Creating Custom Columns in a Windows Forms DataGrid

The sample code contains two event handlers: Form.Load Sets up the sample by creating a DataAdapter and using it to fill a DataTable with data from the ProductID, ProductName, and Discon

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Recipe 7.10 Creating Custom Columns in a Windows Forms DataGrid

Problem

You need to create a DataGrid having columns with custom formatting and attributes

Solution

Use the DataGridTableStyle class

The sample code contains two event handlers:

Form.Load

Sets up the sample by creating a DataAdapter and using it to fill a DataTable with data from the ProductID, ProductName, and Discontinued columns of the Products table in the Northwind database The DataGridTableStyle class is used to define a data grid containing three custom columns—two text boxes and one check box— corresponding to the ProductID, ProductName, and Discontinued columns

Finally, the default view of the Products DataTable is bound to the data grid on the form

Update Button.Click

Uses the DataAdapter created in the Form.Load event handler to update changes made to the Products DataTable back to the database

The C# code is shown in Example 7-18

Example 7-18 File: CustomColumnsInDataGridForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Windows.Forms;

using System.Data;

using System.Data.SqlClient;

private SqlDataAdapter da;

private DataTable dt;

//

private void CustomColumnsInDataGridForm_Load(object sender,

System.EventArgs e)

{

// Create the DataAdapter

String selectCommand = "SELECT ProductID, ProductName, Discontinued " + "FROM Products";

da = new SqlDataAdapter(selectCommand,

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

// Use CommandBuilder to handle updates back to the data source

SqlCommandBuilder cb = new SqlCommandBuilder(da);

// Retrieve the table schema

dt = new DataTable("Products");

da.FillSchema(dt, SchemaType.Source);

// Default the check box column to false

dt.Columns["Discontinued"].DefaultValue = false;

// Fill the table

da.Fill(dt);

// Define the table for the grid

DataGridTableStyle ts = new DataGridTableStyle( );

ts.MappingName = "Products";

// Define and add the columns to the grid

DataGridTextBoxColumn productIDCol = new DataGridTextBoxColumn( ); productIDCol.MappingName = "ProductID";

productIDCol.HeaderText = "Product ID";

productIDCol.ReadOnly = true;

ts.GridColumnStyles.Add(productIDCol);

DataGridTextBoxColumn productNameCol = new DataGridTextBoxColumn( ); productNameCol.MappingName = "ProductName";

productNameCol.HeaderText = "Name";

productNameCol.Width = 200;

productNameCol.Alignment = HorizontalAlignment.Center;

ts.GridColumnStyles.Add(productNameCol);

DataGridBoolColumn discontinuedCol = new DataGridBoolColumn( );

discontinuedCol.MappingName = "Discontinued";

discontinuedCol.HeaderText = "Discontinued";

discontinuedCol.AllowNull = false;

ts.GridColumnStyles.Add(discontinuedCol);

dataGrid.TableStyles.Add(ts);

// Bind the default view of the table to the grid

dataGrid.DataSource = dt.DefaultView;

}

private void updateButton_Click(object sender, System.EventArgs e)

{

// Update the data using the DataAdapter

da.Update(dt);

}

Discussion

The TableStyles property of the DataGrid exposes a collection of DataGridTableStyle objects The GridColumnStyles property of the DataGridTableStyle object exposes a GridColumnStylesCollection containing all DataGridColumnStyle objects for the table This property allows a custom set of column styles to be created for the DataGrid Once defined, the Add( ) method of the DataGridTableStyles object is used to add the custom column styles to the DataGrid

The MappingName property of the DataGridTableStyle is set to the DataSource The MappingName of each DataGridColumnStyle object must be associated with the name of

a DataColumn to synchronize the DataGrid display column with the data column An exception will be thrown if duplicate mapping names are used

The DataGridTextBoxColumn class inherits from the abstract DataGridColumnStyle class It defines the attributes, display format, and behavior of cells in a DataGrid column

At runtime, each cell in the column hosts a DataGridTextBox control

The DataGridBoolColumn inherits from the abstract DataGridColumnStyle class It

defines the attributes, display format, and behavior of cells in a DataGrid column

representing a Boolean value At runtime, each cell in the column hosts a CheckBox

control that can have one of three states: checked (true), unchecked (false), or unchecked (DBNull.Value) The allowable states of the check box are controlled by the properties described in Table 7-10

Table 7-10 DataGridBoolColumn properties related to the underlying value Property Description

AllowNull Gets or sets a Boolean value indicating whether null values are allowed

FalseValue Gets or sets the value pushed to the data source when the column value is

set to false NullValue Gets or sets the value pushed to the data source when the column value is

null TrueValue Gets or sets the value pushed to the data source when the column value is

set to true

A new column class can be created to meet special requirements by inheriting from DataGridColumnStyle, where the Abort( ), Commit( ), Edit( ), and Paint( ) methods must

be overridden

By default, a collection of DataGridColumnStyle objects is created behind the scenes when the DataSource property of the DataGrid is set The class used for each column depends on the DataType of the DataColumn associated with the DataGridColumnStyle object A column with a Boolean data type will be represented by a

DataGridBoolColumn object while other columns will be represented by a

DataGridTextBoxColumn object You can use the GetType( ) method of the

DataGridColumnStyle object to determine the column's data type

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