# Print output for @column tags ?>
public
class
ScrollView
extends FrameLayout
java.lang.Object | ||||
↳ | android.view.View | |||
↳ | android.view.ViewGroup | |||
↳ | android.widget.FrameLayout | |||
↳ | android.widget.ScrollView |
A view group that allows the view hierarchy placed within it to be scrolled.
Scroll view may have only one direct child placed within it.
To add multiple views within the scroll view, make
the direct child you add a view group, for example LinearLayout
, and
place additional views within that LinearLayout.
Scroll view supports vertical scrolling only. For horizontal scrolling,
use HorizontalScrollView
instead.
Never add a RecyclerView
or ListView
to
a scroll view. Doing so results in poor user interface performance and a poor user
experience.
For vertical scrolling, consider NestedScrollView
instead of scroll view which offers greater user interface flexibility and
support for the material design scrolling patterns.
Material Design offers guidelines on how the appearance of several UI components, including app bars and banners, should respond to gestures.
XML attributes | |
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android:fillViewport |
Defines whether the scrollview should stretch its content to fill the viewport. |
Inherited XML attributes | |
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Inherited constants |
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Inherited fields |
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Public constructors | |
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ScrollView(Context context)
|
|
ScrollView(Context context, AttributeSet attrs)
|
|
ScrollView(Context context, AttributeSet attrs, int defStyleAttr)
|
|
ScrollView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes)
|
Public methods | |
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void
|
addView(View child, int index)
Adds a child view. |
void
|
addView(View child, ViewGroup.LayoutParams params)
Adds a child view with the specified layout parameters. |
void
|
addView(View child, int index, ViewGroup.LayoutParams params)
Adds a child view with the specified layout parameters. |
void
|
addView(View child)
Adds a child view. |
boolean
|
arrowScroll(int direction)
Handle scrolling in response to an up or down arrow click. |
void
|
computeScroll()
Called by a parent to request that a child update its values for mScrollX and mScrollY if necessary. |
boolean
|
dispatchKeyEvent(KeyEvent event)
Dispatch a key event to the next view on the focus path. |
void
|
draw(Canvas canvas)
Manually render this view (and all of its children) to the given Canvas. |
boolean
|
executeKeyEvent(KeyEvent event)
You can call this function yourself to have the scroll view perform scrolling from a key event, just as if the event had been dispatched to it by the view hierarchy. |
void
|
fling(int velocityY)
Fling the scroll view |
boolean
|
fullScroll(int direction)
Handles scrolling in response to a "home/end" shortcut press. |
CharSequence
|
getAccessibilityClassName()
Return the class name of this object to be used for accessibility purposes. |
int
|
getBottomEdgeEffectColor()
Returns the bottom edge effect color. |
int
|
getMaxScrollAmount()
|
int
|
getTopEdgeEffectColor()
Returns the top edge effect color. |
boolean
|
isFillViewport()
Indicates whether this ScrollView's content is stretched to fill the viewport. |
boolean
|
isSmoothScrollingEnabled()
|
boolean
|
onGenericMotionEvent(MotionEvent event)
Implement this method to handle generic motion events. |
boolean
|
onInterceptTouchEvent(MotionEvent ev)
Implement this method to intercept all touch screen motion events. |
boolean
|
onNestedFling(View target, float velocityX, float velocityY, boolean consumed)
Request a fling from a nested scroll. |
void
|
onNestedScroll(View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed)
React to a nested scroll in progress. |
void
|
onNestedScrollAccepted(View child, View target, int axes)
React to the successful claiming of a nested scroll operation. |
boolean
|
onStartNestedScroll(View child, View target, int nestedScrollAxes)
React to a descendant view initiating a nestable scroll operation, claiming the nested scroll operation if appropriate. |
void
|
onStopNestedScroll(View target)
React to a nested scroll operation ending. |
boolean
|
onTouchEvent(MotionEvent ev)
Implement this method to handle touch screen motion events. |
boolean
|
pageScroll(int direction)
Handles scrolling in response to a "page up/down" shortcut press. |
void
|
requestChildFocus(View child, View focused)
