Android 使用 OnPreDrawListener 获取 ImageView 的宽度和高度

Question

我使用 OnPreDrawListener 获取 imageview 宽度和 Hieght 它正确返回但我不能在该方法之外使用

在 OnCreate 中:

    @Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.drawingarea);
    img=(ImageView)findViewById(R.id.imageView1);

    ViewTreeObserver vto = img.getViewTreeObserver();
    vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {     
        public boolean onPreDraw(){
            // at this point, true width and height are already determined
          int width = img.getMeasuredWidth();
          int height = img.getMeasuredHeight();
          System.out.println(width);// it return value correctly
          System.out.println(height);//it return value correctly
            img.getViewTreeObserver().removeOnPreDrawListener(this);
            return false;
        }
    });
     System.out.println(width);// it return 0
     System.out.println(height);//it return 0
    }

我怎样才能得到外部addOnPreDrawListener的值(value)请帮助

Answer 1

全局声明变量...

private int width;
private int height;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.drawingarea);
    img = (ImageView) findViewById(R.id.imageView1);

    ViewTreeObserver vto = img.getViewTreeObserver();
    vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
        public boolean onPreDraw() {
            // at this point, true width and height are already determined
            width = img.getMeasuredWidth();
            height = img.getMeasuredHeight();
            System.out.println(width);// it return value correctly
            System.out.println(height);// it return value correctly
            img.getViewTreeObserver().removeOnPreDrawListener(this);
            return false;
        }
    });
    System.out.println(width);// it return 0
    System.out.println(height);// it return 0
}

并且您在 onCreate() 中获得了正确的值，我的意思是宽度和高度在 onCreate() 中将为零，因为您的 ImageView 的绘制尚未执行。 .. 您可以在 onWindowFocusChanged() 中检查这些值。并且您的 onPreDrawListener 回调将在绘制宽度和高度值时被调用，因为 ImageView 在绘制之前已经测量和布局...