ios - 使用__block变量阻止泄漏

Question

我发现在requestContentEditingInputWithOptions:方法中/上发生了很大的内存泄漏。如果我理解正确，它会发生在img变量中。如果将其设置为__block __weak，则在将其分配给(img = [UIImage...])后，该图像已经为nil。我在某个地方傻吗？还是我将如何避免这种内存泄漏？

- (UIImage*) getRightlySizedImgFromAsset:(PHAsset*)asset {

    __block UIImage *img;


    PHContentEditingInputRequestOptions *coptions = [PHContentEditingInputRequestOptions new];
    coptions.canHandleAdjustmentData = ^BOOL(PHAdjustmentData *adjustmentData) { return NO; };

    //semaphore used so the block runs synchronously and I can return img from this method at the end
    dispatch_semaphore_t sem = dispatch_semaphore_create(0);

    [asset requestContentEditingInputWithOptions:coptions completionHandler:^(PHContentEditingInput *contentEditingInput, NSDictionary *info) {
        NSURL* url = [contentEditingInput fullSizeImageURL];
        int orientation = [contentEditingInput fullSizeImageOrientation];

        CIImage* inputImage = [CIImage imageWithContentsOfURL:url options:nil];
        inputImage = [inputImage imageByApplyingOrientation:orientation];
        CIContext *context = [CIContext contextWithOptions:nil];

        img = [UIImage imageWithCGImage:[context createCGImage:inputImage fromRect:inputImage.extent]];

        dispatch_semaphore_signal(sem);
    }];
    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);


    if (needToDoSomethingWithImg){
        [self doSomethingWithImage:img];
    }


    return img;
}

Answer 1

通过静态分析器运行此代码(shift + command + B或从“产品”菜单中选择“分析”)，它将指出createCGImage正在创建您永远不会释放的CGImageRef。

您可能想要执行以下操作:

CGImageRef imageRef = [context createCGImage:inputImage fromRect:inputImage.extent];
img = [UIImage imageWithCGImage:imageRef];
CFRelease(imageRef);

顺便说一句，您不应该同步执行此操作。您应该执行以下操作:

- (void) getRightlySizedImgFromAsset:(PHAsset*)asset completionHandler:(void (^)(UIImage *))completionHandler {

    PHContentEditingInputRequestOptions *coptions = [PHContentEditingInputRequestOptions new];
    coptions.canHandleAdjustmentData = ^BOOL(PHAdjustmentData *adjustmentData) { return NO; };

    [asset requestContentEditingInputWithOptions:coptions completionHandler:^(PHContentEditingInput *contentEditingInput, NSDictionary *info) {
        NSURL* url = [contentEditingInput fullSizeImageURL];
        int orientation = [contentEditingInput fullSizeImageOrientation];

        CIImage* inputImage = [CIImage imageWithContentsOfURL:url options:nil];
        inputImage = [inputImage imageByApplyingOrientation:orientation];
        CIContext *context = [CIContext contextWithOptions:nil];

        CGImageRef imageRef = [context createCGImage:inputImage fromRect:inputImage.extent];
        UIImage *image = [UIImage imageWithCGImage:imageRef];
        CFRelease(imageRef);

        // if this stuff needs to happen on main thread, then dispatch it to the main thread

        if (needtodosomethingwithit)
            [self doSomethingWithImage:image];

        if (completionHandler) {
            completionHandler(image);
        }
    }];
}