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ViewDragHelper

public class ViewDragHelper
extends Object

java.lang.Object
↳	android.support.v4.widget.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 classes
`class`	`ViewDragHelper.Callback` A Callback is used as a communication channel with the ViewDragHelper back to the parent view using it.

Constants
`int`	`DIRECTION_ALL` Indicates that a check should occur along all axes
`int`	`DIRECTION_HORIZONTAL` Indicates that a check should occur along the horizontal axis
`int`	`DIRECTION_VERTICAL` Indicates that a check should occur along the vertical axis
`int`	`EDGE_ALL` Edge flag set indicating all edges should be affected.
`int`	`EDGE_BOTTOM` Edge flag indicating that the bottom edge should be affected.
`int`	`EDGE_LEFT` Edge flag indicating that the left edge should be affected.
`int`	`EDGE_RIGHT` Edge flag indicating that the right edge should be affected.
`int`	`EDGE_TOP` Edge flag indicating that the top edge should be affected.
`int`	`INVALID_POINTER` A null/invalid pointer ID.
`int`	`STATE_DRAGGING` A view is currently being dragged.
`int`	`STATE_IDLE` A view is not currently being dragged or animating as a result of a fling/snap.
`int`	`STATE_SETTLING` A view is currently settling into place as a result of a fling or predefined non-interactive motion.

Public methods
`void`	`abort()` `cancel()`, but also abort all motion in progress and snap to the end of any animation.
`void`	`cancel()` The result of a call to this method is equivalent to `processTouchEvent(android.view.MotionEvent)` receiving an ACTION_CANCEL event.
`void`	`captureChildView(View childView, int activePointerId)` Capture a specific child view for dragging within the parent.
`boolean`	`checkTouchSlop(int directions, int pointerId)` Check if the specified pointer tracked in the current gesture has crossed the required slop threshold.
`boolean`	`checkTouchSlop(int directions)` Check if any pointer tracked in the current gesture has crossed the required slop threshold.
`boolean`	`continueSettling(boolean deferCallbacks)` Move the captured settling view by the appropriate amount for the current time.
`static ViewDragHelper`	`create(ViewGroup forParent, float sensitivity, ViewDragHelper.Callback cb)` Factory method to create a new ViewDragHelper.
`static ViewDragHelper`	`create(ViewGroup forParent, ViewDragHelper.Callback cb)` Factory method to create a new ViewDragHelper.
`View`	`findTopChildUnder(int x, int y)` Find the topmost child under the given point within the parent view's coordinate system.
`void`	`flingCapturedView(int minLeft, int minTop, int maxLeft, int maxTop)` Settle the captured view based on standard free-moving fling behavior.
`int`	`getActivePointerId()`
`View`	`getCapturedView()`
`int`	`getEdgeSize()` Return the size of an edge.
`float`	`getMinVelocity()` Return the currently configured minimum velocity.
`int`	`getTouchSlop()`
`int`	`getViewDragState()` Retrieve the current drag state of this helper.
`boolean`	`isCapturedViewUnder(int x, int y)` Determine if the currently captured view is under the given point in the parent view's coordinate system.
`boolean`	`isEdgeTouched(int edges)` Check if any of the edges specified were initially touched in the currently active gesture.
`boolean`	`isEdgeTouched(int edges, int pointerId)` Check if any of the edges specified were initially touched by the pointer with the specified ID.
`boolean`	`isPointerDown(int pointerId)` 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, int x, int y)` Determine if the supplied view is under the given point in the parent view's coordinate system.
`void`	`processTouchEvent(MotionEvent ev)` Process a touch event received by the parent view.
`void`	`setEdgeTrackingEnabled(int edgeFlags)` Enable edge tracking for the selected edges of the parent view.
`void`	`setMinVelocity(float minVel)` Set the minimum velocity that will be detected as having a magnitude greater than zero in pixels per second.
`boolean`	`settleCapturedViewAt(int finalLeft, int finalTop)` Settle the captured view at the given (left, top) position.
`boolean`	`shouldInterceptTouchEvent(MotionEvent ev)` Check if this event as provided to the parent view's onInterceptTouchEvent should cause the parent to intercept the touch event stream.
`boolean`	`smoothSlideViewTo(View child, int finalLeft, int finalTop)` Animate the view `child` to the given (left, top) position.

Protected methods
`boolean`	`canScroll(View v, boolean checkV, int dx, int dy, int x, int y)` Tests scrollability within child views of v given a delta of dx.

Inherited methods

From class


  
    java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long millis, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void`	`wait(long millis)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void`	`wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

Constants

DIRECTION_ALL

int DIRECTION_ALL

Indicates that a check should occur along all axes

Constant Value: 3 (0x00000003)

DIRECTION_HORIZONTAL

int DIRECTION_HORIZONTAL

Indicates that a check should occur along the horizontal axis

Constant Value: 1 (0x00000001)

DIRECTION_VERTICAL

int DIRECTION_VERTICAL

Indicates that a check should occur along the vertical axis

Constant Value: 2 (0x00000002)

EDGE_ALL

int EDGE_ALL

Edge flag set indicating all edges should be affected.

