得到ImageView中drawable显示的区域的计算方法

我们都知道Imageview中有不同的拉伸比率，比如fitStart，centCrop这样的，所以imageview中的drawable不一定和imageview占有相同的位置和大小，那么怎么计算呢？

思路：

1.得到imageview现在的宽高

2.得到imageview现在显示的区域(Rect)

3.得到drawable本身图片的宽高

4.得到drawable显示时的缩放比例

5.计算得到drawable现在显示的宽高

6.通过drawable显示的宽高和imageview显示的宽高来计算出imageview距离内部drawable的内边距

7.通过imageview的显示区域和內边距计算出drawable的显示区域

        // view的实际宽高
        float vWidth = v.getWidth();
        float vHeight = v.getHeight();
 
        // 得到imageview中的矩阵，准备得到drawable的拉伸比率
        Matrix m = v.getImageMatrix();
        float[] values = new float[10];
        m.getValues(values);
 
        // drawable的本身宽高
        float dOriginalWidth = drawable.getIntrinsicWidth();
        float dOriginalHeight = drawable.getIntrinsicHeight();
        float dRatio = dOriginalWidth / dOriginalHeight;//如果大于1，表示drawable宽>高
        drawable = null;
 
        //Image在绘制过程中的变换矩阵，从中获得x和y方向的缩放系数  value[0],[4]
        //得到drawable的实际显示时的宽高
        int dWidth = (int)(dOriginalWidth * values[0]);
        int dHeight = (int)(dOriginalHeight * values[4]);  
 
        //得到imageview的宽高和drawable的宽高的差值
        float w = vWidth - dWidth;
        float h = vHeight - dHeight;
 
        Rect startBounds = new Rect();
        v.getGlobalVisibleRect(startBounds);

之后通过对startBounds进行修改，就可以求出drawable实际显示的范围了。因为拉伸模式不同，所以计算方式也不同，下面给出几种模式的计算方式

if (originalType == ScaleType.CENTER_INSIDE) {
            //finalBounds = getCentInside_originalPic_finalBounds(v, dRatio, startBounds);
            finalBounds.left = (int) (startBounds.left + (w / 2) + 0.5f);
            finalBounds.top = (int) (startBounds.top + (h / 2) +0.5f);
            finalBounds.right = (int) (startBounds.right - (w / 2) + 0.5f);
            finalBounds.bottom = (int) (startBounds.bottom - (h / 2) + 0.5f);
        }
        else if (originalType == ScaleType.FIT_START) {
            //finalBounds = getFitStart_originalPic_finalBounds(dRatio, startBounds);
            finalBounds.right = (int) (startBounds.right - w + 0.5f);
            finalBounds.top = startBounds.top;
            finalBounds.left = startBounds.left;
            finalBounds.bottom = (int) (startBounds.bottom - h + 0.5f);
        }
        else if (originalType == ScaleType.FIT_CENTER) {
            //finalBounds = getFitCenter_originalPic_finalBounds(dRatio, startBounds);
            finalBounds.left = (int) (startBounds.left + (w / 2) + 0.5f);
            finalBounds.top = (int) (startBounds.top + (h / 2) +0.5f);
            finalBounds.right = (int) (startBounds.right - (w / 2) + 0.5f);
            finalBounds.bottom = (int) (startBounds.bottom - (h / 2) + 0.5f);
        }
        else if (originalType == ScaleType.FIT_END) {
            //finalBounds = getFitEnd_originalPic_finalBounds(dRatio, startBounds);
            finalBounds.left = (int) (startBounds.left + w + 0.5f);
            finalBounds.top = (int) (startBounds.top + h + 0.5f);
            finalBounds.right = startBounds.right;
            finalBounds.bottom = startBounds.bottom;
        }

参考自：http://blog.csdn.net/liu_zhen_wei/article/details/8349400