Event-driven design pattern in C Sharp (C#) - Interactive Code Practice

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'

AOnClick

BClicked

CClick

DClickEvent

Attempts:

3 left

💡 Hint

Common Mistakes

Using method-like names such as 'OnClick' instead of event names.

Using past tense like 'Clicked' which is less common 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 'DataReceived'.

C Sharp (C#)

someObject.DataReceived [1]= HandlerMethod;

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A+=

B==

C+

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which overwrites existing handlers.

Using '+' which is invalid syntax for event subscription.

In C#, you subscribe to an event using the '+=' operator.

3fill in blank

hard

Fix the error in the event invocation code.

C Sharp (C#)

if ([1] != null)
{
    [1](this, EventArgs.Empty);
}

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ADataReceived

BDataReceived()

CDataReceived?.Invoke

DDataReceived.Invoke

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses in the null check condition.

Using the null-conditional operator '?.Invoke' inside the if condition.

Before invoking an event, check if it is not null, then call it like a method with parameters.

4fill in blank

hard

Fill both blanks to declare and raise a custom event with EventHandler.

C Sharp (C#)

public event EventHandler [1];

protected virtual void On[2](EventArgs e)
{
    [1]?.Invoke(this, e);
}

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ADataProcessed

BDataProcessedEvent

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for event and method.

Adding 'Event' suffix inconsistently.

The event name and the method name usually share the same base name. The event is 'DataProcessed' and the method is 'OnDataProcessed'.

5fill in blank

hard

Fill all three blanks to create a custom event with a delegate and raise it.

C Sharp (C#)

public delegate void [1](object sender, EventArgs e);

public event [1] [2];

protected virtual void On[2](EventArgs e)
{
    [2]?.Invoke(this, e);
}

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

ADataChangedHandler

BDataChanged

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing delegate and event names.

Not matching the method name with the event name.

The delegate is named 'DataChangedHandler', the event uses that delegate type, and the event name is 'DataChanged'. The method raising the event is 'OnDataChanged'.