iOS设置按钮的图片为Aspetfit

通过以下代码实现:

UIButton *backBtn = [UIButtonbuttonWithType:UIButtonTypeCustom];

    [backBtn setImage:[UIImageimageNamed:@"return"]forState:UIControlStateNormal];

    backBtn.frame = CGRectMake(20, 40, 15,15);

    backBtn.imageView.contentMode =UIViewContentModeScaleAspectFill;

    [backBtn addTarget:selfaction:@selector(backItemClicked)forControlEvents:UIControlEventTouchUpInside];