class android.view.View
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Inherited Fields
From class android.view.View
Public Constructors
NestedScrollView(Context context)
NestedScrollView(Context context, AttributeSet attrs)
NestedScrollView(Context context, AttributeSet attrs, int defStyleAttr)
Public Methods
void addView(View child, int index)
Adds a child view.
void addView(View child, int index, ViewGroup.LayoutParams params)
Adds a child view with the specified layout parameters.
void addView(View child)

Adds a child view.

void addView(View child, ViewGroup.LayoutParams params)
Adds a child view with the specified layout parameters.
boolean arrowScroll(int direction)
Handle scrolling in response to an up or down arrow click.
void computeScroll()
Called by a parent to request that a child update its values for mScrollX and mScrollY if necessary.
boolean dispatchKeyEvent(KeyEvent event)
Dispatch a key event to the next view on the focus path.
boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed)
Dispatch a fling to a nested scrolling parent.
boolean dispatchNestedPreFling(float velocityX, float velocityY)
Dispatch a fling to a nested scrolling parent before it is processed by this view.
boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow)
Dispatch one step of a nested scroll in progress before this view consumes any portion of it.
boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow)
Dispatch one step of a nested scroll in progress.
void draw(Canvas canvas)
Manually render this view (and all of its children) to the given Canvas.
boolean executeKeyEvent(KeyEvent event)
You can call this function yourself to have the scroll view perform scrolling from a key event, just as if the event had been dispatched to it by the view hierarchy.
void fling(int velocityY)
Fling the scroll view
boolean fullScroll(int direction)

Handles scrolling in response to a "home/end" shortcut press.

int getMaxScrollAmount()
int getNestedScrollAxes()
Return the current axes of nested scrolling for this ViewGroup.
boolean hasNestedScrollingParent()
Returns true if this view has a nested scrolling parent.
boolean isFillViewport()
Indicates whether this ScrollView's content is stretched to fill the viewport.
boolean isNestedScrollingEnabled()
Returns true if nested scrolling is enabled for this view.
boolean isSmoothScrollingEnabled()
void onAttachedToWindow()
This is called when the view is attached to a window.
boolean onGenericMotionEvent(MotionEvent event)
Implement this method to handle generic motion events.
boolean onInterceptTouchEvent(MotionEvent ev)
Implement this method to intercept all touch screen motion events.
boolean onNestedFling(View target, float velocityX, float velocityY, boolean consumed)
Request a fling from a nested scroll.
boolean onNestedPreFling(View target, float velocityX, float velocityY)
React to a nested fling before the target view consumes it.
void onNestedPreScroll(View target, int dx, int dy, int[] consumed)
React to a nested scroll in progress before the target view consumes a portion of the scroll.
void onNestedScroll(View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed)
React to a nested scroll in progress.
void onNestedScrollAccepted(View child, View target, int nestedScrollAxes)
React to the successful claiming of a nested scroll operation.
boolean onStartNestedScroll(View child, View target, int nestedScrollAxes)
React to a descendant view initiating a nestable scroll operation, claiming the nested scroll operation if appropriate.
void onStopNestedScroll(View target)
React to a nested scroll operation ending.
boolean onTouchEvent(MotionEvent ev)
Implement this method to handle touch screen motion events.
boolean pageScroll(int direction)

Handles scrolling in response to a "page up/down" shortcut press.

void requestChildFocus(View child, View focused)
Called when a child of this parent wants focus
boolean requestChildRectangleOnScreen(View child, Rect rectangle, boolean immediate)
Called when a child of this group wants a particular rectangle to be positioned onto the screen.
void requestDisallowInterceptTouchEvent(boolean disallowIntercept)
Called when a child does not want this parent and its ancestors to intercept touch events with onInterceptTouchEvent(MotionEvent).
void requestLayout()
Call this when something has changed which has invalidated the layout of this view.
void scrollTo(int x, int y)
Set the scrolled position of your view.

