使用TPL异步更新进度条

Question

I have the following code here:

public class ProcessTaskAsyncExProgress
{
    public int ProgressPercentage { get; set; }

    public string Text { get; set; }
}

public static class ProcessTask
{
    public static async Task<string> Start(IProgress<ProcessTaskAsyncExProgress> progress)
    {
        const int total = 10;
        for (var i = 0; i <= total; i++)
        {
            Thread.Sleep(300);
            if (progress != null)
            {
                var args = new ProcessTaskAsyncExProgress
                {
                    ProgressPercentage = (int)(i / (double)total * 100.0),
                    Text = "processing " + i
                };
                progress.Report(args);
            }
        }
        return "Done";
    }
}

And in Form1.cs

    private async void button1_Click(object sender, EventArgs e)
    {
        var result = await StartTask();
    }

    private async Task<string> StartTask()
    {
        var progress = new Progress<ProcessTaskAsyncExProgress>();
        progress.ProgressChanged += (s, e) =>
        {
            progressBar1.Value = e.ProgressPercentage;
            listBox1.Items.Add(e.Text);
            listBox1.SelectedIndex = listBox1.Items.Count - 1;
        };
        return await ProcessTask.Start(progress);
    }

The problem I'm having is that the progress bar, and listbox doesn't populate while the loop is running. the UI is only updated after the whole loop is completed, and what gets displayed are 10 items in the listview and a 100% progress bar.

How should my code be such that the the UI thread isn't hanged?

Answer 1

Thread.Sleep(300); is a blocking call, it is running on UI thread that's why you are not getting the updates on UI. You need to use await Task.Delay(300); instead