用进度更新异步ObservableCollection

Question

My problem is that my task is changing an observable collection that is data-bound to a UI element. my task will report progress and this data will be updated to the ui via the observable collection :

async private void getProductData()
{
    await Task.Run(() => getTableDataFromDb(new Progress<string>(
       data => _prc.Add(new ProductList() { Taxe = data })
       ), "List"));
}
private void getTableDataFromDb(IProgress<string> progress, string tabelName)
{
   //simple exemple
   for(var i =0; i < 100; i++)
     progress.Report( "test"+i);
}

if i run this code i get this error:

This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread.

How can i access the main thread to update this collections? Thanks

Answer 1

The problem is that you are creating the Progress<string> object in the wrong thread. It's being created in the same worker thread that's actually doing the work, which means it doesn't capture the correct SynchronizationContext object to marshal the work back to the thread you want.

Instead, you want something like this:

async private void getProductData()
{
    IProgress<string> progress = new Progress<string>(
       data => _prc.Add(new ProductList() { Taxe = data }));

    await Task.Run(() => getTableDataFromDb(progress, "List"));
}

That will create the Progress<string> object in the thread that calls the getProductData() , which is presumably your UI thread. Then when the IProgress<string>.Report() method is called, the delegate invocation will be marshalled back to the UI thread as intended.