在我的绘图代码中没有调用 'dispatch_async' 的匹配函数

Question

我正尝试对我在上发布的绘图代码执行 dispatch_async。我得到一个错误：“没有匹配的函数来调用 'dispatch_async'。我正在尝试做的，因为这是一个占用大量内存的操作，试图为在后台发生的渲染操作创建队列，当图像出现时已准备好放入主队列，因为 UI 更新过程在主线程中进行。所以大家在这个线程上指导我。我发布了整个代码。

#pragma mark Blurring the image
- (UIImage *)blurWithCoreImage:(UIImage *)sourceImage
{
    // Set up output context.
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
    dispatch_async(queue, ^{
        CIImage *inputImage = [CIImage imageWithCGImage:sourceImage.CGImage];

        // Apply Affine-Clamp filter to stretch the image so that it does not
        // look shrunken when gaussian blur is applied
        CGAffineTransform transform = CGAffineTransformIdentity;
        CIFilter *clampFilter = [CIFilter filterWithName:@"CIAffineClamp"];
        [clampFilter setValue:inputImage forKey:@"inputImage"];
        [clampFilter setValue:[NSValue valueWithBytes:&transform objCType:@encode(CGAffineTransform)] forKey:@"inputTransform"];

        // Apply gaussian blur filter with radius of 30
        CIFilter *gaussianBlurFilter = [CIFilter filterWithName: @"CIGaussianBlur"];
        [gaussianBlurFilter setValue:clampFilter.outputImage forKey: @"inputImage"];
        [gaussianBlurFilter setValue:@10 forKey:@"inputRadius"]; //30

        CIContext *context = [CIContext contextWithOptions:nil];
        CGImageRef cgImage = [context createCGImage:gaussianBlurFilter.outputImage fromRect:[inputImage extent]];
        UIGraphicsBeginImageContext(self.view.frame.size);
        CGContextRef outputContext = UIGraphicsGetCurrentContext();

        // Invert image coordinates
        CGContextScaleCTM(outputContext, 1.0, -1.0);
        CGContextTranslateCTM(outputContext, 0, -self.view.frame.size.height);

        // Draw base image.
        CGContextDrawImage(outputContext, self.view.frame, cgImage);

        // Apply white tint
        CGContextSaveGState(outputContext);
        CGContextSetFillColorWithColor(outputContext, [UIColor colorWithWhite:1 alpha:0.2].CGColor);
        CGContextFillRect(outputContext, self.view.frame);
        CGContextRestoreGState(outputContext);

        dispatch_async(dispatch_get_main_queue(), ^{
            UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();

            return outputImage;
        })

    });



// Output image is ready.


}

它在这段代码 dispatch_async(dispatch_get_main_queue() 上抛出错误，即当我试图将它带回主线程时，因为 UI 在主线程中工作线程。我缺少什么？

Answer 1

我觉得你的代码看起来不错，但你使用的方式可能不对。所以请像下面这样尝试

像下面这样创建一个方法

- (UIImage *)blurWithCoreImage:(UIImage *)sourceImage
{


    // Set up output context.
//    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
//    dispatch_async(queue, ^{
        CIImage *inputImage = [CIImage imageWithCGImage:sourceImage.CGImage];

        // Apply Affine-Clamp filter to stretch the image so that it does not
        // look shrunken when gaussian blur is applied
        CGAffineTransform transform = CGAffineTransformIdentity;
        CIFilter *clampFilter = [CIFilter filterWithName:@"CIAffineClamp"];
        [clampFilter setValue:inputImage forKey:@"inputImage"];
        [clampFilter setValue:[NSValue valueWithBytes:&transform objCType:@encode(CGAffineTransform)] forKey:@"inputTransform"];

        // Apply gaussian blur filter with radius of 30
        CIFilter *gaussianBlurFilter = [CIFilter filterWithName: @"CIGaussianBlur"];
        [gaussianBlurFilter setValue:clampFilter.outputImage forKey: @"inputImage"];
        [gaussianBlurFilter setValue:@10 forKey:@"inputRadius"]; //30

        CIContext *context = [CIContext contextWithOptions:nil];
        CGImageRef cgImage = [context createCGImage:gaussianBlurFilter.outputImage fromRect:[inputImage extent]];
        UIGraphicsBeginImageContext(self.view.frame.size);
        CGContextRef outputContext = UIGraphicsGetCurrentContext();

        // Invert image coordinates
        CGContextScaleCTM(outputContext, 1.0, -1.0);
        CGContextTranslateCTM(outputContext, 0, -self.view.frame.size.height);

        // Draw base image.
        CGContextDrawImage(outputContext, self.view.frame, cgImage);

        // Apply white tint
        CGContextSaveGState(outputContext);
        CGContextSetFillColorWithColor(outputContext, [UIColor colorWithWhite:1 alpha:0.2].CGColor);
        CGContextFillRect(outputContext, self.view.frame);
        CGContextRestoreGState(outputContext);

        UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        return outputImage;
}

并像下面这样使用这个方法

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
        dispatch_async(queue, ^{
            UIImage *img = [self blurWithCoreImage:[UIImage imageNamed:@"imagename.png"]];
            dispatch_async(dispatch_get_main_queue(), ^{
                [self.view addSubview:[[UIImageView alloc] initWithImage:img]];
            });
        });

我只是像下面那样尝试进行测试，它给了我正确的结果。试试看吧

如果您遇到任何问题，请告诉我，祝一切顺利

Answer 2

查看类似问题的答案：

Is this Core Graphics code thread safe?

您在一个线程上开始绘图，然后在另一个线程上完成它。那是一颗定时炸弹。

此外，在主线程上执行的 "return outputImage" 对您没有任何好处，因为没有人会收到 return 值。您应该在同一个线程中完成所有绘图，提取图像，然后在处理完整图像的主线程上调用一些东西。

在我的绘图代码中没有调用 'dispatch_async' 的匹配函数

No matching function for call to 'dispatch_async' in my drawing code

objective-c

ios

quartz-core