1. Chapter 13: Handling Events

2. Event Handling Event Event driven
Occurs when something interesting happens to an object
Used to notify a client program when something happens to a class object the program is using
Event driven
An event “drives” the program to perform a task
Events can be raised, fired, or triggered
Event handler
A method that performs a task in response to an event
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3. Event Handling (cont’d.)
Microsoft Visual C# 2012, Fifth Edition

4. Event Handling (cont’d.)
private void button1_Click(object sender,EventArgs e) {
label1.Text=sender.ToString(); }
Microsoft Visual C# 2012, Fifth Edition

5. Event Handling (cont’d.)
private void button1_Click(object sender,EventArgs e) {
label1.Text=e.ToString(); }
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6. Event Handling (cont’d.)
Event handler (cont’d.)
Conventionally named using:
The identifier of the Control
An underscore
The name of the event
Example:
changeButton_Click()
Also known as an event receiver
Event sender
A Control that generates an event
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7. Event Handling (cont’d.)
Event handler example:
private void changeButton_Click(object sender, EventArgs e) {
helloLabel.Text = e.ToString(); }
EventArgs
A C# class designed for holding event information
Click event
Generated when a Button object is clicked
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8. Using the Built-in Event Handler
The .NET Framework provides guidelines
an event takes two parameters:
The source of the event
The EventArgs parameter
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9. Handling Control Component Events
Existing Control components already have events with names
See Table 13-1
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10. Handling Control Component Events (cont’d.)
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11. Handling Control Component Events (cont’d.)
(continued)
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12. Handling Control Component Events (cont’d.)
(continued)
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13. Handling Control Component Events (cont’d.)
You have already used the IDE to create some event-handling methods
The default events generated for a Control in the IDE
Using the Events icon in the Properties window
The IDE saves you time by automatically entering the needed statement correctly
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14. Handling Control Component Events (cont’d.)
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15. Handling Control Component Events (cont’d.)
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16. Handling Mouse Events Mouse events Actions a user takes with a mouse
Including clicking, pointing, and dragging
Handled through an object of the class MouseEventArgs
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17. Handling Mouse Events (cont’d.)
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18. Handling Mouse Events (cont’d.)
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19. Handling Mouse Events (cont’d.)
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20. Handling Mouse Events (cont’d.)
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21. Handling Keyboard Events
Key events
Keyboard events
Occur when the user presses and releases keyboard keys
KeyEventHandler and KeyPressEventHandler
KeyEventArgs and KeyPressEventArgs
Classes used to handle key events
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22. Handling Keyboard Events (cont’d.)
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23. Handling Keyboard Events (cont’d.)
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24. Handling Keyboard Events (cont’d.)
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25. Handling Keyboard Events (cont’d.)
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26. Managing Multiple Controls
When Forms contain multiple Controls, you often want several actions to have a single consequence
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27. Handling Multiple Events with a Single Handler
You can associate the same event with multiple Controls
Use the Events icons in the Properties window
Displays all the existing events that have the correct signature to be the event handler for the event
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28. Managing Multiple Controls
Microsoft Visual C# 2012, Fifth Edition