added in version 22.1.0
belongs to Maven artifact com.android.support:support-compat:28.0.0-alpha1
Summary: Constants | Ctors | Methods | Inherited Methods | [Expand All]

AutoScrollHelper

public abstract class AutoScrollHelper
extends Object implements View.OnTouchListener

java.lang.Object
   ↳ android.support.v4.widget.AutoScrollHelper
Known Direct Subclasses

AutoScrollHelper is a utility class for adding automatic edge-triggered scrolling to Views.

Note: Implementing classes are responsible for overriding the scrollTargetBy(int, int), canTargetScrollHorizontally(int), and canTargetScrollVertically(int) methods. See ListViewAutoScrollHelper for a ListView -specific implementation.

Activation

Automatic scrolling starts when the user touches within an activation area. By default, activation areas are defined as the top, left, right, and bottom 20% of the host view's total area. Touching within the top activation area scrolls up, left scrolls to the left, and so on.

As the user touches closer to the extreme edge of the activation area, scrolling accelerates up to a maximum velocity. When using the default edge type, EDGE_TYPE_INSIDE_EXTEND, moving outside of the view bounds will scroll at the maximum velocity.

The following activation properties may be configured:

Scrolling

When automatic scrolling is active, the helper will repeatedly call scrollTargetBy(int, int) to apply new scrolling offsets.

The following scrolling properties may be configured:

  • Acceleration ramp-up duration, see setRampUpDuration(int). Default value is 500 milliseconds.
  • Acceleration ramp-down duration, see setRampDownDuration(int). Default value is 500 milliseconds.
  • Target velocity relative to view size, see setRelativeVelocity(float, float). Default value is 100% per second for both vertical and horizontal.
  • Minimum velocity used to constrain relative velocity, see setMinimumVelocity(float, float). When set, scrolling will accelerate to the larger of either this value or the relative target value. Default value is approximately 5 centimeters or 315 dips per second.
  • Maximum velocity used to constrain relative velocity, see setMaximumVelocity(float, float). Default value is approximately 25 centimeters or 1575 dips per second.

Summary

Constants

int EDGE_TYPE_INSIDE

Edge type that specifies an activation area starting at the view bounds and extending inward.

int EDGE_TYPE_INSIDE_EXTEND

Edge type that specifies an activation area starting at the view bounds and extending inward.

int EDGE_TYPE_OUTSIDE

Edge type that specifies an activation area starting at the view bounds and extending outward.

float NO_MAX

Constant passed to setMaximumEdges(float, float), setMaximumVelocity(float, float), or setMinimumVelocity(float, float).

float NO_MIN

Constant passed to setMaximumEdges(float, float), or setMaximumVelocity(float, float), or setMinimumVelocity(float, float).

float RELATIVE_UNSPECIFIED

Constant passed to setRelativeEdges(float, float) or setRelativeVelocity(float, float).

Public constructors

AutoScrollHelper(View target)

Creates a new helper for scrolling the specified target view.

Public methods

abstract boolean canTargetScrollHorizontally(int direction)

Override this method to return whether the target view can be scrolled horizontally in a certain direction.

abstract boolean canTargetScrollVertically(int direction)

Override this method to return whether the target view can be scrolled vertically in a certain direction.

boolean isEnabled()
boolean isExclusive()

Indicates whether the scroll helper handles touch events exclusively during scrolling.

boolean onTouch(View v, MotionEvent event)

Handles touch events by activating automatic scrolling, adjusting scroll velocity, or stopping.

abstract void scrollTargetBy(int deltaX, int deltaY)

Override this method to scroll the target view by the specified number of pixels.

AutoScrollHelper setActivationDelay(int delayMillis)

Sets the delay after entering an activation edge before activation of auto-scrolling.

AutoScrollHelper setEdgeType(int type)

Sets the activation edge type, one of:

  • EDGE_TYPE_INSIDE for edges that respond to touches inside the bounds of the host view.

AutoScrollHelper setEnabled(boolean enabled)

Sets whether the scroll helper is enabled and should respond to touch events.

AutoScrollHelper setExclusive(boolean exclusive)

Enables or disables exclusive handling of touch events during scrolling.

AutoScrollHelper setMaximumEdges(float horizontalMax, float verticalMax)

Sets the absolute maximum edge size.

AutoScrollHelper setMaximumVelocity(float horizontalMax, float verticalMax)

Sets the absolute maximum scrolling velocity.

AutoScrollHelper setMinimumVelocity(float horizontalMin, float verticalMin)

Sets the absolute minimum scrolling velocity.

AutoScrollHelper setRampDownDuration(int durationMillis)

Sets the amount of time after de-activation of auto-scrolling that is takes to slow to a stop.

