把CGImageRef保存到PNG文件错误？ （引起ARC？）

Question

这段代码以前有用，但我认为Xcode的新ARC可能已经杀了它

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    CGDirectDisplayID displayID = CGMainDisplayID();
    CGImageRef image = CGDisplayCreateImage(displayID); //this is a screenshot (works fine)
    [self savePNGImage:image path:@"~/Desktop"];
}


-(void)savePNGImage:(CGImageRef)imageRef path:(NSString *)path {
    NSURL *outURL = [[NSURL alloc] initFileURLWithPath:path]; 
    //here xcode suggests using __bridge for CFURLRef?
    CGImageDestinationRef dr = CGImageDestinationCreateWithURL ((__bridge CFURLRef)outURL, (CFStringRef)@"public.png" , 1, NULL);    
    CGImageDestinationAddImage(dr, imageRef, NULL);
    CGImageDestinationFinalize(dr);
}

此代码返回错误：

  

ImageIO：CGImageDestinationAddImage图像目的地   参数是nil

我认为这意味着没有正确创建CGImageDestinationRef。我无法找到一个这样的实现，新的Xcode没有给出相同的错误，我做错了什么？

Answer 1

您发布的代码无论是否使用ARC都无法使用，因为您需要在传递代码之前展开路径名中的代字号。

您发布的代码也泄漏了CGDisplayCreateImage和CGImageDestinationCreateWithURL返回的项目。这是一个有效且无泄漏的例子：

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    CGDirectDisplayID displayID = CGMainDisplayID();
    CGImageRef imageRef = CGDisplayCreateImage(displayID); //this is a screenshot (works fine)

    NSString *path = [@"~/Desktop/public.png" stringByExpandingTildeInPath];
    [self savePNGImage:imageRef path:path];

    CFRelease(imageRef);
}

- (void)savePNGImage:(CGImageRef)imageRef path:(NSString *)path
{
    NSURL *fileURL = [NSURL fileURLWithPath:path]; 
    CGImageDestinationRef dr = CGImageDestinationCreateWithURL((__bridge CFURLRef)fileURL, kUTTypePNG , 1, NULL);

    CGImageDestinationAddImage(dr, imageRef, NULL);
    CGImageDestinationFinalize(dr);

    CFRelease(dr);
}