Problem in Updating DataGridView via a thread ( when Scrolling )

Question

Hi Experts,

I am stuck with this problem of mine and it will be great help if someone solves this

problem for me

What I am trying to do is :

1) Intialize a DataTable datatable in form load event and assign its defaultview to a

datagridview dgvresult

2) On click of a button start an STA thread (I am actually working with WatIN IE hence the

need for making the thread STA ) which calls a method which creates an identical DataTable

dt as datatable created in step 1 and then adds 300 rows to this datatable.

3) calls a delegate which merges this dt with datatable and thus updates the dgvresult Well here is my problem :

Here is the code Snippet for the steps I just described :

static class Program
{
    /// <summary>
    /// The main entry point for the application.This method is made STAThread as I need to intialize WatIN IE in the form load of frmMain
    /// </summary>
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new frmMain());
    }
}

///frmmain code

 /// <summary>
    /// Delegate which Binds updated Datatable to gridview 
    /// </summary>
    /// <param name="dt">The Datatable to be merged with main datatable</param>

    delegate void Bind_DataTable_to_GridView_Delegate(DataTable dt);

    private void bind_DataTable_to_GridView(DataTable dt)
    {

            if (dgvResult.InvokeRequired)
            {
                Bind_DataTable_to_GridView_Delegate del = new Bind_DataTable_to_GridView_Delegate(bind_DataTable_to_GridView);
                dgvResult.Invoke(del, new object[] { dt });
            }
            else
            {



                    datatable.Merge(dt);


                    dgvResult.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;               //Autosizes the gridview 



                    foreach (DataGridViewColumn dgvcol in dgvResult.Columns)
                    {
                        dgvcol.SortMode = DataGridViewColumnSortMode.NotSortable;
                    }


            }


    }

     WatiN.Core.IE ie;     

    private void frmMain_Load(object sender, EventArgs e)
    {

        //intialize WatIN IE
         ie = new IE(URLs.mainURL);

        //initialization of columns in datatable
        DataColumn datacolumn1 = new DataColumn("Words");

        //Adding of columns in datatable
        datatable.Columns.Add(datacolumn1);


        //Making the datatable permanent
        datatable.AcceptChanges();

        //Assigning default view of datatble as dgvResult's datasource
        dgvResult.DataSource = datatable.DefaultView;

        foreach (DataGridViewColumn  dgvcol in dgvResult.Columns)
        {
            dgvcol.SortMode = DataGridViewColumnSortMode.NotSortable;
        }
    }

    private void btnGenerateWords_Click(object sender, EventArgs e)
    {
        try
        {

            if (datatable.Rows.Count > 0)
            {
                //Initializes the GenerateWords Thread           
                GenerateWords = new Thread(GenW);

                //Sets the apartment state to Static
                GenerateWords.SetApartmentState(ApartmentState.STA);

                //Starts the GenerateWords Thread           
                GenerateWords.Start();
            }

    }
    #endregion



    #region function of GenerateWords thread
    /// <summary>
    /// function of GenerateWords thread
    /// </summary>

    void GenW()
    {

                DataColumn datacolumn1 = new DataColumn("Words");

                //Adding of columns in datatable
                DataTable dt = new DataTable();
                dt.Columns.Add(datacolumn1);

            //At this point datatable has say 20 rows
            for (int dtindex = 0; dtindex < datatable.Rows.Count; dtindex++)
            {
                /*Code Which adds successfully 300 fresh rows to dt*/

                //sends datasource of dgvresult as dt
                bind_DataTable_to_GridView(dt);
                dt.Clear();
            }
        }

    }

Now the problem arises when I have many rows in datagridview(lets assume 1000)

Now if in UI I dont do anything with datagridview this code works fine without errors

But if I keep scrolling the datgridview when the bind method is called the application gives error and just terminates due to its failure to update the datgridview I suppose ( or maybe due to failure in invoking the datagridview )

Here is the error :-- When I run the exe I get this :-

Unhandled exception has occured in your application.

Object reference not set to an object.

System.NullReferenceException: Object reference not set to an instance of an object. at System.Windows.Forms.DataGridViewTextBoxCell.PaintPrivate(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, Int32 rowIndex, DataGridViewElementStates cellState, Object formattedValue, String errorText, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts, Boolean computeContentBounds, Boolean computeErrorIconBounds, Boolean paint) at System.Windows.Forms.DataGridViewTextBoxCell.Paint(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, Int32 rowIndex, DataGridViewElementStates cellState, Object value, Object formattedValue, String errorText, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts) at System.Windows.Forms.DataGridViewCell.PaintWork(Graphics graphics, Rectangle clipBounds, Rectangle cellBounds, Int32 rowIndex, DataGridViewElementStates cellState, DataGridViewCellStyle cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle, DataGridViewPaintParts paintParts) at System.Windows.Forms.DataGridViewRow.PaintCells(Graphics graphics, Rectangle clipBounds, Rectangle rowBounds, Int32 rowIndex, DataGridViewElementStates rowState, Boolean isFirstDisplayedRow, Boolean isLastVisibleRow, DataGridViewPaintParts paintParts) at System.Windows.Forms.DataGridViewRow.Paint(Graphics graphics, Rectangle clipBounds, Rectangle rowBounds, Int32 rowIndex, DataGridViewElementStates rowState, Boolean isFirstDisplayedRow, Boolean isLastVisibleRow) at System.Windows.Forms.DataGridView.PaintRows(Graphics g, Rectangle boundingRect, Rectangle clipRect, Boolean singleHorizontalBorderAdded) at System.Windows.Forms.DataGridView.PaintGrid(Graphics g, Rectangle gridBounds, Rectangle clipRect, Boolean singleVerticalBorderAdded, Boolean singleHorizontalBorderAdded) at System.Windows.Forms.DataGridView.OnPaint(PaintEventArgs e) at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer, Boolean disposeEventArgs) at System.Windows.Forms.Control.WmPaint(Message& m) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.DataGridView.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

I checked it through the VS , It gives this error in Program.cs in this line :- Application.Run(new frmMain());

How to get around this problem?

Any help will be appreciated. Thank You :)

Answer 1

you should try

this.Invoke(del, new object[] { dt }); //Should Work

instead of

dgvResult.Invoke(del, new object[] { dt }); //Error

in bind_DataTable_to_GridView()