This version also clamps the scrolling to the bounds of our child.

void setFillViewport(boolean fillViewport)
Indicates this ScrollView whether it should stretch its content height to fill the viewport or not.
void setNestedScrollingEnabled(boolean enabled)
Enable or disable nested scrolling for this view.
void setSmoothScrollingEnabled(boolean smoothScrollingEnabled)
Set whether arrow scrolling will animate its transition.
boolean shouldDelayChildPressedState()
Return true if the pressed state should be delayed for children or descendants of this ViewGroup.
final void smoothScrollBy(int dx, int dy)
Like scrollBy(int, int), but scroll smoothly instead of immediately.
final void smoothScrollTo(int x, int y)
Like scrollTo(int, int), but scroll smoothly instead of immediately.
boolean startNestedScroll(int axes)
Begin a nestable scroll operation along the given axes.
void stopNestedScroll()
Stop a nested scroll in progress.
Protected Methods
int computeScrollDeltaToGetChildRectOnScreen(Rect rect)
Compute the amount to scroll in the Y direction in order to get a rectangle completely on the screen (or, if taller than the screen, at least the first screen size chunk of it).
int computeVerticalScrollOffset()

Compute the vertical offset of the vertical scrollbar's thumb within the horizontal range.

int computeVerticalScrollRange()

The scroll range of a scroll view is the overall height of all of its children.

float getBottomFadingEdgeStrength()
Returns the strength, or intensity, of the bottom faded edge.
float getTopFadingEdgeStrength()
Returns the strength, or intensity, of the top faded edge.
void measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)
Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding.
void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed)
Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding and margins.
void onLayout(boolean changed, int l, int t, int r, int b)
Called from layout when this view should assign a size and position to each of its children.
void onMeasure(int widthMeasureSpec, int heightMeasureSpec)

Measure the view and its content to determine the measured width and the measured height.

void onOverScrolled(int scrollX, int scrollY, boolean clampedX, boolean clampedY)
Called by overScrollBy(int, int, int, int, int, int, int, int, boolean) to respond to the results of an over-scroll operation.
boolean onRequestFocusInDescendants(int direction, Rect previouslyFocusedRect)
When looking for focus in children of a scroll view, need to be a little more careful not to give focus to something that is scrolled off screen.
void onRestoreInstanceState(Parcelable state)
Hook allowing a view to re-apply a representation of its internal state that had previously been generated by onSaveInstanceState().
Parcelable onSaveInstanceState()
Hook allowing a view to generate a representation of its internal state that can later be used to create a new instance with that same state.
void onSizeChanged(int w, int h, int oldw, int oldh)
This is called during layout when the size of this view has changed.
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Inherited Methods
From class android.widget.FrameLayout
From class android.view.ViewGroup
From class android.view.View
From class java.lang.Object
From interface android.view.ViewParent
From interface android.view.ViewManager
From interface android.graphics.drawable.Drawable.Callback
From interface android.view.KeyEvent.Callback
From interface android.view.accessibility.AccessibilityEventSource
From interface android.support.v4.view.NestedScrollingParent
From interface android.support.v4.view.NestedScrollingChild

XML Attributes

android:fillViewport

Defines whether the scrollview should stretch its content to fill the viewport.

Must be a boolean value, either "true" or "false".

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form "?[package:][type:]name") containing a value of this type.

This corresponds to the global attribute resource symbol fillViewport.

Related Methods

Public Constructors

public NestedScrollView (Context context)

public NestedScrollView (Context context, AttributeSet attrs)

public NestedScrollView (Context context, AttributeSet attrs, int defStyleAttr)

Public Methods

public void addView (View child, int index)

Adds a child view. If no layout parameters are already set on the child, the default parameters for this ViewGroup are set on the child.

Note: do not invoke this method from draw(android.graphics.Canvas), onDraw(android.graphics.Canvas), dispatchDraw(android.graphics.Canvas) or any related method.

Parameters
child the child view to add
index the position at which to add the child

public void addView (View child, int index, ViewGroup.LayoutParams params)

Adds a child view with the specified layout parameters.

Note: do not invoke this method from draw(android.graphics.Canvas), onDraw(android.graphics.Canvas), dispatchDraw(android.graphics.Canvas) or any related method.

Parameters
child the child view to add
index the position at which to add the child or -1 to add last
params the layout parameters to set on the child

public void addView (View child)

Adds a child view. If no layout parameters are already set on the child, the default parameters for this ViewGroup are set on the child.

Note: do not invoke this method from draw(android.graphics.Canvas), onDraw(android.graphics.Canvas), dispatchDraw(android.graphics.Canvas) or any related method.

Parameters
child the child view to add

public void addView (View child, ViewGroup.LayoutParams params)

Adds a child view with the specified layout parameters.

Note: do not invoke this method from draw(android.graphics.Canvas), onDraw(android.graphics.Canvas), dispatchDraw(android.graphics.Canvas) or any related method.

Parameters
child the child view to add
params the layout parameters to set on the child

public boolean arrowScroll (int direction)

Handle scrolling in response to an up or down arrow click.

