ViewDragHelper


class ViewDragHelper


ViewDragHelper is a utility class for writing custom ViewGroups. It offers a number of useful operations and state tracking for allowing a user to drag and reposition views within their parent ViewGroup.

Summary

Nested types

A Callback is used as a communication channel with the ViewDragHelper back to the parent view using it.

Constants

const Int

Indicates that a check should occur along all axes

const Int

Indicates that a check should occur along the horizontal axis

const Int

Indicates that a check should occur along the vertical axis

const Int

Edge flag set indicating all edges should be affected.

const Int

Edge flag indicating that the bottom edge should be affected.

const Int

Edge flag indicating that the left edge should be affected.

const Int

Edge flag indicating that the right edge should be affected.

const Int

Edge flag indicating that the top edge should be affected.

const Int

A null/invalid pointer ID.

const Int

A view is currently being dragged.

const Int

A view is not currently being dragged or animating as a result of a fling/snap.

const Int

A view is currently settling into place as a result of a fling or predefined non-interactive motion.

Public functions

Unit

cancel, but also abort all motion in progress and snap to the end of any animation.

Unit

The result of a call to this method is equivalent to processTouchEvent receiving an ACTION_CANCEL event.

Unit
captureChildView(childView: View, activePointerId: Int)

Capture a specific child view for dragging within the parent.

Boolean
checkTouchSlop(directions: Int)

Check if any pointer tracked in the current gesture has crossed the required slop threshold.

Boolean
checkTouchSlop(directions: Int, pointerId: Int)

Check if the specified pointer tracked in the current gesture has crossed the required slop threshold.

Boolean
continueSettling(deferCallbacks: Boolean)

Move the captured settling view by the appropriate amount for the current time.

java-static ViewDragHelper

Factory method to create a new ViewDragHelper.

java-static ViewDragHelper
create(
    forParent: ViewGroup,
    sensitivity: Float,
    cb: ViewDragHelper.Callback
)

Factory method to create a new ViewDragHelper.

View?

Find the topmost child under the given point within the parent view's coordinate system.

Unit
flingCapturedView(minLeft: Int, minTop: Int, maxLeft: Int, maxTop: Int)

Settle the captured view based on standard free-moving fling behavior.

Int
View?
@Px Int

Return the default size used for edge tracking.

@Px Int

Return the size of an edge.

Float

Return the currently configured minimum velocity.

@Px Int
Int

Retrieve the current drag state of this helper.

Boolean

Determine if the currently captured view is under the given point in the parent view's coordinate system.

Boolean

Check if any of the edges specified were initially touched in the currently active gesture.

Boolean
isEdgeTouched(edges: Int, pointerId: Int)

Check if any of the edges specified were initially touched by the pointer with the specified ID.

Boolean
isPointerDown(pointerId: Int)

Check if the given pointer ID represents a pointer that is currently down (to the best of the ViewDragHelper's knowledge).

Boolean
isViewUnder(view: View?, x: Int, y: Int)

Determine if the supplied view is under the given point in the parent view's coordinate system.

Unit

Process a touch event received by the parent view.

Unit
setEdgeSize(size: @Px @IntRange(from = 0) Int)

Set the range in pixels along the edges of this view that will actively detect edge touches or drags if edge tracking is enabled.

Unit

Enable edge tracking for the selected edges of the parent view.

Unit

Set the minimum velocity that will be detected as having a magnitude greater than zero in pixels per second.

Boolean
settleCapturedViewAt(finalLeft: Int, finalTop: Int)

Settle the captured view at the given (left, top) position.

Boolean

Check if this event as provided to the parent view's onInterceptTouchEvent should cause the parent to intercept the touch event stream.

Boolean
smoothSlideViewTo(child: View, finalLeft: Int, finalTop: Int)

Animate the view child to the given (left, top) position.

Protected functions

Boolean
canScroll(v: View, checkV: Boolean, dx: Int, dy: Int, x: Int, y: Int)

Tests scrollability within child views of v given a delta of dx.

Constants

DIRECTION_ALL

Added in 1.0.0
const val DIRECTION_ALL = 3: Int

Indicates that a check should occur along all axes

DIRECTION_HORIZONTAL

Added in 1.0.0
const val DIRECTION_HORIZONTAL = 1: Int

Indicates that a check should occur along the horizontal axis

DIRECTION_VERTICAL

Added in 1.0.0
const val DIRECTION_VERTICAL = 2: Int

Indicates that a check should occur along the vertical axis

EDGE_ALL

Added in 1.0.0
const val EDGE_ALL = 15: Int

Edge flag set indicating all edges should be affected.

