1. BIM211 – Visual Programming Interacting with Users Graphics 1

2. Contents Interacting with Users – MessageBox – Custom Dialog Boxes – Keyboard Events – Mouse Events Graphics – Drawing into a Form or Control – Persisting Graphics in a PictureBox 2

3. MessageBox MessageBox.Show(MessageText, Caption, Buttons, Icon, DefaultButton, Options) 3

4. MessageBoxButtons AbortRetryIgnore OK OKCancel YesNoCancel YesNo RetryCancel 4

5. MessageBoxIcons NameIcon Asterisk Information Error Hand Stop Exclamation Warning Question 5

6. Determining Which Button is Clicked The MessageBox.Show() method returns the button clicked as a DialogResult enumeration. if (MessageBox.Show(…) == DialogResult.OK) { // OK button is clicked } DialogResult result = MessageBox.Show(…); switch (result) { … } 6

7. Enumerations for DialogResult OK Cancel Yes No Retry Ignore Abort None (for Modal Dialog Boxes) 7

8. Creating Good Messages Use a formal tone Don’t use large words Make the text immediately understandable Limit messages to two or three lines Make the question as succinct as possible Spell-check all message text Avoid technical jargon Be sure that buttons and the icon match the text 8

9. Creating Custom Dialog Boxes Most of the time, the MessageBox.Show() method should be a sufficient means to display messages to a user. At times, however, the MessageBox.Show() method is too limited for a given purpose. Suppose that you want to display a lot of text to the user, such as a log file of some sort, for example, so you want a message box that the user can size. 9

10. Creating Custom Dialog Boxes Custom dialog boxes are nothing more than standard modal forms, with one notable exception: One or more buttons are designated to return a dialog result, just as the buttons on a message box shown with the MessageBox.Show() method return a dialog result. 10

11. Exercise Create a new form in a new project Design the contents of the new form Put some buttons and set their DialogResult properties to one of the suitable DialogResult enumerations (When you select a dialog result, you don’t need to handle the click events of the buttons) Open the form from the main form with ShowDialog() method 11

12. Exercise at Runtime 12

13. Interacting with the Keyboard Event NameDescription KeyDownOccurs when a key is pressed while the control has focus KeyPressOccurs when a key is pressed while the control has the focus. If the user holds down the key, this event fires multiple times KeyUpOccurs when a key is released while the control has the focus 13

14. Exercise Write a program with a TextBox in which only numbers can be entered. Solution: Handle the KeyPress event and set e.Handled property to true when any key except a digit is pressed. 14

15. Using the Common Mouse Events Event NameDescription MouseEnterOccurs when the pointer enters a control MouseMoveOccurs when the pointer moves over a control MouseHoverOccurs when the pointer hovers over a control MouseDownOccurs when the pointer is over a control and a button is pressed MouseUpOccurs when the pointer is over a control and a button is released MouseLeaveOccurs when the pointer leaves a control MouseClickOccurs between the MouseDown and MouseUp events, after the Click event ClickOccurs between the MouseDown and MouseUp events 15

16. Exercise Write a program which enables the user to draw on a form. 1.Create a Graphics object member variable 2.Instantiate it in the Load event handler 3.Dispose it in the FormClosed event handler 4.Handle the MouseMove event and draw an ellipse at the mouse coordinate if the Left mouse button is clicked during the mouse move 16

17. Exercise at Runtime 17

18. Creating a Graphics Object If you want to draw something an a control, you should get a reference to its drawing surface: Graphics g = textBox1.CreateGraphics(); 18

19. Drawing on Bitmaps The Bitmap objects are created with the new command: Bitmap bmp = new Bitmap(640, 480); Graphics object of a Bitmap is acquired with the static Graphics.FromImage() method: Graphics g = Graphics.FromImage(bmp); All drawings on g are drawn on the bitmap then. 19

20. Drawing on a PictureBox The drawn shapes on the Graphics object of a PictureBox disappear if you minimize and restore your program. If you want them to appear again, you should either handle the Paint event of the form or draw everything on the bitmap Image of the picture box. The second one is easier. 20

21. Load Event Initialize the Image of the picture box in Load event of the form: Bitmap bmp = new Bitmap(pictureBox1.Width, pictureBox1.Height); Graphics g = Graphics.FromImage(bmp); g.FillRectangle(Brushes.White, 0, 0, bmp.Width, bmp.Height); pictureBox1.Image = bmp; 21

22. MouseMove Event Get the Bitmap image of the picture box Create the Graphics object from the Bitmap using Graphics.FromImage() method and draw: if (e.Button == MouseButtons.Left) { Bitmap bmp = (Bitmap)pictureBox1.Image; Graphics g = Graphics.FromImage(bmp); g.DrawEllipse(Pens.Red, e.X, e.Y, 2, 2); pictureBox1.Invalidate(); } 22

23. Invalidate() If you want a control to draw itself, you should call its Invalidate() method. If you don’t call it in the previous code, your drawings does not appear on the picture box unless you minimize and restore the form. Restoring the form window forces the form and all its controls to Paint themselves. 23

24. Some Drawing Methods DrawLine() DrawEllipse() DrawRectangle() DrawString() FillEllipse() FillRectangle() … 24