Why task is not running even when execution is inside the task method?答案

【问题标题】：Why task is not running even when execution is inside the task method?Why task is not running even when execution is inside the task method?
【发布时间】：2022-12-02 13:54:37
【问题描述】：

So this is WPF + MVVM + .NET 4.8 + WCT.

I have an AsyncRelayCommand in my VM class defined like this:

private AsyncRelayCommand _StartSyncCommand;
public AsyncRelayCommand StartSyncCommand
{
  get
  {
    _StartSyncCommand ??= new AsyncRelayCommand(Pump, () => !_StartSyncCommand.IsRunning);
    return _StartSyncCommand;
  }
}

The actual task method contains an async iterator and looks like this:

private async Task Pump(CancellationToken token)
{
  OnPropertyChanged(nameof(IsBusy));

  try
  {
    await foreach (var item in applicationService.FetchItems())
    {
      token.ThrowIfCancellationRequested();
      ...
    }
  }
  catch(Exception ee)
  {
    ...
  }
  finally
  {
    ...
  }
}

This method raises property change notification on IsBusy property (to show wait cursor in the UI). However when I check the status of StartSyncCommand in the property, it tells me that it is not running.

public bool IsBusy => StartSyncCommand.IsRunning;

I can\'t see why this should be the case. The method is actually running when the property change notification occurs. I can see the method in the call stack.

What am I missing here?

Update

This is getting weirder. StartSyncCommand.ExecutionTask itself is null while I\'m inside the task method:

标签： c# asynchronous mvvm async-await task-parallel-library

【解决方案1】：