Called when a child of this parent wants focus |
boolean
|
requestChildRectangleOnScreen(View child, Rect rectangle, boolean immediate)
Called when a child of this group wants a particular rectangle to be positioned onto the screen. |
void
|
requestDisallowInterceptTouchEvent(boolean disallowIntercept)
Called when a child does not want this parent and its ancestors to
intercept touch events with
|
void
|
requestLayout()
Call this when something has changed which has invalidated the layout of this view. |
void
|
scrollTo(int x, int y)
Set the scrolled position of your view. This version also clamps the scrolling to the bounds of our child. |
void
|
scrollToDescendant(View child)
Scrolls the view to the given child. |
void
|
setBottomEdgeEffectColor(int color)
Sets the bottom edge effect color. |
void
|
setEdgeEffectColor(int color)
Sets the edge effect color for both top and bottom edge effects. |
void
|
setFillViewport(boolean fillViewport)
Indicates this ScrollView whether it should stretch its content height to fill the viewport or not. |
void
|
setSmoothScrollingEnabled(boolean smoothScrollingEnabled)
Set whether arrow scrolling will animate its transition. |
void
|
setTopEdgeEffectColor(int color)
Sets the top edge effect color. |
boolean
|
shouldDelayChildPressedState()
Return true if the pressed state should be delayed for children or descendants of this ViewGroup. |
final
void
|
smoothScrollBy(int dx, int dy)
Like |
final
void
|
smoothScrollTo(int x, int y)
Like |
Protected methods | |
---|---|
int
|
computeScrollDeltaToGetChildRectOnScreen(Rect rect)
Compute the amount to scroll in the Y direction in order to get a rectangle completely on the screen (or, if taller than the screen, at least the first screen size chunk of it). |
int
|
computeVerticalScrollOffset()
Compute the vertical offset of the vertical scrollbar's thumb within the horizontal range. |
int
|
computeVerticalScrollRange()
The scroll range of a scroll view is the overall height of all of its children. |
float
|
getBottomFadingEdgeStrength()
Returns the strength, or intensity, of the bottom faded edge. |
float
|
getTopFadingEdgeStrength()
Returns the strength, or intensity, of the top faded edge. |
void
|
measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)
Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding. |
void
|
measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed)
Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding and margins. |
void
|
onDetachedFromWindow()
This is called when the view is detached from a window. |
void
|
onLayout(boolean changed, int l, int t, int r, int b)
Called from layout when this view should assign a size and position to each of its children. |
void
|
onMeasure(int widthMeasureSpec, int heightMeasureSpec)
Measure the view and its content to determine the measured width and the measured height. |
void
|
onOverScrolled(int scrollX, int scrollY, boolean clampedX, boolean clampedY)
Called by |
boolean
|
onRequestFocusInDescendants(int direction, Rect previouslyFocusedRect)
When looking for focus in children of a scroll view, need to be a little more careful not to give focus to something that is scrolled off screen. |
void
|
onRestoreInstanceState(Parcelable state)
Hook allowing a view to re-apply a representation of its internal state that had previously
been generated by |
Parcelable
|
onSaveInstanceState()
Hook allowing a view to generate a representation of its internal state that can later be used to create a new instance with that same state. |
void
|
onSizeChanged(int w, int h, int oldw, int oldh)
This is called during layout when the size of this view has changed. |
Inherited methods | |
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Defines whether the scrollview should stretch its content to fill the viewport.
May be a boolean value, such as "true
" or
"false
".
Related methods:
public ScrollView (Context context, AttributeSet attrs)
Parameters | |
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context |
Context |
attrs |
AttributeSet |
public ScrollView (Context context, AttributeSet attrs, int defStyleAttr)
Parameters | |
---|---|
context |
Context |
attrs |
AttributeSet |
defStyleAttr |
int |
public ScrollView (Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes)
Parameters | |
---|---|
context |
Context |
attrs |
AttributeSet |
defStyleAttr |
int |
defStyleRes |
int |
public void addView (View child, int index)
Adds a child view. If no layout parameters are already set on the child, the default parameters for this ViewGroup are set on the child.
