Android初级教程_获取Android控件的宽和高 .

我们都知道在onCreate()里面获取控件的高度是0,这是为什么呢?我们来看一下示例:

首先我们自己写一个控件,这个控件非常简单:

 

public class MyImageView extends ImageView {

     public MyImageView(Context context, AttributeSet attrs) {
         super(context, attrs);
    }
     public MyImageView(Context context) {
         super(context);
    }

     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         super.onMeasure(widthMeasureSpec, heightMeasureSpec);
         System.out.println("onMeasure 我被调用了"+System.currentTimeMillis());
    }

     @Override
     protected void onDraw(Canvas canvas) {
         super.onDraw(canvas);
         System.out.println("onDraw 我被调用了"+System.currentTimeMillis());
    }

}

public class MyImageView extends ImageView {

	public MyImageView(Context context, AttributeSet attrs) {
		super(context, attrs);
	}
	public MyImageView(Context context) {
		super(context);
	}
	
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
		System.out.println("onMeasure 我被调用了"+System.currentTimeMillis());
	}
	
	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		System.out.println("onDraw 我被调用了"+System.currentTimeMillis());
	}

}

 

 

布局文件:

 

<com.test.MyImageView
     android:id="@+id/imageview"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:src="@drawable/test" />

    <com.test.MyImageView
        android:id="@+id/imageview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/test" />

测试的Activity的onCreate():

 

 

@Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
     System.out.println("执行完毕.."+System.currentTimeMillis());
}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);        
        System.out.println("执行完毕.."+System.currentTimeMillis());
    }

现在我们现在来看一下结果:

 

说明等onCreate方法执行完了,我们定义的控件才会被度量(measure),所以我们在onCreate方法里面通过view.getHeight()获取控件的高度或者宽度肯定是0,因为它自己还没有被度量,也就是说他自己都不知道自己有多高,而你这时候去获取它的尺寸,肯定是不行的.

 

现在碰到这个问题我们不能不解决,在网上找到了如下办法:

 

//------------------------------------------------方法一
 int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
 int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
imageView.measure(w, h);
 int height =imageView.getMeasuredHeight();
 int width =imageView.getMeasuredWidth();
 textView.append("\n"+height+","+width);




 //-----------------------------------------------方法二
ViewTreeObserver vto = imageView.getViewTreeObserver();
 vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
     public boolean onPreDraw() {
         int height = imageView.getMeasuredHeight();
         int width = imageView.getMeasuredWidth();
         textView.append("\n"+height+","+width);
         return true;
    }
});
 //-----------------------------------------------方法三
ViewTreeObserver vto2 = imageView.getViewTreeObserver();
 vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
     @Override
     public void onGlobalLayout() {
         imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
         textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
    }
});

        //------------------------------------------------方法一
        int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
        int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
        imageView.measure(w, h);
        int height =imageView.getMeasuredHeight();
        int width =imageView.getMeasuredWidth();
        textView.append("\n"+height+","+width);
        
        
        

        //-----------------------------------------------方法二
        ViewTreeObserver vto = imageView.getViewTreeObserver();
        vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
            public boolean onPreDraw() {
                int height = imageView.getMeasuredHeight();
                int width = imageView.getMeasuredWidth();
                textView.append("\n"+height+","+width);
                return true;
            }
        });
        //-----------------------------------------------方法三   
        ViewTreeObserver vto2 = imageView.getViewTreeObserver();  
        vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
            @Override  
            public void onGlobalLayout() {
            	imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);  
                textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
            }  
        });  

这三个方法是哪里找到现在已经忘了.

 

 

现在要讨论的是当我们需要时候使用哪个方法呢?

现在把测试的Activity改成如下:

 

@Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
       final ImageView imageView = (ImageView) findViewById(R.id.imageview);

       //------------------------------------------------方法一
       int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
       int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
      imageView.measure(w, h);
       int height =imageView.getMeasuredHeight();
       int width =imageView.getMeasuredWidth();
       textView.append("\n"+height+","+width);

       System.out.println("执行完毕.."+System.currentTimeMillis());
  }

  @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        final ImageView imageView = (ImageView) findViewById(R.id.imageview);      
        
        //------------------------------------------------方法一
        int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
        int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
        imageView.measure(w, h);
        int height =imageView.getMeasuredHeight();
        int width =imageView.getMeasuredWidth();
        textView.append("\n"+height+","+width);
        
        System.out.println("执行完毕.."+System.currentTimeMillis());
    }

 

 

接着来看下面几种方式输出结果:

把测试Activity改成如下:

 

@Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
     final ImageView imageView = (ImageView) findViewById(R.id.imageview);
-----------------------------------------------方法二
    ViewTreeObserver vto = imageView.getViewTreeObserver();
     vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
         public boolean onPreDraw() {
             int height = imageView.getMeasuredHeight();
             int width = imageView.getMeasuredWidth();
             textView.append("\n"+height+","+width);
             return true;
        }
    });
}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        final ImageView imageView = (ImageView) findViewById(R.id.imageview);
		//-----------------------------------------------方法二
        ViewTreeObserver vto = imageView.getViewTreeObserver();
        vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
            public boolean onPreDraw() {
                int height = imageView.getMeasuredHeight();
                int width = imageView.getMeasuredWidth();
                textView.append("\n"+height+","+width);
                return true;
            }
        });
    }

结果如下:

 

 

方法三就不再测试了同方法二!!!

 

那么方法而和方法三在执行上有什么区别呢?

我们在布局文件中加入一个TextView来记录这个控件的宽高.

 

<ScrollView
     android:layout_width="wrap_content"
     android:layout_height="wrap_content" >

    <TextView
         android:id="@+id/text"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content" />
</ScrollView>

    <ScrollView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >

        <TextView
            android:id="@+id/text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </ScrollView>

先来测试方法而:

 

 

@Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
     final ImageView imageView = (ImageView) findViewById(R.id.imageview);
-----------------------------------------------方法二
    ViewTreeObserver vto = imageView.getViewTreeObserver();
     vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
         public boolean onPreDraw() {
             int height = imageView.getMeasuredHeight();
             int width = imageView.getMeasuredWidth();
             textView.append("\n"+height+","+width);
             return true;
        }
    });
}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        final ImageView imageView = (ImageView) findViewById(R.id.imageview);
		//-----------------------------------------------方法二
        ViewTreeObserver vto = imageView.getViewTreeObserver();
        vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
            public boolean onPreDraw() {
                int height = imageView.getMeasuredHeight();
                int width = imageView.getMeasuredWidth();
                textView.append("\n"+height+","+width);
                return true;
            }
        });
    }

结果如下:

 

 

我们再来测试方法三

 

@Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
     final ImageView imageView = (ImageView) findViewById(R.id.imageview);
     //-----------------------------------------------方法三
    ViewTreeObserver vto2 = imageView.getViewTreeObserver();
     vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
         @Override
         public void onGlobalLayout() {
             imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
             textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
        }
    });
}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        final ImageView imageView = (ImageView) findViewById(R.id.imageview);
        //-----------------------------------------------方法三   
        ViewTreeObserver vto2 = imageView.getViewTreeObserver();  
        vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
            @Override  
            public void onGlobalLayout() {
            	imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);  
                textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
            }  
        });  
    }

输出结果如下:

 

 

我想这方法二和方法三之间的区别就不用说了吧.

 总结:那么需要获取控件的宽高该用那个方法呢?

方法一: 比其他的两个方法多了一次计算,也就是多调用了一次onMeasure()方法,该方法虽然看上去简单,但是如果要目标控件计算耗时比较大的话(如listView等),不建议使用.

方法二,它的回调方法会调用很多次,并且滑动TextView的时候任然会调用,所以不建议使用.

方法三,比较合适.

当然,实际应用的时候需要根据实际情况而定.

 

谢谢!! 欢迎转载:http://blog.csdn.net/johnny901114/article/details/7839512