Parameters
direction The direction corresponding to the arrow key that was pressed
Returns
  • True if we consumed the event, false otherwise

public void computeScroll ()

Called by a parent to request that a child update its values for mScrollX and mScrollY if necessary. This will typically be done if the child is animating a scroll using a Scroller object.

public boolean dispatchKeyEvent (KeyEvent event)

Dispatch a key event to the next view on the focus path. This path runs from the top of the view tree down to the currently focused view. If this view has focus, it will dispatch to itself. Otherwise it will dispatch the next node down the focus path. This method also fires any key listeners.

Parameters
event The key event to be dispatched.
Returns
  • True if the event was handled, false otherwise.

public boolean dispatchNestedFling (float velocityX, float velocityY, boolean consumed)

Dispatch a fling to a nested scrolling parent.

This method should be used to indicate that a nested scrolling child has detected suitable conditions for a fling. Generally this means that a touch scroll has ended with a velocity in the direction of scrolling that meets or exceeds the minimum fling velocity along a scrollable axis.

If a nested scrolling child view would normally fling but it is at the edge of its own content, it can use this method to delegate the fling to its nested scrolling parent instead. The parent may optionally consume the fling or observe a child fling.

Parameters
velocityX Horizontal fling velocity in pixels per second
velocityY Vertical fling velocity in pixels per second
consumed true if the child consumed the fling, false otherwise
Returns
  • true if the nested scrolling parent consumed or otherwise reacted to the fling

public boolean dispatchNestedPreFling (float velocityX, float velocityY)

Dispatch a fling to a nested scrolling parent before it is processed by this view.

Nested pre-fling events are to nested fling events what touch intercept is to touch and what nested pre-scroll is to nested scroll. dispatchNestedPreFling offsets an opportunity for the parent view in a nested fling to fully consume the fling before the child view consumes it. If this method returns true, a nested parent view consumed the fling and this view should not scroll as a result.

For a better user experience, only one view in a nested scrolling chain should consume the fling at a time. If a parent view consumed the fling this method will return false. Custom view implementations should account for this in two ways:

  • If a custom view is paged and needs to settle to a fixed page-point, do not call dispatchNestedPreFling; consume the fling and settle to a valid position regardless.
  • If a nested parent does consume the fling, this view should not scroll at all, even to settle back to a valid idle position.

Views should also not offer fling velocities to nested parent views along an axis where scrolling is not currently supported; a ScrollView should not offer a horizontal fling velocity to its parents since scrolling along that axis is not permitted and carrying velocity along that motion does not make sense.

Parameters
velocityX Horizontal fling velocity in pixels per second
velocityY Vertical fling velocity in pixels per second
Returns
  • true if a nested scrolling parent consumed the fling

public boolean dispatchNestedPreScroll (int dx, int dy, int[] consumed, int[] offsetInWindow)

Dispatch one step of a nested scroll in progress before this view consumes any portion of it.

Nested pre-scroll events are to nested scroll events what touch intercept is to touch. dispatchNestedPreScroll offers an opportunity for the parent view in a nested scrolling operation to consume some or all of the scroll operation before the child view consumes it.

Parameters
dx Horizontal scroll distance in pixels
dy Vertical scroll distance in pixels
consumed Output. If not null, consumed[0] will contain the consumed component of dx and consumed[1] the consumed dy.
offsetInWindow Optional. If not null, on return this will contain the offset in local view coordinates of this view from before this operation to after it completes. View implementations may use this to adjust expected input coordinate tracking.
Returns
  • true if the parent consumed some or all of the scroll delta

public boolean dispatchNestedScroll (int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow)

Dispatch one step of a nested scroll in progress.

Implementations of views that support nested scrolling should call this to report info about a scroll in progress to the current nested scrolling parent. If a nested scroll is not currently in progress or nested scrolling is not enabled for this view this method does nothing.

Compatible View implementations should also call dispatchNestedPreScroll before consuming a component of the scroll event themselves.

Parameters
dxConsumed Horizontal distance in pixels consumed by this view during this scroll step
dyConsumed Vertical distance in pixels consumed by this view during this scroll step
dxUnconsumed Horizontal scroll distance in pixels not consumed by this view
dyUnconsumed Horizontal scroll distance in pixels not consumed by this view
offsetInWindow Optional. If not null, on return this will contain the offset in local view coordinates of this view from before this operation to after it completes. View implementations may use this to adjust expected input coordinate tracking.
Returns
  • true if the event was dispatched, false if it could not be dispatched.

public void draw (Canvas canvas)

Manually render this view (and all of its children) to the given Canvas. The view must have already done a full layout before this function is called. When implementing a view, implement onDraw(android.graphics.Canvas) instead of overriding this method. If you do need to override this method, call the superclass version.

