废话不多说，直接上代码！
创建imageView的时候这么写就OK
UIImageView *imgV_proPic = [[UIImageView alloc]initWithFrame:CGRectMake(15, 15, 100, 100)];
imgV_proPic.backgroundColor = [UIColor orangeColor];
[self.contentView addSubview:imgV_proPic];
[imgV_proPic setContentScaleFactor:[[UIScreen mainScreen] scale]];
imgV_proPic.contentMode = UIViewContentModeScaleAspectFill;
imgV_proPic.clipsToBounds = YES;
