.NET Class 4 – Windows-based Application

WinForm Application Homogeny programming model. Rich class library Classes are shared by all.NET languages. A programming model for GUI applications.

The Windows Forms Programming Model A Form is a top level window. An application ’ s main window is a form, and any other top-level window the application has. Using.NET namespaces, mainly System.WinForms. Includes classes such as: –Form (behavior of windows) –Menu –Control classes: TextBox, Button, ListView etc. (referred as Button or System.WinForms.Button)

WinForms Prog. Model - Cont. An instance of WinForms.Form represents the main application window. Needed properties are accessed easily: –Form ’ s border style – BorderStyle property. Any windows application must run a static method Run of an System.WinForms.Application class. This method displays the window and provides a message loop. (Messages – for instance, mouse moves, input, choice from menus etc.)

Each class contains some virtual methods which can be overridden, such as a respond to a ‘ message ’ like mouse movement. System.WinForms.Form.OnPaint() is called when a form ’ s client area needs updating.

Form’s events All control classes fire events – such as: System.WinForms.Button fire Click events when they are clicked. To respond to a button click – the following code must be included: MyButton.Click += new EventHandler (OnButtonClicked); private void OnButtonClicked(object sender, EventArgs e) { MessageBox.Show ("Click!"); } EventHandlers are delegates – defined in the System Namespage. The first parameter OnButtonClicked: who fired the event. The second parameter, can be ignored in click events, may be used when more information should be passed.

Hello World Windows Forms using System; using System.WinForms; using System.Drawing; public class MyForm : Form { public MyForm () { Text = "Windows Forms Demo"; } protected override void OnPaint (PaintEventArgs e) { e.Graphics.DrawString ("Hello, world", Font, new SolidBrush (Color.Black), ClientRectangle); } public static void Main (string[] args) { Application.Run (new MyForm ()); } }

In the constructor, the Text property is initialized (title of window). Override virtual OnPaint – which is responsible of rendering the form on screen. Here, it will write “ Hello World ” in the form ’ s client area. OnPaint is passed PaintEventArgs object, which contains properties such as Graphics and ClipRectangle. Graphics – reference to a Graphics object (device context). ClipRectangle – a rectangle object which describes which part of the form is invalid.

ImageView Application (Ver. 1) using System; using System.WinForms; using System.Drawing; public class MyForm : Form { public MyForm () { // Set the form's title Text = "Image Viewer"; // Set the form's size ClientSize = new Size (640, 480); } public static void Main (string[] args) { Application.Run (new MyForm ()); } }

ImageView Application (Ver. 2) (Add an Option Menu) public class MyForm : Form { public MyForm () {... // Create a menu MainMenu menu = new MainMenu (); MenuItem item = menu.MenuItems.Add ("&Options"); item.MenuItems.Add (new MenuItem ("E&xit", new EventHandler (OnExit))); // Attach the menu to the form Menu = menu; } // Handler for the Exit command private void OnExit (object sender, EventArgs e) { Close (); }... public static void Main (string[] args) { Application.Run (new MyForm ()); } }

Add An Open Command (Ver. 3) public class MyForm : Form { protected int _FilterIndex = -1; protected Bitmap _MyBitmap; public MyForm () {... MenuItem item = menu.MenuItems.Add ("&Options"); item.MenuItems.Add (new MenuItem ("&Open...", new EventHandler (OnOpenImage), Shortcut.CtrlO)); item.MenuItems.Add ("-"); item.MenuItems.Add (new MenuItem ("E&xit", new EventHandler (OnExit))); // Attach the menu to the form Menu = menu; }...

// Handler for the Open command private void OnOpenImage (object sender, EventArgs e) { OpenFileDialog ofd = new OpenFileDialog (); ofd.Filter = "Image Files (JPEG, GIF, BMP, etc.)|" + "*.jpg;*.jpeg;*.gif;*.bmp;*.tif;*.tiff;*.png|" + "JPEG files (*.jpg;*.jpeg)|*.jpg;*.jpeg|" + "GIF Files (*.gif)|*.gif|" + "BMP Files (*.bmp)|*.bmp|" + "TIFF Files (*.tif;*.tiff)|*.tif;*.tiff|" + "PNG Files (*.png)|*.png|" + "All files (*.*)|*.*"; if (_FilterIndex != -1) ofd.FilterIndex = _FilterIndex; if (ofd.ShowDialog() == DialogResult.OK) { String fileName = ofd.FileName; if (fileName.Length != 0) { _FilterIndex = ofd.FilterIndex; try { _MyBitmap = new Bitmap (fileName); Text = "Image Viewer - " +fileName; Invalidate (); } catch { MessageBox.Show (String.Format ("{0} is not " + "a valid image file", fileName), "Error", MessageBox.OK | MessageBox.IconError); } } } }...

Ver. 3 notes Shortcut -- System.WinForms enumeration. OnOpenImage creates an OpenFile Dialog object, initializes it with the filter string, for ‘ files of type ’ field. If user clicks ‘ ok ’ name of file is extracted by reading it from OpenFileDialog ’ s FileName proerty. Bitmap is a System.Drawing.Bitmap shorthand, for handling image files. Try-catch to avoid opening a non-image file. MessageBox.Show method is used to print and error. Invalidating is a Form method that forces a repaint by invalidating a form ’ s client area. Still no code to render the image into the form.

Notes – Ver. 4 – Override OnPaint Make use of the Graphics object: Graphics g=e.Graphics; g.Drawings(_MyBitmap, 0, 0, _MyBitmap.Width, _MyBitmap.Height); DrawImage is doing the actual painting.

Notes – Ver 5 – Add Scroll Bars. Use a pair of properties from System.WinForms.ScrolableControl. Enable (boolean) autoscrolling – scroll will automatically apear AutoScrollMinSize is set to the chosen BitMap Add scroll parameters to ‘ OnPaint ’ to locate the scroll bars on windows.

Notes – ver. 6 – a size fit option Add a field to store user ’ s preference. Add the menu items in constructor. Add command handlers. SetStyle – called with the ControlStyles parameter ResizeRedraw

Notes – ver 7 – Add code to check/uncheck menu items Handle the choice when menu is opened One event handler Connected to the item.Popup (main option choice event)