Parameters
canvas The Canvas to which the View is rendered.

public boolean executeKeyEvent (KeyEvent event)

You can call this function yourself to have the scroll view perform scrolling from a key event, just as if the event had been dispatched to it by the view hierarchy.

Parameters
event The key event to execute.
Returns
  • Return true if the event was handled, else false.

public void fling (int velocityY)

Fling the scroll view

Parameters
velocityY The initial velocity in the Y direction. Positive numbers mean that the finger/cursor is moving down the screen, which means we want to scroll towards the top.

public boolean fullScroll (int direction)

Handles scrolling in response to a "home/end" shortcut press. This method will scroll the view to the top or bottom and give the focus to the topmost/bottommost component in the new visible area. If no component is a good candidate for focus, this scrollview reclaims the focus.

Parameters
direction the scroll direction: FOCUS_UP to go the top of the view or FOCUS_DOWN to go the bottom
Returns
  • true if the key event is consumed by this method, false otherwise

public int getMaxScrollAmount ()

Returns
  • The maximum amount this scroll view will scroll in response to an arrow event.

public int getNestedScrollAxes ()

Return the current axes of nested scrolling for this ViewGroup.

A ViewGroup returning something other than SCROLL_AXIS_NONE is currently acting as a nested scrolling parent for one or more descendant views in the hierarchy.

Returns
  • Flags indicating the current axes of nested scrolling

public boolean hasNestedScrollingParent ()

Returns true if this view has a nested scrolling parent.

The presence of a nested scrolling parent indicates that this view has initiated a nested scroll and it was accepted by an ancestor view further up the view hierarchy.

Returns
  • whether this view has a nested scrolling parent

public boolean isFillViewport ()

Indicates whether this ScrollView's content is stretched to fill the viewport.

Related XML Attributes
Returns
  • True if the content fills the viewport, false otherwise.

public boolean isNestedScrollingEnabled ()

Returns true if nested scrolling is enabled for this view.

If nested scrolling is enabled and this View class implementation supports it, this view will act as a nested scrolling child view when applicable, forwarding data about the scroll operation in progress to a compatible and cooperating nested scrolling parent.

Returns
  • true if nested scrolling is enabled

public boolean isSmoothScrollingEnabled ()

Returns
  • Whether arrow scrolling will animate its transition.

public void onAttachedToWindow ()

This is called when the view is attached to a window. At this point it has a Surface and will start drawing. Note that this function is guaranteed to be called before onDraw(android.graphics.Canvas), however it may be called any time before the first onDraw -- including before or after onMeasure(int, int).

public boolean onGenericMotionEvent (MotionEvent event)

Implement this method to handle generic motion events.

Generic motion events describe joystick movements, mouse hovers, track pad touches, scroll wheel movements and other input events. The source of the motion event specifies the class of input that was received. Implementations of this method must examine the bits in the source before processing the event. The following code example shows how this is done.

Generic motion events with source class SOURCE_CLASS_POINTER are delivered to the view under the pointer. All other generic motion events are delivered to the focused view. 

 public boolean onGenericMotionEvent(MotionEvent event) {
     if (event.isFromSource(InputDevice.SOURCE_CLASS_JOYSTICK)) {
         if (event.getAction() == MotionEvent.ACTION_MOVE) {
             // process the joystick movement...
             return true;
         }
     }
     if (event.isFromSource(InputDevice.SOURCE_CLASS_POINTER)) {
         switch (event.getAction()) {
             case MotionEvent.ACTION_HOVER_MOVE:
                 // process the mouse hover movement...
                 return true;
             case MotionEvent.ACTION_SCROLL:
                 // process the scroll wheel movement...
                 return true;
         }
     }
     return super.onGenericMotionEvent(event);
 }

Parameters
event The generic motion event being processed.
Returns
  • True if the event was handled, false otherwise.

public boolean onInterceptTouchEvent (MotionEvent ev)

Implement this method to intercept all touch screen motion events. This allows you to watch events as they are dispatched to your children, and take ownership of the current gesture at any point.

