Added in API level 1

Summary: Nested Classes | Methods | Inherited Methods

ViewTreeObserver

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Kotlin |Java

public final class ViewTreeObserver
extends Object

java.lang.Object
↳	android.view.ViewTreeObserver

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A view tree observer is used to register listeners that can be notified of global changes in the view tree. Such global events include, but are not limited to, layout of the whole tree, beginning of the drawing pass, touch mode change.... A ViewTreeObserver should never be instantiated by applications as it is provided by the views hierarchy. Refer to View.getViewTreeObserver() for more information.

Summary

Nested classes
interface	ViewTreeObserver.OnDrawListener Interface definition for a callback to be invoked when the view tree is about to be drawn.
interface	ViewTreeObserver.OnGlobalFocusChangeListener Interface definition for a callback to be invoked when the focus state within the view tree changes.
interface	ViewTreeObserver.OnGlobalLayoutListener Interface definition for a callback to be invoked when the global layout state or the visibility of views within the view tree changes.
interface	ViewTreeObserver.OnPreDrawListener Interface definition for a callback to be invoked when the view tree is about to be drawn.
interface	ViewTreeObserver.OnScrollChangedListener Interface definition for a callback to be invoked when something in the view tree has been scrolled.
interface	ViewTreeObserver.OnTouchModeChangeListener Interface definition for a callback to be invoked when the touch mode changes.
interface	ViewTreeObserver.OnWindowAttachListener Interface definition for a callback to be invoked when the view hierarchy is attached to and detached from its window.
interface	ViewTreeObserver.OnWindowFocusChangeListener Interface definition for a callback to be invoked when the view hierarchy's window focus state changes.
interface	ViewTreeObserver.OnWindowVisibilityChangeListener Interface definition for a callback to be invoked when the view hierarchy's window visibility changes.

Public methods
void	addOnDrawListener(ViewTreeObserver.OnDrawListener listener) Register a callback to be invoked when the view tree is about to be drawn.
void	addOnGlobalFocusChangeListener(ViewTreeObserver.OnGlobalFocusChangeListener listener)
void	addOnGlobalLayoutListener(ViewTreeObserver.OnGlobalLayoutListener listener) Register a callback to be invoked when the global layout state or the visibility of views within the view tree changes
void	addOnPreDrawListener(ViewTreeObserver.OnPreDrawListener listener) Register a callback to be invoked when the view tree is about to be drawn
void	addOnScrollChangedListener(ViewTreeObserver.OnScrollChangedListener listener) Register a callback to be invoked when a view has been scrolled.
void	addOnSystemGestureExclusionRectsChangedListener(Consumer<List<Rect>> listener) Add a listener to be notified when the tree's transformed gesture exclusion rects change.
void	addOnTouchModeChangeListener(ViewTreeObserver.OnTouchModeChangeListener listener) Register a callback to be invoked when the invoked when the touch mode changes.
void	addOnWindowAttachListener(ViewTreeObserver.OnWindowAttachListener listener) Register a callback to be invoked when the view hierarchy is attached to a window.
void	addOnWindowFocusChangeListener(ViewTreeObserver.OnWindowFocusChangeListener listener) Register a callback to be invoked when the window focus state within the view tree changes.
void	addOnWindowVisibilityChangeListener(ViewTreeObserver.OnWindowVisibilityChangeListener listener) Register a callback to be invoked when the window visibility changes.
void	dispatchOnDraw() Notifies registered listeners that the drawing pass is about to start.
void	dispatchOnGlobalLayout() Notifies registered listeners that a global layout happened.
boolean	dispatchOnPreDraw() Notifies registered listeners that the drawing pass is about to start.
boolean	isAlive() Indicates whether this ViewTreeObserver is alive.
void	registerFrameCommitCallback(Runnable callback) Adds a frame commit callback.
void	removeGlobalOnLayoutListener(ViewTreeObserver.OnGlobalLayoutListener victim) This method was deprecated in API level 16. Use #removeOnGlobalLayoutListener instead
void	removeOnDrawListener(ViewTreeObserver.OnDrawListener victim) Remove a previously installed pre-draw callback.
void	removeOnGlobalFocusChangeListener(ViewTreeObserver.OnGlobalFocusChangeListener victim) Remove a previously installed focus change callback.
void	removeOnGlobalLayoutListener(ViewTreeObserver.OnGlobalLayoutListener victim) Remove a previously installed global layout callback
void	removeOnPreDrawListener(ViewTreeObserver.OnPreDrawListener victim) Remove a previously installed pre-draw callback
void	removeOnScrollChangedListener(ViewTreeObserver.OnScrollChangedListener victim) Remove a previously installed scroll-changed callback
void	removeOnSystemGestureExclusionRectsChangedListener(Consumer<List<Rect>> listener) Unsubscribe the given listener from gesture exclusion rect changes.
void	removeOnTouchModeChangeListener(ViewTreeObserver.OnTouchModeChangeListener victim) Remove a previously installed touch mode change callback
void	removeOnWindowAttachListener(ViewTreeObserver.OnWindowAttachListener victim) Remove a previously installed window attach callback.
void	removeOnWindowFocusChangeListener(ViewTreeObserver.OnWindowFocusChangeListener victim) Remove a previously installed window focus change callback.
void	removeOnWindowVisibilityChangeListener(ViewTreeObserver.OnWindowVisibilityChangeListener victim) Remove a previously installed window visibility callback.
boolean	unregisterFrameCommitCallback(Runnable callback) Attempts to remove the given callback from the list of pending frame complete callbacks.

