print barcode vb.net LIST CONTROLS in C#.NET

Draw Data Matrix ECC200 in C#.NET LIST CONTROLS

CREATE THE CONTROLS FOR OUR NEW APPLICATION (continued) Action 8 Set the properties for the MainForm form.

Note: When you enter the new Size setting, note how the controls automatically resize within the form based on the assigned Anchor settings.

Our form is now ready. You can compile and run if you like. Before we talk about this in any detail, we will add some code to make our new ListBox display the photographs in an album. Some of the new code added by the following steps mimics code we provided for our MyPhotos application. This is to be expected, since both interfaces operate on photo album collections.

DISPLAY THE CONTENTS OF AN ALBUM IN THE LISTBOX CONTROL Action 9 In the MainForm.cs file, indicate we are using the Manning.MyPhotoAlbum namespace. Add some member variables to track the current album and whether it has changed. Override the OnLoad method to initialize the album. Note: The OnLoad method is called a single time after the form has been created and before the form is initially displayed. This method is a good place to perform one-time initialization for a form. 12 Add a Click handler for the Close button to exit the application. Result

. . . using Manning.MyPhotoAlbum;

private PhotoAlbum _album; private bool _bAlbumChanged = false;

protected override void OnLoad (EventArgs e) { // Initialize the album _album = new PhotoAlbum(); base.OnLoad(e); }

private void btnClose_Click (object sender, System.EventArgs e) { Close(); }

DISPLAY THE CONTENTS OF AN ALBUM IN THE LISTBOX CONTROL (continued) Action 13 Add a CloseAlbum method to close a previously opened album.

private void CloseAlbum() { if (_bAlbumChanged) { _bAlbumChanged = false; DialogResult result = MessageBox.Show("Do you want " + "to save your changes to " + _album.FileName + ' ', "Save Changes ", MessageBoxButtons.YesNo, MessageBoxIcon.Question); if (result == DialogResult.Yes) { _album.Save(); } } _album.Clear(); }

protected override void OnClosing (CancelEventArgs e) { CloseAlbum(); } private void btnOpen_Click (object sender, System.EventArgs e) { CloseAlbum(); using (OpenFileDialog dlg = new OpenFileDialog()) { dlg.Title = "Open Album"; dlg.Filter = "abm files (*.abm)" + "|*.abm|All Files (*.*)|*.*"; dlg.InitialDirectory = PhotoAlbum.DefaultDir; try { if (dlg.ShowDialog() == DialogResult.OK) { _album.Open(dlg.FileName); this.Text = _album.FileName; UpdateList(); } } catch (Exception) { MessageBox.Show("Unable to open " + "album\n" + dlg.FileName, "Open Album Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } } }

a. Close any previously open album. b. Use the OpenFileDialog class to allow the user to select an album. c. Use the PhotoAlbum.Open method to open the file. d. Assign the album s file name to the title bar of the form. e. Use a separate method for updating the contents of the list box.

DISPLAY THE CONTENTS OF AN ALBUM IN THE LISTBOX CONTROL (continued) Action 16 Implement a protected UpdateList method to initialize the ListBox control. Result

protected void UpdateList() { lstPhotos.DataSource = _album; }

That s it! No need to add individual photographs one by one or perform other complicated steps to fill in the list box. Much of the code is similar to code we saw in previous chapters. The one exception, the UpdateList method, simply assigns the DataSource property of the ListBox control to the current photo album.

protected void UpdateList() { lstPhotos.DataSource = _album; }

The DataSource property is part of the data binding support in Windows Forms. Data binding refers to the idea of assigning one or more values from some source of data to the settings for one or more controls. A data source is basically any array of objects, and in particular any class that supports the IList interface.1 Since the PhotoAlbum class is based on IList, each item in the list, in this case each Photograph, is displayed by the control. By default, the ToString property for each contained item is used as the display string. If you recall, we implemented this method for the Photograph class in chapter 5 to return the file name associated with the photo. Compile and run your code to display your own album. An example of the output is shown in figure 10.2. In the figure, an album called colors.abm is displayed, with each photograph in the album named after a well-known color. Note how the GroupBox controls display their keyboard access keys, namely Alt+A and Alt+P. When activated, the focus is set to the first control in the group box, based on the assigned tab order.