Using this function takes some care, as it has a fairly complicated interaction with View.onTouchEvent(MotionEvent), and using it requires implementing that method as well as this one in the correct way. Events will be received in the following order:

  1. You will receive the down event here.
  2. The down event will be handled either by a child of this view group, or given to your own onTouchEvent() method to handle; this means you should implement onTouchEvent() to return true, so you will continue to see the rest of the gesture (instead of looking for a parent view to handle it). Also, by returning true from onTouchEvent(), you will not receive any following events in onInterceptTouchEvent() and all touch processing must happen in onTouchEvent() like normal.
  3. For as long as you return false from this function, each following event (up to and including the final up) will be delivered first here and then to the target's onTouchEvent().
  4. If you return true from here, you will not receive any following events: the target view will receive the same event but with the action ACTION_CANCEL, and all further events will be delivered to your onTouchEvent() method and no longer appear here.

Parameters
ev The motion event being dispatched down the hierarchy.
Returns
  • Return true to steal motion events from the children and have them dispatched to this ViewGroup through onTouchEvent(). The current target will receive an ACTION_CANCEL event, and no further messages will be delivered here.

public boolean onNestedFling (View target, float velocityX, float velocityY, boolean consumed)

Request a fling from a nested scroll.

This method signifies that a nested scrolling child has detected suitable conditions for a fling. Generally this means that a touch scroll has ended with a velocity in the direction of scrolling that meets or exceeds the minimum fling velocity along a scrollable axis.

If a nested scrolling child view would normally fling but it is at the edge of its own content, it can use this method to delegate the fling to its nested scrolling parent instead. The parent may optionally consume the fling or observe a child fling.

Parameters
target View that initiated the nested scroll
velocityX Horizontal velocity in pixels per second
velocityY Vertical velocity in pixels per second
consumed true if the child consumed the fling, false otherwise
Returns
  • true if this parent consumed or otherwise reacted to the fling

public boolean onNestedPreFling (View target, float velocityX, float velocityY)

React to a nested fling before the target view consumes it.

This method siginfies that a nested scrolling child has detected a fling with the given velocity along each axis. Generally this means that a touch scroll has ended with a velocity in the direction of scrolling that meets or exceeds the minimum fling velocity along a scrollable axis.

If a nested scrolling parent is consuming motion as part of a pre-scroll, it may be appropriate for it to also consume the pre-fling to complete that same motion. By returning true from this method, the parent indicates that the child should not fling its own internal content as well.

Parameters
target View that initiated the nested scroll
velocityX Horizontal velocity in pixels per second
velocityY Vertical velocity in pixels per second
Returns
  • true if this parent consumed the fling ahead of the target view

public void onNestedPreScroll (View target, int dx, int dy, int[] consumed)

React to a nested scroll in progress before the target view consumes a portion of the scroll.

When working with nested scrolling often the parent view may want an opportunity to consume the scroll before the nested scrolling child does. An example of this is a drawer that contains a scrollable list. The user will want to be able to scroll the list fully into view before the list itself begins scrolling.

onNestedPreScroll is called when a nested scrolling child invokes dispatchNestedPreScroll(int, int, int[], int[]). The implementation should report how any pixels of the scroll reported by dx, dy were consumed in the consumed array. Index 0 corresponds to dx and index 1 corresponds to dy. This parameter will never be null. Initial values for consumed[0] and consumed[1] will always be 0.

Parameters
target View that initiated the nested scroll
dx Horizontal scroll distance in pixels
dy Vertical scroll distance in pixels
consumed Output. The horizontal and vertical scroll distance consumed by this parent

public void onNestedScroll (View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed)

React to a nested scroll in progress.

This method will be called when the ViewParent's current nested scrolling child view dispatches a nested scroll event. To receive calls to this method the ViewParent must have previously returned true for a call to onStartNestedScroll(View, View, int).

Both the consumed and unconsumed portions of the scroll distance are reported to the ViewParent. An implementation may choose to use the consumed portion to match or chase scroll position of multiple child elements, for example. The unconsumed portion may be used to allow continuous dragging of multiple scrolling or draggable elements, such as scrolling a list within a vertical drawer where the drawer begins dragging once the edge of inner scrolling content is reached.

Parameters
target The descendent view controlling the nested scroll
dxConsumed Horizontal scroll distance in pixels already consumed by target
dyConsumed Vertical scroll distance in pixels already consumed by target
dxUnconsumed Horizontal scroll distance in pixels not consumed by target
dyUnconsumed Vertical scroll distance in pixels not consumed by target

public void onNestedScrollAccepted (View child, View target, int nestedScrollAxes)

React to the successful claiming of a nested scroll operation.