EDGE_BOTTOM

Added in 1.0.0
const val EDGE_BOTTOM = 8: Int

Edge flag indicating that the bottom edge should be affected.

EDGE_LEFT

Added in 1.0.0
const val EDGE_LEFT = 1: Int

Edge flag indicating that the left edge should be affected.

EDGE_RIGHT

Added in 1.0.0
const val EDGE_RIGHT = 2: Int

Edge flag indicating that the right edge should be affected.

EDGE_TOP

Added in 1.0.0
const val EDGE_TOP = 4: Int

Edge flag indicating that the top edge should be affected.

INVALID_POINTER

Added in 1.0.0
const val INVALID_POINTER = -1: Int

A null/invalid pointer ID.

STATE_DRAGGING

Added in 1.0.0
const val STATE_DRAGGING = 1: Int

A view is currently being dragged. The position is currently changing as a result of user input or simulated user input.

STATE_IDLE

Added in 1.0.0
const val STATE_IDLE = 0: Int

A view is not currently being dragged or animating as a result of a fling/snap.

STATE_SETTLING

Added in 1.0.0
const val STATE_SETTLING = 2: Int

A view is currently settling into place as a result of a fling or predefined non-interactive motion.

Public functions

abort

Added in 1.0.0
fun abort(): Unit

cancel, but also abort all motion in progress and snap to the end of any animation.

cancel

Added in 1.0.0
fun cancel(): Unit

The result of a call to this method is equivalent to processTouchEvent receiving an ACTION_CANCEL event.

captureChildView

Added in 1.0.0
fun captureChildView(childView: View, activePointerId: Int): Unit

Capture a specific child view for dragging within the parent. The callback will be notified but tryCaptureView will not be asked permission to capture this view.

Parameters
childView: View

Child view to capture

activePointerId: Int

ID of the pointer that is dragging the captured child view

checkTouchSlop

Added in 1.0.0
fun checkTouchSlop(directions: Int): Boolean

Check if any pointer tracked in the current gesture has crossed the required slop threshold.

This depends on internal state populated by shouldInterceptTouchEvent or processTouchEvent. You should only rely on the results of this method after all currently available touch data has been provided to one of these two methods.

Parameters
directions: Int

Combination of direction flags, see DIRECTION_HORIZONTAL, DIRECTION_VERTICAL, DIRECTION_ALL

Returns
Boolean

true if the slop threshold has been crossed, false otherwise

checkTouchSlop

Added in 1.0.0
fun checkTouchSlop(directions: Int, pointerId: Int): Boolean

Check if the specified pointer tracked in the current gesture has crossed the required slop threshold.

This depends on internal state populated by shouldInterceptTouchEvent or processTouchEvent. You should only rely on the results of this method after all currently available touch data has been provided to one of these two methods.

Parameters
directions: Int

Combination of direction flags, see DIRECTION_HORIZONTAL, DIRECTION_VERTICAL, DIRECTION_ALL

pointerId: Int

ID of the pointer to slop check as specified by MotionEvent

Returns
Boolean

true if the slop threshold has been crossed, false otherwise

continueSettling

Added in 1.0.0
fun continueSettling(deferCallbacks: Boolean): Boolean

Move the captured settling view by the appropriate amount for the current time. If continueSettling returns true, the caller should call it again on the next frame to continue.

Parameters
deferCallbacks: Boolean

true if state callbacks should be deferred via posted message. Set this to true if you are calling this method from computeScroll or similar methods invoked as part of layout or drawing.

Returns
Boolean

true if settle is still in progress

create

Added in 1.0.0
java-static fun create(forParent: ViewGroup, cb: ViewDragHelper.Callback): ViewDragHelper

Factory method to create a new ViewDragHelper.

Parameters
forParent: ViewGroup

Parent view to monitor

cb: ViewDragHelper.Callback

Callback to provide information and receive events

Returns
ViewDragHelper

a new ViewDragHelper instance

create

Added in 1.0.0
java-static fun create(
    forParent: ViewGroup,
    sensitivity: Float,
    cb: ViewDragHelper.Callback
): ViewDragHelper

Factory method to create a new ViewDragHelper.

