在 ViewModel 中处理对话框的最佳方式是什么？

Question

Following-up on the IDialogService approach:

What about the System.Windows.MessageBoxResult enum? Is the better approach to keep it out of the interface and only involve it in the implementation?

Approach I chose for the System.Windows.MessageBoxResult enum :

I added an enum next to the IDialogInterface that covers Yes, NO, Ok, Cancel:

namespace Foo.Bar.Dialogs
{
    public enum DialogResult { Ok, Yes, No, Cancel }

    public interface IDialogService
    {
        void ShowErrorBox(string error_message);

        DialogResult ShowQuestionBox(string question_message);

        DialogResult ShowQuestionBox(string question_message, string caption);

        DialogResult ShowQuestionBox(string question_message, string caption, bool allow_cancel);

        DialogResult ShowQuestionBox(string question_message, string caption, bool allow_cancel, bool show_as_error);

        void ShowWarningBox(string message, string caption = "");

        void ShowInformationBox(string message);

        void ShowInformationBox(string message, string caption);
    }
}

Initial question:

I am working on moving all the commands from my.asmx.cs file to the ViewModel of the main window of some application.

Now I have to figure out what to do with commands that ask for confirmation(s) from the user.

For now I'll just suck in the necessary types in my ViewModel to launch my dialog boxes directly. I'm pretty sure this is not the best or cleanest way to do this.

I found this article with an interesting and cleaner approach. It uses an IDialogService interface:

public interface IDialogService
{
    int Width { get; set; }
    int Height { get; set; }
    void Show(string title, string message, Action<DialogResult> onClosedCallback);
}

I also found this article which seems even better as it checks if the IDialogInterface is null before trying to use it:

private void PerformAddNewCustomer() 
{ 
    CustomerList.Add(new Customer { Name = "Name" + i }); 
    i++; 

    if (dialogService != null) 
    { 
        dialogService.Show("Customed added"); 
    } 
} 

Is this the best way to separate dialogs from the ViewModel, or is there an even better approach?

Answer 1

I would say the approach in the link you posted is a good one and also very widespread (source: me looking at code on the web;) ). It's rather simple to use, it makes dialogs testable by using a dummy service in your unit tests and it simplifies the process of refactoring your dialogs.

Personally, my DialogService method signature takes a list of Tuple<string, Action> and I create my dialog window's buttons based on that. It allows the ViewModel to request for some special functions from the dialog windows without having to add new methods to my service every time my needs are more than an Ok or YesNo message box (while I do have those as methods on their own for ease of use).

So it's a solid approach and at this point I don't think you will find something that is flat out better, only something you might like more personally.

Answer 2

The article you found is a good approach to deal with dialog windows in MVVM and it is really reusable and with the DI it is easy to use in your views.

I did use something different, most of the time i use MVVM light toolkit and it has a messenger and i used the messenger to send a message to a separated class and then it opened for me the dialog i wanted to show, and the result is messaged back so i can act to the users choice.