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added in version 22.1.0
belongs to Maven artifact com.android.support:support-core-ui:27.0.0

ViewDragHelper.Callback

public static abstract class ViewDragHelper.Callback
extends Object

java.lang.Object
   ↳ android.support.v4.widget.ViewDragHelper.Callback


A Callback is used as a communication channel with the ViewDragHelper back to the parent view using it. on*methods are invoked on siginficant events and several accessor methods are expected to provide the ViewDragHelper with more information about the state of the parent view upon request. The callback also makes decisions governing the range and draggability of child views.

Summary

Public constructors

ViewDragHelper.Callback()

Public methods

int clampViewPositionHorizontal(View child, int left, int dx)

Restrict the motion of the dragged child view along the horizontal axis.

int clampViewPositionVertical(View child, int top, int dy)

Restrict the motion of the dragged child view along the vertical axis.

int getOrderedChildIndex(int index)

Called to determine the Z-order of child views.

int getViewHorizontalDragRange(View child)

Return the magnitude of a draggable child view's horizontal range of motion in pixels.

int getViewVerticalDragRange(View child)

Return the magnitude of a draggable child view's vertical range of motion in pixels.

void onEdgeDragStarted(int edgeFlags, int pointerId)

Called when the user has started a deliberate drag away from one of the subscribed edges in the parent view while no child view is currently captured.

boolean onEdgeLock(int edgeFlags)

Called when the given edge may become locked.

void onEdgeTouched(int edgeFlags, int pointerId)

Called when one of the subscribed edges in the parent view has been touched by the user while no child view is currently captured.

void onViewCaptured(View capturedChild, int activePointerId)

Called when a child view is captured for dragging or settling.

void onViewDragStateChanged(int state)

Called when the drag state changes.

void onViewPositionChanged(View changedView, int left, int top, int dx, int dy)

Called when the captured view's position changes as the result of a drag or settle.

void onViewReleased(View releasedChild, float xvel, float yvel)

Called when the child view is no longer being actively dragged.

abstract boolean tryCaptureView(View child, int pointerId)

Called when the user's input indicates that they want to capture the given child view with the pointer indicated by pointerId.

Inherited methods

From class java.lang.Object

Public constructors

ViewDragHelper.Callback

added in version 22.1.0
ViewDragHelper.Callback ()

Public methods

clampViewPositionHorizontal

added in version 22.1.0
int clampViewPositionHorizontal (View child, 
                int left, 
                int dx)

Restrict the motion of the dragged child view along the horizontal axis. The default implementation does not allow horizontal motion; the extending class must override this method and provide the desired clamping.

Parameters
child View: Child view being dragged

left int: Attempted motion along the X axis

dx int: Proposed change in position for left

Returns
int The new clamped position for left

clampViewPositionVertical

added in version 22.1.0
int clampViewPositionVertical (View child, 
                int top, 
                int dy)

Restrict the motion of the dragged child view along the vertical axis. The default implementation does not allow vertical motion; the extending class must override this method and provide the desired clamping.

Parameters
child View: Child view being dragged

top int: Attempted motion along the Y axis

dy int: Proposed change in position for top

Returns
int The new clamped position for top

getOrderedChildIndex

added in version 22.1.0
int getOrderedChildIndex (int index)

Called to determine the Z-order of child views.

Parameters
index int: the ordered position to query for

Returns
int index of the view that should be ordered at position index

getViewHorizontalDragRange

added in version 22.1.0
int getViewHorizontalDragRange (View child)

Return the magnitude of a draggable child view's horizontal range of motion in pixels. This method should return 0 for views that cannot move horizontally.

Parameters
child View: Child view to check

Returns
int range of horizontal motion in pixels

getViewVerticalDragRange

added in version 22.1.0
int getViewVerticalDragRange (View child)

Return the magnitude of a draggable child view's vertical range of motion in pixels. This method should return 0 for views that cannot move vertically.

