在storyboard中 只有 UIImageView的图片的拉伸可以不用代码设置

UIImage *image = [UIImage imageNamed:@"RedButton"];

    // 通过一张原始图片生成一张可拉伸的图片

    CGFloat imageW = image.size.width * 0.5;

    CGFloat imageH = image.size.height * 0.5;

    UIImage *newImage = [image resizableImageWithCapInsets:UIEdgeInsetsMake(imageH, imageW, imageH, imageW) resizingMode:UIImageResizingModeStretch];

    [self.loginBtn setBackgroundImage:newImage forState:UIControlStateNormal];

    

    UIImage *selImage = [UIImage imageNamed:@"RedButtonPressed"];

    CGFloat selImageW = selImage.size.width * 0.5;

    CGFloat selImageH = selImage.size.height * 0.5;

    UIImage *selNewImage = [selImage resizableImageWithCapInsets:UIEdgeInsetsMake(selImageH, selImageW, selImageH, selImageW) resizingMode:UIImageResizingModeStretch];

    [self.loginBtn setBackgroundImage:selNewImage forState:UIControlStateHighlighted];