UIImageView中图片尺寸模式

尺寸模式枚举：

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,
};

上面每个枚举的意思详解如下：

测试代码：

    UIImageView * imageView = [[UIImageView alloc] init];
    imageView.frame = CGRectMake(100, 200, 200, 300);
    imageView.image = [UIImage imageNamed:@"dog.png"];
    [imageView setBackgroundColor:[UIColor greenColor]];
    [self.view addSubview:imageView];

默认情况：

1、UIViewContentModeScaleToFill 伸缩至高度和宽度与UIImageView的大小一致

    UIImageView * imageView = [[UIImageView alloc] init];
    imageView.frame = CGRectMake(100, 200, 200, 300);
    imageView.image = [UIImage imageNamed:@"dog.png"];
    imageView.contentMode = UIViewContentModeScaleToFill;
    [imageView setBackgroundColor:[UIColor greenColor]];
    [self.view addSubview:imageView];