Question

有一个功能可以尝试扫描给定的文件夹。扫描时，用户可以使用取消按钮。但它不会取消第一次尝试的扫描，但是会在下次尝试时成功。

这是我的代码框架：

 private CancellationTokenSource _tokenSource;

 CallingMethod()
 {
   var cancelationToken = GetCancelationToken();
    Task.Run(() => { MethodA(true, stringVal, cancelationToken); }, cancelationToken);
 }

 internal void MethodA(bool isCreateNewRequested, string directoryPath, CancellationToken token)
    {
        bool sucess = true;            

        if (isCreateNewRequested)
            sucess = MethodB(directoryPath, token);

        if (token.IsCancellationRequested) return;

        //some more code
    }


    private bool MethodB(string directoryPath, CancellationToken token)
    {            
        var fileEntries = ProcessSubDirectories(directoryPath);
        var totalFileCount = fileEntries.Count;

        foreach (var fileEntry in fileEntries)
        {
            if (token.IsCancellationRequested) break;

            //dosomething here
        }

        if (token.IsCancellationRequested) return false;

    }

 private CancellationToken GetCancelationToken()
    {          
        _tokenSource?.Cancel();
        _tokenSource = new CancellationTokenSource();

        return _tokenSource.Token;
    }

Answer 1

首先，您必须创建简单的取消令牌：

CancellationToken cToken = new CancellationToken();

就是这样。该令牌必须传递给异步方法，然后：

CancellationTokenSource cts = CancellationTokenSource.CreateLinkedTokenSource(cToken);

然后使用此cts。

if(cts.Cancelled) //written from head, so there may be other way to check it
    cts.Token.ThrowIfCancellationRequested();

或：

cts.Cancel(true); //if you want to cancel manually something
cts.Token.ThrowIfCancellationRequested();

您不能只返回。您必须抛出以取消操作。

单击“取消”不适用于第一次单击。但这适用于下一次尝试

1 个答案: