iOS UIImageView图片拉伸问题

UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
imageView.image = [UIImage imageNamed:@"01.jpg"];
imageView.contentMode = UIViewContentModeScaleAspectFill;
imageView.clipsToBounds=YES;
[self.view addSubview:imageView];