android.support.v4.widget
Class ViewDragHelper

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

public class ViewDragHelper
extends Object

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.

Nested Class Summary

static class

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

Field Summary

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

Method Summary

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.
protected boolean	canScroll(android.view.View v, boolean checkV, int dx, int dy, int x, int y) Tests scrollability within child views of v given a delta of dx.
void	captureChildView(android.view.View childView, int activePointerId) Capture a specific child view for dragging within the parent.
boolean	checkTouchSlop(int directions) Check if any pointer tracked in the current gesture has crossed the required slop threshold.
boolean	checkTouchSlop(int directions, int pointerId) Check if the specified 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(android.view.ViewGroup forParent, float sensitivity, ViewDragHelper.Callback cb) Factory method to create a new ViewDragHelper.
static ViewDragHelper	create(android.view.ViewGroup forParent, ViewDragHelper.Callback cb) Factory method to create a new ViewDragHelper.
android.view.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()
android.view.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(android.view.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(android.view.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(android.view.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(android.view.View child, int finalLeft, int finalTop) Animate the view child to the given (left, top) position.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

INVALID_POINTER

public static final int INVALID_POINTER

A null/invalid pointer ID.

See Also:

Constant Field Values

STATE_IDLE

public static final int STATE_IDLE

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

See Also:

Constant Field Values

STATE_DRAGGING

public static final int STATE_DRAGGING

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

See Also:

Constant Field Values

STATE_SETTLING

public static final int STATE_SETTLING

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

See Also:

Constant Field Values

EDGE_LEFT

public static final int EDGE_LEFT

Edge flag indicating that the left edge should be affected.

See Also:

Constant Field Values

EDGE_RIGHT

public static final int EDGE_RIGHT

Edge flag indicating that the right edge should be affected.

See Also:

Constant Field Values

EDGE_TOP

public static final int EDGE_TOP

Edge flag indicating that the top edge should be affected.

See Also:

Constant Field Values

EDGE_BOTTOM

public static final int EDGE_BOTTOM

Edge flag indicating that the bottom edge should be affected.

See Also:

Constant Field Values

EDGE_ALL

public static final int EDGE_ALL

Edge flag set indicating all edges should be affected.

See Also:

Constant Field Values

DIRECTION_HORIZONTAL

public static final int DIRECTION_HORIZONTAL

Indicates that a check should occur along the horizontal axis

See Also:

Constant Field Values

DIRECTION_VERTICAL

public static final int DIRECTION_VERTICAL

Indicates that a check should occur along the vertical axis

See Also:

Constant Field Values

DIRECTION_ALL

public static final int DIRECTION_ALL

Indicates that a check should occur along all axes

See Also:

Constant Field Values

Method Detail

create

public static ViewDragHelper create(android.view.ViewGroup forParent,
                                    ViewDragHelper.Callback cb)

Factory method to create a new ViewDragHelper.

Parameters:

forParent - Parent view to monitor

cb - Callback to provide information and receive events

Returns:

a new ViewDragHelper instance

create

public static ViewDragHelper create(android.view.ViewGroup forParent,
                                    float sensitivity,
                                    ViewDragHelper.Callback cb)

Factory method to create a new ViewDragHelper.

Parameters:

forParent - Parent view to monitor

sensitivity - 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 - Callback to provide information and receive events

Returns:

a new ViewDragHelper instance

setMinVelocity

public 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 - Minimum velocity to detect

getMinVelocity

public 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:

the minimum velocity that will be detected

getViewDragState

public int getViewDragState()

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

Returns:

The current drag state

setEdgeTrackingEnabled

public void setEdgeTrackingEnabled(int edgeFlags)

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

Parameters:

edgeFlags - Combination of edge flags describing the edges to watch

See Also:

EDGE_LEFT, EDGE_TOP, EDGE_RIGHT, EDGE_BOTTOM

getEdgeSize

public 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:

The size of an edge in pixels

See Also:

setEdgeTrackingEnabled(int)

captureChildView

public void captureChildView(android.view.View childView,
                             int activePointerId)

Capture a specific child view for dragging within the parent. The callback will be notified but ViewDragHelper.Callback.tryCaptureView(android.view.View, int) will not be asked permission to capture this view.

Parameters:

childView - Child view to capture

activePointerId - ID of the pointer that is dragging the captured child view

getCapturedView

public android.view.View getCapturedView()

Returns:

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

getActivePointerId

public int getActivePointerId()

Returns:

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

getTouchSlop

public int getTouchSlop()

Returns:

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

cancel

public void cancel()

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

abort

public void abort()

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

smoothSlideViewTo

public boolean smoothSlideViewTo(android.view.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 - Child view to capture and animate

finalLeft - Final left position of child

finalTop - Final top position of child

Returns:

true if animation should continue through continueSettling(boolean) calls

settleCapturedViewAt

public 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 - Settled left edge position for the captured view

finalTop - Settled top edge position for the captured view

Returns:

true if animation should continue through continueSettling(boolean) calls

flingCapturedView

public 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 - Minimum X position for the view's left edge

minTop - Minimum Y position for the view's top edge

maxLeft - Maximum X position for the view's left edge

maxTop - Maximum Y position for the view's top edge

continueSettling

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

Returns:

true if settle is still in progress

isPointerDown

public 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 - pointer ID to check; corresponds to IDs provided by MotionEvent

Returns:

true if the pointer with the given ID is still down

canScroll

protected boolean canScroll(android.view.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 to test for horizontal scrollability

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

dx - Delta scrolled in pixels along the X axis

dy - Delta scrolled in pixels along the Y axis

x - X coordinate of the active touch point

y - Y coordinate of the active touch point

Returns:

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

shouldInterceptTouchEvent

public boolean shouldInterceptTouchEvent(android.view.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 provided to onInterceptTouchEvent

Returns:

true if the parent view should return true from onInterceptTouchEvent

processTouchEvent

public void processTouchEvent(android.view.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 - The touch event received by the parent view

checkTouchSlop

public boolean checkTouchSlop(int directions)

Check if any 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 - Combination of direction flags, see DIRECTION_HORIZONTAL, DIRECTION_VERTICAL, DIRECTION_ALL

Returns:

true if the slop threshold has been crossed, false otherwise

checkTouchSlop

public 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 - Combination of direction flags, see DIRECTION_HORIZONTAL, DIRECTION_VERTICAL, DIRECTION_ALL

pointerId - ID of the pointer to slop check as specified by MotionEvent

Returns:

true if the slop threshold has been crossed, false otherwise

isEdgeTouched

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

Returns:

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

isEdgeTouched

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

Returns:

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

isCapturedViewUnder

public 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 - X position to test in the parent's coordinate system

y - Y position to test in the parent's coordinate system

Returns:

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

isViewUnder

public boolean isViewUnder(android.view.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 - Child view of the parent to hit test

x - X position to test in the parent's coordinate system

y - Y position to test in the parent's coordinate system

Returns:

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

findTopChildUnder

public android.view.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 ViewDragHelper.Callback.getOrderedChildIndex(int).

Parameters:

x - X position to test in the parent's coordinate system

y - Y position to test in the parent's coordinate system

Returns:

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