Added in API level 1

ViewTreeObserver

---

Kotlin |Java

class ViewTreeObserver

kotlin.Any
↳	android.view.ViewTreeObserver

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 android.view.View#getViewTreeObserver() for more information.

Summary

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

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

Public methods

addOnDrawListener

Added in API level 16

fun addOnDrawListener(listener: ViewTreeObserver.OnDrawListener!): Unit

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

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

Parameters
listener	ViewTreeObserver.OnDrawListener!: The callback to add

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

addOnGlobalFocusChangeListener

Added in API level 1

fun addOnGlobalFocusChangeListener(listener: ViewTreeObserver.OnGlobalFocusChangeListener!): Unit

addOnGlobalLayoutListener

Added in API level 1

fun addOnGlobalLayoutListener(listener: ViewTreeObserver.OnGlobalLayoutListener!): Unit

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

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

addOnPreDrawListener

Added in API level 1

fun addOnPreDrawListener(listener: ViewTreeObserver.OnPreDrawListener!): Unit

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

Parameters
listener	ViewTreeObserver.OnPreDrawListener!: The callback to add

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

addOnScrollChangedListener

Added in API level 3

fun addOnScrollChangedListener(listener: ViewTreeObserver.OnScrollChangedListener!): Unit

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

Parameters
listener	ViewTreeObserver.OnScrollChangedListener!: The callback to add

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

addOnSystemGestureExclusionRectsChangedListener

Added in API level 29

fun addOnSystemGestureExclusionRectsChangedListener(listener: Consumer<MutableList<Rect!>!>): Unit

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<MutableList<Rect!>!>: listener to add This value cannot be null.

See Also

• android.view.View#setSystemGestureExclusionRects(List)

addOnTouchModeChangeListener

Added in API level 1

fun addOnTouchModeChangeListener(listener: ViewTreeObserver.OnTouchModeChangeListener!): Unit

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

Parameters
listener	ViewTreeObserver.OnTouchModeChangeListener!: The callback to add

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

addOnWindowAttachListener

Added in API level 18

fun addOnWindowAttachListener(listener: ViewTreeObserver.OnWindowAttachListener!): Unit

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

Parameters
listener	ViewTreeObserver.OnWindowAttachListener!: The callback to add

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

addOnWindowFocusChangeListener

Added in API level 18

fun addOnWindowFocusChangeListener(listener: ViewTreeObserver.OnWindowFocusChangeListener!): Unit

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

Parameters
listener	ViewTreeObserver.OnWindowFocusChangeListener!: The callback to add

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

addOnWindowVisibilityChangeListener

Added in API level 34

fun addOnWindowVisibilityChangeListener(listener: ViewTreeObserver.OnWindowVisibilityChangeListener): Unit

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

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

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

dispatchOnDraw

Added in API level 16

fun dispatchOnDraw(): Unit

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

dispatchOnGlobalLayout

Added in API level 1

fun dispatchOnGlobalLayout(): Unit

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

fun dispatchOnPreDraw(): Boolean

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.

Return
Boolean	True if the current draw should be canceled and rescheduled, false otherwise.

isAlive

Added in API level 1

fun isAlive(): Boolean

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.

Return
Boolean	True if this object is alive and be used, false otherwise.

registerFrameCommitCallback

Added in API level 29

fun registerFrameCommitCallback(callback: Runnable): Unit

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

fun removeGlobalOnLayoutListener(victim: ViewTreeObserver.OnGlobalLayoutListener!): Unit

Deprecated: Use #removeOnGlobalLayoutListener instead

Remove a previously installed global layout callback

Parameters
victim	ViewTreeObserver.OnGlobalLayoutListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnGlobalLayoutListener(OnGlobalLayoutListener)

removeOnDrawListener

Added in API level 16

fun removeOnDrawListener(victim: ViewTreeObserver.OnDrawListener!): Unit

Remove a previously installed pre-draw callback.

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

Parameters
victim	ViewTreeObserver.OnDrawListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnDrawListener(OnDrawListener)

removeOnGlobalFocusChangeListener

Added in API level 1

fun removeOnGlobalFocusChangeListener(victim: ViewTreeObserver.OnGlobalFocusChangeListener!): Unit

Remove a previously installed focus change callback.

Parameters
victim	ViewTreeObserver.OnGlobalFocusChangeListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnGlobalFocusChangeListener(OnGlobalFocusChangeListener)

removeOnGlobalLayoutListener

Added in API level 16

fun removeOnGlobalLayoutListener(victim: ViewTreeObserver.OnGlobalLayoutListener!): Unit

Remove a previously installed global layout callback

Parameters
victim	ViewTreeObserver.OnGlobalLayoutListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnGlobalLayoutListener(OnGlobalLayoutListener)

removeOnPreDrawListener

Added in API level 1

fun removeOnPreDrawListener(victim: ViewTreeObserver.OnPreDrawListener!): Unit

Remove a previously installed pre-draw callback

Parameters
victim	ViewTreeObserver.OnPreDrawListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnPreDrawListener(OnPreDrawListener)

removeOnScrollChangedListener

Added in API level 3

fun removeOnScrollChangedListener(victim: ViewTreeObserver.OnScrollChangedListener!): Unit

Remove a previously installed scroll-changed callback

Parameters
victim	ViewTreeObserver.OnScrollChangedListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnScrollChangedListener(OnScrollChangedListener)

removeOnSystemGestureExclusionRectsChangedListener

Added in API level 29

fun removeOnSystemGestureExclusionRectsChangedListener(listener: Consumer<MutableList<Rect!>!>): Unit

Unsubscribe the given listener from gesture exclusion rect changes.

Parameters
listener	Consumer<MutableList<Rect!>!>: This value cannot be null.

See Also

• #addOnSystemGestureExclusionRectsChangedListener(Consumer)
• android.view.View#setSystemGestureExclusionRects(List)

removeOnTouchModeChangeListener

Added in API level 1

fun removeOnTouchModeChangeListener(victim: ViewTreeObserver.OnTouchModeChangeListener!): Unit

Remove a previously installed touch mode change callback

Parameters
victim	ViewTreeObserver.OnTouchModeChangeListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnTouchModeChangeListener(OnTouchModeChangeListener)

removeOnWindowAttachListener

Added in API level 18

fun removeOnWindowAttachListener(victim: ViewTreeObserver.OnWindowAttachListener!): Unit

Remove a previously installed window attach callback.

Parameters
victim	ViewTreeObserver.OnWindowAttachListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnWindowAttachListener(android.view.ViewTreeObserver.OnWindowAttachListener)

removeOnWindowFocusChangeListener

Added in API level 18

fun removeOnWindowFocusChangeListener(victim: ViewTreeObserver.OnWindowFocusChangeListener!): Unit

Remove a previously installed window focus change callback.

Parameters
victim	ViewTreeObserver.OnWindowFocusChangeListener!: The callback to remove

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnWindowFocusChangeListener(android.view.ViewTreeObserver.OnWindowFocusChangeListener)

removeOnWindowVisibilityChangeListener

Added in API level 34

fun removeOnWindowVisibilityChangeListener(victim: ViewTreeObserver.OnWindowVisibilityChangeListener): Unit

Remove a previously installed window visibility callback.

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

Exceptions
java.lang.IllegalStateException	If isAlive() returns false

See Also

• #addOnWindowVisibilityChangeListener( * android.view.ViewTreeObserver.OnWindowVisibilityChangeListener)

unregisterFrameCommitCallback

Added in API level 29

fun unregisterFrameCommitCallback(callback: Runnable): Boolean

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.

Return
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