This method will be called after onStartNestedScroll returns true. It offers an opportunity for the view and its superclasses to perform initial configuration for the nested scroll. Implementations of this method should always call their superclass's implementation of this method if one is present.

Parameters
child Direct child of this ViewParent containing target
target View that initiated the nested scroll
nestedScrollAxes Flags consisting of SCROLL_AXIS_HORIZONTAL, SCROLL_AXIS_VERTICAL or both

public boolean onStartNestedScroll (View child, View target, int nestedScrollAxes)

React to a descendant view initiating a nestable scroll operation, claiming the nested scroll operation if appropriate.

This method will be called in response to a descendant view invoking startNestedScroll(int). Each parent up the view hierarchy will be given an opportunity to respond and claim the nested scrolling operation by returning true.

This method may be overridden by ViewParent implementations to indicate when the view is willing to support a nested scrolling operation that is about to begin. If it returns true, this ViewParent will become the target view's nested scrolling parent for the duration of the scroll operation in progress. When the nested scroll is finished this ViewParent will receive a call to onStopNestedScroll(View).

Parameters
child Direct child of this ViewParent containing target
target View that initiated the nested scroll
nestedScrollAxes Flags consisting of SCROLL_AXIS_HORIZONTAL, SCROLL_AXIS_VERTICAL or both
Returns
  • true if this ViewParent accepts the nested scroll operation

public void onStopNestedScroll (View target)

React to a nested scroll operation ending.

Perform cleanup after a nested scrolling operation. This method will be called when a nested scroll stops, for example when a nested touch scroll ends with a ACTION_UP or ACTION_CANCEL event. Implementations of this method should always call their superclass's implementation of this method if one is present.

Parameters
target View that initiated the nested scroll

public boolean onTouchEvent (MotionEvent ev)

Implement this method to handle touch screen motion events.

If this method is used to detect click actions, it is recommended that the actions be performed by implementing and calling performClick(). This will ensure consistent system behavior, including:

  • obeying click sound preferences
  • dispatching OnClickListener calls
  • handling ACTION_CLICK when accessibility features are enabled

Parameters
ev The motion event.
Returns
  • True if the event was handled, false otherwise.

public boolean pageScroll (int direction)

Handles scrolling in response to a "page up/down" shortcut press. This method will scroll the view by one page up or down and give the focus to the topmost/bottommost component in the new visible area. If no component is a good candidate for focus, this scrollview reclaims the focus.

Parameters
direction the scroll direction: FOCUS_UP to go one page up or FOCUS_DOWN to go one page down
Returns
  • true if the key event is consumed by this method, false otherwise

public void requestChildFocus (View child, View focused)

Called when a child of this parent wants focus

Parameters
child The child of this ViewParent that wants focus. This view will contain the focused view. It is not necessarily the view that actually has focus.
focused The view that is a descendant of child that actually has focus

public boolean requestChildRectangleOnScreen (View child, Rect rectangle, boolean immediate)

Called when a child of this group wants a particular rectangle to be positioned onto the screen. ViewGroups overriding this can trust that:

  • child will be a direct child of this group
  • rectangle will be in the child's coordinates

ViewGroups overriding this should uphold the contract:

  • nothing will change if the rectangle is already visible
  • the view port will be scrolled only just enough to make the rectangle visible

Parameters
child The direct child making the request.
rectangle The rectangle in the child's coordinates the child wishes to be on the screen.
immediate True to forbid animated or delayed scrolling, false otherwise
Returns
  • Whether the group scrolled to handle the operation

public void requestDisallowInterceptTouchEvent (boolean disallowIntercept)

Called when a child does not want this parent and its ancestors to intercept touch events with onInterceptTouchEvent(MotionEvent).

This parent should pass this call onto its parents. This parent must obey this request for the duration of the touch (that is, only clear the flag after this parent has received an up or a cancel.

Parameters
disallowIntercept True if the child does not want the parent to intercept touch events.

public void requestLayout ()

Call this when something has changed which has invalidated the layout of this view. This will schedule a layout pass of the view tree. This should not be called while the view hierarchy is currently in a layout pass (isInLayout(). If layout is happening, the request may be honored at the end of the current layout pass (and then layout will run again) or after the current frame is drawn and the next layout occurs.

Subclasses which override this method should call the superclass method to handle possible request-during-layout errors correctly.

public void scrollTo (int x, int y)

Set the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int) and the view will be invalidated.

This version also clamps the scrolling to the bounds of our child.

Parameters
x the x position to scroll to
y the y position to scroll to

public void setFillViewport (boolean fillViewport)

Indicates this ScrollView whether it should stretch its content height to fill the viewport or not.