Parameters
forParent: ViewGroup

Parent view to monitor

sensitivity: Float

Multiplier for how sensitive the helper should be about detecting the start of a drag. Larger values are more sensitive. 1.0f is normal.

cb: ViewDragHelper.Callback

Callback to provide information and receive events

Returns
ViewDragHelper

a new ViewDragHelper instance

findTopChildUnder

Added in 1.0.0
fun findTopChildUnder(x: Int, y: Int): View?

Find the topmost child under the given point within the parent view's coordinate system. The child order is determined using getOrderedChildIndex.

Parameters
x: Int

X position to test in the parent's coordinate system

y: Int

Y position to test in the parent's coordinate system

Returns
View?

The topmost child view under (x, y) or null if none found.

flingCapturedView

Added in 1.0.0
fun flingCapturedView(minLeft: Int, minTop: Int, maxLeft: Int, maxTop: Int): Unit

Settle the captured view based on standard free-moving fling behavior. The caller should invoke continueSettling on each subsequent frame to continue the motion until it returns false.

Parameters
minLeft: Int

Minimum X position for the view's left edge

minTop: Int

Minimum Y position for the view's top edge

maxLeft: Int

Maximum X position for the view's left edge

maxTop: Int

Maximum Y position for the view's top edge

getActivePointerId

Added in 1.0.0
fun getActivePointerId(): Int
Returns
Int

The ID of the pointer currently dragging the captured view, or INVALID_POINTER.

getCapturedView

Added in 1.0.0
fun getCapturedView(): View?
Returns
View?

The currently captured view, or null if no view has been captured.

getDefaultEdgeSize

Added in 1.1.0
fun getDefaultEdgeSize(): @Px Int

Return the default size used for edge tracking.

Returns
@Px Int

The default edge size

getEdgeSize

Added in 1.0.0
fun getEdgeSize(): @Px Int

Return the size of an edge. This is the range in pixels along the edges of this view that will actively detect edge touches or drags if edge tracking is enabled.

Returns
@Px Int

The size of an edge in pixels

getMinVelocity

Added in 1.0.0
fun getMinVelocity(): Float

Return the currently configured minimum velocity. Any flings with a magnitude less than this value in pixels per second. Callback methods accepting a velocity will receive zero as a velocity value if the real detected velocity was below this threshold.

Returns
Float

the minimum velocity that will be detected

getTouchSlop

Added in 1.0.0
fun getTouchSlop(): @Px Int
Returns
@Px Int

The minimum distance in pixels that the user must travel to initiate a drag

getViewDragState

Added in 1.0.0
fun getViewDragState(): Int

Retrieve the current drag state of this helper. This will return one of STATE_IDLE, STATE_DRAGGING or STATE_SETTLING.

Returns
Int

The current drag state

isCapturedViewUnder

Added in 1.0.0
fun isCapturedViewUnder(x: Int, y: Int): Boolean

Determine if the currently captured view is under the given point in the parent view's coordinate system. If there is no captured view this method will return false.

Parameters
x: Int

X position to test in the parent's coordinate system

y: Int

Y position to test in the parent's coordinate system

Returns
Boolean

true if the captured view is under the given point, false otherwise

isEdgeTouched

Added in 1.0.0
fun isEdgeTouched(edges: Int): Boolean

Check if any of the edges specified were initially touched in the currently active gesture. If there is no currently active gesture this method will return false.

Parameters
edges: Int

Edges to check for an initial edge touch. See EDGE_LEFT, EDGE_TOP, EDGE_RIGHT, EDGE_BOTTOM and EDGE_ALL

Returns
Boolean

true if any of the edges specified were initially touched in the current gesture

isEdgeTouched

Added in 1.0.0
fun isEdgeTouched(edges: Int, pointerId: Int): Boolean

Check if any of the edges specified were initially touched by the pointer with the specified ID. If there is no currently active gesture or if there is no pointer with the given ID currently down this method will return false.

Parameters
edges: Int

Edges to check for an initial edge touch. See EDGE_LEFT, EDGE_TOP, EDGE_RIGHT, EDGE_BOTTOM and EDGE_ALL

Returns
Boolean

true if any of the edges specified were initially touched in the current gesture

isPointerDown

Added in 1.0.0
fun isPointerDown(pointerId: Int): Boolean

Check if the given pointer ID represents a pointer that is currently down (to the best of the ViewDragHelper's knowledge).

