UIImageView *imgView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"图片"]];
/*
UIViewContentModeScaleToFill,
UIViewContentModeScaleAspectFit, // contents scaled to fit with fixed aspect. remainder is transparent
UIViewContentModeScaleAspectFill,
*/
imgView.contentMode = UIViewContentModeScaleAspectFit;
Fill(填充) Fit(试用）Aspect（方向）scale(比例)
- 如果子类view比父类的view大 那么它的坐标为负的, bounds为本身
