Introduction to viewtreeobserver

/** Register a callback function. This callback function is called when the focus status in a view tree changes.

* Callback function to be added with the listener Parameter

* Exception illegalstateexception if isalive () returns false

*/

Public void addonglobalfocuschangelistener (viewtreeobserver. onglobalfocuschangelistener listener)

 

/** Registers a callback function. This callback function is called when the global layout of a view tree changes or the visual status of a view in the view tree changes.

* Callback function to be added with the listener Parameter

* Exception illegalstateexception if isalive () returns false

*/

Public void addongloballayoutlistener (viewtreeobserver. ongloballayoutlistener listener)

 

/** Register a callback function, which is called when a view tree is to be drawn.

* Callback function to be added with the listener Parameter

* Exception illegalstateexception if isalive () returns false

*/

Public void addonpredrawlistener (viewtreeobserver. onpredrawlistener listener)

 

/** Register a callback function, which is called when a view is rolled.

* Callback function to be added with the listener Parameter

* Exception illegalstateexception if isalive () returns false

*/

Public void addonscrollchangedlistener (viewtreeobserver. onscrollchangedlistener listener)

 

/** Register a callback function, which is called when the touch mode changes.

* Callback function to be added with the listener Parameter

* Exception illegalstateexception if isalive () returns false

*/

Public void addontouchmodechangelistener (viewtreeobserver. ontouchmodechangelistener listener)

 

// Notify the corresponding registration listener when the entire layout changes. If you force the view layout or a view that is not attached to a window or in the gone status, it can be manually called

Public final void dispatchongloballayout ()

/** Notify the corresponding registration listener when a view tree is to be drawn. If the listener returns true, the painting will be canceled and rescheduled. If you force a view layout or a view hierarchy that is not attached to a window, or in a gone state, it can be manually called

* If the current painting can be canceled and rescheduled, true is returned; otherwise, false is returned.

*/

Public final Boolean dispatchonpredraw ()

 

/** Indicates whether the current viewtreeobserver is available (alive ). When the observer is unavailable, any method call (except this method) will throw an exception. If an application maintains a long reference with viewtreeobserver, it always needs to detect the return value of this method before calling other methods.

* Return value. If this object is available, true is returned. Otherwise, false is returned.

*/

Public Boolean isalive ()

/** Remove the previously registered global layout callback function.

* Callback function with the victim parameter to be removed

* Exception illegalstateexception if isalive () returns false

*/

Public void removeglobalonlayoutlistener (viewtreeobserver. ongloballayoutlistener victim)

/** Remove the previously registered focus change callback function.

* Callback function with the victim parameter to be removed

* Exception illegalstateexception if isalive () returns false

*/

Public void removeonglobalfocuschangelistener (viewtreeobserver. onglobalfocuschangelistener victim)

/** Remove the previously registered pre-drawn callback function.

* Callback function with the victim parameter to be removed

* Exception illegalstateexception if isalive () returns false

*/

Public void removeonpredrawlistener (viewtreeobserver. onpredrawlistener victim)

/** Remove the previously registered rolling change callback function.

* Callback function with the victim parameter to be removed

* Exception illegalstateexception if isalive () returns false

*/

Public void removeonscrollchangedlistener (viewtreeobserver. onscrollchangedlistener victim)

/** Remove the previously registered touch mode change callback function

* Callback function with the victim parameter to be removed

* Exception illegalstateexception if isalive () returns false

*/

Public void removeontouchmodechangelistener (viewtreeobserver. ontouchmodechangelistener victim)

overview of viewtreeobserver