DataGridView repeatedly recreating columns

Question

I have a problem when assigning the DataSource propery on a DataGridView control. My DataSource is a DataTable's DefaultView and, as expected, columns are automatically created in the DataGridView to match those in the DataTable when I assign it.

What happens next is that the columns seem to be automatically removed and recreated a further 2 times by the DataGridView. Why would this happen?

In a form's constructor:

//A DataTable is created with 5 columns
//The DataTable is populated with some rows.

myDgv.AutoGenerateColumns = true;
myDgv.DataSource = myDataTable.DefaultView;
// myDgv.ColumnAdded event is fired 5 times.
// WHY: myDgv.ColumnRemoved event is fired 5 times.
// WHY: myDgv.ColumnAdded event is fired 5 times.
// WHY: myDgv.ColumnRemoved event is fired 5 times.
// WHY: myDgv.ColumnAdded event is fired 5 times.

Edit: Added a (hopefully) self contained example. If I set breakpoints in the event handlers, I hit the 'Added' one 6 times and the 'Removed' one 4 times. The DataTable contains 2 columns and I never ask for any columns to be removed in my code.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace asdasdgf
{
    public class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            DataTable dt = new DataTable();
            dt.Columns.Add("Col1", typeof(int));
            dt.Columns.Add("Col2", typeof(string));

            foreach (int i in Enumerable.Range(0, 10))
            {
                var row = dt.NewRow();
                row["Col1"] = i;
                row["Col2"] = "stackoverflow";
                dt.Rows.Add(row);
            }

            dataGridView1.ColumnAdded += new DataGridViewColumnEventHandler(dataGridView1_ColumnAdded);
            dataGridView1.ColumnRemoved += new DataGridViewColumnEventHandler(dataGridView1_ColumnRemoved);

            dataGridView1.DataSource = dt.DefaultView;
        }

        void dataGridView1_ColumnRemoved(object sender, DataGridViewColumnEventArgs e)
        {
            // Break here
        }

        void dataGridView1_ColumnAdded(object sender, DataGridViewColumnEventArgs e)
        {
            // Break here
        }

        // Form1.Designer.cs contents:
        #region Windows Form Designer generated code
        private System.ComponentModel.IContainer components = null;
        private System.Windows.Forms.DataGridView dataGridView1;

        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }



        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.dataGridView1 = new System.Windows.Forms.DataGridView();
            ((System.ComponentModel.ISupportInitialize)(this.dataGridView1)).BeginInit();
            this.SuspendLayout();
            // 
            // dataGridView1
            // 
            this.dataGridView1.ColumnHeadersHeightSizeMode = System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
            this.dataGridView1.Location = new System.Drawing.Point(12, 41);
            this.dataGridView1.Name = "dataGridView1";
            this.dataGridView1.Size = new System.Drawing.Size(240, 150);
            this.dataGridView1.TabIndex = 0;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(284, 264);
            this.Controls.Add(this.dataGridView1);
            this.Name = "Form1";
            this.Text = "Form1";
            ((System.ComponentModel.ISupportInitialize)(this.dataGridView1)).EndInit();
            this.ResumeLayout(false);

        }

        #endregion
    }
}

I added a (hopefully) self contained example. If I set breakpoints in the event handlers, I hit the 'Added' one 6 times and the 'Removed' one 4 times. The DataTable contains 2 columns and I never ask for any columns to be removed in my code. — xyz

ChrisF ChrisF · Accepted Answer · 2009-04-20T13:47:01

I have an app that uses a DataGridView to display the contents of a DataTable, but I link them like this:

dataGridView.DataSource = dataTable;

Can you try this?

EDIT:

I also have the following in the auto generated code:

this.dataGridView.EditMode = System.Windows.Forms.DataGridViewEditMode.EditProgrammatically;

Not sure why this would make a difference though.

DataGridView repeatedly recreating columns

5 Answers