ios - 当一个 block 试图将自己设置为 nil 时，如何避免保留循环警告？

Question

我正在阅读 SimpleAudioPlayer 的源代码并发现当 playBlock 尝试将其自身设置为 nil 时，Xcode 会发出警告。

我不知道如何摆脱这个警告，或者我们必须将 playBlock 设置为 nil？

- (void) playFiles:(NSArray*) filesList withCompletionBlock:(CompletionBlock) completion
{
    __block int idx = 0;
    __block void(^playBlock)();
    playBlock = ^() {
        if (idx >= filesList.count) {
            if (completion) {
                completion ( YES );
            }
            playBlock = nil; //Capturing 'playBlock' strongly in this block is likely to lead to a retain cycle
            return ;
        }
        [self playFile:filesList[idx] withCompletionBlock:^(BOOL completed) {
            playBlock ();
        }];
        idx ++;
    };

    playBlock ();
}

Answer 1

无需设置 playBlock = nil; 也无需使用 __block 修饰符进行声明。修改后的代码(见下文)编译时没有警告或错误。

- (void) playFiles:(NSArray*) filesList withCompletionBlock:(CompletionBlock) completion
{
    __block int idx = 0;
    void(^playBlock)();
    playBlock = ^() {
        if (idx >= filesList.count) {
            if (completion) {
                completion ( YES );
            }
            return ;
        }
        [self playFile:filesList[idx] withCompletionBlock:^(BOOL completed) {
            playBlock ();
        }];
        idx ++;
    };

    playBlock ();
}