How to implement if, else statement in CanExecute command or Delegate command in wpf c#?

Question

I'm new to WPF and Prism. How do I use an if else statement when using CommandCanExecute(), CommandExecute()/Delegate commands?

I have a code to load and get the instance of livechart. However, if the file for the chart does not exist in the users desktop, my application will crash. I want to implement a if else statement to say if you cannot find the graph, show up a message box notifying that there is an error, instead of crashing the program.

I tried searching up on RaiseCanExecuteChanged but unsure how to implement.

   private bool BEYieldCommandCanExecute()
    {
        return true;
    }

    private void BEYieldCommandExecute() 

    {
        if (true)
        {
            _eventAggregator.GetEvent<GraphPubSubEvent>().Publish(_viewName);

        }

        else
        {//Check
            MessageBox.Show("Error loading. Please ensure Excel file/Server file exist in Desktop/Server to generate Chart.", "Invalid Request", MessageBoxButton.OK, MessageBoxImage.Exclamation);
        }
    }

Thanks alot!!

Answer 1

In XAML: <Button Command="{Binding OpenDialogCommand }" />

public class ViewModel
{
    public DelegateCommand OpenDialogCommand { get; set; }

    public ViewModel()
    {
        OpenDialogCommand = new DelegateCommand(BrowseFile);
    }

    private void BrowseFile()
    {
        var openDialog = new OpenFileDialog()
        {
            Title = "Choose File",
            // TODO: etc v.v
        };
        openDialog.ShowDialog();
        if (File.Exists(openDialog.FileName))
        {
            // TODO: Code logic is here


        }
        else
        {
            // TODO: Code logic is here
        }
    }
}

`