ViewDragHelper.Callback

abstract class 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

Public functions

Int
clampViewPositionHorizontal(child: View, left: Int, dx: Int)

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

Int
clampViewPositionVertical(child: View, top: Int, dy: Int)

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

Int

Called to determine the Z-order of child views.

Int

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

Int

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

Unit
onEdgeDragStarted(edgeFlags: Int, pointerId: Int)

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(edgeFlags: Int)

Called when the given edge may become locked.

Unit
onEdgeTouched(edgeFlags: Int, pointerId: Int)

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

Unit
onViewCaptured(capturedChild: View, activePointerId: Int)

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

Unit

Called when the drag state changes.

Unit
onViewPositionChanged(
    changedView: View,
    left: Int,
    top: Int,
    dx: @Px Int,
    dy: @Px Int
)

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

Unit
onViewReleased(releasedChild: View, xvel: Float, yvel: Float)

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

abstract Boolean
tryCaptureView(child: View, pointerId: Int)

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

Public constructors

Callback

Added in 1.0.0
Callback()

Public functions

clampViewPositionHorizontal

Added in 1.0.0
fun clampViewPositionHorizontal(child: View, left: Int, dx: Int): Int

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 1.0.0
fun clampViewPositionVertical(child: View, top: Int, dy: Int): Int

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 1.0.0
fun getOrderedChildIndex(index: Int): Int

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 1.0.0
fun getViewHorizontalDragRange(child: View): Int

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 1.0.0
fun getViewVerticalDragRange(child: View): Int

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 1.0.0
fun onEdgeDragStarted(edgeFlags: Int, pointerId: Int): Unit

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)

onEdgeLock

Added in 1.0.0
fun onEdgeLock(edgeFlags: Int): Boolean

Called when the given edge may become locked. This can happen if an edge drag was preliminarily rejected before beginning, but after onEdgeTouched 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 1.0.0
fun onEdgeTouched(edgeFlags: Int, pointerId: Int): Unit

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)

onViewCaptured

Added in 1.0.0
fun onViewCaptured(capturedChild: View, activePointerId: Int): Unit

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 1.0.0
fun onViewDragStateChanged(state: Int): Unit

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

Parameters
state: Int

The new drag state

onViewPositionChanged

Added in 1.0.0
fun onViewPositionChanged(
    changedView: View,
    left: Int,
    top: Int,
    dx: @Px Int,
    dy: @Px Int
): Unit

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: @Px Int

Change in X position from the last call

dy: @Px Int

Change in Y position from the last call

onViewReleased

Added in 1.0.0
fun onViewReleased(releasedChild: View, xvel: Float, yvel: Float): Unit

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 or flingCapturedView. 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 1.0.0
abstract fun tryCaptureView(child: View, pointerId: Int): Boolean

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 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