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:
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/icon" />

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());
}

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。解决方法如下：

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());
    }
});