Custom event arguments in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a custom event argument class inheriting from EventArgs.

C Sharp (C#)

public class MyEventArgs : [1] {
    public int Value { get; set; }
}

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AEventArgs

BEventHandler

CEvent

DEventArgsBase

Attempts:

3 left

💡 Hint

Common Mistakes

Using EventHandler instead of EventArgs as base class.

Trying to inherit from a non-existent class like EventArgsBase.

Custom event argument classes should inherit from EventArgs to be used in events.

2fill in blank

medium

Complete the code to declare an event using the custom event argument class.

C Sharp (C#)

public event EventHandler<[1]> OnValueChanged;

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AEventArgs

BMyEventArgs

CValueChangedArgs

DCustomArgs

Attempts:

3 left

💡 Hint

Common Mistakes

Using the base EventArgs instead of the custom class.

Using a class name that was not declared.

The event uses the custom event argument class MyEventArgs as the generic parameter.

3fill in blank

hard

Fix the error in the event invocation by completing the code.

C Sharp (C#)

OnValueChanged?.Invoke(this, new [1] { Value = 10 });

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AEventArgs

BEventHandler

CMyEventArgs

DCustomEventArgs

Attempts:

3 left

💡 Hint

Common Mistakes

Using EventArgs instead of MyEventArgs when invoking the event.

Trying to invoke the event with EventHandler instead of event args.

The event must be invoked with an instance of the custom event argument class MyEventArgs.

4fill in blank

hard

Fill both blanks to complete the event handler method signature.

C Sharp (C#)

private void [1](object [2], MyEventArgs e) {
    Console.WriteLine($"Value changed to {e.Value}");
}

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AOnValueChangedHandler

Bsender

Cargs

DHandleValueChange

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid method names.

Using incorrect parameter names that do not match event handler conventions.

The method name can be any valid identifier, here OnValueChangedHandler, and the sender parameter is conventionally named sender.

5fill in blank

hard

Fill all three blanks to subscribe to the event and trigger it.

C Sharp (C#)

MyClass obj = new MyClass();
obj.[1] += [2];
obj.TriggerEvent();

// Event handler method
private void [3](object sender, MyEventArgs e) {
    Console.WriteLine($"New value: {e.Value}");
}

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AOnValueChanged

BOnValueChangedHandler

DValueChanged

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching event and handler names.

Using incorrect event names that do not exist.

Subscribe to the event OnValueChanged with the handler OnValueChangedHandler, which is defined below.