Handling of multiple forms

Question

New to MVVM. I haven't used any MVVM framework (WAF/MVVM Light) .I use relayCommand class from Josh Smith.

Got two forms , Win_Login (btnCancel and btnNext),Other one a selection form with combobox and two buttons(btnBack,btnNext) - Where user select stockticker like GOOG,MSFT etc.

I wrote a basic skeleton of View, and ViewModel for login and selection form.

What I want to achieve is on succesfull login , close the Login view and open Selection form, and click on (btnBack) should show loginForm again.Windows being Singleton.

I set view's dataContext like

<Window         
    x:Class="Ticker.Win_Login"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:Ticker"
    Title="Ticker-Login"  Height="312" Width="394" WindowStartupLocation="CenterScreen" Background="#F9FBF4" >   

<Window.DataContext>
    <local:Win_LoginViewModel/>
</Window.DataContext>

<Grid></Grid

in the Win_LoginViewModel

private void LoginExecute()
    {
        if (!CanLoginExecute()) return;

        try
        {  
        //how I'll call close the current view

            //how I'll call selectTicker view

        }
        catch (Exception)
        {
            throw;
        }
    }

in Win_SelectTickerViewModel

 private Boolean CanBackExecute()
    {
        return true;
    }

    private void BackExecute()
    {
        if (!CanCancelExecute())
        {
            return;
        }

    //how I'll implement back here.
    }

I'd really appreciate if anyone can help me with some simple solution for given scenario (pbbly with some sample code).

The Window class isn't good here. I've assumed that you can create two user controls (1 user control for 1 view model) and want to switch between them. — vortexwolf, Mar 04 '12 at 15:22

score 0 · Answer 1 · edited May 23 '17 at 11:55

I can't write a complete solution at this moment, but I know how it can be done.

In the most simple scenario you should create a parent view model for both the view models and bind methods of this model to commands of the child view models.

Something like this:

MainViewModel:

public class MainViewModel
{
    // store instances of child view models so that the entered data aren't lost
    private Win_LoginViewModel _loginViewModel;
    private Win_SelectTickerViewModel _selectTickerViewModel;

    private UserControl _currentView;
    // will be bound to the view and dynamically changed
    public UserControl CurrentView
    {
        get { return _currentView; }
        set 
        {
            _currentView = value;
            RaisePropertyChanged("CurrentView");
        }
    }

    public void GoToSelectTickerView()
    {
        // create _selectTickerViewModel if it is necessary

        this.CurrentView = new SelectTickerView { DataContext = _selectTickerViewModel };
    }

    public void GoToLoginView()
    {
        // create _loginViewModel if it is necessary

        this.CurrentView = new LoginView { DataContext = _loginViewModel };
    }
}

SelectTickerViewModel:

public Win_SelectTickerViewModel
{
    private MainViewModel _parentModel;

    private void BackExecute()
    {
        //...
        _parentModel.GoToLoginView();
    }
}

And the xaml code will be like this:

<Window x:Class="Ticker.MainWindow" ...>
    <Window.DataContext>
        <local:MainViewModel/>
    </Window.DataContext>

    <ContentControl Content="{Binding CurrentView}" />
</Window>

You can improve this code by using the DataTemplateSelector class so that there is no user controls in view model: https://stackoverflow.com/a/5310213/427225

Also you can look at possible ways to organize communication between parent and child view models: https://stackoverflow.com/a/8551832/427225

Handling of multiple forms

1 Answers1