BIM211 – Visual Programming

Interacting with UsersGraphics

1

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

MessageBox

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

3

MessageBoxButtons

• AbortRetryIgnore• OK• OKCancel• YesNoCancel• YesNo• RetryCancel

4

MessageBoxIcons

Name Icon

AsteriskInformation

ErrorHandStop

ExclamationWarning

Question

5

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

Enumerations for DialogResult

• OK• Cancel• Yes• No• Retry• Ignore• Abort• None (for Modal Dialog Boxes)

7

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

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

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

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

Exercise at Runtime

12

Interacting with the Keyboard

Event Name DescriptionKeyDown Occurs when a key is pressed while

the control has focusKeyPress Occurs when a key is pressed while

the control has the focus. If theuser holds down the key, this event fires multiple times

KeyUp Occurs when a key is released while the control has the focus

13

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

Using the Common Mouse EventsEvent Name Description

MouseEnter Occurs when the pointer enters a control

MouseMove Occurs when the pointer moves over a control

MouseHover Occurs when the pointer hovers over a control

MouseDown Occurs when the pointer is over a control and a button is pressed

MouseUp Occurs when the pointer is over a control and a button is released

MouseLeave Occurs when the pointer leaves a control

MouseClick Occurs between the MouseDown and MouseUp events, after the Click event

Click Occurs between the MouseDown and MouseUp events

15

Exercise

• Write a program which enables the user to draw on a form.

1.Create a Graphics object member variable2.Instantiate it in the Load event handler3.Dispose it in the FormClosed event handler4.Handle the MouseMove event and draw an

ellipse at the mouse coordinate if the Left mouse button is clicked during the mouse move

16

Exercise at Runtime

17

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

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

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

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

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

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

Some Drawing Methods

• DrawLine()• DrawEllipse()• DrawRectangle()• DrawString()• FillEllipse()• FillRectangle()• …

24