Activity中获取view的高度和宽度为0的原因以及解决方案

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

 View view=findViewById(R.id.tv);
    	view.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				int width = v.getWidth();
			}
		});

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

  @Override
    public void onWindowFocusChanged(boolean hasFocus) {
    	View iv1 = findViewById(R.id.iv1);
		View iv2=findViewById(R.id.iv2);
		String msg1="iv1' width:"+iv1.getWidth()+" height:"+iv1.getHeight()+"  measuredWidth:"+iv1.getMeasuredWidth()+"measuredHeight:"+iv1.getMeasuredHeight();
		String msg2="iv2' width:"+iv2.getWidth()+" height:"+iv2.getHeight()+"  measuredWidth:"+iv2.getMeasuredWidth()+"measuredHeight:"+iv2.getMeasuredHeight();
		i("onWindowFocusChanged() "+msg1);
		i("onWindowFocusChanged() "+msg2);
    	super.onWindowFocusChanged(hasFocus);
    }

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

view.postDelayed(new Runnable() {
			
			@Override
			public void run() {
				View iv1 = findViewById(R.id.iv1);
				View iv2=findViewById(R.id.iv2);
				String msg1="iv1' width:"+iv1.getWidth()+" height:"+iv1.getHeight()+"  measuredWidth:"+iv1.getMeasuredWidth()+"measuredHeight:"+iv1.getMeasuredHeight();
				String msg2="iv2' width:"+iv2.getWidth()+" height:"+iv2.getHeight()+"  measuredWidth:"+iv2.getMeasuredWidth()+"measuredHeight:"+iv2.getMeasuredHeight();
				i("onWindowFocusChanged() "+msg1);
				i("onWindowFocusChanged() "+msg2);
			}
		}, 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

	view.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
			
			@Override
			public void onGlobalLayout() {
				view.postDelayed(new Runnable() {
					
					@Override
					public void run() {
						View iv1 = findViewById(R.id.iv1);
						View iv2=findViewById(R.id.iv2);
						String msg1="iv1' width:"+iv1.getWidth()+" height:"+iv1.getHeight()+"  measuredWidth:"+iv1.getMeasuredWidth()+"measuredHeight:"+iv1.getMeasuredHeight();
						String msg2="iv2' width:"+iv2.getWidth()+" height:"+iv2.getHeight()+"  measuredWidth:"+iv2.getMeasuredWidth()+"measuredHeight:"+iv2.getMeasuredHeight();
						i("onWindowFocusChanged() "+msg1);
						i("onWindowFocusChanged() "+msg2);
					}
				}, 300);
			}
		});

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

boolean measure;
    View iv1;
    View iv2;
    @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
        if(hasFocus && !measure){
            measure=true;
            measure();
        }
    }
    private void findViews(){
        iv1 = findViewById(R.id.iv1);
        iv2 =findViewById(R.id.iv2);
    }
    private void measure(){
        String msg1="iv1' width:"+iv1.getWidth()+" height:"+iv1.getHeight()+"  measuredWidth:"+iv1.getMeasuredWidth()+"measuredHeight:"+iv1.getMeasuredHeight();
        String msg2="iv2' width:"+iv2.getWidth()+" height:"+iv2.getHeight()+"  measuredWidth:"+iv2.getMeasuredWidth()+"measuredHeight:"+iv2.getMeasuredHeight();
        i("onWindowFocusChanged() "+msg1);
        i("onWindowFocusChanged() "+msg2);
    }