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 timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Public methods

addOnDrawListener

Added in API level 16

public void addOnDrawListener (ViewTreeObserver.OnDrawListener listener)

Register a callback to be invoked when the view tree is about to be drawn.

Note: this method cannot be invoked from ViewTreeObserver.OnDrawListener.onDraw().

Parameters
listener	ViewTreeObserver.OnDrawListener: The callback to add

Throws
IllegalStateException	If isAlive() returns false

addOnGlobalFocusChangeListener

Added in API level 1

public void addOnGlobalFocusChangeListener (ViewTreeObserver.OnGlobalFocusChangeListener listener)

Parameters
listener	ViewTreeObserver.OnGlobalFocusChangeListener

addOnGlobalLayoutListener

Added in API level 1

public void addOnGlobalLayoutListener (ViewTreeObserver.OnGlobalLayoutListener listener)

Register a callback to be invoked when the global layout state or the visibility of views within the view tree changes

Parameters
listener	ViewTreeObserver.OnGlobalLayoutListener: The callback to add

Throws
IllegalStateException	If isAlive() returns false

addOnPreDrawListener

Added in API level 1

public void addOnPreDrawListener (ViewTreeObserver.OnPreDrawListener listener)

Register a callback to be invoked when the view tree is about to be drawn

Parameters
listener	ViewTreeObserver.OnPreDrawListener: The callback to add

Throws
IllegalStateException	If isAlive() returns false

addOnScrollChangedListener

Added in API level 3

public void addOnScrollChangedListener (ViewTreeObserver.OnScrollChangedListener listener)

Register a callback to be invoked when a view has been scrolled.

Parameters
listener	ViewTreeObserver.OnScrollChangedListener: The callback to add

Throws
IllegalStateException	If isAlive() returns false

addOnSystemGestureExclusionRectsChangedListener

Added in API level 29

public void addOnSystemGestureExclusionRectsChangedListener (Consumer<List<Rect>> listener)

Add a listener to be notified when the tree's transformed gesture exclusion rects change. This could be the result of an animation or other layout change, or a view calling View#setSystemGestureExclusionRects(List).

Parameters
listener	Consumer: listener to add This value cannot be null.

