In this section we will simply move our existing DataGrid control into an Album tab, and create a Photo tab containing the controls shown in the figure. The following steps implement this change.

Set the version number of the MyAlbumData application to 17.4.

CREATE THE CONTROLS WITHIN A TAB CONTROL OBJECT

CREATE THE CONTROLS WITHIN A TAB CONTROL OBJECT (continued)

That took a bit of work. As we mentioned earlier in the book, you can reduce the amount of time spent drawing forms in Visual Studio by sketching out your controls on paper before using Visual Studio. While not illustrated in these pages, I really did sketch the Photo tab page by hand before creating this page in Visual Studio .NET.

With our controls defined, we are ready for our data binding discussion.

17.4.2PERFORMING SIMPLE BINDING

The binding of controls to data involves four distinct roles, each with a corresponding class. These correspond to the work performed by the .NET Framework on behalf of bound controls, namely tracking which data has been bound to which control, managing a bound data source, tracking specific bindings to a control, and managing the actual bindings. A summary of these roles, along with the Windows Forms class and property related to these roles, is outlined in the following table:

Roles required for simple data binding

We will discuss these classes and properties in more detail as we build our example. As a brief explanation, the BindingContext class manages a collection of BindingManagerBase objects. While any control can create an instance of this class in its BindingContext property, the Form class creates one automatically to serve as the

default container for all data bound to the form. In our case, we will simply use the default BindingContext for our form, and not discuss this class in too much detail.

A single BindingManagerBase object exists for each bound data object. In our case, with a single PhotoAlbum object bound to our controls, our application will have a single BindingManagerBase created. For an object with multiple members, such as a database with multiple tables, a BindingManagerBase will exist for each member bound to a control.

A ControlBindingsCollection object contains the collection of actual bindings created for a control. The DataBindings property in the Control class contains the collection of these binding objects.

Each binding object is a Binding class instance. The Binding class permits any property of any control to be bound to any column or property of a data source. We will see this in our application shortly.

Let’s discuss the previous table from the bottom up, beginning with the Binding class. Typically, it is not necessary to access this class directly. Even so, it is likely useful to see the properties that make up each individual binding, so a summary of this class appears in .NET Table 17.6. Note that the possible data sources for simple data binding correspond to those shown earlier in the chapter for the DataGrid control.

As you can see, this class is fairly generic, and permits any property to be bound to pretty much anything. The Format and Parse events can even be used to specify exactly how this binding will take place when converting between the data source and the control’s property.

If you are thoroughly confused at this point, don’t fret. We will lay this out step by step for our application, which should aid your understanding. Let’s start with a summary of exactly what should be bound to what. The following table shows our controls, the property in each control that we would like to bind, and the member of the Photograph object within our PhotoAlbum data source that can provide this value.

Details of our initial data binding approach

.NET Table 17.6 Binding class

The Binding class represents a simple data binding between a data source entry and a Windows Form control. The Binding instances defined for a control are contained by the DataBindings property of that control. This class is part of the System.Windows.Forms namespace.

So let’s do this. We already have a PhotoAlbum field in our MainForm class, so we can bind these controls in our OnLoad method, as shown in the following table.