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c#user-interfaceasynchronousasync-await
Keylee
Keylee

Reputation: 783

c# Async/Await not updating UI

I am learning to implement async/await on one of my task which takes a long time to complete. Once the task is completed, it should update the DGV.

    private async void frmA_DragDrop(object sender, DragEventArgs e)
    {
        // Some codes to accept dropped files

        // Run task asynchronously
        Task<DataTable> task = Task.Run(() => PDF.CheckPDFs(Files, tblPDFs));
        dgvPDF.DataSource = await task;
     }

I found that after the task is completed, it is not updating the DGV. So, I added the InvokeRequired bit to manually update the table and also to prevent cross-thread exception. 

        // Update UI
        if (dgvPDF.InvokeRequired)
        {
            dgvPDF.Invoke((MethodInvoker)(() => { dgvPDF.Refresh(); }));
        }
        else
        {
            dgvPDF.Refresh();
        }

I also have a separate event handler which highlights the row red is a file is invalid:

    private void dgvPDF_RowsAdded(object sender, DataGridViewRowsAddedEventArgs e)
    {
        if (dgvPDF["Pages",e.RowIndex].Value.ToString() == "0")
            dgvPDF.Rows[e.RowIndex].DefaultCellStyle.BackColor = System.Drawing.Color.MistyRose;
    }

What happened is that the RowAdded event handler is not triggered at all. If I made the code synchronous i.e removing await/async and invoke, everything works fine except with the UI freezing

My question is using InvokedRequired the correct way to update the UI in async await? What can I do to fix this issue?

Upvotes: 0

Views: 1134

Answers (1)

Sam
Sam

Reputation: 133

no, you don't have to "invoke", the context will switch back after async method call complete, i.e., the statements after await will get executed in UI thread.

Upvotes: 1

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