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.
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:
setActivationDelay(int)
. Default value is
getTapTimeout()
to avoid conflicting with taps.
setEdgeType(int)
. Default value is
EDGE_TYPE_INSIDE_EXTEND
.
setRelativeEdges(float, float)
. Default value is 20% for both vertical and
horizontal edges.
setMaximumEdges(float, float)
. Default value is NO_MAX
.
scrollTargetBy(int, int)
to apply new scrolling offsets.
The following scrolling properties may be configured:
setRampUpDuration(int)
. Default
value is 500 milliseconds.
setRampDownDuration(int)
.
Default value is 500 milliseconds.
setRelativeVelocity(float, float)
.
Default value is 100% per second for both vertical and horizontal.
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.
setMaximumVelocity(float, float)
. Default value is approximately 25 centimeters or
1575 dips per second.
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 | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Creates a new helper for scrolling the specified target view.
|
Public Methods | |||||||||||
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Override this method to return whether the target view can be scrolled
horizontally in a certain direction.
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Override this method to return whether the target view can be scrolled
vertically in a certain direction.
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Indicates whether the scroll helper handles touch events exclusively
during scrolling.
| |||||||||||
Handles touch events by activating automatic scrolling, adjusting scroll
velocity, or stopping.
| |||||||||||
Override this method to scroll the target view by the specified number of
pixels.
| |||||||||||
Sets the delay after entering an activation edge before activation of
auto-scrolling.
| |||||||||||
Sets the activation edge type, one of:
| |||||||||||
Sets whether the scroll helper is enabled and should respond to touch
events.
| |||||||||||
Enables or disables exclusive handling of touch events during scrolling.
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Sets the absolute maximum edge size.
| |||||||||||
Sets the absolute maximum scrolling velocity.
| |||||||||||
Sets the absolute minimum scrolling velocity.
| |||||||||||
Sets the amount of time after de-activation of auto-scrolling that is
takes to slow to a stop.
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Sets the amount of time after activation of auto-scrolling that is takes
to reach target velocity for the current touch position.
| |||||||||||
Sets the activation edge size relative to the host view's dimensions.
| |||||||||||
Sets the target scrolling velocity relative to the host view's
dimensions.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.lang.Object
| |||||||||||
From interface
android.view.View.OnTouchListener
|
Edge type that specifies an activation area starting at the view bounds and extending inward. Moving outside the view bounds will stop scrolling.
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.
Edge type that specifies an activation area starting at the view bounds and extending outward. Moving inside the view bounds will stop scrolling.
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 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 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.
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)
.
target | The view to automatically scroll. |
---|
Override this method to return whether the target view can be scrolled horizontally in a certain direction.
direction | Negative to check scrolling left, positive to check scrolling right. |
---|
Override this method to return whether the target view can be scrolled vertically in a certain direction.
direction | Negative to check scrolling up, positive to check scrolling down. |
---|
Indicates whether the scroll helper handles touch events exclusively during scrolling.
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.
v | The view the touch event has been dispatched to. |
---|---|
event | The MotionEvent object containing full information about the event. |
Override this method to scroll the target view by the specified number of pixels.
deltaX | The number of pixels to scroll by horizontally. |
---|---|
deltaY | The number of pixels to scroll by vertically. |
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.
delayMillis | The activation delay in milliseconds. |
---|
Sets the activation edge type, one of:
EDGE_TYPE_INSIDE
for edges that respond to touches inside
the bounds of the host view. If touch moves outside the bounds, scrolling
will stop.
EDGE_TYPE_INSIDE_EXTEND
for inside edges that continued to
scroll when touch moves outside the bounds of the host view.
EDGE_TYPE_OUTSIDE
for edges that only respond to touches
that move outside the bounds of the host view.
type | The type of edge to use. |
---|
Sets whether the scroll helper is enabled and should respond to touch events.
enabled | Whether the scroll helper is enabled. |
---|
Enables or disables exclusive handling of touch events during scrolling. By default, exclusive handling is disabled and the target view receives all touch events.
When enabled, onTouch(View, MotionEvent)
will return true if the helper is
currently scrolling and false otherwise.
exclusive | True to exclusively handle touch events during scrolling, false to allow the target view to receive all touch events. |
---|
Sets the absolute maximum edge size.
If relative edge size is not specified, activation edges will always be the maximum edge size. If both relative and maximum edges are specified, the maximum edge will be used to constrain the calculated relative edge size.
horizontalMax | The maximum horizontal edge size in pixels, or
NO_MAX to use the unconstrained calculated relative
value. |
---|---|
verticalMax | The maximum vertical edge size in pixels, or
NO_MAX to use the unconstrained calculated relative
value. |
Sets the absolute maximum scrolling velocity.
If relative velocity is not specified, scrolling will always reach the same maximum velocity. If both relative and maximum velocities are specified, the maximum velocity will be used to clamp the calculated relative velocity.
horizontalMax | The maximum horizontal scrolling velocity, or
NO_MAX to leave the relative value unconstrained. |
---|---|
verticalMax | The maximum vertical scrolling velocity, or
NO_MAX to leave the relative value unconstrained. |
Sets the absolute minimum scrolling velocity.
If both relative and minimum velocities are specified, the minimum velocity will be used to clamp the calculated relative velocity.
horizontalMin | The minimum horizontal scrolling velocity, or
NO_MIN to leave the relative value unconstrained. |
---|---|
verticalMin | The minimum vertical scrolling velocity, or
NO_MIN to leave the relative value unconstrained. |
Sets the amount of time after de-activation of auto-scrolling that is takes to slow to a stop.
Specifying a duration greater than zero prevents sudden jumps in velocity.
durationMillis | The ramp-down duration in milliseconds. |
---|
Sets the amount of time after activation of auto-scrolling that is takes to reach target velocity for the current touch position.
Specifying a duration greater than zero prevents sudden jumps in velocity.
durationMillis | The ramp-up duration in milliseconds. |
---|
Sets the activation edge size relative to the host view's dimensions.
If both relative and maximum edges are specified, the maximum edge will be used to constrain the calculated relative edge size.
horizontal | The horizontal edge size as a fraction of the host view
width, or RELATIVE_UNSPECIFIED to always use the
maximum value. |
---|---|
vertical | The vertical edge size as a fraction of the host view
height, or RELATIVE_UNSPECIFIED to always use the
maximum value. |
Sets the target scrolling velocity relative to the host view's dimensions.
If both relative and maximum velocities are specified, the maximum velocity will be used to clamp the calculated relative velocity.
horizontal | The target horizontal velocity as a fraction of the
host view width per second, or RELATIVE_UNSPECIFIED
to ignore. |
---|---|
vertical | The target vertical velocity as a fraction of the host
view height per second, or RELATIVE_UNSPECIFIED to
ignore. |