主要内容：
1、contentMode
2、layer contentsRect
contentMode 就是描述内容的填充模式。
typedef NS_ENUM(NSInteger, UIViewContentMode) {
UIViewContentModeScaleToFill,
UIViewContentModeScaleAspectFit, // contents scaled to fit with fixed aspect. remainder is transparent
UIViewContentModeScaleAspectFill, // contents scaled to fill with fixed aspect. some portion of content may be clipped.
UIViewContentModeRedraw, // redraw on bounds change (calls -setNeedsDisplay)
UIViewContentModeCenter, // contents remain same size. positioned adjusted.
UIViewContentModeTop,
UIViewContentModeBottom,
UIViewContentModeLeft,
UIViewContentModeRight,
UIViewContentModeTopLeft,
UIViewContentModeTopRight,
UIViewContentModeBottomLeft,
UIViewContentModeBottomRight,
};
网上截图.png
contentsRect
/* A rectangle in normalized image coordinates defining the
- subrectangle of the `contents' property that will be drawn into the
- layer. If pixels outside the unit rectangles are requested, the edge
- pixels of the contents image will be extended outwards. If an empty
- rectangle is provided, the results are undefined. Defaults to the
- unit rectangle [0 0 1 1]. Animatable. */
在现在的图像坐标系统中，contentsRect描述了一个在layer层重画的一个子矩形。控制图层内容的显示。
在实际应用中，类似微信朋友圈，照片的显示，当显示多张图片的时候，由于我们会固定显示view 的大小为一个矩形，但是如果我们直接将照片放入会发生变形。
变形图片.png
但是在大多数情况下面我们都希望能够不变形。图片按照长宽来分，大概分为3种，W>H , W=H, W <H， 这三种情况。举个例子，在我们要显示图片的UIImageView是一个W=H的情况。所以要求不变形，主要有两个方法：
例子：
1: W > H
UIImageView *squerImage = [[UIImageView alloc]initWithFrame:CGRectMake(30, 300, 100, 100)];
squerImage.layer.borderColor = [UIColor redColor].CGColor;
squerImage.layer.borderWidth = 1;
squerImage.layer.masksToBounds = true;
UIImage *widthImage = [UIImage imageNamed:@"zisehua.jpg"];
squerImage.image = widthImage;
squerImage.contentMode = UIViewContentModeScaleAspectFill;
[self.view addSubview:squerImage];
结果：
W > H 显示中间.png
2: H > W
UIImageView *qingting = [[UIImageView alloc]initWithFrame:CGRectMake(30, 430, 100, 100)];
qingting.layer.borderColor = [UIColor redColor].CGColor;
qingting.layer.borderWidth = 1;
qingting.layer.masksToBounds = true;
UIImage *qingtingImage = [UIImage imageNamed:@"qingting.jpg"];
qingting.image = qingtingImage;
qingting.layer.contentsRect = CGRectMake(0, 0,1, qingtingImage.size.width/qingtingImage.size.height);
qingting.contentMode = UIViewContentModeScaleToFill;
[self.view addSubview:qingting];
结果：
H > W 显示上面.png
