When and Why Is `async void` a Bad Practice in C#?

When and Why Is async void Considered Bad Practice?

Understanding the Context:

Async methods in C# can return either Task or void. While async void methods can appear convenient in certain scenarios, they introduce potential drawbacks that make them generally discouraged. Let's examine why async void is considered bad practice and how to approach these situations more effectively.

Reasons to Avoid async void:

1. Error Handling Challenges:
   Unlike async Task methods, exceptions escaping from async void methods have unconventional error-handling semantics, making it challenging to handle them appropriately.
2. Composing Challenges:
   Async void methods cannot be easily composed into higher-level async methods. This limits code maintainability and reuse.
3. Testing Difficulties:
   Unit testing async void methods is significantly more complex than testing async Task methods, due to the unique error-handling and composition semantics.

Alternative Approaches:

In the provided example, where the focus lies on reacting to a button click without awaiting the result, a more suitable approach is to define the PrimeCustomTask method as async Task and utilize the OnLoad method as an entry point for starting the asynchronous operation. This way, all the benefits of async Task methods are preserved:

protected override async void OnLoad(EventArgs e)
{
    if (CustomTask == null)
        await PrimeCustomTask();
}

private async Task PrimeCustomTask()
{
    CustomTask = new TaskCompletionSource<int>();
    while (CustomTask.Task.IsCompleted == false && IsDisposed == false) 
    {
        // Wait for button click to set the value
        await Task.Delay(100); 
    }

    int result = CustomTask.Task.Result;

    // Show the value
    if (result != 0) MessageBox.Show(result.ToString());
}

By adhering to these guidelines, you can avoid the pitfalls of async void methods and improve the maintainability, reusability, and testability of your code.

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