Xamarin PCL - Making API calls based on user entry, how to dampen requests?

Question

I have a search task that makes a request to an API, within a portable class library, when the user enters text in the textbox, this works as expected but I have a concern over performance at scale. When we have a large userbase all making requests to this API on every key press I can foresee performance issues.

I have limited the API call to only fire when there are more than three valid characters but I want to dampen this further. I could implement a timer over the top of this but it does not feel like a good solution and is not present in the PCL framework.

Is there a recommended pattern to achieve this type of request dampening?

    private async Task GetClubs()
    {
        try
        {
            if (!string.IsNullOrWhiteSpace(ClubSearch) && ClubSearch.Replace(" ", "").Length >= 3)
            {
                Clubs = await dataService.GetClubs(ClubSearch);
            }
        }
        catch (DataServiceException ex)
        {
            ...
        }
    }

Answer 1

Usually that is done with timer. When search text changes you start (or reuse) a timer which will fire after delay and execute search request. If more text is typed during that delay - timer is reset. Sample code:

public class MyClass {
    private readonly Timer _timer;
    const int ThrottlePeriod = 500; // ms
    public MyClass() {
        _timer = new System.Threading.Timer(_ => {
            ExecuteRequest();
        }, null, Timeout.Infinite, Timeout.Infinite);
    }

    private string _searchTerm;
    public string SearchTerm
    {
        get { return _searchTerm; }
        set
        {
            _searchTerm = value;
            ResetTimer();
        }
    }

    private void ResetTimer() {
        _timer.Change(ThrottlePeriod, Timeout.Infinite);
    }

    private void ExecuteRequest() {
        Console.WriteLine(SearchTerm);
    }
}

If timer is not available, you can do the same with Task.Delay:

public class MyClass
{        
    const int ThrottlePeriod = 500; // ms
    private string _searchTerm;
    public string SearchTerm
    {
        get { return _searchTerm; }
        set
        {
            _searchTerm = value;
            SearchWithDelay();              
        }
    }

    private async void SearchWithDelay() {
        var before = this.SearchTerm;
        await Task.Delay(ThrottlePeriod);
        if (before == this.SearchTerm) {
            // did not change while we were waiting
            ExecuteRequest();
        }
    }        

    private void ExecuteRequest()
    {
        Console.WriteLine(SearchTerm);
    }
}