The state used to report this information is populated by the methods shouldInterceptTouchEvent or processTouchEvent. If one of these methods has not been called for all relevant MotionEvents to track, the information reported by this method may be stale or incorrect.

Parameters
pointerId: Int

pointer ID to check; corresponds to IDs provided by MotionEvent

Returns
Boolean

true if the pointer with the given ID is still down

isViewUnder

Added in 1.0.0
fun isViewUnder(view: View?, x: Int, y: Int): Boolean

Determine if the supplied view is under the given point in the parent view's coordinate system.

Parameters
view: View?

Child view of the parent to hit test

x: Int

X position to test in the parent's coordinate system

y: Int

Y position to test in the parent's coordinate system

Returns
Boolean

true if the supplied view is under the given point, false otherwise

processTouchEvent

Added in 1.0.0
fun processTouchEvent(ev: MotionEvent): Unit

Process a touch event received by the parent view. This method will dispatch callback events as needed before returning. The parent view's onTouchEvent implementation should call this.

Parameters
ev: MotionEvent

The touch event received by the parent view

setEdgeSize

Added in 1.1.0
fun setEdgeSize(size: @Px @IntRange(from = 0) Int): Unit

Set the range in pixels along the edges of this view that will actively detect edge touches or drags if edge tracking is enabled.

Parameters
size: @Px @IntRange(from = 0) Int

Edge size in pixels

setEdgeTrackingEnabled

Added in 1.0.0
fun setEdgeTrackingEnabled(edgeFlags: Int): Unit

Enable edge tracking for the selected edges of the parent view. The callback's onEdgeTouched and onEdgeDragStarted methods will only be invoked for edges for which edge tracking has been enabled.

Parameters
edgeFlags: Int

Combination of edge flags describing the edges to watch

setMinVelocity

Added in 1.0.0
fun setMinVelocity(minVel: Float): Unit

Set the minimum velocity that will be detected as having a magnitude greater than zero in pixels per second. Callback methods accepting a velocity will be clamped appropriately.

Parameters
minVel: Float

Minimum velocity to detect

settleCapturedViewAt

Added in 1.0.0
fun settleCapturedViewAt(finalLeft: Int, finalTop: Int): Boolean

Settle the captured view at the given (left, top) position. The appropriate velocity from prior motion will be taken into account. If this method returns true, the caller should invoke continueSettling on each subsequent frame to continue the motion until it returns false. If this method returns false there is no further work to do to complete the movement.

Parameters
finalLeft: Int

Settled left edge position for the captured view

finalTop: Int

Settled top edge position for the captured view

Returns
Boolean

true if animation should continue through continueSettling calls

shouldInterceptTouchEvent

Added in 1.0.0
fun shouldInterceptTouchEvent(ev: MotionEvent): Boolean

Check if this event as provided to the parent view's onInterceptTouchEvent should cause the parent to intercept the touch event stream.

Parameters
ev: MotionEvent

MotionEvent provided to onInterceptTouchEvent

Returns
Boolean

true if the parent view should return true from onInterceptTouchEvent

smoothSlideViewTo

Added in 1.0.0
fun smoothSlideViewTo(child: View, finalLeft: Int, finalTop: Int): Boolean

Animate the view child to the given (left, top) position. If this method returns true, the caller should invoke continueSettling on each subsequent frame to continue the motion until it returns false. If this method returns false there is no further work to do to complete the movement.

This operation does not count as a capture event, though getCapturedView will still report the sliding view while the slide is in progress.

Parameters
child: View

Child view to capture and animate

finalLeft: Int

Final left position of child

finalTop: Int

Final top position of child

Returns
Boolean

true if animation should continue through continueSettling calls

Protected functions

canScroll

Added in 1.0.0
protected fun canScroll(v: View, checkV: Boolean, dx: Int, dy: Int, x: Int, y: Int): Boolean

Tests scrollability within child views of v given a delta of dx.

Parameters
v: View

View to test for horizontal scrollability

checkV: Boolean

Whether the view v passed should itself be checked for scrollability (true), or just its children (false).

dx: Int

Delta scrolled in pixels along the X axis

dy: Int

Delta scrolled in pixels along the Y axis

x: Int

X coordinate of the active touch point

y: Int

Y coordinate of the active touch point

Returns
Boolean

true if child views of v can be scrolled by delta of dx.