Note: do not invoke this method from
View.draw(android.graphics.Canvas)
, View.onDraw(android.graphics.Canvas)
,
dispatchDraw(android.graphics.Canvas)
or any related method.
Parameters | |
---|---|
child |
View : the child view to add |
index |
int : the position at which to add the child |
public void addView (View child, ViewGroup.LayoutParams params)
Adds a child view with the specified layout parameters.
Note: do not invoke this method from
View.draw(android.graphics.Canvas)
, View.onDraw(android.graphics.Canvas)
,
dispatchDraw(android.graphics.Canvas)
or any related method.
Parameters | |
---|---|
child |
View : the child view to add |
params |
ViewGroup.LayoutParams : the layout parameters to set on the child |
public void addView (View child, int index, ViewGroup.LayoutParams params)
Adds a child view with the specified layout parameters.
Note: do not invoke this method from
View.draw(android.graphics.Canvas)
, View.onDraw(android.graphics.Canvas)
,
dispatchDraw(android.graphics.Canvas)
or any related method.
Parameters | |
---|---|
child |
View : the child view to add |
index |
int : the position at which to add the child or -1 to add last |
params |
ViewGroup.LayoutParams : the layout parameters to set on the child |
public void addView (View child)
Adds a child view. If no layout parameters are already set on the child, the default parameters for this ViewGroup are set on the child.
Note: do not invoke this method from
View.draw(android.graphics.Canvas)
, View.onDraw(android.graphics.Canvas)
,
dispatchDraw(android.graphics.Canvas)
or any related method.
Parameters | |
---|---|
child |
View : the child view to add |
public boolean arrowScroll (int direction)
Handle scrolling in response to an up or down arrow click.
Parameters | |
---|---|
direction |
int : The direction corresponding to the arrow key that was
pressed |
Returns | |
---|---|
boolean |
True if we consumed the event, false otherwise |
public void computeScroll ()
Called by a parent to request that a child update its values for mScrollX
and mScrollY if necessary. This will typically be done if the child is
animating a scroll using a Scroller
object.
public boolean dispatchKeyEvent (KeyEvent event)
Dispatch a key event to the next view on the focus path. This path runs from the top of the view tree down to the currently focused view. If this view has focus, it will dispatch to itself. Otherwise it will dispatch the next node down the focus path. This method also fires any key listeners.
Parameters | |
---|---|
event |
KeyEvent : The key event to be dispatched. |
Returns | |
---|---|
boolean |
True if the event was handled, false otherwise. |
public void draw (Canvas canvas)
Manually render this view (and all of its children) to the given Canvas.
The view must have already done a full layout before this function is
called. When implementing a view, implement
onDraw(android.graphics.Canvas)
instead of overriding this method.
If you do need to override this method, call the superclass version.
If you override this method you must call through to the
superclass implementation.
Parameters | |
---|---|
canvas |
Canvas : The Canvas to which the View is rendered. |
public boolean executeKeyEvent (KeyEvent event)
You can call this function yourself to have the scroll view perform scrolling from a key event, just as if the event had been dispatched to it by the view hierarchy.
Parameters | |
---|---|
event |
KeyEvent : The key event to execute. |
Returns | |
---|---|
boolean |
Return true if the event was handled, else false. |
public void fling (int velocityY)
Fling the scroll view
Parameters | |
---|---|
velocityY |
int : The initial velocity in the Y direction. Positive
numbers mean that the finger/cursor is moving down the screen,
which means we want to scroll towards the top. |
public boolean fullScroll (int direction)
Handles scrolling in response to a "home/end" shortcut press. This method will scroll the view to the top or bottom and give the focus to the topmost/bottommost component in the new visible area. If no component is a good candidate for focus, this scrollview reclaims the focus.
