objective-c - 将 CGImageRef 保存为 PNG 文件时出错？ (电弧引起的？)

Question

这段代码曾经可以工作，但我认为 Xcode 的新 ARC 可能已经杀死了它

- (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 image destination parameter is nil

我认为这意味着 CGImageDestinationRef 没有正确创建。我一直无法找到新的 Xcode 不会给出相同错误的实现，我做错了什么？

Answer 1

无论有没有 ARC，您发布的代码都无法工作，因为您需要在传递路径名之前扩展路径名中的波浪号。

您发布的代码还泄漏了 CGDisplayCreateImage 和 CGImageDestinationCreateWithURL 返回的项目。这是一个有效且不会泄漏的示例:

- (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);
}