setCompletionBlock在Objective-C中的奇怪行为

Question

GPUImageOutput<GPUImageInput> *filter;
GPUImageMovieWriter *movieWriter;
.
.
.
__block BOOL finished = NO;
__weak id weakMovieWriter = movieWriter;
[movieWriter setCompletionBlock:^{
    NSLog(@"Completed Successfully");
    __strong id strongMovieWritier = weakMovieWriter;
    [strongMovieWritier finishRecording];
    [filter removeTarget:strongMovieWritier];
    finished = YES;
    NSLog(finished ? @"Yes" : @"No");

}];
while (!finished);
[self completeTransaction]; // this method is not executed!!!

关于上述代码，即使我知道变量“ finished”已更改为“ YES”，也不会执行方法[self completeTransaction]。

但是如果我更改这段代码

while (!finished);

至

while (!finished){
    NSLog(@"Whatever");
}

调用方法[self completeTransaction]。

有人知道为什么会这样吗？

谢谢你的时间。

Answer 1

再次检查您的代码，我想如果

[self completeTransaction];

执行很少，因为完成块

[movieWriter setCompletionBlock:^{
    NSLog(@"Completed Successfully");
    __strong id strongMovieWritier = weakMovieWriter;
    [strongMovieWritier finishRecording];
    [filter removeTarget:strongMovieWritier];
    finished = YES;
    NSLog(finished ? @"Yes" : @"No");

}];

同步执行a和您的[self completeTransaction]; 我假设在主线程上执行，我建议您这样做

GPUImageOutput<GPUImageInput> *filter;
GPUImageMovieWriter *movieWriter;
.
.
.
__weak id weakMovieWriter = movieWriter;
__weak weakSelf = self;
[movieWriter setCompletionBlock:^{
    NSLog(@"Completed Successfully");
    __strong id strongMovieWritier = weakMovieWriter;
    [strongMovieWritier finishRecording];
    [filter removeTarget:strongMovieWritier];
    [weakSelf completeTransaction];
}];

相反，正如我在之前的评论中所说，希望这对您有所帮助