How to Suspend Async Method Execution Until an Event Occurs in a Metro App?

Pausing Asynchronous Operations Awaiting User Input in UWP Apps

This guide demonstrates how to temporarily halt the execution of an asynchronous method within a Universal Windows Platform (UWP) application until a specific event, such as a button click, is triggered. This is particularly useful when a long-running asynchronous process (GetResults in this example) needs user interaction before proceeding.

Method 1: Using SemaphoreSlim as a Signal

The SemaphoreSlim class offers a straightforward signaling mechanism. Here's how to implement it:

private SemaphoreSlim signal = new SemaphoreSlim(0, 1); // Initially 0 permits, max 1

// Event handler to release the semaphore
private void buttonContinue_Click(object sender, RoutedEventArgs e)
{
    signal.Release();
}

// Asynchronous method pausing for the signal
private async Task GetResults()
{
    // ... Perform lengthy operations ...
    await signal.WaitAsync(); // Pause until the signal is released
    // ... Continue execution after the event ...
}

Method 2: Leveraging TaskCompletionSource<bool>

TaskCompletionSource<bool> provides a more flexible approach by creating a Task<bool> that represents the completion of the user interaction.

private TaskCompletionSource<bool> tcs = new TaskCompletionSource<bool>();

// Event handler to set the task's result
private void buttonContinue_Click(object sender, RoutedEventArgs e)
{
    tcs.SetResult(true);
}

// Asynchronous method awaiting task completion
private async Task GetResults()
{
    // ... Perform lengthy operations ...
    await tcs.Task; // Pause until the task completes
    // ... Continue execution after the event ...
}

Both methods effectively pause the GetResults asynchronous operation until the specified event occurs, avoiding inefficient polling techniques. Choose the method that best suits your application's architecture and complexity.

The above is the detailed content of How to Suspend Async Method Execution Until an Event Occurs in a Metro App?. For more information, please follow other related articles on the PHP Chinese website!