Package icyllis.modernui.view

Class ViewTreeObserver

java.lang.Object

icyllis.modernui.view.ViewTreeObserver

public final class ViewTreeObserver
extends Object

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.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	ViewTreeObserver.OnGlobalFocusChangeListener	Interface definition for a callback to be invoked when the focus state within the view tree changes.
static 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.
static interface	ViewTreeObserver.OnPreDrawListener	Interface definition for a callback to be invoked when the view tree is about to be drawn.
static interface	ViewTreeObserver.OnScrollChangedListener	Interface definition for a callback to be invoked when something in the view tree has been scrolled.

Method Summary

Modifier and Type	Method	Description
void	addOnGlobalFocusChangeListener(ViewTreeObserver.OnGlobalFocusChangeListener listener)	Register a callback to be invoked when the focus state within the view tree changes.
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	dispatchOnGlobalLayout()	Notifies registered listeners that a global layout happened.
boolean	dispatchOnPreDraw()	Notifies registered listeners that the drawing pass is about to start.
void	dispatchOnScrollChanged()	Notifies registered listeners that something has scrolled.
boolean	isAlive()	Indicates whether this ViewTreeObserver is alive.
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

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

addOnGlobalFocusChangeListener

public void addOnGlobalFocusChangeListener(@NonNull
 ViewTreeObserver.OnGlobalFocusChangeListener listener)

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

Parameters:

listener - The callback to add

Throws:

IllegalStateException - If isAlive() returns false

removeOnGlobalFocusChangeListener

public void removeOnGlobalFocusChangeListener(@NonNull
 ViewTreeObserver.OnGlobalFocusChangeListener victim)

Remove a previously installed focus change callback.

Parameters:

victim - The callback to remove

Throws:

IllegalStateException - If isAlive() returns false

See Also:

• addOnGlobalFocusChangeListener(OnGlobalFocusChangeListener)

addOnGlobalLayoutListener

public void addOnGlobalLayoutListener(@NonNull
 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 - The callback to add

Throws:

IllegalStateException - If isAlive() returns false

removeOnGlobalLayoutListener

public void removeOnGlobalLayoutListener(@NonNull
 ViewTreeObserver.OnGlobalLayoutListener victim)

Remove a previously installed global layout callback

Parameters:

victim - The callback to remove

Throws:

IllegalStateException - If isAlive() returns false

See Also:

• addOnGlobalLayoutListener(OnGlobalLayoutListener)

addOnPreDrawListener

public void addOnPreDrawListener(@NonNull
 ViewTreeObserver.OnPreDrawListener listener)

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

Parameters:

listener - The callback to add

Throws:

IllegalStateException - If isAlive() returns false

removeOnPreDrawListener

public void removeOnPreDrawListener(@NonNull
 ViewTreeObserver.OnPreDrawListener victim)

Remove a previously installed pre-draw callback

Parameters:

victim - The callback to remove

Throws:

IllegalStateException - If isAlive() returns false

See Also:

• addOnPreDrawListener(OnPreDrawListener)

addOnScrollChangedListener

public void addOnScrollChangedListener(@NonNull
 ViewTreeObserver.OnScrollChangedListener listener)

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

Parameters:

listener - The callback to add

Throws:

IllegalStateException - If isAlive() returns false

removeOnScrollChangedListener

public void removeOnScrollChangedListener(@NonNull
 ViewTreeObserver.OnScrollChangedListener victim)

Remove a previously installed scroll-changed callback

Parameters:

victim - The callback to remove

Throws:

IllegalStateException - If isAlive() returns false

See Also:

• addOnScrollChangedListener(OnScrollChangedListener)

isAlive

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:

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

dispatchOnGlobalLayout

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

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:

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

dispatchOnScrollChanged

public void dispatchOnScrollChanged()

Notifies registered listeners that something has scrolled.