Chapter 13: Handling Events · Microsoft Visual C# 2012, Fifth Edition 13 •You have already used...

Chapter 13:

Handling Events

2 Microsoft Visual C# 2012, Fifth Edition

Event Handling

• Event

– 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


Event Handling (cont’d.)



private void button1_Click(object sender,EventArgs

e)

{

label1.Text=sender.ToString();

}



private void button1_Click(object sender,EventArgs

e)

{

label1.Text=e.ToString();

}



• 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



• 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


Using the Built-in Event Handler

• The .NET Framework provides guidelines

– an event takes two parameters: • The source of the event

• The EventArgs parameter


Handling Control Component Events

• Existing Control components already have events with names

– See Table 13-1


Handling Control Component Events (cont’d.)


(continued)



• 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



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


Handling Mouse Events (cont’d.)


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


Handling Keyboard Events (cont’d.)


Managing Multiple Controls

• When Forms contain multiple Controls, you often want several actions to have a single consequence


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


Managing Multiple Controls

Chapter 13: Handling Events · Microsoft Visual C# 2012, Fifth Edition 13 •You have already used...

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