Parameters | |
---|---|
direction |
int : the scroll direction: View.FOCUS_UP
to go the top of the view or
View.FOCUS_DOWN to go the bottom |
Returns | |
---|---|
boolean |
true if the key event is consumed by this method, false otherwise |
public CharSequence getAccessibilityClassName ()
Return the class name of this object to be used for accessibility purposes.
Subclasses should only override this if they are implementing something that
should be seen as a completely new class of view when used by accessibility,
unrelated to the class it is deriving from. This is used to fill in
AccessibilityNodeInfo#setClassName
.
Returns | |
---|---|
CharSequence |
public int getBottomEdgeEffectColor ()
Returns the bottom edge effect color.
Returns | |
---|---|
int |
The bottom edge effect color. |
public int getMaxScrollAmount ()
Returns | |
---|---|
int |
The maximum amount this scroll view will scroll in response to an arrow event. |
public int getTopEdgeEffectColor ()
Returns the top edge effect color.
Returns | |
---|---|
int |
The top edge effect color. |
public boolean isFillViewport ()
Indicates whether this ScrollView's content is stretched to fill the viewport.
Related XML Attributes:
Returns | |
---|---|
boolean |
True if the content fills the viewport, false otherwise. |
public boolean isSmoothScrollingEnabled ()
Returns | |
---|---|
boolean |
Whether arrow scrolling will animate its transition. |
public boolean onGenericMotionEvent (MotionEvent event)
Implement this method to handle generic motion events.
Generic motion events describe joystick movements, mouse hovers, track pad
touches, scroll wheel movements and other input events. The
MotionEvent#getSource()
of the motion event specifies
the class of input that was received. Implementations of this method
must examine the bits in the source before processing the event.
The following code example shows how this is done.
Generic motion events with source class InputDevice#SOURCE_CLASS_POINTER
are delivered to the view under the pointer. All other generic motion events are
delivered to the focused view.
public boolean onGenericMotionEvent(MotionEvent event) { if (event.isFromSource(InputDevice.SOURCE_CLASS_JOYSTICK)) { if (event.getAction() == MotionEvent.ACTION_MOVE) { // process the joystick movement... return true; } } if (event.isFromSource(InputDevice.SOURCE_CLASS_POINTER)) { switch (event.getAction()) { case MotionEvent.ACTION_HOVER_MOVE: // process the mouse hover movement... return true; case MotionEvent.ACTION_SCROLL: // process the scroll wheel movement... return true; } } return super.onGenericMotionEvent(event); }
Parameters | |
---|---|
event |
MotionEvent : The generic motion event being processed. |
Returns | |
---|---|
boolean |
True if the event was handled, false otherwise. |
public boolean onInterceptTouchEvent (MotionEvent ev)
Implement this method to intercept all touch screen motion events. This allows you to watch events as they are dispatched to your children, and take ownership of the current gesture at any point.
Using this function takes some care, as it has a fairly complicated
interaction with View#onTouchEvent(MotionEvent)
, and using it requires implementing
that method as well as this one in the correct way. Events will be
received in the following order:
MotionEvent#ACTION_CANCEL
, and all further
events will be delivered to your onTouchEvent() method and no longer
appear here.
Parameters | |
---|---|
ev |
MotionEvent : The motion event being dispatched down the hierarchy. |
Returns | |
---|---|
boolean |
Return true to steal motion events from the children and have them dispatched to this ViewGroup through onTouchEvent(). The current target will receive an ACTION_CANCEL event, and no further messages will be delivered here. |
public boolean onNestedFling (View target, float velocityX, float velocityY, boolean consumed)
Request a fling from a nested scroll.
This method signifies that a nested scrolling child has detected suitable conditions
for a fling. Generally this means that a touch scroll has ended with a
VelocityTracker
in the direction of scrolling that meets or exceeds
the ViewConfiguration#getScaledMinimumFlingVelocity()
along a scrollable axis.
