Returning Task<bool> that involves boolean test for null value of an awaited Task result

Question

@Viorel , @AgaveJoe , @Michael Taylor thank you for your patience.

This is a simplified version of this question and I am restating the same question with a concise and complete code.

For simple illustration, SecureStorage.GetAsync(string keyName), a well known API (Xamarin and .NET MAUI) for retrieving a stored secret, that is previously saved by SecureStorage.SetAsync(string keyName, string mySecret), is used. See for instance, here.

The following simply tests if an encryption key has been set.

USING ASYNC/AWAIT:

public async Task<bool> IsEncryptionKeySet(string keyName)  
{  
    string secretKey = await SecureStorage.GetAsync(keyName); // if secret by keyName is set, returns a non-null string.  
    return secretKey != null;   // returns true if the key exists.  
}  

I test if an encryption key is set as: bool isSet = await IsEncryptionKeySet("keyName");

RETURNING TASK WITHOUT ASYNC/AWAIT:

public Task<string> GetEncryptionKey(string keyName)  
{  
   return SecureStorage.GetAsync(keyName);   
}  

I can test if an encryption key is set as: bool isSet = await GetEncryptionKey("keyName") != null;

My question is, instead of returning Task<string> and evaluate the Boolean by the caller, is it possible to return Task<bool> of the first form above without using async and await as well as Task.Result or Task.Wait(), thus:

public Task<bool> IsEncryptionKeySet(string keyName)  
{  
    // I'm assuming an async programming may exist to return Task<bool>  
    return Task_StateMachine_Returning(SecureStorage.GetAsync(keyName) != null); // can this be put into code?  
}  

We know that return SecureStorage.GetAsync(keyName) != null); is incorrect as it always returns true (because an awaitable that is pending is always non-null).

Answer 1

Hello,

is it possible to return Task<bool> of the first form above without using async and await

Yes, you can try to use the following code.

   public  Task<bool> IsEncryptionKeySet(string keyname)  
           {  
               bool result = false;  
               var res =  SecureStorage.GetAsync(keyname).Result;  
     
               if (!string.IsNullOrEmpty(res))  
               {  
                   result = true;  
               }  
     
               return  Task.FromResult(result);  
           }  

But It is recommended to you to achieve it by using async and await. If the value is too long. It will block the UI thread.

   public async Task<bool> IsEncryptionKeySet(string keyname)  
           {  
               bool result = false;  
               var res = await SecureStorage.GetAsync(keyname);  
     
               if (!string.IsNullOrEmpty(res))  
               {  
                   result = true;  
               }  
     
               return await Task.FromResult(result);  
           }  

Best Regards,

Leon Lu

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Answer 2

The ContinueWith() method solves this programming problem as explained by cooldadtx in your other thread.

static async Task<bool> IsEncryptionKeySetAsync(string keyName)  
{  
    return await SecureStorage.GetAsync(keyName).ContinueWith((key) => { return key.Result != null; });       
}  

The caller has the following pattern.

var result = IsEncryptionKeySetAsync("Hello");  
Console.WriteLine("Do other stuff");  
Console.WriteLine($"IsEncryptionKeySetAsync = {await result}");  

I just thought there may be more clever ways along the line of return Task.FromResult(<some manipulations here>) that I don't know.

No. As explained in your other thread, Task.FromResult() wraps a type in a Task. Task.FromResult() is used when you want to bypass executing an asynchronous task but need to return a Task to the caller. For example, returning an item from cache. If the item exists in cache then there is not reason to fetch the item.