iOS：在 UIImage 上绘制 NSString 和边框

我想在我已有的 UIImage 上绘制一个 NSString 和一个边框。我找到了一种将 NSString 绘制为 UIImage 的方法，但我需要它在我提供的图像上绘制。

-(UIImage *)imageFromText:(NSString *)text
{
    // set the font type and size
    UIFont *font = [UIFont systemFontOfSize:20.0];  
    CGSize size  = [text sizeWithFont:font];

    // check if UIGraphicsBeginImageContextWithOptions is available (iOS is 4.0+)
    if (UIGraphicsBeginImageContextWithOptions != NULL)
        UIGraphicsBeginImageContextWithOptions(size,NO,0.0);
    else
        // iOS is < 4.0 
        UIGraphicsBeginImageContext(size);

    // optional: add a shadow, to avoid clipping the shadow you should make the context size bigger 
    //
    // CGContextRef ctx = UIGraphicsGetCurrentContext();
    // CGContextSetShadowWithColor(ctx, CGSizeMake(1.0, 1.0), 5.0, [[UIColor grayColor] CGColor]);

    // draw in context, you can use also drawInRect:withFont:
    [text drawAtPoint:CGPointMake(0.0, 0.0) withFont:font];

    // transfer image
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();    

    return image;
}

我如何修改此方法以提供我自己的背景图像并添加边框？

如果您在 UIImageView 中显示 UIImage，您可以设置UIImageView.layer.delegate并使用类似的东西：

- (void) drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
  CGContextSetFillColorWithColor(ctx, [[UIColor darkTextColor] CGColor]);

  UIGraphicsPushContext(ctx);

  [word drawAtPoint:CGPointMake(30.0f, 30.0f) 
           forWidth:200.0f 
           withFont:[UIFont boldSystemFontOfSize:32] 
      lineBreakMode:UILineBreakModeClip];

  UIGraphicsPopContext();
}

代码来自添加文本到 CALayer https://stackoverflow.com/questions/2209734/add-text-to-calayer

边框很简单，只需使用 CALayer 属性即可：

imageview.layer.borderColor = [UIColor blackColor].CGColor;
imageview.sublayer.borderWidth = 2.0;