CancellationToken with await Task - wpf

Question

I want to use CancellationToken in my GUI but it doesn't work.
When I click on the cancel button I want to cancel the operation
this.tokenSource.Cancel();
In other place I have other button that need to do main operation. The main part includes Task and CancellationToken token and this part doesn works
private CancellationTokenSource tokenSource;
private async void DataSynchronization(object notInUse)
{
this.tokenSource = new CancellationTokenSource();
CancellationToken ct = new CancellationToken();
ct.ThrowIfCancellationRequested();
await Task.Run(() =>
{
try
{
// do main operation
}
catch (Exception e)
{
}
finally
{
// final operation
}
if (ct.IsCancellationRequested)
{
ct.ThrowIfCancellationRequested();
}
}, this.tokenSource.Token)
.ContinueWith(
completedTaskResult =>
{
// I want to check if cancel was presed
}
);
}
This is main structure but something wrong. I don't receive cancel operation

Answer 1

There are several problems here. First you shouldn't create your own CancellationToken, that's what CancellationTokenSource is for! It's the source for your token. Second, you should use the Run overload that takes a CancellationToken as the second argument, and third, you need to check the CancellationToken.IsCancellationRequested property in your do main operation to see if it's been cancelled and stop doing what you are doing if it is.
See here for a good example.
So you code might end up looking something like:
this.tokenSource = new CancellationTokenSource();
var token = tokenSource.Token;
await Task.Run(() =>
{
while(notDone && !token.IsCancellationRequested)
{
// do some stuff
}
}, token);
Now when you do:
this.tokenSource.Cancel();
It will signal to the associated Token that the operation is cancelled and somewhere inside your task you'll pick that up and stop doing that thing.