RelayCommand CanExecute behavior

Question

I have following command:

<Button x:Name="bOpenConnection" Content="Start Production"
        Grid.Row="0" Grid.Column="0"
        Height="30" Width="120" Margin="10"
        HorizontalAlignment="Left" VerticalAlignment="Top" 
        Command="{Binding Path=StartProductionCommand}"/>

StartProductionCommand = new RelayCommand(OpenConnection, CanStartProduction);

private bool CanStartProduction()
{
   return LogContent != null && !_simulationObject.Connected;
}

CanStartProduction is checked only when I re-size the UI and not updated on the fly. Any idea why it's not updated every time they change the values ?

Answer 1

The CommandManager has no way of knowing that the command depends on LogContent and _simulationObject.Connected, so it can't reevaluate CanExecute automatically when these properties change.

You can explicitly request a reevaluation by calling CommandManager.InvalidateRequerySuggested. Note that it will reevaluate CanExecute for all commands; if you want to refresh only one, you need to raise the CanExecuteChanged event on the command itself by calling StartProductionCommand.RaiseCanExecuteChanged.