If a nested scrolling child view would normally fling but it is at the edge of its own content, it can use this method to delegate the fling to its nested scrolling parent instead. The parent may optionally consume the fling or observe a child fling.
Parameters | |
---|---|
target |
View : View that initiated the nested scroll |
velocityX |
float : Horizontal velocity in pixels per second |
velocityY |
float : Vertical velocity in pixels per second |
consumed |
boolean : true if the child consumed the fling, false otherwise |
Returns | |
---|---|
boolean |
true if this parent consumed or otherwise reacted to the fling |
public void onNestedScroll (View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed)
React to a nested scroll in progress.
This method will be called when the ViewParent's current nested scrolling child view
dispatches a nested scroll event. To receive calls to this method the ViewParent must have
previously returned true
for a call to
onStartNestedScroll(android.view.View, android.view.View, int)
.
Both the consumed and unconsumed portions of the scroll distance are reported to the ViewParent. An implementation may choose to use the consumed portion to match or chase scroll position of multiple child elements, for example. The unconsumed portion may be used to allow continuous dragging of multiple scrolling or draggable elements, such as scrolling a list within a vertical drawer where the drawer begins dragging once the edge of inner scrolling content is reached.
Parameters | |
---|---|
target |
View : The descendent view controlling the nested scroll |
dxConsumed |
int : Horizontal scroll distance in pixels already consumed by target |
dyConsumed |
int : Vertical scroll distance in pixels already consumed by target |
dxUnconsumed |
int : Horizontal scroll distance in pixels not consumed by target |
dyUnconsumed |
int : Vertical scroll distance in pixels not consumed by target |
public void onNestedScrollAccepted (View child, View target, int axes)
React to the successful claiming of a nested scroll operation.
This method will be called after
onStartNestedScroll
returns true. It offers
an opportunity for the view and its superclasses to perform initial configuration
for the nested scroll. Implementations of this method should always call their superclass's
implementation of this method if one is present.
Parameters | |
---|---|
child |
View : Direct child of this ViewParent containing target |
target |
View : View that initiated the nested scroll |
axes |
int : Flags consisting of View#SCROLL_AXIS_HORIZONTAL ,
View#SCROLL_AXIS_VERTICAL or both |
public boolean onStartNestedScroll (View child, View target, int nestedScrollAxes)
React to a descendant view initiating a nestable scroll operation, claiming the nested scroll operation if appropriate.
This method will be called in response to a descendant view invoking
View#startNestedScroll(int)
. Each parent up the view hierarchy will be
given an opportunity to respond and claim the nested scrolling operation by returning
true
.
This method may be overridden by ViewParent implementations to indicate when the view
is willing to support a nested scrolling operation that is about to begin. If it returns
true, this ViewParent will become the target view's nested scrolling parent for the duration
of the scroll operation in progress. When the nested scroll is finished this ViewParent
will receive a call to onStopNestedScroll(android.view.View)
.
Parameters | |
---|---|
child |
View : Direct child of this ViewParent containing target |
target |
View : View that initiated the nested scroll |
nestedScrollAxes |
int : Flags consisting of View#SCROLL_AXIS_HORIZONTAL ,
View#SCROLL_AXIS_VERTICAL or both |
Returns | |
---|---|
boolean |
true if this ViewParent accepts the nested scroll operation |
public void onStopNestedScroll (View target)
React to a nested scroll operation ending.
Perform cleanup after a nested scrolling operation.
This method will be called when a nested scroll stops, for example when a nested touch
scroll ends with a MotionEvent#ACTION_UP
or MotionEvent#ACTION_CANCEL
event.
Implementations of this method should always call their superclass's implementation of this
method if one is present.
Parameters | |
---|---|
target |
View : View that initiated the nested scroll |
public boolean onTouchEvent (MotionEvent ev)
Implement this method to handle touch screen motion events.
