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Create a .NET Framework Windows Forms user control that supports lookup data binding

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Datasets and related classes are legacy .NET Framework technologies from the early 2000s that enable applications to work with data in memory while the applications are disconnected from the database. The technologies are especially useful for applications that enable users to modify data and persist the changes back to the database. Although datasets have proven to be a very successful technology, we recommend that new .NET applications use Entity Framework Core. Entity Framework provides a more natural way to work with tabular data as object models, and it has a simpler programming interface.

When displaying data on Windows Forms, you can choose existing controls from the Toolbox, or you can author custom controls if your application requires functionality not available in the standard controls. This walkthrough shows how to create a control that implements the LookupBindingPropertiesAttribute. Controls that implement the LookupBindingPropertiesAttribute can contain three properties that can be bound to data. Such controls are similar to a ComboBox.

For more information on control authoring, see Developing Windows Forms controls at design time.

When authoring controls for use in data-binding scenarios, you need to implement one of the following data-binding attributes:

Data-binding attribute usage
Implement the DefaultBindingPropertyAttribute on simple controls, like a TextBox, that display a single column (or property) of data. For more information, see Create a Windows Forms user control that supports simple data binding.
Implement the ComplexBindingPropertiesAttribute on controls, like a DataGridView, that display lists (or tables) of data. For more information, see Create a Windows Forms user control that supports complex data binding.
Implement the LookupBindingPropertiesAttribute on controls, like a ComboBox, that display lists (or tables) of data, but also need to present a single column or property. (This process is described in this walkthrough page.)

This walkthrough creates a lookup control that binds to data from two tables. This example uses the Customers and Orders tables from the Northwind sample database. The lookup control is bound to the CustomerID field from the Orders table. It uses this value to look up the CompanyName from the Customers table.

During this walkthrough, you'll learn how to:

  • Create a new Windows Forms App (.NET Framework).

  • Add a new User Control to your project.

  • Visually design the user control.

  • Implement the LookupBindingProperty attribute.

  • Create a dataset with the Data Source Configuration wizard.

  • Set the CustomerID column on the Orders table, in the Data Sources window, to use the new control.

  • Create a form to display data in the new control.

Prerequisites

To complete this tutorial, you need the .NET desktop development and Data storage and processing workloads installed in Visual Studio. To install them, open Visual Studio Installer and choose Modify (or More > Modify) next to the version of Visual Studio you want to modify. See Modify Visual Studio.

This walkthrough uses SQL Server Express LocalDB and the Northwind sample database.

  1. If you don't have SQL Server Express LocalDB, install it either from the SQL Server Express download page, or through the Visual Studio Installer. In the Visual Studio Installer, you can install SQL Server Express LocalDB as part of the Data storage and processing workload, or as an individual component.

  2. Install the Northwind sample database by following these steps:

    1. In Visual Studio, open the SQL Server Object Explorer window. (SQL Server Object Explorer is installed as part of the Data storage and processing workload in the Visual Studio Installer.) Expand the SQL Server node. Right-click on your LocalDB instance and select New Query.

      A query editor window opens.

    2. Copy the Northwind Transact-SQL script to your clipboard. This T-SQL script creates the Northwind database from scratch and populates it with data.

    3. Paste the T-SQL script into the query editor, and then choose the Execute button.

      After a short time, the query finishes running and the Northwind database is created.

Create a Windows Forms app project

The first step is to create a Windows Forms App (.NET Framework) project.

  1. In Visual Studio, on the File menu, select New > Project.

  2. Expand either Visual C# or Visual Basic in the left-hand pane, then select Windows Desktop.

  3. In the middle pane, select the Windows Forms App project type.

  4. Name the project LookupControlWalkthrough, and then choose OK.

    The LookupControlWalkthrough project is created, and added to Solution Explorer.

Add a user control to the project

This walkthrough creates a lookup control from a User Control, so add a User Control item to the LookupControlWalkthrough project.

  1. From the Project menu, select Add User Control.

  2. Type LookupBox in the Name area, and then select Add.

    The LookupBox control is added to Solution Explorer, and opens in the designer.

Design the LookupBox control

To design the LookupBox control, drag a ComboBox from the Toolbox onto the user control's design surface.

Add the required data-binding attribute

For lookup controls that support data binding, you can implement the LookupBindingPropertiesAttribute.

  1. Switch the LookupBox control to code view. (On the View menu, choose Code.)

  2. Replace the code in the LookupBox with the following:

    using System.Windows.Forms;

namespace CS
{
    [System.ComponentModel.LookupBindingProperties("DataSource", "DisplayMember", "ValueMember", "LookupMember")]
    public partial class LookupBox : UserControl
    {
        public object DataSource
        {
            get{ return comboBox1.DataSource; }
            set{ comboBox1.DataSource = value; }
        }

        public string DisplayMember
        {
            get{ return comboBox1.DisplayMember; }
            set{ comboBox1.DisplayMember = value; }
        }

        public string ValueMember
        {
            get{ return comboBox1.ValueMember; }
            set{ comboBox1.ValueMember = value; }
        }

        public string LookupMember
        {
            get{ return comboBox1.SelectedValue.ToString(); }
            set{ comboBox1.SelectedValue = value; }
        }


        public LookupBox()
        {
            InitializeComponent();
        }
    }
}

  3. From the Build menu, choose Build Solution.

Create a data source from your database

This step creates a data source using the Data Source Configuration wizard, based on the Customers and Orders tables in the Northwind sample database.

  1. To open the Data Sources window, on the Data menu, click Show Data Sources.

  2. In the Data Sources window, select Add New Data Source to start the Data Source Configuration wizard.

  3. Select Database on the Choose a Data Source Type page, and then select Next.

  4. On the Choose your Data Connection page do one of the following:

    • If a data connection to the Northwind sample database is available in the dropdown list, select it.

    • Select New Connection to launch the Add/Modify Connection dialog box.

  5. If your database requires a password, select the option to include sensitive data, and then select Next.

  6. On the Save connection string to the Application Configuration file page, click Next.

  7. On the Choose your Database Objects page, expand the Tables node.

  8. Select the Customers and Orders tables, and then select Finish.

    The NorthwindDataSet is added to your project, and the Customers and Orders tables appear in the Data Sources window.

Set the CustomerID column of the Orders table to use the LookupBox control

Within the Data Sources window, you can set the control to be created prior to dragging items onto your form.

  1. Open Form1 in the designer.

  2. Expand the Customers node in the Data Sources window.

  3. Expand the Orders node (the one in the Customers node below the Fax column).

  4. Click the dropdown list arrow on the Orders node, and choose Details from the control list.

  5. Click the dropdown list arrow on the CustomerID column (in the Orders node), and choose Customize.

  6. Select the LookupBox from the list of Associated Controls in the Data UI Customization Options dialog box.

  7. Click OK.

  8. Click the dropdown list arrow on the CustomerID column, and choose LookupBox.

Add controls to the form

You can create the data-bound controls by dragging items from the Data Sources window onto Form1.

To create data-bound controls on the Windows Form, drag the Orders node from the Data Sources window onto the Windows Form, and verify that the LookupBox control is used to display the data in the CustomerID column.

Bind the control to look up CompanyName from the Customers table

To set up the lookup bindings, select the main Customers node in the Data Sources window, and drag it onto the combo box in the CustomerIDLookupBox on Form1.

This sets up the data binding to display the CompanyName from the Customers table, while maintaining the CustomerID value from the Orders table.

Run the application

  • Press F5 to run the application.

  • Navigate through some records, and verify that the CompanyName appears in the LookupBox control.

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