Why events are needed in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an event in C#.

C Sharp (C#)

public event EventHandler [1];

Drag options to blanks, or click blank then click option'

AClick

BOnClick

CClicked

DClickEvent

Attempts:

3 left

💡 Hint

Common Mistakes

Using method-like names with 'On' prefix for the event declaration.

Using past tense verbs for event names.

The event name is typically a noun or noun phrase like Click. Here, Click is the correct event name.

2fill in blank

medium

Complete the code to subscribe to an event named Click.

C Sharp (C#)

button.Click [1]= Button_ClickHandler;

Drag options to blanks, or click blank then click option'

A+

B-

C+=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '+='.

Using '==' which is a comparison operator.

To subscribe to an event in C#, use the += operator.

3fill in blank

hard

Fix the error in the event handler signature for the Click event.

C Sharp (C#)

private void Button_ClickHandler(object [1], EventArgs e) { /* handler code */ }

Drag options to blanks, or click blank then click option'

Aobj

Bsource

CeventSource

Dsender

Attempts:

3 left

💡 Hint

Common Mistakes

Using arbitrary parameter names that confuse the event source.

Using names that don't clearly indicate the sender.

The first parameter of an event handler is conventionally named sender, representing the source of the event.

4fill in blank

hard

Fill both blanks to raise an event safely in C#.

C Sharp (C#)

EventHandler handler = [1];
if (handler [2] null) handler(this, EventArgs.Empty);

Drag options to blanks, or click blank then click option'

AClick

B!=

C==

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if handler == null instead of != null.

Using wrong variable names.

Assign the event to a local variable (here Click) and check if it is not null before invoking it.

5fill in blank

hard

Fill all three blanks to declare, subscribe, and raise an event named DataReceived.

C Sharp (C#)

public event EventHandler [1];

void Subscribe() {
    [2] += OnDataReceived;
}

void Raise() {
    [3] handler = [2];
    if (handler != null) handler(this, EventArgs.Empty);
}

Drag options to blanks, or click blank then click option'

ADataReceived

BEventHandler

Cvar

DEventArgs

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the event in different places.

Using incorrect types for the handler variable.

The event is named DataReceived. Subscription uses the event name DataReceived. Use EventHandler as the type for the local handler variable.