Question

我正在尝试将文本转换为图片并将该图片用作子视图。但是我收到了一些错误。我从另一个stackoverflow帖子中得到了一段脚本;

/* Creates an image with a home-grown graphics context, burns the supplied string into it. */
- (UIImage *)burnTextIntoImage:(NSString *)text :(UIImage *)img {

    UIGraphicsBeginImageContext(img.size);

    CGRect aRectangle = CGRectMake(0,0, img.size.width, img.size.height);
    [img drawInRect:aRectangle];

    [[UIColor redColor] set];           // set text color
    NSInteger fontSize = 14;
    if ( [text length] > 200 ) {
        fontSize = 10;
    }
    UIFont *font = [UIFont boldSystemFontOfSize: fontSize];     // set text font

    [ text drawInRect : aRectangle                      // render the text
             withFont : font
        lineBreakMode : UILineBreakModeTailTruncation  // clip overflow from end of last line
            alignment : UITextAlignmentCenter ];

    UIImage *theImage=UIGraphicsGetImageFromCurrentImageContext();   // extract the image
    UIGraphicsEndImageContext();     // clean  up the context.
    return theImage;
}

我用代码调用这段代码：

[self burnTextIntoImage:textInsert :textImage];

我得到的错误是：

<Error>: CGContextSetFillColorWithColor: invalid context 0x0
<Error>: CGContextSetStrokeColorWithColor: invalid context 0x0
<Error>: CGContextSetFont: invalid context 0x0
<Error>: CGContextSetTextMatrix: invalid context 0x0
<Error>: CGContextSetFontSize: invalid context 0x0
<Error>: CGContextSetTextPosition: invalid context 0x0
<Error>: CGContextShowGlyphsWithAdvances: invalid context 0x0

先谢谢！

Answer 1

////Drawing text using Quartz 2D in an iOS application

- (void)drawRect:(CGRect)rect

{

  CGContextRef theContext = UIGraphicsGetCurrentContext();

  CGRect viewBounds = self.bounds;



  CGContextTranslateCTM(theContext, 0, viewBounds.size.height);

  CGContextScaleCTM(theContext, 1, -1);



  // Draw the text using the MyDrawText function

  MyDrawText(theContext, viewBounds);
}

 ////Drawing text
void MyDrawText (CGContextRef myContext, CGRect contextRect) // 1

{

float w, h;

w = contextRect.size.width;

h = contextRect.size.height;



CGAffineTransform myTextTransform; // 2

CGContextSelectFont (myContext, // 3

                "Helvetica-Bold",

                 h/10,

                 kCGEncodingMacRoman);

CGContextSetCharacterSpacing (myContext, 10); // 4

CGContextSetTextDrawingMode (myContext, kCGTextFillStroke); // 5



CGContextSetRGBFillColor (myContext, 0, 1, 0, .5); // 6

CGContextSetRGBStrokeColor (myContext, 0, 0, 1, 1); // 7

myTextTransform =  CGAffineTransformMakeRotation  (MyRadians (45)); // 8

CGContextSetTextMatrix (myContext, myTextTransform); // 9

CGContextShowTextAtPoint (myContext, 40, 0, "Quartz 2D", 9); // 10

UIImage *theImage=  UIGraphicsGetImageFromCurrentImageContext();

 UIGraphicsEndImageContext();

}

更多访问以下链接...

How Quartz 2D Draws Text

希望，这会帮助你......冷静......

Answer 2

<Error>: CGContextSetFillColorWithColor: invalid context 0x0
...

没有活动的图形上下文。 IOW，您正在请求抽奖，但没有运营商或目的地。

当本地存在图形上下文时（例如，调用drawRect:时），您需要执行此调用，或者必须为流程明确创建上下文（例如CGBitmapContextCreate）。

如果你正在使用UIGraphicsBeginImageContext，那应该仅来自主线程。您可以使用任何主题中的CGBitmapContext。

尝试将文本转换为图像时出现CGContext错误

2 个答案: