With our initial window in place, we are ready to display some album data in the window.

17.1.2DISPLAYING DATA IN A DATA GRID

Our main window in the MyAlbumData application contains a combo box and a data grid. Our ComboBox control will contain a list of the albums located in the default album directory, while our DataGrid control will display the contents of the selected album. This section will make the changes required for this behavior. Section 17.2 will look at customizing the information displayed by the grid.

Fortunately, our existing MyPhotoAlbum project can do most of the work here. The changes required are detailed in the following steps.

Set the version number of the MyAlbumData application to 17.1.

DISPLAY ALBUM DATA IN THE MYPHOTOALBUM APPLICATION

DISPLAY ALBUM DATA IN THE MYPHOTOALBUM APPLICATION (continued)

This code opens the selected album and assigns the title of the album to appear in the caption area of the data grid. The collection of photographs in the album is bound to the contents of the data grid. The result is shown in figure 17.3.

Figure 17.3

The DataGrid control supports two types of entries by default. Boolean values, such as the IsImageValid property, appear as check boxes. All other properties display the result of their ToString property as a text entry.

The caption area at the top of the control is assigned using the CaptionText property. In the figure, the title of the colors.abm album is “Lots of Colors” as is shown in the caption. The data source for the grid is assigned using the SetDataBinding method. This method has the following signature:

public void SetDataBinding(object dataSource, string dataMember);

The dataSource parameter is assigned to the DataSource property of the control, while the dataMember parameter is assigned to the DataMember property. In our application, the control recognizes our PhotoAlbum object as an IList interface containing a collection of Photograph objects. This is performed internally using the GetType method available on all object instances.

The properties of the Photograph object are determined internally using the members of the System.Reflection namespace. These properties are then used as the columns in the grid, and each Photograph in the album is presented as a row in the grid.

We will not discuss the System.Reflection namespace in detail here. This namespace permits .NET objects such as the DataGrid control to determine the type of object and members of that type at runtime. In this way our data grid can understand how the PhotoAlbum object is organized, and automatically create an appropriate grid structure.

Since the order of columns in the grid corresponds to the internal order of properties in the PhotoAlbum class, your columns might be ordered differently than is shown in figure 17.3. Also note that properties which only provide a get access method are treated as read-only, while properties with both a get and set access method are modifiable. As a result the Image and IsImageValid columns in our grid are read-only, while the Photographer and Notes columns can be modified. We will look at how to update the class with these changes shortly.

Back to our SetDataBinding method, there are a number of different classes that can serve as a source of data, depending on the type of C# interfaces they support. A summary of data sources for the DataGrid class is given in the following table.

Data sources for the data grid control

a. The term transaction indicates that a series of steps either fully completes or appears to never have happened. For example, when transferring money between bank accounts, you must debit the first account and then credit the second account. By making such a transfer transactional, you ensure that the first account is never debited without guaranteeing that the second account is also credited. Aborting an operation part-way through the required steps is said to roll back, or undo, the operation.