AutoScrollHelper setRampUpDuration(int durationMillis)

Sets the amount of time after activation of auto-scrolling that is takes to reach target velocity for the current touch position.

AutoScrollHelper setRelativeEdges(float horizontal, float vertical)

Sets the activation edge size relative to the host view's dimensions.

AutoScrollHelper setRelativeVelocity(float horizontal, float vertical)

Sets the target scrolling velocity relative to the host view's dimensions.

Inherited methods

From class java.lang.Object
From interface android.view.View.OnTouchListener

Constants

EDGE_TYPE_INSIDE

added in version 22.1.0 
int EDGE_TYPE_INSIDE

Edge type that specifies an activation area starting at the view bounds and extending inward. Moving outside the view bounds will stop scrolling.

See also:

Constant Value: 0 (0x00000000)

EDGE_TYPE_INSIDE_EXTEND

added in version 22.1.0 
int EDGE_TYPE_INSIDE_EXTEND

Edge type that specifies an activation area starting at the view bounds and extending inward. After activation begins, moving outside the view bounds will continue scrolling.

See also:

Constant Value: 1 (0x00000001)

EDGE_TYPE_OUTSIDE

added in version 22.1.0 
int EDGE_TYPE_OUTSIDE

Edge type that specifies an activation area starting at the view bounds and extending outward. Moving inside the view bounds will stop scrolling.

See also:

Constant Value: 2 (0x00000002)

NO_MAX

added in version 22.1.0 
float NO_MAX

Constant passed to setMaximumEdges(float, float), setMaximumVelocity(float, float), or setMinimumVelocity(float, float). Using this value ensures that the computed relative value is always used without constraining to a particular minimum or maximum value.

Constant Value: 3.4028235E38

NO_MIN

added in version 22.1.0 
float NO_MIN

Constant passed to setMaximumEdges(float, float), or setMaximumVelocity(float, float), or setMinimumVelocity(float, float). Using this value ensures that the computed relative value is always used without constraining to a particular minimum or maximum value.

Constant Value: 0.0

RELATIVE_UNSPECIFIED

added in version 22.1.0 
float RELATIVE_UNSPECIFIED

Constant passed to setRelativeEdges(float, float) or setRelativeVelocity(float, float). Using this value ensures that the computed relative value is ignored and the absolute maximum value is always used.

Constant Value: 0.0

Public constructors

AutoScrollHelper

added in version 22.1.0
AutoScrollHelper (View target)

Creates a new helper for scrolling the specified target view.

The resulting helper may be configured by chaining setter calls and should be set as a touch listener on the target view.

By default, the helper is disabled and will not respond to touch events until it is enabled using setEnabled(boolean).

Parameters
target View: The view to automatically scroll.

Public methods

canTargetScrollHorizontally

added in version 22.1.0
boolean canTargetScrollHorizontally (int direction)

Override this method to return whether the target view can be scrolled horizontally in a certain direction.

Parameters
direction int: Negative to check scrolling left, positive to check scrolling right.
Returns
boolean true if the target view is able to horizontally scroll in the specified direction.

canTargetScrollVertically

added in version 22.1.0
boolean canTargetScrollVertically (int direction)

Override this method to return whether the target view can be scrolled vertically in a certain direction.

Parameters
direction int: Negative to check scrolling up, positive to check scrolling down.
Returns
boolean true if the target view is able to vertically scroll in the specified direction.

isEnabled

added in version 22.1.0
boolean isEnabled ()

Returns
boolean True if this helper is enabled and responding to touch events.

isExclusive

added in version 22.1.0
boolean isExclusive ()

Indicates whether the scroll helper handles touch events exclusively during scrolling.

Returns
boolean True if exclusive handling of touch events during scrolling is enabled, false otherwise.

onTouch

added in version 22.1.0
boolean onTouch (View v, 
                MotionEvent event)

Handles touch events by activating automatic scrolling, adjusting scroll velocity, or stopping.

If isExclusive() is false, always returns false so that the host view may handle touch events. Otherwise, returns true when automatic scrolling is active and false otherwise.

Parameters
v View

event MotionEvent

Returns
boolean

scrollTargetBy

added in version 22.1.0
void scrollTargetBy (int deltaX, 
                int deltaY)

Override this method to scroll the target view by the specified number of pixels.

Parameters
deltaX int: The number of pixels to scroll by horizontally.
deltaY int: The number of pixels to scroll by vertically.

setActivationDelay

added in version 22.1.0
AutoScrollHelper setActivationDelay (int delayMillis)

Sets the delay after entering an activation edge before activation of auto-scrolling. By default, the activation delay is set to getTapTimeout().

Specifying a delay of zero will start auto-scrolling immediately after the touch position enters an activation edge.

Parameters
delayMillis