Make WPF UI responsible while reading data from Database

Question

I have C# WPF application which reads data from database then does some work. But the problem is when I am reading data my UI doesn't respond. I have tried Tasks and dispatcher. None of them helps. Code below is in the button_click event. Here is code:

DataSet ds;
DataTable dt = new DataTable();

Task myTask = new Task(new Action(() =>
{
     //GetMyDataSet() returns DataSet
     ds = GetMyDataSet();
     dt = ds.Tables["MyTableName"];
}));

myTask.Start();

while (!myTask.IsCompleted)
{
    System.Threading.Thread.Sleep(1000);
}

//Continue

Why are you sleeping on the UI thread until the task completes? That's why your UI is unresponsive! — Oded
– Oded, Commented Jun 7, 2012 at 12:34
@NikhilAgrawal can you recomend me any site which introduces BackroundWorker briefly? — Adil Mammadov
– Adil Mammadov, Commented Jun 7, 2012 at 12:46

Tudor · Accepted Answer · 2012-06-07 12:36:15Z

7

First off, get rid of the sleep-spin, it completely defeats the purpose of using a Task since it doesn't allow the UI thread to proceed until the Task completes. You don't want that!

Task myTask = Task.Factory.StartNew(
     new Action(() =>
     {
         DataSet ds;
         DataTable dt = new DataTable();    

         //GetMyDataSet() returns DataSet
         ds = GetMyDataSet();
         dt = ds.Tables["MyTableName"];

         // use Invoke/BeginInvoke to update UI
      }));

Now your task will run in parallel with the UI thread until completion. At the end of the Task code use Dispatcher.BeginInvoke to update the UI. It should be ok now.

answered Jun 7, 2012 at 12:36

Tudor

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5 Comments

Adil Mammadov Over a year ago

I can't use Task.Factory.StartNew(). Am I missing reference or what is problem?

Adil Mammadov Over a year ago

System.Threading.Tasks.Task.Factory' is a 'property' but is used like a 'type'

Tudor Over a year ago

@Adil Mammadov: This is very strange. Can you update the code in the question with what you have now?

Patryk Ćwiek Over a year ago

And if you'd like a bit different approach, instead of using the Dispatcher at the end, you can use task continuation with TaskScheduler.FromCurrentSynchronizationContext. :) After you solve your TPL problems, of course.

Adil Mammadov Over a year ago

I did What same Task myTask = new Task.Factory.StartNew(). But I deleted Thread.Sleep() and wrote logic which I used to read data from DataTable in the same Task. Everything works fine now. Thank you

Roman Sokk · Accepted Answer · 2012-06-07 12:50:08Z

-2

Try

while (!myTask.IsCompleted)
{
    Dispatcher.Invoke(DispatcherPriority.Background, new ThreadStart(delegate { }));
    System.Threading.Thread.Sleep(20);
}

answered Jun 7, 2012 at 12:50

Roman Sokk

1754 bronze badges

3 Comments

Tudor Over a year ago

This is just wrong. The reason for the UI freezing is exactly this while loop which should not exist.

Tudor Over a year ago

But he wants the UI to keep responding while the Task is working, not block.

Roman Sokk Over a year ago

Dispatcher.Invoke(DispatcherPriority.Background, new ThreadStart(delegate { })) simulates "Application.DoEvents" and UI become accessible (process events) every 20 ms. Try simple button handler: private void button1_Click(object sender, RoutedEventArgs e) { while (true) { Dispatcher.Invoke(DispatcherPriority.Background, new ThreadStart(delegate { })); Thread.Sleep(20); } }

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