Should I set a cancellation token to null after cancelling it?

Question

My code declares a cancellation token here in a view model, creates it in the OnAppearing and Cancels in the OnDisappearing:

public partial class DeckTabViewModel : BaseViewModel
{
    public CancellationTokenSource cts;
}

Then in OnAppearing:

public partial class DeckTabViewModel : BaseViewModel
{
    public async Task OnAppearingAsync()
    {
        cts = new CancellationTokenSource();
        await GetCards(cts.Token);
    }
}

And on Disappearing:

public partial class DeckTabViewModel : BaseViewModel
{
    public async Task OnDisappearingAsync()
    {
       cts.Cancel();
    }
}

Could someone tell me if this is the correct way to use the Cancellation token and should I in the OnDisappearing, also set it to null?

Answer 1

As CancellationTokenSource implements IDisposable, you should dispose the instance of CancellationTokenSource (in your example, cts) when you have finished using it: you can do so directly by calling the Dispose method, or indirectly using the using construct.

In your case, you would call Dispose after calling Cancel on cts:

public partial class DeckTabViewModel : BaseViewModel
{
    public async Task OnDisappearingAsync()
    {
        try
        {
            cts.Cancel();
        }
        finally
        {
             if(cts != null)
             {
                 cts.Dispose();
             }
        }
    }
}