WPF - Run an async Task with DispatcherTimer

Question

I have a small application that checks some system status and display it details. I have the following code which is working. But I want to make sure it's optimal:

public partial class MainWindow : Window
{

    // Dictionary to hold info
    Dictionary<string, int> dataHolder = new Dictionary<string, string>
    {
        {"status_code", "" },
        {"memory", "" },
        {"process", "" }
    };

    public MainWindow()
    {
        InitializeComponent();
    }

    private void StartBtn_Click(object sender, RoutedEventArgs e)
    {
        StartBtn.IsEnabled = false;

        System.Windows.Threading.DispatcherTimer dispatcherTimer = new System.Windows.Threading.DispatcherTimer();
        dispatcherTimer.Tick += new EventHandler(updateUI);
        dispatcherTimer.Interval = new TimeSpan(0, 5, 0);
        dispatcherTimer.Start();  
    }

    private async void updateUI(object source, EventArgs e)
    {
        await loadInfo();
        StartBtn.IsEnabled = true;

        foreach(KeyValuePair<string, string> entry in dataHolder)
        {
            // Display in the UI
        }
    }

    private async Task loadInfo()
    {
        int page = 1;
        var keys = new List<string>(dataHolder.Keys);            
        foreach (string key in keys)
        {
            dataHolder[key] = "";
            //await asyncCall(key, page);
        }

        // Better asynchronously and in parallel
        await Task.WhenAll(keys.Select(key => asyncCall(key, page)));
    }

    private async Task asyncCall(string key, int page)
    {
        var htClient = new HttpClient();
        // code to retrieve data...
    }
}

So as I said before, this code is working but I read somewhere that having an async void method is not good practice as in private async void updateUI(object source, EventArgs e). I could change it to private async Task updateUI(object source, EventArgs e) but then I would not be able to do dispatcherTimer.Tick += new EventHandler(await updateUI);

Also how to start counting (Timer) only after the previous process is done?

Thank you

EDIT: I am using the DispatcherTimer because I want the application to retrieve the status information and update the UI every 5 minutes.

Answer 1

Async void should be avoided, but they are acceptable when in an EventHandler so it's fine.

Why are you copying the keys of the dictionary into a list? Do you want a snapshot at a random point in time?

If you have potentially race conditions, I would change the Dictionary to a ConcurrentDictionary.

public partial class MainWindow : Window
{

    // Dictionary to hold info
    private readonly Dictionary<string, string> _dataHolder = new Dictionary<string, string>
    {
        {"status_code", "" },
        {"memory", "" },
        {"process", "" }
    };

    public MainWindow()
    {
        InitializeComponent();
    }

    private async void StartBtn_Click(object sender, RoutedEventArgs e)
    {
        StartBtn.IsEnabled = false;

        while (true) // Your exit condition instead of the true.
        {
            await LoadInfo();

            foreach (var entry in _dataHolder)
            {
                // Display in the UI
            }

            await Task.Delay(TimeSpan.FromMinutes(5));

            //StartBtn.IsEnabled = true;
        }
    }

    private async Task LoadInfo()
    {
        const int page = 1;

        var keys = new List<string>(_dataHolder.Keys);

        foreach (var key in keys)
        {
            _dataHolder[key] = "";
            //await asyncCall(key, page);
        }

        // Better asynchronously and in parallel
        await Task.WhenAll(keys.Select(key => AsyncCall(key, page)));
    }

    private static async Task AsyncCall(string key, int page)
    {
        var htClient = new HttpClient();
        // code to retrieve data...
    }