Exception has been thrown by the target of an invocation in C#

Question

I am using BackGround Worker for Loading data from DB(MS Access). In my Form_Load i use:

 bgw.RunWorkerAsync();

In my DoWork event I laod the data from DB

private void bgw_DoWork(object sender, DoWorkEventArgs e)
    {

        int iResult = OpenDB();
        if (iResult != 0)
        {
            MessageBox.Show("Error in Opening DataBase", Constants.TITLE);
            return ;
        }
        DataSet ds = GetAllUserInfo();
        e.Result = ds;


    }

And in My RunWorkerCompleted i assign data to DataGridView.

    private void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {

        dgUsers.Rows[0].Cells[0].Value = e.Result; 


    }

//Error Comes here after executing above code

[STAThread]
        static void Main()
        {
            Application.Run(new frmMain());
        }

Any help is appreciated. Thanks.

Answer 1

This happens when an exception happens on another thread.

Check that exceptions inner exception to find the real exception that was thrown by your DoWork method..

Answer 2

Use SyncronizationContext mechanism for UI update . Example here http://www.codeproject.com/KB/threads/SynchronizationContext.aspx

1 .Have this as a global object :

System.Threading.SynchronizationContext synchronizationContext;

1. Instantiate the object "synchronizationContext" on Form_Load event :

   synchronizationContext = System.Threading.SynchronizationContext.Current;

2. Modify bgw_RonWorkerCompleted to :

   private void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) {

     synchronizationContext.Post(new SendOrPostCallback( delegate { dgUsers.DatSource =e.Result as DataSet; }), null); 

   }

Answer 3

You should'nt handle the exception in bgw_DoWork.

 private void bgw_DoWork(object sender, DoWorkEventArgs e)
 {
            OpenDB();
            e.Result = GetAllUserInfo();
 }

instead you have to check the Error Property of RunWorkerCompletedEventArgs back on the UI thread.

 private void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
 {
     if (e.Error ==null)
        dgUsers.Rows[0].Cells[0].Value = e.Result; 
     else
       MessageBox.Show("Error in Opening DataBase", Constants.TITLE);

 }

Answer 4

You may have a cross-thread operation : the RunWorkerCompleted isn't raised in the UI thread, resulting in a cross-thread operation on .Value . Could you try this :

                    private void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
                {
                    if (this.InvokeRequired)
                    {
                        this.Invoke(bgw_RunWorkerCompleted, sender, e);
                        return;
                    }
                    dgUsers.Rows[0].Cells[0].Value = e.Result; 
                }