If this method is used to detect click actions, it is recommended that
the actions be performed by implementing and calling
performClick()
. This will ensure consistent system behavior,
including:
AccessibilityNodeInfo#ACTION_CLICK
when
accessibility features are enabled
Parameters | |
---|---|
ev |
MotionEvent : The motion event. |
Returns | |
---|---|
boolean |
True if the event was handled, false otherwise. |
public boolean pageScroll (int direction)
Handles scrolling in response to a "page up/down" shortcut press. This method will scroll the view by one page up or down and give the focus to the topmost/bottommost component in the new visible area. If no component is a good candidate for focus, this scrollview reclaims the focus.
Parameters | |
---|---|
direction |
int : the scroll direction: View.FOCUS_UP
to go one page up or
View.FOCUS_DOWN to go one page down |
Returns | |
---|---|
boolean |
true if the key event is consumed by this method, false otherwise |
public void requestChildFocus (View child, View focused)
Called when a child of this parent wants focus
Parameters | |
---|---|
child |
View : The child of this ViewParent that wants focus. This view
will contain the focused view. It is not necessarily the view that
actually has focus. |
focused |
View : The view that is a descendant of child that actually has
focus |
public boolean requestChildRectangleOnScreen (View child, Rect rectangle, boolean immediate)
Called when a child of this group wants a particular rectangle to be
positioned onto the screen. ViewGroup
s overriding this can trust
that:
ViewGroup
s overriding this should uphold the contract:
Parameters | |
---|---|
child |
View : The direct child making the request. |
rectangle |
Rect : The rectangle in the child's coordinates the child
wishes to be on the screen. |
immediate |
boolean : True to forbid animated or delayed scrolling,
false otherwise |
Returns | |
---|---|
boolean |
Whether the group scrolled to handle the operation |
public void requestDisallowInterceptTouchEvent (boolean disallowIntercept)
Called when a child does not want this parent and its ancestors to
intercept touch events with
ViewGroup#onInterceptTouchEvent(MotionEvent)
.
This parent should pass this call onto its parents. This parent must obey this request for the duration of the touch (that is, only clear the flag after this parent has received an up or a cancel.
Parameters | |
---|---|
disallowIntercept |
boolean : True if the child does not want the parent to
intercept touch events. |
public void requestLayout ()
Call this when something has changed which has invalidated the
layout of this view. This will schedule a layout pass of the view
tree. This should not be called while the view hierarchy is currently in a layout
pass (isInLayout()
. If layout is happening, the request may be honored at the
end of the current layout pass (and then layout will run again) or after the current
frame is drawn and the next layout occurs.
Subclasses which override this method should call the superclass method to handle possible request-during-layout errors correctly.
public void scrollTo (int x, int y)
Set the scrolled position of your view. This will cause a call to
onScrollChanged(int, int, int, int)
and the view will be
invalidated.
This version also clamps the scrolling to the bounds of our child.
Parameters | |
---|---|
x |
int : the x position to scroll to |
y |
int : the y position to scroll to |
public void scrollToDescendant (View child)
Scrolls the view to the given child.
Parameters | |
---|---|
child |
View : the View to scroll to
This value cannot be null . |
public void setBottomEdgeEffectColor (int color)
Sets the bottom edge effect color.
Parameters | |
---|---|
color |
int : The color for the bottom edge effect. |
public void setEdgeEffectColor (int color)
Sets the edge effect color for both top and bottom edge effects.
Parameters | |
---|---|
color |
int : The color for the edge effects. |
public void setFillViewport (boolean fillViewport)
Indicates this ScrollView whether it should stretch its content height to fill the viewport or not.
Related XML Attributes:
Parameters | |
---|---|
fillViewport |
boolean : True to stretch the content's height to the viewport's
boundaries, false otherwise. |
public void setSmoothScrollingEnabled (boolean smoothScrollingEnabled)
Set whether arrow scrolling will animate its transition.
Parameters | |
---|---|
smoothScrollingEnabled |
boolean : whether arrow scrolling will animate its transition |
public void setTopEdgeEffectColor (int color)
Sets the top edge effect color.