See also:

• View.setSystemGestureExclusionRects(List)

addOnTouchModeChangeListener

Added in API level 1

public void addOnTouchModeChangeListener (ViewTreeObserver.OnTouchModeChangeListener listener)

Register a callback to be invoked when the invoked when the touch mode changes.

Parameters
listener	ViewTreeObserver.OnTouchModeChangeListener: The callback to add

Throws
IllegalStateException	If isAlive() returns false

addOnWindowAttachListener

Added in API level 18

public void addOnWindowAttachListener (ViewTreeObserver.OnWindowAttachListener listener)

Register a callback to be invoked when the view hierarchy is attached to a window.

Parameters
listener	ViewTreeObserver.OnWindowAttachListener: The callback to add

Throws
IllegalStateException	If isAlive() returns false

addOnWindowFocusChangeListener

Added in API level 18

public void addOnWindowFocusChangeListener (ViewTreeObserver.OnWindowFocusChangeListener listener)

Register a callback to be invoked when the window focus state within the view tree changes.

Parameters
listener	ViewTreeObserver.OnWindowFocusChangeListener: The callback to add

Throws
IllegalStateException	If isAlive() returns false

addOnWindowVisibilityChangeListener

Added in API level 34

public void addOnWindowVisibilityChangeListener (ViewTreeObserver.OnWindowVisibilityChangeListener listener)

Register a callback to be invoked when the window visibility changes.

Parameters
listener	ViewTreeObserver.OnWindowVisibilityChangeListener: The callback to add This value cannot be null.

Throws
IllegalStateException	If isAlive() returns false

dispatchOnDraw

Added in API level 16

public void dispatchOnDraw ()

Notifies registered listeners that the drawing pass is about to start.

dispatchOnGlobalLayout

Added in API level 1

public void dispatchOnGlobalLayout ()

Notifies registered listeners that a global layout happened. This can be called manually if you are forcing a layout on a View or a hierarchy of Views that are not attached to a Window or in the GONE state.

dispatchOnPreDraw

Added in API level 1

public boolean dispatchOnPreDraw ()

Notifies registered listeners that the drawing pass is about to start. If a listener returns true, then the drawing pass is canceled and rescheduled. This can be called manually if you are forcing the drawing on a View or a hierarchy of Views that are not attached to a Window or in the GONE state.

Returns
boolean	True if the current draw should be canceled and rescheduled, false otherwise.

isAlive

Added in API level 1

public boolean isAlive ()

Indicates whether this ViewTreeObserver is alive. When an observer is not alive, any call to a method (except this one) will throw an exception. If an application keeps a long-lived reference to this ViewTreeObserver, it should always check for the result of this method before calling any other method.

Returns
boolean	True if this object is alive and be used, false otherwise.

registerFrameCommitCallback

Added in API level 29

public void registerFrameCommitCallback (Runnable callback)

Adds a frame commit callback. This callback will be invoked when the current rendering content has been rendered into a frame and submitted to the swap chain. The frame may not currently be visible on the display when this is invoked, but it has been submitted. This callback is useful in combination with PixelCopy to capture the current rendered content of the UI reliably. Note: Only works with hardware rendering. Does nothing otherwise.

Parameters
callback	Runnable: The callback to invoke when the frame is committed. This value cannot be null.

removeGlobalOnLayoutListener

Added in API level 1
Deprecated in API level 16

public void removeGlobalOnLayoutListener (ViewTreeObserver.OnGlobalLayoutListener victim)

This method was deprecated in API level 16.
Use #removeOnGlobalLayoutListener instead

Remove a previously installed global layout callback

Parameters
victim	ViewTreeObserver.OnGlobalLayoutListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnGlobalLayoutListener(OnGlobalLayoutListener)

removeOnDrawListener

Added in API level 16

public void removeOnDrawListener (ViewTreeObserver.OnDrawListener victim)

Remove a previously installed pre-draw callback.

Note: this method cannot be invoked from ViewTreeObserver.OnDrawListener.onDraw().

