绘制UIImage时无效的上下文错误 [英] invalid context error when drawing a UIImage

问题描述

我试图画一个UIImage到我的UIView的上下文。我使用这个代码与上下文的东西注释和输出...

   - （void）drawRect：（CGRect） rect 
 {
 //UIGraphicsBeginImageContextWithOptions(rect.size,YES,[[UIScreen mainScreen] scale]）; 
 //UIGraphicsBeginImageContext(rect.size）; 
 
 UIImage * newImage = [UIImage imageNamed：@character_1_0001.png]; 
 // [newImage drawAtPoint：CGPointMake（200，200）]; 
 [newImage drawInRect：rect]; 
 
 // UIGraphicsEndImageContext（）; 
} 
  

根据我的理解，我不需要设置图像上下文这个，确实没有它我看到在视图中绘制的图像，但我也得到这个错误在日志...

  <错误> ;: CGContextSaveGState：无效上下文0x0 
  

如果我取消注释UIGraphicsBeginImageContext行，任何绘制的和没有错误。

我需要使用默认的图形上下文，并以这种方式声明？我需要绘制图像，因为我想在上下文中添加它，不能只生成一个UIImageView对象的负载。

解决方案

听起来你直接调用 drawRect：。所以它从你的电话，一次从真正的绘图循环被调用一次。

• 随着上下文创建的存在，你可以在一个新的上下文中绘制所有的图形，然后丢弃它，
  
• 在上下文创建缺失的情况下，您会从手动调用 drawRect：得到错误，实际绘图发生在真正的<$ c $ c> drawRect：，以便您看到自己的图片。

< drawRect：。在适当的时候调用 setNeedsDisplay 和 drawRect：。

I am trying to draw a UIImage to the context of my UIView. I've used this code with the context stuff commented in and out ...

- (void)drawRect:(CGRect)rect
{
    //UIGraphicsBeginImageContextWithOptions(rect.size,YES,[[UIScreen mainScreen] scale]);
    //UIGraphicsBeginImageContext(rect.size);

    UIImage *newImage = [UIImage imageNamed:@"character_1_0001.png"];
    //[newImage drawAtPoint:CGPointMake(200, 200)];
    [newImage drawInRect:rect];

    //UIGraphicsEndImageContext();
}

As I understand it I shouldn't need to set the image context to do this and indeed without it I do see the image drawn in the view but I also get this error in the log ...

<Error>: CGContextSaveGState: invalid context 0x0

If I uncomment the UIGraphicsBeginImageContext lines I don't get anything drawn and no error.

Do I need to use the default graphics context and declare this somehow?

I need to draw the image because I want to add to it on the context and can't just generate a load of UIImageView objects.

解决方案

It sounds like you are calling drawRect: directly. So it is getting called once from your call, and once from the genuine drawing loop.

• With the context creation present, you do all the drawing in a new context then discard it, so you never see anything
• With the context creation missing, you get the error from the manually called drawRect:, and the actual drawing takes place in the genuine drawRect: so you see your image.

Don't call drawRect: directly. Call setNeedsDisplay and drawRect: will be called for you at the appropriate point.

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