[Turn] Get the Android controls the width and height

Original link: http://www.cnblogs.com/butterfly-clover/p/5453431.html

We all know that in onCreate () Gets the height of which is 0, which is why we look at the example?:

First, a write our own control, the control is very simple:

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 the onDraw (the Canvas Canvas) {
         Super .onDraw (Canvas); 
        System.out.println ( "I was called the onDraw" + System.currentTimeMillis ()); 
    } 

}

Layout file:

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

Test Activity of onCreate ():

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

Now we look at the results:

Descriptions onCreate method execution is over, we define the controls will be measured (measure), so we () obtained by view.getHeight onCreate method in which the height or width of the control must be 0, because it has not been their own measure, also that he himself did not know how high, but this time you get to its size, it is definitely impossible.

 

Now we can not solve the problem encountered in the Internet to find the following way:

        //------------------------------------------------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());
            }  
        });  

 

Now to be discussed is when we need the time which method to use it?

Now the test Activity read as follows:

  @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());
    }

Next look at the following several ways to output:

Testing Activity to read as follows:

    @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;
            }
        });
    }

The results are as follows:

Method three is no longer the same test method two !!!

 

Method Two Method three and then what difference does it in the execution?

We add a TextView in the layout file to record the width and height of the control.

    <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>

First to Test Method II:

    @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;
            }
        });
    }

The results are as follows:

Let's test three:

    @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.

转载于:https://www.cnblogs.com/butterfly-clover/p/5453431.html