Constant Value: 15 (0x0000000f)

EDGE_BOTTOM

int EDGE_BOTTOM

Edge flag indicating that the bottom edge should be affected.

Constant Value: 8 (0x00000008)

EDGE_LEFT

int EDGE_LEFT

Edge flag indicating that the left edge should be affected.

Constant Value: 1 (0x00000001)

EDGE_RIGHT

int EDGE_RIGHT

Edge flag indicating that the right edge should be affected.

Constant Value: 2 (0x00000002)

EDGE_TOP

int EDGE_TOP

Edge flag indicating that the top edge should be affected.

Constant Value: 4 (0x00000004)

INVALID_POINTER

int INVALID_POINTER

A null/invalid pointer ID.

Constant Value: -1 (0xffffffff)

STATE_DRAGGING

int STATE_DRAGGING

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

Constant Value: 1 (0x00000001)

STATE_IDLE

int STATE_IDLE

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

Constant Value: 0 (0x00000000)

STATE_SETTLING

int STATE_SETTLING

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

Constant Value: 2 (0x00000002)

Public methods

abort

void abort ()

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

cancel

void cancel ()

The result of a call to this method is equivalent to processTouchEvent(android.view.MotionEvent) receiving an ACTION_CANCEL event.

captureChildView

void captureChildView (View childView, 
                int activePointerId)

Capture a specific child view for dragging within the parent. The callback will be notified but tryCaptureView(android.view.View, int) 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

boolean checkTouchSlop (int directions, 
                int pointerId)

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

This depends on internal state populated by shouldInterceptTouchEvent(android.view.MotionEvent) or processTouchEvent(android.view.MotionEvent). 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

checkTouchSlop

boolean checkTouchSlop (int directions)

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

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

continueSettling

boolean continueSettling (boolean deferCallbacks)

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

ViewDragHelper create (ViewGroup forParent, 
                float sensitivity, 
                ViewDragHelper.Callback cb)

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

create

ViewDragHelper create (ViewGroup forParent, 
                ViewDragHelper.Callback cb)

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

findTopChildUnder

View findTopChildUnder (int x, 
                int y)

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

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

void flingCapturedView (int minLeft, 
                int minTop, 
                int maxLeft, 
                int maxTop)

Settle the captured view based on standard free-moving fling behavior. The caller should invoke continueSettling(boolean) 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

int getActivePointerId ()

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

getCapturedView

View getCapturedView ()

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

getEdgeSize

int getEdgeSize ()

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
`int`	The size of an edge in pixels

See also:

setEdgeTrackingEnabled(int)

getMinVelocity

float getMinVelocity ()

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

int getTouchSlop ()

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

getViewDragState

int getViewDragState ()

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

boolean isCapturedViewUnder (int x, 
                int y)

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

boolean isEdgeTouched (int edges)

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

boolean isEdgeTouched (int edges, 
                int pointerId)

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`
`pointerId`	`int`

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

isPointerDown

boolean isPointerDown (int pointerId)

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(android.view.MotionEvent) or processTouchEvent(android.view.MotionEvent). 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

boolean isViewUnder (View view, 
                int x, 
                int y)

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

void processTouchEvent (MotionEvent ev)

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

setEdgeTrackingEnabled

void setEdgeTrackingEnabled (int edgeFlags)

Enable edge tracking for the selected edges of the parent view. The callback's onEdgeTouched(int, int) and onEdgeDragStarted(int, int) 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

See also:

setMinVelocity

void setMinVelocity (float minVel)

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

boolean settleCapturedViewAt (int finalLeft, 
                int finalTop)

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(boolean) 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(boolean)` calls

shouldInterceptTouchEvent

boolean shouldInterceptTouchEvent (MotionEvent ev)

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

boolean smoothSlideViewTo (View child, 
                int finalLeft, 
                int finalTop)

Animate the view child to the given (left, top) position. If this method returns true, the caller should invoke continueSettling(boolean) 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(boolean)` calls

Protected methods

canScroll

boolean canScroll (View v, 
                boolean checkV, 
                int dx, 
                int dy, 
                int x, 
                int y)

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.

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Recently visited

Results for

ViewDragHelper

Summary

Nested classes

Constants

Public methods

Protected methods

Inherited methods

Constants

DIRECTION_ALL

DIRECTION_HORIZONTAL

DIRECTION_VERTICAL

EDGE_ALL

EDGE_BOTTOM

EDGE_LEFT

EDGE_RIGHT

EDGE_TOP

INVALID_POINTER

STATE_DRAGGING

STATE_IDLE

STATE_SETTLING

Public methods

abort

cancel

captureChildView

checkTouchSlop

checkTouchSlop

continueSettling

create

create

findTopChildUnder

flingCapturedView

getActivePointerId

getCapturedView

getEdgeSize

getMinVelocity

getTouchSlop

getViewDragState

isCapturedViewUnder

isEdgeTouched

isEdgeTouched

isPointerDown

isViewUnder

processTouchEvent

setEdgeTrackingEnabled

setMinVelocity

settleCapturedViewAt

shouldInterceptTouchEvent

smoothSlideViewTo

Protected methods

canScroll