C# Xamarin Forms异步任务结果获取：是否需使用回调？

I have a piece of code that checks if a device is registered in the database via an asynchronous method:

if (CrossConnectivity.Current.IsConnected) { return await App._deviceService.GetDevice(id); }

I originally thought that await would wait for GetDevice to finish executing and return its result, but after deeper research, I think I might need to use callbacks to get the actual result of the call and process it. Is my thinking correct?

Here's the code for the called async task:

public async Task<bool> GetDevice(string deviceID) { 
    string url = Resources.Urls.dev + Resources.DeviceApi.Get + "?id=" + deviceID; 
    HttpResponseMessage result; 
    result = await App.HttpClientInstance().GetAsync(url); 
    if (result.StatusCode == System.Net.HttpStatusCode.OK) { 
        return true; 
    } 
    return false; 
}

Short Answer #

Your thinking isn’t correct — you don’t need callbacks here! The await keyword already does exactly what you initially assumed: it pauses execution of the current method until the GetDevice task completes, then returns the actual bool result directly.

Detailed Explanation #

Let’s break down what’s actually happening with your code:

1. When you call await App._deviceService.GetDevice(id), the runtime:

   • Starts running the GetDevice method until it hits its own await App.HttpClientInstance().GetAsync(url)
   • Suspends the calling method (the one with the connectivity check) and gives control back to the caller (freeing up the thread to handle other work in the meantime)
   • Once the HTTP request finishes, the runtime resumes GetDevice, checks the status code, and returns the bool value
   • Finally, the calling method picks back up and returns that bool result.

2. Callbacks (like using Task.ContinueWith) were a common pattern before async/await existed, but async/await was specifically designed to replace that messy callback-style code with cleaner, "synchronous-looking" asynchronous logic.

Example of Processing the Result #

If you want to work with the result instead of just returning it, you can do this easily with await:

if (CrossConnectivity.Current.IsConnected) 
{
    bool isDeviceRegistered = await App._deviceService.GetDevice(id);
    
    // Process the result right here
    if (isDeviceRegistered)
    {
        // Handle registered device case (e.g., navigate to main screen)
    }
    else
    {
        // Handle unregistered device (e.g., show registration prompt)
    }
    
    return isDeviceRegistered;
}
else
{
    // Handle no internet connection (maybe return false or show an error message)
    return false;
}

Quick Cleanup Tip for Your GetDevice Method #

You can simplify it for better readability using string interpolation and a direct return:

public async Task<bool> GetDevice(string deviceID) 
{ 
    string url = $"{Resources.Urls.dev}{Resources.DeviceApi.Get}?id={deviceID}"; 
    HttpResponseMessage result = await App.HttpClientInstance().GetAsync(url); 
    return result.StatusCode == System.Net.HttpStatusCode.OK;
}

内容的提问来源于stack exchange，提问作者DarkW1nter