学步园

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.

从上面的描述中，不难看出，ViewTreeObserver是用来帮助我们监听某些View的某些变化的。

 

在
ViewTreeObserver
中，包含了以下几个接口：

interface

ViewTreeObserver.OnGlobalFocusChangeListener

interface

ViewTreeObserver.OnGlobalLayoutListener

interface

ViewTreeObserver.OnPreDrawListener

interface

ViewTreeObserver.OnScrollChangedListener

interface

ViewTreeObserver.OnTouchModeChangeListener

本文将测试除
ViewTreeObserver.OnScrollChangedListener
外的四个接口

 

1.    



创建一个
Android
Project
，修改
main.xml
使之如下：

<?
xml
version
=
"1.0"

encoding
=
"utf-8"

?>

<
LinearLayout
xmlns:android
=
"http://schemas.android.com/apk/res/android"

android:id

=

"@+id/full_screen"

   


android:orientation
=
"vertical"

   


android:layout_width
=
"fill_parent"

   


android:layout_height
=
"fill_parent"

>
 

   

   

<
TextView

                  
android:id
=
"@+id/tv_show"

        
   
android:layout_width
=
"fill_parent"

        
   
android:layout_height
=
"wrap_content"

        
   
android:text
=
""

        
   
android:textSize
=
"32px"

        
   
android:textColor
=
"#FFFF00"

   

/>

   

   

<
EditText

   


android:id
=
"@+id/ed_enter1"

   


android:layout_width
=
"fill_parent"

        
   
android:layout_height
=
"wrap_content"

        
   
android:text
=
""

        
/>

        

   

<
EditText

   


android:id
=
"@+id/ed_enter2"

   


android:layout_width
=
"fill_parent"

        
   
android:layout_height
=
"wrap_content"

        
   
android:text
=
""

        
/>

        

        

<
TextView

                  
android:id
=
"@+id/tv_display"

        
   
android:layout_width
=
"fill_parent"

        
   
android:layout_height
=
"wrap_content"

        
   
android:text
=
""

   

/>

   

        

<
Button

                  
android:id
=
"@+id/button"

        
   
android:layout_width
=
"fill_parent"

        
   
android:layout_height
=
"wrap_content"

        
   

android:text
=
"OK"

   
/>
   

</
LinearLayout
>

 

注意：给
layout
增加一个
id
：
full_screen

 

2.    



Activity
对应的
Java
代码如下：

public

class
ControlViewTreeObserver
extends
Activity

implements

OnClickListener,

ViewTreeObserver.OnTouchModeChangeListener,    
      

//
用于监听
Touch
和非
Touch
模式的转换

ViewTreeObserver.OnGlobalLayoutListener,            
         

//
用于监听布局之类的变化，比如某个空间消失了

ViewTreeObserver.OnPreDrawListener,                              

//
用于在屏幕上画
View
之前，要做什么额外的工作

ViewTreeObserver.OnGlobalFocusChangeListener
        

//
用于监听焦点的变化

{

        

private
TextView
tv_show
;

   

private
ViewTreeObserver
vto
;

   

private
View
all
;

   

   

private
EditText
ed1
;

   

private
EditText
ed2
;   

   

private
TextView
tv_display
;

   

private
Button
button
;

   

private

boolean

btnClicked
;

   

   

@Override

   

public

void
onCreate(Bundle savedInstanceState)

   
{

       

super
.onCreate(savedInstanceState);

       
setContentView(R.layout.
main

);

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