Variable 'bop' is uninitialized when captured by block

代码：

- (void)doTest {
    NSBlockOperation * bop = [NSBlockOperation blockOperationWithBlock:^{
        if (!bop.isCancelled) {
            // ...
            // doSomething
        }

    }];

    [mQueue addOperation:bop];
}

这段代码是有明显问题的，如果用Analyze来检查的话，就会有警告Variable 'bop' is uninitialized when captured by block.

其实很简单，问题出在block内部对于bop的使用上. 在进入block的时候，bop是一个未初始化的变量.

解决方法很简单，加上__block修饰为block变量就好了.

- (void)doTest {
    __block NSBlockOperation * bop = [NSBlockOperation blockOperationWithBlock:^{
        if (!bop.isCancelled) {
            // ...
            // doSomething
        }

    }];

    [mQueue addOperation:bop];
}