停靠模式

帶有scale單詞的：圖片有可能會(huì)拉伸
沒有scale單詞的：圖片絕對(duì)不會(huì)被拉伸，保持圖片的原尺寸
將圖片拉伸至填充整個(gè)imageView
UIViewContentModeScaleToFill 

帶有aspect單詞的：保持圖片原來的寬高比
UIViewContentModeScaleAspectFit
保證剛好能看到圖片的全部

UIViewContentModeScaleAspectFill
拉伸至圖片的寬度或者高度跟imageView一樣

//下面的就是字面意思
UIViewContentModeCenter 

UIViewContentModeTop

UIViewContentModeBottom

UIViewContentModeLeft

UIViewContentModeRight

UIViewContentModeTopLeft

UIViewContentModeTopRight

UIViewContentModeBottomLeft

UIViewContentModeBottomRight

修改imageView的size等于圖片的size

//修改imageView的size等于圖片的size
UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(50, 200, 300, 300)];
imageView.image = [UIImage imageNamed:@"header"];

//image.size = 144*144
CGRect rect = imageView.frame;
rect.size = imageView.image.size;
imageView.frame = rect;

//實(shí)際顯示的imgView的size就是144*144
[self.view addSubview:imageView];