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Drag Once DataBinding with Custom Controls : Page 2

Visual Studio 2005 will ship some great new controls, but suppose you want your own control to play in the Data Sources Window? To do that, you need to set up a new data source using the new binding attributes.


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Setting Up a Data Source
Use VS 2005 to create a new Windows Forms project. It doesn't really matter whether you choose VB, C#, J#, or even C++. Open the Data Sources Window and choose Add New Data Source. Choose Database to start with. (This article will cover objects a bit later). It doesn't really matter what database you use, but I'll use Northwind.
 
Figure 1: Selecting Customize from the Data Sources Window.
Once you provide a connection, you'll be prompted for a connection string name. If you're using Beta 1, be sure to check both checkboxes to save your connection string. We've changed this a bit in Beta 2 to be more intuitive, which hopefully doesn't need explanation, but that's what feedback is all about. (See sidebar, MSDN Feedback Center).

Choose one or more tables from the Database Objects step of the wizard. I've chosen Employees, Orders, and Products because they have columns with several data types, which will be helpful for this example. In the Data Sources Window, expand some of the tables to see the list of columns. Under the Orders table you can see some controls mapped to DateTimePicker, and Photo defaults to none. Test question: Why does the Northwind Employees.Photo column default to None as opposed to a PictureBox? Answer: The column in the dataset comes through as a byte array. We don't actually know if this is an image, Word document, or the binaries for Halo® 2. You can see that Products.Discontinued defaults to a CheckBox, but if you click the dropdown list you may notice a TextBox available as well.

Let's say you want to limit Boolean data types to a CheckBox and you know that most, if not all, of your applications use binary data as Photo. You want to "customize" the list, and change the defaults. Changing the Controls
In the Data Sources Window, select any of the nodes in the TreeView. You'll see the list of controls associated with that data type (see Figure 1). For Employee.Photo you can see the list of controls associated with Byte Array. For Products.Discontinued, you see controls associated with Boolean. Choose "Customize" to launch the Tools-Options dialog box. Note that you're not necessarily customizing just one of these columns. This is just a shortcut to the Tools-Options pane (see Figure 2).



 
Figure 2: Data UI customizations.
Notice that this Data UI Customizations tab is under the Windows Forms Designer. The changes you make here will be specific to Windows Forms. They'll have no affect on the Devices Designer, Visual Studio Tools for Office, or Microsoft Reports. Each designer has its own list of controls. Different Controls per Designer
Although there are many healthy debates about write once, run anywhere, this notion is still not near reality. Each application model has unique characteristics that require a different interface design. On a Tablet PC, users work with an Ink Pen. On a device, they tap. In Office, users work with Excel and Word documents. As a result, we have different controls based on the project type, or more specifically, the form designer.

Designing for the unknown is a key element when designing developer tools.
In order to enable different designers, and thus allow developers to map their own set of controls to different data types, the Visual Basic team designed an infrastructure to support different controls per designer. Based on the designer (Windows Forms, Devices, Visual Studio Tools for Office, Microsoft Reporting Services...), you will see a different set of controls. The logical extension would be Web Forms, but unfortunately the Data Sources Window will not be supported for Web development in Visual Studio 2005. For VS 2005 we only plan to support control customization for Windows Forms. However, based on your feedback, we'll likely add control customization for all designers and add support for the Data Sources Window in Web projects in a post-VS 2005 release.


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