Parameters | |
---|---|
color |
int : The color for the top edge effect. |
public boolean shouldDelayChildPressedState ()
Return true if the pressed state should be delayed for children or descendants of this ViewGroup. Generally, this should be done for containers that can scroll, such as a List. This prevents the pressed state from appearing when the user is actually trying to scroll the content. The default implementation returns true for compatibility reasons. Subclasses that do not scroll should generally override this method and return false.
Returns | |
---|---|
boolean |
public final void smoothScrollBy (int dx, int dy)
Like View#scrollBy
, but scroll smoothly instead of immediately.
Parameters | |
---|---|
dx |
int : the number of pixels to scroll by on the X axis |
dy |
int : the number of pixels to scroll by on the Y axis |
public final void smoothScrollTo (int x, int y)
Like scrollTo(int, int)
, but scroll smoothly instead of immediately.
Parameters | |
---|---|
x |
int : the position where to scroll on the X axis |
y |
int : the position where to scroll on the Y axis |
protected int computeScrollDeltaToGetChildRectOnScreen (Rect rect)
Compute the amount to scroll in the Y direction in order to get a rectangle completely on the screen (or, if taller than the screen, at least the first screen size chunk of it).
Parameters | |
---|---|
rect |
Rect : The rect. |
Returns | |
---|---|
int |
The scroll delta. |
protected int computeVerticalScrollOffset ()
Compute the vertical offset of the vertical scrollbar's thumb within the horizontal range. This value is used to compute the position of the thumb within the scrollbar's track.
The range is expressed in arbitrary units that must be the same as the
units used by computeVerticalScrollRange()
and
computeVerticalScrollExtent()
.
The default offset is the scroll offset of this view.
Returns | |
---|---|
int |
the vertical offset of the scrollbar's thumb |
protected int computeVerticalScrollRange ()
The scroll range of a scroll view is the overall height of all of its children.
Returns | |
---|---|
int |
the total vertical range represented by the vertical scrollbar
The default range is the drawing height of this view. |
protected float getBottomFadingEdgeStrength ()
Returns the strength, or intensity, of the bottom faded edge. The strength is a value between 0.0 (no fade) and 1.0 (full fade). The default implementation returns 0.0 or 1.0 but no value in between. Subclasses should override this method to provide a smoother fade transition when scrolling occurs.
Returns | |
---|---|
float |
the intensity of the bottom fade as a float between 0.0f and 1.0f |
protected float getTopFadingEdgeStrength ()
Returns the strength, or intensity, of the top faded edge. The strength is a value between 0.0 (no fade) and 1.0 (full fade). The default implementation returns 0.0 or 1.0 but no value in between. Subclasses should override this method to provide a smoother fade transition when scrolling occurs.
Returns | |
---|---|
float |
the intensity of the top fade as a float between 0.0f and 1.0f |
protected void measureChild (View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)
Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding. The heavy lifting is done in getChildMeasureSpec.
Parameters | |
---|---|
child |
View : The child to measure |
parentWidthMeasureSpec |
int : The width requirements for this view |
parentHeightMeasureSpec |
int : The height requirements for this view |
protected void measureChildWithMargins (View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed)
Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding and margins. The child must have MarginLayoutParams The heavy lifting is done in getChildMeasureSpec.
Parameters | |
---|---|
child |
View : The child to measure |
parentWidthMeasureSpec |
int : The width requirements for this view |
widthUsed |
int : Extra space that has been used up by the parent
horizontally (possibly by other children of the parent) |
parentHeightMeasureSpec |
int : The height requirements for this view |
heightUsed |
int : Extra space that has been used up by the parent
vertically (possibly by other children of the parent) |
protected void onDetachedFromWindow ()
This is called when the view is detached from a window. At this point it
no longer has a surface for drawing.
If you override this method you must call through to the
superclass implementation.
protected void onLayout (boolean changed, int l, int t, int r, int b)
Called from layout when this view should assign a size and position to each of its children. Derived classes with children should override this method and call layout on each of their children.
