Activity中获取view的高度和宽度为0的原因以及解决方案

Posted 2020-07-01 鸭子船长

在activity中可以调用View.getWidth、View.getHeight()、View.getMeasuredWidth() 、View.getgetMeasuredHeight()来获得某个view的宽度或高度，但是在onCreate()、onStrart()、onResume()方法中会返回0，这是应为当前activity所代表的界面还没显示出来没有添加到WindowPhone的DecorView上或要获取的view没有被添加到DecorView上或者该View的visibility属性为gone 或者该view的width或height真的为0  所以只有上述条件都不成立时才能得到非0的width和height  

所以要想获取到的width和height为真实有效的 则有以下方法

1.在该View的事件回调里使用  这时候该view已经被显示即被添加到DecorView上  如点击事件  触摸事件   焦点事件等

1 View view=findViewById(R.id.tv);  
2     view.setOnClickListener(new OnClickListener() {  
3           
4         @Override  
5         public void onClick(View v) {  
6             int width = v.getWidth();  
7         }  
8     });  

2.在activity被显示出来时即添加到了DecorView上时获取宽和高如onWindowFocusChanged() 回调方法

 

 

 1 @Override  
 2   public void onWindowFocusChanged(boolean hasFocus) {  
 3     View iv1 = findViewById(R.id.iv1);  
 4 View iv2=findViewById(R.id.iv2);  
 5 String msg1="iv1‘ width:"+iv1.getWidth()+" height:"+iv1.getHeight()+"  measuredWidth:"+iv1.getMeasuredWidth()+"measuredHeight:"+iv1.getMeasuredHeight();  
 6 String msg2="iv2‘ width:"+iv2.getWidth()+" height:"+iv2.getHeight()+"  measuredWidth:"+iv2.getMeasuredWidth()+"measuredHeight:"+iv2.getMeasuredHeight();  
 7 i("onWindowFocusChanged() "+msg1);  
 8 i("onWindowFocusChanged() "+msg2);  
 9     super.onWindowFocusChanged(hasFocus);  
10   }  

3.或在onResume方法最后开线程300毫秒左右后获取宽和高   因为onResume执行完后300毫秒后 界面就显示出来了  

当然地2种和地3种方法要保证获取宽高的view是在setContentView时设进去的View或它的子View

 1 view.postDelayed(new Runnable() {  
 2               
 3             @Override  
 4             public void run() {  
 5                 View iv1 = findViewById(R.id.iv1);  
 6                 View iv2=findViewById(R.id.iv2);  
 7                 String msg1="iv1‘ width:"+iv1.getWidth()+" height:"+iv1.getHeight()+"  measuredWidth:"+iv1.getMeasuredWidth()+"measuredHeight:"+iv1.getMeasuredHeight();  
 8                 String msg2="iv2‘ width:"+iv2.getWidth()+" height:"+iv2.getHeight()+"  measuredWidth:"+iv2.getMeasuredWidth()+"measuredHeight:"+iv2.getMeasuredHeight();  
 9                 i("onWindowFocusChanged() "+msg1);  
10                 i("onWindowFocusChanged() "+msg2);  
11             }  
12         }, 300);  

4.在onCreate()或onResume()等方法中需要获取宽高时使用getViewTreeObserver().addOnGlobalLayoutListener()来添为view加回调在回调里获得宽度或者高度获取完后让view删除该回调

 1 view.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {  
 2           
 3         @Override  
 4         public void onGlobalLayout() {  
 5             view.postDelayed(new Runnable() {  
 6                   
 7                 @Override  
 8                 public void run() {  
 9                     View iv1 = findViewById(R.id.iv1);  
10                     View iv2=findViewById(R.id.iv2);  
11                     String msg1="iv1‘ width:"+iv1.getWidth()+" height:"+iv1.getHeight()+"  measuredWidth:"+iv1.getMeasuredWidth()+"measuredHeight:"+iv1.getMeasuredHeight();  
12                     String msg2="iv2‘ width:"+iv2.getWidth()+" height:"+iv2.getHeight()+"  measuredWidth:"+iv2.getMeasuredWidth()+"measuredHeight:"+iv2.getMeasuredHeight();  
13                     i("onWindowFocusChanged() "+msg1);  
14                     i("onWindowFocusChanged() "+msg2);  
15                 }  
16             }, 300);  
17         }  
18     });  

5.在窗口焦点发生变化时获取宽高 onResume完后就会把界面渲染到窗口上 渲染完后将执行窗口焦点花生变化回调   所以onResume到 onWindowFocusChanged为把界面渲染到窗口的时间

 1 boolean measure;  
 2     View iv1;  
 3     View iv2;  
 4     @Override  
 5     public void onWindowFocusChanged(boolean hasFocus) {  
 6         super.onWindowFocusChanged(hasFocus);  
 7         if(hasFocus && !measure){  
 8             measure=true;  
 9             measure();  
10         }  
11     }  
12     private void findViews(){  
13         iv1 = findViewById(R.id.iv1);  
14         iv2 =findViewById(R.id.iv2);  
15     }  
16     private void measure(){  
17         String msg1="iv1‘ width:"+iv1.getWidth()+" height:"+iv1.getHeight()+"  measuredWidth:"+iv1.getMeasuredWidth()+"measuredHeight:"+iv1.getMeasuredHeight();  
18         String msg2="iv2‘ width:"+iv2.getWidth()+" height:"+iv2.getHeight()+"  measuredWidth:"+iv2.getMeasuredWidth()+"measuredHeight:"+iv2.getMeasuredHeight();  
19         i("onWindowFocusChanged() "+msg1);  
20         i("onWindowFocusChanged() "+msg2);  
21     }