如何使用 SDWebImage 在 cgcontext 中绘制图像

Question

我想使用 SDWebImage 下载带有 url 的图像并在 UIView 中绘制（使用 cgcontext），但是当下载完成时，没有任何反应

 func drawImage(){
    var imageView = UIImageView()
    println("drawimageaaaaa")
    imageView.sd_setImageWithURL(NSURL(string: drawObj.ctn!)!, placeholderImage: UIImage(named: "defaultphoto")!, completed: { (image:UIImage!, error:NSError!, type:SDImageCacheType, url:NSURL!) -> Void in
        println("drawimagebbbb")
        var context = UIGraphicsGetCurrentContext();
        CGContextSaveGState(context)
        var cgimg = image!.CGImage;
        var rect = CGRect(x: drawObj.points![0].x,y: drawObj.points![0].y,width: drawObj.currentWidth!,height: drawObj.currentHeight!)
        CGContextTranslateCTM(context, rect.origin.x, rect.origin.y)
        CGContextScaleCTM(context, 1.0, -1.0)
        CGContextRotateCTM(context,-CGFloat(Double(drawObj.angle!)*M_PI/180))
        if drawObj.isFlip == true{
            CGContextTranslateCTM(context, -rect.width/2, rect.height/2)
        }else{
            CGContextTranslateCTM(context, -rect.width/2, -rect.height/2)
        }
        CGContextTranslateCTM(context, -rect.origin.x, -rect.origin.y)
        CGContextDrawImage(context, rect, cgimg);
        CGContextRestoreGState(context)
    })
  }


  override func drawRect(rect: CGRect) {
       for drawObj in drawObjs {
          if drawObj.drawPara!.drawType == MouseStatus.attach{
             drawImage(drawObj)
          }
       }
   }

现在我尝试再次运行 drawImage 函数（相同的 url）图像出现在 UIView 中

download完成后如何在UIView中绘制？

Answer 1

如果我猜对了，你想在调用 drawRect 时绘制 SDWebImage

现在的问题是……绘图必须是同步的。您不能随时绘制屏幕：D 这是您正在尝试但没有看到的内容。

（您需要更改整个“想法”，以便在被要求时实际绘制（当调用 drawRect 时）

例如

func drawImage(drawObj) {
        println("drawimagebbbb")
        var context = UIGraphicsGetCurrentContext();
        CGContextSaveGState(context)
        var cgimg = image!.CGImage;
        var rect = CGRect(x: drawObj.points![0].x,y: drawObj.points![0].y,width: drawObj.currentWidth!,height: drawObj.currentHeight!)
        CGContextTranslateCTM(context, rect.origin.x, rect.origin.y)
        CGContextScaleCTM(context, 1.0, -1.0)
        CGContextRotateCTM(context,-CGFloat(Double(drawObj.angle!)*M_PI/180))
        if drawObj.isFlip == true{
            CGContextTranslateCTM(context, -rect.width/2, rect.height/2)
        }else{
            CGContextTranslateCTM(context, -rect.width/2, -rect.height/2)
        }
        CGContextTranslateCTM(context, -rect.origin.x, -rect.origin.y)
        CGContextDrawImage(context, rect, cgimg);
        CGContextRestoreGState(context) 
}

func loadImage(drawObj){
    var imageView = UIImageView()
    println("drawimageaaaaa")
    imageView.sd_setImageWithURL(NSURL(string: drawObj.ctn!)!, placeholderImage: UIImage(named: "defaultphoto")!, completed: { (image:UIImage!, error:NSError!, type:SDImageCacheType, url:NSURL!) -> Void in
        dispatch_async(dispatch_get_main_queue() ) {
            drawObj.image = image
            self.setNeedsDisplay() //tell iOS to ready for drawing
        }
    })

drawObj.imageViewUsedForLoading = imageView //保留它！ }

  override func drawRect(rect: CGRect) {
       for drawObj in drawObjs {
          if drawObj.drawPara!.drawType == MouseStatus.attach{
            if drawObj.image /*you have to manage this somehow*/ {
                drawImage(drawObj)
            }
            else { 
                loadImage(drawObj)
            }
          }
       }
   }