搞明白这个花的时间有点多，最后将代码copy出来运行断点后才知道原来是这样子的

方法一：

img.setAdjustViewBounds(true);

解析：

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

····

位置一

if (mAdjustViewBounds) {

resizeWidth = widthSpecMode != MeasureSpec.EXACTLY;

resizeHeight = heightSpecMode != MeasureSpec.EXACTLY;

desiredAspect = (float) w / (float) h;

}

}

·····

位置二

if (resizeWidth || resizeHeight) {

/* If we get here, it means we want to resize to match the

drawables aspect ratio, and we have the freedom to change at

least one dimension.

*/

// Get the max possible width given our constraints

widthSize = resolveAdjustedSize(w + pleft + pright, mMaxWidth, widthMeasureSpec);

// Get the max possible height given our constraints

heightSize = resolveAdjustedSize(h + ptop + pbottom, mMaxHeight, heightMeasureSpec);

if (desiredAspect != 0.0f) {

// See what our actual aspect ratio is

final float actualAspect = (float)(widthSize - pleft - pright) /

(heightSize - ptop - pbottom);

if (Math.abs(actualAspect - desiredAspect) > 0.0000001) {

boolean done = false;

// Try adjusting width to be proportional to height

if (resizeWidth) {

int newWidth = (int)(desiredAspect * (heightSize - ptop - pbottom)) +

pleft + pright;

// Allow the width to outgrow its original estimate if height is fixed.

if (!resizeHeight && !sCompatAdjustViewBounds) {

widthSize = resolveAdjustedSize(newWidth, mMaxWidth, widthMeasureSpec);

}

if (newWidth <= widthSize) {

widthSize = newWidth;

done = true;

}

}

// Try adjusting height to be proportional to width

if (!done && resizeHeight) {

int newHeight = (int)((widthSize - pleft - pright) / desiredAspect) +

ptop + pbottom;

// Allow the height to outgrow its original estimate if width is fixed.

if (!resizeWidth && !sCompatAdjustViewBounds) {

heightSize = resolveAdjustedSize(newHeight, mMaxHeight,

heightMeasureSpec);

}

if (newHeight <= heightSize) {

heightSize = newHeight;

}

}

}

}

} else {

/* We are either don't want to preserve the drawables aspect ratio,

or we are not allowed to change view dimensions. Just measure in

the normal way.

*/

w += pleft + pright;

h += ptop + pbottom;

w = Math.max(w, getSuggestedMinimumWidth());

h = Math.max(h, getSuggestedMinimumHeight());

widthSize = resolveSizeAndState(w, widthMeasureSpec, 0);

heightSize = resolveSizeAndState(h, heightMeasureSpec, 0);

}

setMeasuredDimension(widthSize, heightSize);

}

1.上面那一行解决问题的代码的含义是改变mAdjustViewBounds的值

2.根据代码二的位置可以看出，imageview的测量其实分了两种情况，默认情况是在一定空间中按比例显示最小的尺寸(else中的代码)，其次是按比例放大或缩小(为wrap的情况赋值)，mAdjustViewBounds则控制这两种情况。

mAdjustViewBounds默认为false，这里我们需要改为true，来满足宽度充满全屏，高度按比例确定

方法二：

后记

喵印～～～