Parameters
child View: Child view to check

Returns
int range of vertical motion in pixels

onEdgeDragStarted

added in version 22.1.0
void onEdgeDragStarted (int edgeFlags, 
                int pointerId)

Called when the user has started a deliberate drag away from one of the subscribed edges in the parent view while no child view is currently captured.

Parameters
edgeFlags int: A combination of edge flags describing the edge(s) dragged

pointerId int: ID of the pointer touching the described edge(s)

See also:

onEdgeLock

added in version 22.1.0
boolean onEdgeLock (int edgeFlags)

Called when the given edge may become locked. This can happen if an edge drag was preliminarily rejected before beginning, but after onEdgeTouched(int, int) was called. This method should return true to lock this edge or false to leave it unlocked. The default behavior is to leave edges unlocked.

Parameters
edgeFlags int: A combination of edge flags describing the edge(s) locked

Returns
boolean true to lock the edge, false to leave it unlocked

onEdgeTouched

added in version 22.1.0
void onEdgeTouched (int edgeFlags, 
                int pointerId)

Called when one of the subscribed edges in the parent view has been touched by the user while no child view is currently captured.

Parameters
edgeFlags int: A combination of edge flags describing the edge(s) currently touched

pointerId int: ID of the pointer touching the described edge(s)

See also:

onViewCaptured

added in version 22.1.0
void onViewCaptured (View capturedChild, 
                int activePointerId)

Called when a child view is captured for dragging or settling. The ID of the pointer currently dragging the captured view is supplied. If activePointerId is identified as INVALID_POINTER the capture is programmatic instead of pointer-initiated.

Parameters
capturedChild View: Child view that was captured

activePointerId int: Pointer id tracking the child capture

onViewDragStateChanged

added in version 22.1.0
void onViewDragStateChanged (int state)

Called when the drag state changes. See the STATE_* constants for more information.

Parameters
state int: The new drag state

See also:

onViewPositionChanged

added in version 22.1.0
void onViewPositionChanged (View changedView, 
                int left, 
                int top, 
                int dx, 
                int dy)

Called when the captured view's position changes as the result of a drag or settle.

Parameters
changedView View: View whose position changed

left int: New X coordinate of the left edge of the view

top int: New Y coordinate of the top edge of the view

dx int: Change in X position from the last call

dy int: Change in Y position from the last call

onViewReleased

added in version 22.1.0
void onViewReleased (View releasedChild, 
                float xvel, 
                float yvel)

Called when the child view is no longer being actively dragged. The fling velocity is also supplied, if relevant. The velocity values may be clamped to system minimums or maximums.

Calling code may decide to fling or otherwise release the view to let it settle into place. It should do so using settleCapturedViewAt(int, int) or flingCapturedView(int, int, int, int). If the Callback invokes one of these methods, the ViewDragHelper will enter STATE_SETTLING and the view capture will not fully end until it comes to a complete stop. If neither of these methods is invoked before onViewReleased returns, the view will stop in place and the ViewDragHelper will return to STATE_IDLE.

Parameters
releasedChild View: The captured child view now being released

xvel float: X velocity of the pointer as it left the screen in pixels per second.

yvel float: Y velocity of the pointer as it left the screen in pixels per second.

tryCaptureView

added in version 22.1.0
boolean tryCaptureView (View child, 
                int pointerId)

Called when the user's input indicates that they want to capture the given child view with the pointer indicated by pointerId. The callback should return true if the user is permitted to drag the given view with the indicated pointer.

ViewDragHelper may call this method multiple times for the same view even if the view is already captured; this indicates that a new pointer is trying to take control of the view.

If this method returns true, a call to onViewCaptured(android.view.View, int) will follow if the capture is successful.

Parameters
child View: Child the user is attempting to capture

pointerId int: ID of the pointer attempting the capture

Returns
boolean true if capture should be allowed, false otherwise

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