什么是缓冲区> CGImageRef-> UIImage的正确内存管理模式？ [英] What's the right memory management pattern for buffer->CGImageRef->UIImage?

问题描述

我有一个函数，它接受一些位图数据并从中返回一个UIImage *。它看起来像这样：

I have a function that takes some bitmap data and returns a UIImage * from it. It looks something like so:

UIImage * makeAnImage() 
{
    unsigned char * pixels = malloc(...);
    // ...
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, pixels, pixelBufferSize, NULL);
    CGImageRef imageRef = CGImageCreate(..., provider, ...);
    UIImage * image =  [[UIImage alloc] initWithCGImage:imageRef];
    return [image autorelease];
}

任何人都可以确切地解释谁在这里拥有什么内存？我想要正确清理，但我不确定如何安全地进行清理。文档在这些上是模糊的。如果我在创建UIImage后在此函数结尾处 free 像素，然后使用UIImage，我崩溃了。如果我在创建UIImage之后释放提供者或imageRef，我没有看到崩溃，但他们显然已经将像素一直传递过来，所以我对释放这些中间状态感到不安。

Can anyone explain exactly who owns what memory here? I want to clean up properly, but I'm not sure how to do it safely. Docs are fuzzy on these. If I free pixels at the end of this function after creating the UIImage, and then use the UIImage, I crash. If I Release the provider or the imageRef after creating the UIImage, I don't see a crash, but they're apparently passing the pixels all the way through, so I'm skittish about releasing these intermediate states.

（我知道每个CF文档我需要在后者上调用release，因为它们来自Create函数，但我可以在使用UIImage之前执行此操作？）大概我可以使用提供者的dealloc回调来清理像素缓冲区，但还有什么呢？

(I know per CF docs that I should need to call release on both of the latter because they come from Create functions, but can I do that before the UIImage is used?) Presumably I can use the provider's dealloc callback to cleanup the pixels buffer, but what else?

谢谢！

推荐答案

这里的拇指规则是 -release *它，如果你不需要它。

The thumb rule here is "-release* it if you don't need it".

因为之后你不再需要提供者和 imageRef ，你应该 -release 所有这些，即

Because you no longer need provider and imageRef afterwards, you should -release all of them, i.e.

UIImage * image =  [[UIImage alloc] initWithCGImage:imageRef];
CGDataProviderRelease(provider);
CGImageRelease(imageRef);
return [image autorelease];

像素不通过引用计数来管理，所以你需要告诉CG API在必要时为你释放它们。这样做：

pixel is not managed by ref-counting, so you need to tell the CG API to free them for you when necessary. Do this:

void releasePixels(void *info, const void *data, size_t size) {
   free((void*)data);
}
....

CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, pixels, pixelBufferSize, releasePixels);

顺便说一下，你可以使用 + imageWithCGImage：而不是 [[[* alloc] initWithCGImage：] autorelease] 。更好的是，有 + imageWithData：所以你不需要搞乱CG和 malloc 的东西。

By the way, you can use +imageWithCGImage: instead of [[[* alloc] initWithCGImage:] autorelease]. Even better, there is +imageWithData: so you don't need to mess with the CG and malloc stuff.

（*：除非 retainCount 从一开始就被认为是零。）

(*: Except when the retainCount is already supposedly zero from the beginning.)

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