Parallel Process is not updating WPF Collection List - parallel-processing

Question

In my WPF application, I have a Data Grid which populates with a ObservableCollection collection. Suppose I have such 10 student data in the grid. Each student is capable of doing 2 long running works or process and updates the status of the process back to the grid. I want to do those 2 process simultaneously. So I used Task and Parallel.Invoke methods. The work flow is as follows.
I populated the Student data collection in the Grid.
I clicked on a start button.
In the click event of the start button, i did the following code.
foreach (Student stud in StudentLists)
{
stud.Status = "started..";
Task.Factory.StartNew(() => StartProcess(stud));
}
In the StartProcess,
Parallel.Invoke(() =>
{
MarkService ms = new MarkService(stud_data);
Student s = ms.GetMarkProcess(); // This will return the stud_data in the above line
Student studitem = StudentLists.Where(x => x.RollID == s.RollID).FirstOrDefault(); // find the student in the grid
if (studitem != null)
{
studitem.Status = "Mark Got it"; // if find, updating the status
}
},
() =>
{
SentMarks(poll); // this is another method to be executed parallel
}
);
When executing all the 10 students process, each student in the grid became the same data.
Or only 2 or 1 student in the Grid is showing Status "Mark Got it". Other rows show "started.." status only.
Why this is not updating the collection.
I have used INotofyPropertyChanged and raisng the event when property updated.
In the XAML, each binding is used in Two way mode.
There is no error. But the 1 or 2 items in the student collection is updating some times. Sometimes the collection contains the last students data for all the 9 items.
It is not updating the exact student object in the Grid. what is wrong in my code ?
Any help in this case ???

Answer 1

The problem here is that your referencing a UI control from another thread. You should create an in memory data structure that a grid can use as DataSource (anything that implements IEnumerable). I would suggest using the ConcurrentBag data structure for parallelized code (http://msdn.microsoft.com/en-us/library/dd997305.aspx). Once you've updated each of the student records in the ConcurrentBag you set the grid's datasource to that bag.