Parameters
victim	ViewTreeObserver.OnDrawListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnDrawListener(OnDrawListener)

removeOnGlobalFocusChangeListener

Added in API level 1

public void removeOnGlobalFocusChangeListener (ViewTreeObserver.OnGlobalFocusChangeListener victim)

Remove a previously installed focus change callback.

Parameters
victim	ViewTreeObserver.OnGlobalFocusChangeListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnGlobalFocusChangeListener(OnGlobalFocusChangeListener)

removeOnGlobalLayoutListener

Added in API level 16

public void removeOnGlobalLayoutListener (ViewTreeObserver.OnGlobalLayoutListener victim)

Remove a previously installed global layout callback

Parameters
victim	ViewTreeObserver.OnGlobalLayoutListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnGlobalLayoutListener(OnGlobalLayoutListener)

removeOnPreDrawListener

Added in API level 1

public void removeOnPreDrawListener (ViewTreeObserver.OnPreDrawListener victim)

Remove a previously installed pre-draw callback

Parameters
victim	ViewTreeObserver.OnPreDrawListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnPreDrawListener(OnPreDrawListener)

removeOnScrollChangedListener

Added in API level 3

public void removeOnScrollChangedListener (ViewTreeObserver.OnScrollChangedListener victim)

Remove a previously installed scroll-changed callback

Parameters
victim	ViewTreeObserver.OnScrollChangedListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnScrollChangedListener(OnScrollChangedListener)

removeOnSystemGestureExclusionRectsChangedListener

Added in API level 29

public void removeOnSystemGestureExclusionRectsChangedListener (Consumer<List<Rect>> listener)

Unsubscribe the given listener from gesture exclusion rect changes.

Parameters
listener	Consumer: This value cannot be null.

See also:

• addOnSystemGestureExclusionRectsChangedListener(Consumer)
• View.setSystemGestureExclusionRects(List)

removeOnTouchModeChangeListener

Added in API level 1

public void removeOnTouchModeChangeListener (ViewTreeObserver.OnTouchModeChangeListener victim)

Remove a previously installed touch mode change callback

Parameters
victim	ViewTreeObserver.OnTouchModeChangeListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnTouchModeChangeListener(OnTouchModeChangeListener)

removeOnWindowAttachListener

Added in API level 18

public void removeOnWindowAttachListener (ViewTreeObserver.OnWindowAttachListener victim)

Remove a previously installed window attach callback.

Parameters
victim	ViewTreeObserver.OnWindowAttachListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnWindowAttachListener(android.view.ViewTreeObserver.OnWindowAttachListener)

removeOnWindowFocusChangeListener

Added in API level 18

public void removeOnWindowFocusChangeListener (ViewTreeObserver.OnWindowFocusChangeListener victim)

Remove a previously installed window focus change callback.

Parameters
victim	ViewTreeObserver.OnWindowFocusChangeListener: The callback to remove

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnWindowFocusChangeListener(android.view.ViewTreeObserver.OnWindowFocusChangeListener)

removeOnWindowVisibilityChangeListener

Added in API level 34

public void removeOnWindowVisibilityChangeListener (ViewTreeObserver.OnWindowVisibilityChangeListener victim)

Remove a previously installed window visibility callback.

Parameters
victim	ViewTreeObserver.OnWindowVisibilityChangeListener: The callback to remove This value cannot be null.

Throws
IllegalStateException	If isAlive() returns false

See also:

• addOnWindowVisibilityChangeListener(android.view.ViewTreeObserver.OnWindowVisibilityChangeListener)

unregisterFrameCommitCallback

Added in API level 29

public boolean unregisterFrameCommitCallback (Runnable callback)

Attempts to remove the given callback from the list of pending frame complete callbacks.

Parameters
callback	Runnable: The callback to remove This value cannot be null.

Returns
boolean	Whether or not the callback was removed. If this returns true the callback will not be invoked. If false is returned then the callback was either never added or may already be pending execution and was unable to be removed