Related XML Attributes
Parameters
fillViewport True to stretch the content's height to the viewport's boundaries, false otherwise.

public void setNestedScrollingEnabled (boolean enabled)

Enable or disable nested scrolling for this view.

If this property is set to true the view will be permitted to initiate nested scrolling operations with a compatible parent view in the current hierarchy. If this view does not implement nested scrolling this will have no effect. Disabling nested scrolling while a nested scroll is in progress has the effect of stopping the nested scroll.

Parameters
enabled true to enable nested scrolling, false to disable

public void setSmoothScrollingEnabled (boolean smoothScrollingEnabled)

Set whether arrow scrolling will animate its transition.

Parameters
smoothScrollingEnabled whether arrow scrolling will animate its transition

public boolean shouldDelayChildPressedState ()

Return true if the pressed state should be delayed for children or descendants of this ViewGroup. Generally, this should be done for containers that can scroll, such as a List. This prevents the pressed state from appearing when the user is actually trying to scroll the content. The default implementation returns true for compatibility reasons. Subclasses that do not scroll should generally override this method and return false.

public final void smoothScrollBy (int dx, int dy)

Like scrollBy(int, int), but scroll smoothly instead of immediately.

Parameters
dx the number of pixels to scroll by on the X axis
dy the number of pixels to scroll by on the Y axis

public final void smoothScrollTo (int x, int y)

Like scrollTo(int, int), but scroll smoothly instead of immediately.

Parameters
x the position where to scroll on the X axis
y the position where to scroll on the Y axis

public boolean startNestedScroll (int axes)

Begin a nestable scroll operation along the given axes.

A view starting a nested scroll promises to abide by the following contract:

The view will call startNestedScroll upon initiating a scroll operation. In the case of a touch scroll this corresponds to the initial ACTION_DOWN. In the case of touch scrolling the nested scroll will be terminated automatically in the same manner as requestDisallowInterceptTouchEvent(boolean). In the event of programmatic scrolling the caller must explicitly call stopNestedScroll() to indicate the end of the nested scroll.

If startNestedScroll returns true, a cooperative parent was found. If it returns false the caller may ignore the rest of this contract until the next scroll. Calling startNestedScroll while a nested scroll is already in progress will return true.

At each incremental step of the scroll the caller should invoke dispatchNestedPreScroll once it has calculated the requested scrolling delta. If it returns true the nested scrolling parent at least partially consumed the scroll and the caller should adjust the amount it scrolls by.

After applying the remainder of the scroll delta the caller should invoke dispatchNestedScroll, passing both the delta consumed and the delta unconsumed. A nested scrolling parent may treat these values differently. See onNestedScroll(View, int, int, int, int).

Parameters
axes Flags consisting of a combination of SCROLL_AXIS_HORIZONTAL and/or SCROLL_AXIS_VERTICAL.
Returns
  • true if a cooperative parent was found and nested scrolling has been enabled for the current gesture.

public void stopNestedScroll ()

Stop a nested scroll in progress.

Calling this method when a nested scroll is not currently in progress is harmless.

Protected Methods

protected int computeScrollDeltaToGetChildRectOnScreen (Rect rect)

Compute the amount to scroll in the Y direction in order to get a rectangle completely on the screen (or, if taller than the screen, at least the first screen size chunk of it).

Parameters
rect The rect.
Returns
  • The scroll delta.

protected int computeVerticalScrollOffset ()

Compute the vertical offset of the vertical scrollbar's thumb within the horizontal range. This value is used to compute the position of the thumb within the scrollbar's track.

The range is expressed in arbitrary units that must be the same as the units used by computeVerticalScrollRange() and computeVerticalScrollExtent().

The default offset is the scroll offset of this view.

Returns
  • the vertical offset of the scrollbar's thumb

protected int computeVerticalScrollRange ()

The scroll range of a scroll view is the overall height of all of its children.

Returns
  • the total vertical range represented by the vertical scrollbar

    The default range is the drawing height of this view.

protected float getBottomFadingEdgeStrength ()

Returns the strength, or intensity, of the bottom faded edge. The strength is a value between 0.0 (no fade) and 1.0 (full fade). The default implementation returns 0.0 or 1.0 but no value in between. Subclasses should override this method to provide a smoother fade transition when scrolling occurs.