Parameters | |
---|---|
changed |
boolean : This is a new size or position for this view |
l |
int : Left position, relative to parent |
t |
int : Top position, relative to parent |
r |
int : Right position, relative to parent |
b |
int : Bottom position, relative to parent |
protected void onMeasure (int widthMeasureSpec, int heightMeasureSpec)
Measure the view and its content to determine the measured width and the
measured height. This method is invoked by measure(int, int)
and
should be overridden by subclasses to provide accurate and efficient
measurement of their contents.
CONTRACT: When overriding this method, you
must call setMeasuredDimension(int, int)
to store the
measured width and height of this view. Failure to do so will trigger an
IllegalStateException
, thrown by
measure(int, int)
. Calling the superclass'
onMeasure(int, int)
is a valid use.
The base class implementation of measure defaults to the background size,
unless a larger size is allowed by the MeasureSpec. Subclasses should
override onMeasure(int, int)
to provide better measurements of
their content.
If this method is overridden, it is the subclass's responsibility to make
sure the measured height and width are at least the view's minimum height
and width (getSuggestedMinimumHeight()
and
getSuggestedMinimumWidth()
).
Parameters | |
---|---|
widthMeasureSpec |
int : horizontal space requirements as imposed by the parent.
The requirements are encoded with
View.MeasureSpec . |
heightMeasureSpec |
int : vertical space requirements as imposed by the parent.
The requirements are encoded with
View.MeasureSpec . |
protected void onOverScrolled (int scrollX, int scrollY, boolean clampedX, boolean clampedY)
Called by overScrollBy(int, int, int, int, int, int, int, int, boolean)
to
respond to the results of an over-scroll operation.
Parameters | |
---|---|
scrollX |
int : New X scroll value in pixels |
scrollY |
int : New Y scroll value in pixels |
clampedX |
boolean : True if scrollX was clamped to an over-scroll boundary |
clampedY |
boolean : True if scrollY was clamped to an over-scroll boundary |
protected boolean onRequestFocusInDescendants (int direction, Rect previouslyFocusedRect)
When looking for focus in children of a scroll view, need to be a little
more careful not to give focus to something that is scrolled off screen.
This is more expensive than the default ViewGroup
implementation, otherwise this behavior might have been made the default.
Parameters | |
---|---|
direction |
int : One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and FOCUS_RIGHT |
previouslyFocusedRect |
Rect : The rectangle (in this View's coordinate system)
to give a finer grained hint about where focus is coming from. May be null
if there is no hint. |
Returns | |
---|---|
boolean |
Whether focus was taken. |
protected void onRestoreInstanceState (Parcelable state)
Hook allowing a view to re-apply a representation of its internal state that had previously
been generated by onSaveInstanceState()
. This function will never be called with a
null state.
If you override this method you must call through to the
superclass implementation.
Parameters | |
---|---|
state |
Parcelable : The frozen state that had previously been returned by
onSaveInstanceState() . |
protected Parcelable onSaveInstanceState ()
Hook allowing a view to generate a representation of its internal state that can later be used to create a new instance with that same state. This state should only contain information that is not persistent or can not be reconstructed later. For example, you will never store your current position on screen because that will be computed again when a new instance of the view is placed in its view hierarchy.
Some examples of things you may store here: the current cursor position
in a text view (but usually not the text itself since that is stored in a
content provider or other persistent storage), the currently selected
item in a list view.
If you override this method you must call through to the
superclass implementation.
Returns | |
---|---|
Parcelable |
Returns a Parcelable object containing the view's current dynamic state, or null if there is nothing interesting to save. |
protected void onSizeChanged (int w, int h, int oldw, int oldh)
This is called during layout when the size of this view has changed. If you were just added to the view hierarchy, you're called with the old values of 0.
Parameters | |
---|---|
w |
int : Current width of this view. |
h |
int : Current height of this view. |
oldw |
int : Old width of this view. |
oldh |
int : Old height of this view. |