C# DataGridView Decimal ComboBox column

Question

I have a datagridview with a bound combobox column which contains decimal value. There is a range of valid decimal values so user can choose one of them. However I face a strange problem - when you click on a combobox in the selected value somehow resets to the first one in a list thus losing the one already selected. Look at the pictures

This is the initial view of a window:

This is when I select similar column with a double value in it(note the selection in combobox's list)

This is when I select column with a decimal value. The selection(number 293) is missing

Here is the code I use:

        public Form1()
        {
            InitializeComponent();

            dgwResult.AutoGenerateColumns = false;
            var list = new List<string>(){"A", "B", "C", "D"};
            var list2 = new List<double>();
            var list3 = new List<decimal>();
            for (int i = 0; i < 300; i++)
            {
                list2.Add((double)i);
                list3.Add((decimal)i);
            }
            dgw_2.DataSource = list;
            dgw_2.DataPropertyName = "two";
            dgw_3.DataSource = list2;
            dgw_3.DataPropertyName = "three";
            dgw_4.DataSource = list3;
            dgw_4.DataPropertyName = "four";
            DataTable dt = new DataTable();
            dt.Columns.Add("one", typeof(string));
            dt.Columns.Add("two", typeof(string));
            dt.Columns.Add("three", typeof(double));
            dt.Columns.Add("four", typeof(decimal));
            dt.Rows.Add(new object[] { "akjsgdf", "A", 10.0, 10.0m });
            dt.Rows.Add(new object[] { "akjsgdf", "B", 15.0, 15.0m });
            dt.Rows.Add(new object[] { "akjsgdf", "C", 20.0, 20.0m });
            dt.Rows.Add(new object[] { "akjsgdf", "D", 15.0, 15.0m });
            dt.Rows.Add(new object[] { "akjsgdf", "C", 293.0, 293.0m });
            dgwResult.DataSource = dt;
        }

private void InitializeComponent()
        {
            this.dgwResult = new System.Windows.Forms.DataGridView();
            this.dgw_1 = new System.Windows.Forms.DataGridViewTextBoxColumn();
            this.dgw_2 = new System.Windows.Forms.DataGridViewComboBoxColumn();
            this.dgw_3 = new System.Windows.Forms.DataGridViewComboBoxColumn();
            this.dgw_4 = new System.Windows.Forms.DataGridViewComboBoxColumn();
            ((System.ComponentModel.ISupportInitialize)(this.dgwResult)).BeginInit();
            this.SuspendLayout();
            // 
            // dgwResult
            // 
            this.dgwResult.AllowUserToAddRows = false;
            this.dgwResult.AllowUserToDeleteRows = false;
            this.dgwResult.AutoSizeColumnsMode = System.Windows.Forms.DataGridViewAutoSizeColumnsMode.Fill;
            this.dgwResult.ColumnHeadersHeightSizeMode = System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
            this.dgwResult.Columns.AddRange(new System.Windows.Forms.DataGridViewColumn[] {
            this.dgw_1,
            this.dgw_2,
            this.dgw_3,
            this.dgw_4});
            this.dgwResult.Location = new System.Drawing.Point(12, 12);
            this.dgwResult.Name = "dgwResult";
            this.dgwResult.RowHeadersVisible = false;
            this.dgwResult.Size = new System.Drawing.Size(268, 150);
            this.dgwResult.TabIndex = 0;
            this.dgwResult.CellClick += new System.Windows.Forms.DataGridViewCellEventHandler(this.dgwResult_CellClick);
            // 
            // dgw_1
            // 
            this.dgw_1.DataPropertyName = "one";
            this.dgw_1.HeaderText = "One";
            this.dgw_1.Name = "dgw_1";
            // 
            // dgw_2
            // 
            this.dgw_2.DataPropertyName = "two";
            this.dgw_2.HeaderText = "Two";
            this.dgw_2.Name = "dgw_2";
            // 
            // dgw_3
            // 
            this.dgw_3.DataPropertyName = "three";
            this.dgw_3.HeaderText = "Double";
            this.dgw_3.Name = "dgw_3";
            // 
            // dgw_4
            // 
            this.dgw_4.DataPropertyName = "four";
            this.dgw_4.HeaderText = "Decimal";
            this.dgw_4.Name = "dgw_4";
            this.dgw_4.Resizable = System.Windows.Forms.DataGridViewTriState.True;
            this.dgw_4.SortMode = System.Windows.Forms.DataGridViewColumnSortMode.Automatic;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(292, 273);
            this.Controls.Add(this.dgwResult);
            this.Name = "Form1";
            this.Text = "Form1";
            ((System.ComponentModel.ISupportInitialize)(this.dgwResult)).EndInit();
            this.ResumeLayout(false);

        }

        private System.Windows.Forms.DataGridView dgwResult;
        private System.Windows.Forms.DataGridViewTextBoxColumn dgw_1;
        private System.Windows.Forms.DataGridViewComboBoxColumn dgw_2;
        private System.Windows.Forms.DataGridViewComboBoxColumn dgw_3;
        private System.Windows.Forms.DataGridViewComboBoxColumn dgw_4;

Can someone point out why the behavior is so strange for decimal? Maybe I'm missing something simple here?

Answer 1

The reason you're getting that 'strange' operation is because the decimal numbers are not in the list used to populate the column's DataSource.

The problem is fixed by changing the code that populates the DataTable to this:

dt.Rows.Add(new object[] { "akjsgdf", "A", 10.0, 10m });
dt.Rows.Add(new object[] { "akjsgdf", "B", 15.0, 15m });
dt.Rows.Add(new object[] { "akjsgdf", "C", 20.0, 20m });
dt.Rows.Add(new object[] { "akjsgdf", "D", 15.0, 15m });
dt.Rows.Add(new object[] { "akjsgdf", "C", 293.0, 293m });

I reckon the DataGridView calls the .ToString() function on each element in the column's DataSource to find the match. Since 1.0 does not equal 1 (in string terms), no item is selected when you open the drop down menu of the combo box.