Imageview 按比例适应屏幕大小

DisplayMetrics  dm = new DisplayMetrics();
//取得窗口属性
getWindowManager().getDefaultDisplay().getMetrics(dm);
//窗口的宽度
int screenWidth = dm.widthPixels;

　　　　 ImageView mImageView = (ImageView)findViewById(R.id.login_icon);       
        ViewGroup.LayoutParams lp = mImageView.getLayoutParams();
        lp.width = screenWidth;
        lp.height = RelativeLayout.LayoutParams.WRAP_CONTENT;
        mImageView.setLayoutParams(lp);

        mImageView.setMaxWidth(screenWidth);
        mImageView.setMaxHeight(screenWidth * 5); 

需要注意：

必须设置ImageView 的属性。 android:adjustViewBounds="true"

RelativeLayout 布局是指mImageView 所在上级布局