UIImageView居中裁剪显示

UIImageView *pictureImg1 = (UIImageView *)[cell viewWithTag:102 + i];
[pictureImg1 setContentScaleFactor:[[UIScreen mainScreen] scale]];
pictureImg1.contentMode =  UIViewContentModeScaleAspectFill;
pictureImg1.autoresizingMask = UIViewAutoresizingFlexibleHeight;
pictureImg1.clipsToBounds  = YES;