C#•2mo ago

✅ Help needed: Buttons update enabled state after two clicks.

Hello, I need help to find out why it takes two clicks before the buttons change the enabled state. Please see the attached video and also my code below:

  <StackLayout>
      <Button Text="Start the service" Command="{Binding StartTheServiceCommand}" />
  </StackLayout>
  
  <StackLayout>
      <Button Text="Stop the service" Command="{Binding StopTheServiceCommand}" />
  </StackLayout>

  <StackLayout>
      <Button Text="Start the service" Command="{Binding StartTheServiceCommand}" />
  </StackLayout>
  
  <StackLayout>
      <Button Text="Stop the service" Command="{Binding StopTheServiceCommand}" />
  </StackLayout>

public MainPageViewModel(ILogger<MainPageViewModel> logger, WorkerService workerService)
{
  _logger = logger;
  _workerService = workerService;

  StartTheServiceCommand = new Command(
    execute: () =>
      {
        _logger.LogInformation("Starting the service at: {time}", DateTimeOffset.Now);
        Task.Run(async () => await _workerService.StartAsync(new()));
        RefreshCanExecutes();
      },
    canExecute: () => !_workerService.IsRunning);
        
  StopTheServiceCommand = new Command(
    execute: () =>
    {
      _logger.LogInformation("Stopping the service at: {time}", DateTimeOffset.Now);
      Task.Run(async () => await _workerService.StopAsync(new()));
      RefreshCanExecutes();
    },
    canExecute: () => _workerService.IsRunning);
}
    
public ICommand StartTheServiceCommand { get; }
public ICommand StopTheServiceCommand { get; }

private void RefreshCanExecutes()
{
  (StartTheServiceCommand as Command)!.ChangeCanExecute();
  (StopTheServiceCommand as Command)!.ChangeCanExecute();
}

public MainPageViewModel(ILogger<MainPageViewModel> logger, WorkerService workerService)
{
  _logger = logger;
  _workerService = workerService;

  StartTheServiceCommand = new Command(
    execute: () =>
      {
        _logger.LogInformation("Starting the service at: {time}", DateTimeOffset.Now);
        Task.Run(async () => await _workerService.StartAsync(new()));
        RefreshCanExecutes();
      },
    canExecute: () => !_workerService.IsRunning);
        
  StopTheServiceCommand = new Command(
    execute: () =>
    {
      _logger.LogInformation("Stopping the service at: {time}", DateTimeOffset.Now);
      Task.Run(async () => await _workerService.StopAsync(new()));
      RefreshCanExecutes();
    },
    canExecute: () => _workerService.IsRunning);
}
    
public ICommand StartTheServiceCommand { get; }
public ICommand StopTheServiceCommand { get; }

private void RefreshCanExecutes()
{
  (StartTheServiceCommand as Command)!.ChangeCanExecute();
  (StopTheServiceCommand as Command)!.ChangeCanExecute();
}

4 Replies

canton7•2mo ago

RefreshCanExecutes(); doesn't wait for the service to actually start. You queue a bit of work onto the thread pool to start the worker at some point in the future, then immediately call RefreshCanExecutes();, which calls _workerService.IsRunning. But the worker isn't running yet You shouldn't be discarding tasks. The fact that you had to throw a Task.Run into the mix is presumably to work around the fact that the compiler was moaning at you for now awaiting the _workerService.StartAsync call? That was your clue 😉

public MainPageViewModel(ILogger<MainPageViewModel> logger, WorkerService workerService)
{
  _logger = logger;
  _workerService = workerService;

  StartTheServiceCommand = new Command(
    execute: async () =>
      {
        _logger.LogInformation("Starting the service at: {time}", DateTimeOffset.Now);
        await _workerService.StartAsync(new());
        RefreshCanExecutes();
      },
    canExecute: () => !_workerService.IsRunning);
        
  StopTheServiceCommand = new Command(
    execute: async () =>
    {
      _logger.LogInformation("Stopping the service at: {time}", DateTimeOffset.Now);
      await _workerService.StopAsync(new());
      RefreshCanExecutes();
    },
    canExecute: () => _workerService.IsRunning);
}
    
public ICommand StartTheServiceCommand { get; }
public ICommand StopTheServiceCommand { get; }

private void RefreshCanExecutes()
{
  (StartTheServiceCommand as Command)!.ChangeCanExecute();
  (StopTheServiceCommand as Command)!.ChangeCanExecute();
}

public MainPageViewModel(ILogger<MainPageViewModel> logger, WorkerService workerService)
{
  _logger = logger;
  _workerService = workerService;

  StartTheServiceCommand = new Command(
    execute: async () =>
      {
        _logger.LogInformation("Starting the service at: {time}", DateTimeOffset.Now);
        await _workerService.StartAsync(new());
        RefreshCanExecutes();
      },
    canExecute: () => !_workerService.IsRunning);
        
  StopTheServiceCommand = new Command(
    execute: async () =>
    {
      _logger.LogInformation("Stopping the service at: {time}", DateTimeOffset.Now);
      await _workerService.StopAsync(new());
      RefreshCanExecutes();
    },
    canExecute: () => _workerService.IsRunning);
}
    
public ICommand StartTheServiceCommand { get; }
public ICommand StopTheServiceCommand { get; }

private void RefreshCanExecutes()
{
  (StartTheServiceCommand as Command)!.ChangeCanExecute();
  (StopTheServiceCommand as Command)!.ChangeCanExecute();
}

Also, if you use as, always check for null. If you don't expect the cast to fail, use a normal cast, not as. The reason is that if you use as but the cast does fail unexpectedly, you'll get an unhelpful NullReferenceException, rather than a helpful InvalidCastException. So:

private void RefreshCanExecutes()
{
  ((Command)StartTheServiceCommand).ChangeCanExecute();
  ((Command)StopTheServiceCommand).ChangeCanExecute();
}

private void RefreshCanExecutes()
{
  ((Command)StartTheServiceCommand).ChangeCanExecute();
  ((Command)StopTheServiceCommand).ChangeCanExecute();
}

Eple•2mo ago

@canton7 thank you for your responses, they helped.

canton7•2mo ago

Great! Has that solved your problem?

Eple•2mo ago

Yes it has.

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✅ Help needed: Buttons update enabled state after two clicks.