iOS：在UIImage上绘制NSString和边框

Question

我想在我已经拥有的UIImage上绘制一个NSString和一个边框。我发现了一个将NSString绘制为UIImage的方法，但我需要它来绘制我提供的图像。

-(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;
}

如何修改此方法以提供我自己的背景图像，以及添加边框？

Answer 1

如果您在UIImageView中显示UIImage，您可以设置 UIImageView.layer.delegate 并使用以下内容：

- (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();
}

来自Add text to CALayer的代码

边框很简单，只需使用CALayer属性：

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

Answer 2

您正在寻找CALayers。

这是一个非常好的教程，如何创建和使用它们。

所以基本上你会添加新的CALayer，将图像作为背景，然后在其上绘制文字。

http://www.raywenderlich.com/2502/introduction-to-calayers-tutorial

Answer 3

使用此功能在UIImage上绘制NSString和边框 用于边框检查CGContextSetRGBStrokeColor
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-(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 brownColor] CGColor]);

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

//CGImageRef cimg = UIGraphicsGetCurrentContext();    

// transfer image
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height); 
[image drawInRect:rect blendMode:kCGBlendModeNormal alpha:1.0];

//CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetRGBStrokeColor(ctx, 2.0, 3.5, 5.0, 1.0);
CGContextStrokeRect(ctx, rect);
UIImage *testImg = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();    

return testImg;
}

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