Returns
  • the intensity of the bottom fade as a float between 0.0f and 1.0f

protected float getTopFadingEdgeStrength ()

Returns the strength, or intensity, of the top faded edge. The strength is a value between 0.0 (no fade) and 1.0 (full fade). The default implementation returns 0.0 or 1.0 but no value in between. Subclasses should override this method to provide a smoother fade transition when scrolling occurs.

Returns
  • the intensity of the top fade as a float between 0.0f and 1.0f

protected void measureChild (View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)

Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding. The heavy lifting is done in getChildMeasureSpec.

Parameters
child The child to measure
parentWidthMeasureSpec The width requirements for this view
parentHeightMeasureSpec The height requirements for this view

protected void measureChildWithMargins (View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed)

Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding and margins. The child must have MarginLayoutParams The heavy lifting is done in getChildMeasureSpec.

Parameters
child The child to measure
parentWidthMeasureSpec The width requirements for this view
widthUsed Extra space that has been used up by the parent horizontally (possibly by other children of the parent)
parentHeightMeasureSpec The height requirements for this view
heightUsed Extra space that has been used up by the parent vertically (possibly by other children of the parent)

protected void onLayout (boolean changed, int l, int t, int r, int b)

Called from layout when this view should assign a size and position to each of its children. Derived classes with children should override this method and call layout on each of their children.

Parameters
changed This is a new size or position for this view
l Left position, relative to parent
t Top position, relative to parent
r Right position, relative to parent
b Bottom position, relative to parent

protected void onMeasure (int widthMeasureSpec, int heightMeasureSpec)

Measure the view and its content to determine the measured width and the measured height. This method is invoked by measure(int, int) and should be overridden by subclasses to provide accurate and efficient measurement of their contents.

CONTRACT: When overriding this method, you must call setMeasuredDimension(int, int) to store the measured width and height of this view. Failure to do so will trigger an IllegalStateException, thrown by measure(int, int). Calling the superclass' onMeasure(int, int) is a valid use.

The base class implementation of measure defaults to the background size, unless a larger size is allowed by the MeasureSpec. Subclasses should override onMeasure(int, int) to provide better measurements of their content.

If this method is overridden, it is the subclass's responsibility to make sure the measured height and width are at least the view's minimum height and width (getSuggestedMinimumHeight() and getSuggestedMinimumWidth()).

Parameters
widthMeasureSpec horizontal space requirements as imposed by the parent. The requirements are encoded with View.MeasureSpec.
heightMeasureSpec vertical space requirements as imposed by the parent. The requirements are encoded with View.MeasureSpec.

protected void onOverScrolled (int scrollX, int scrollY, boolean clampedX, boolean clampedY)

Called by overScrollBy(int, int, int, int, int, int, int, int, boolean) to respond to the results of an over-scroll operation.

Parameters
scrollX New X scroll value in pixels
scrollY New Y scroll value in pixels
clampedX True if scrollX was clamped to an over-scroll boundary
clampedY True if scrollY was clamped to an over-scroll boundary

protected boolean onRequestFocusInDescendants (int direction, Rect previouslyFocusedRect)

When looking for focus in children of a scroll view, need to be a little more careful not to give focus to something that is scrolled off screen. This is more expensive than the default ViewGroup implementation, otherwise this behavior might have been made the default.

Parameters
direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and FOCUS_RIGHT
previouslyFocusedRect The rectangle (in this View's coordinate system) to give a finer grained hint about where focus is coming from. May be null if there is no hint.
Returns
  • Whether focus was taken.

protected void onRestoreInstanceState (Parcelable state)

Hook allowing a view to re-apply a representation of its internal state that had previously been generated by onSaveInstanceState(). This function will never be called with a null state.

Parameters
state The frozen state that had previously been returned by onSaveInstanceState().

protected Parcelable onSaveInstanceState ()

Hook allowing a view to generate a representation of its internal state that can later be used to create a new instance with that same state. This state should only contain information that is not persistent or can not be reconstructed later. For example, you will never store your current position on screen because that will be computed again when a new instance of the view is placed in its view hierarchy.

Some examples of things you may store here: the current cursor position in a text view (but usually not the text itself since that is stored in a content provider or other persistent storage), the currently selected item in a list view.

Returns
  • Returns a Parcelable object containing the view's current dynamic state, or null if there is nothing interesting to save. The default implementation returns null.

protected void onSizeChanged (int w, int h, int oldw, int oldh)

This is called during layout when the size of this view has changed. If you were just added to the view hierarchy, you're called with the old values of 0.

Parameters
w Current width of this view.
h Current height of this view.
oldw Old width of this view.
oldh Old height of this view.
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