WPF MVVM Navigation

Question

I'm trying to implement MVVM navigation in my MainWindow after login, before that after click on 'Login' button i've to call MainWindow.xaml to display and after that i used to do navigation in my Mainwindow based on menu/ribbon selection.

Below is the implementation i've done so far:

On 'Login' button command:

private void Entry(object parameter)
    {
        IMainWindowViewModel viewM = new MainWindowViewModel();
        ViewBinder<IMainWindowView> main = new ViewBinder<IMainWindowView>(viewM);
        var view = main.View;
    }

MainWindowViewModel:

public class MainWindowViewModel:ViewModel<IMainWindowView>, IMainWindowViewModel
{

    public int EmpID
    {
        get
        {
            throw new NotImplementedException();
        }
        set
        {
            throw new NotImplementedException();
        }
    }

    public string EmpName
    {
        get
        {
            throw new NotImplementedException();
        }
        set
        {
            throw new NotImplementedException();
        }
    }

    public void GetEmployees()
    {
        throw new NotImplementedException();
    }
public object DataContext
    {
        get
        {
            throw new NotImplementedException();
        }
        set
        {
            throw new NotImplementedException();
        }
    }

    public MainWindowViewModel(IMainWindowView view)
        : base(view)
    { }
}

IMainWindowViewModel:

public interface IMainWindowViewModel:IMainWindowView
{
    int EmpID { get; set; }
    string EmpName { get; set; }
    void GetEmployees();
}

IMainWindowView:

public interface IMainWindowView:IView
{
}

ViewBinder:

public class ViewBinder<T> where T : IView
{
    private T currentView;
    public IView View
    {
        get
        {
            var viewModel = currentView.GetViewModel();
            return (IView)viewModel.View;
        }
    }

    public ViewBinder(T targetView) 
    {
        this.currentView = targetView;
    }

}

But While run this app it's showing error message like below: 'System.Waf.Applications.ViewModel' does not contain a constructor that takes 0 arguments D:\MajorApps\SampleApp\MajorApps.Application\ViewModels\MainWindowViewModel.cs

Can anyone help me this out what i missed/wrong.

Thanks @nag

your questions contains information that seems to contradict each other: on the one hand you have `new MainWindowViewModel()` so your `MainWindowViewModel` has to have an constructor with 0 parameters (which you did not show) and on the other hand you get the error - can you please tell us what you are binding? Do you use a `ViewModel` as a `DataContext` or something (like ``)? If so there is your problem! — Random Dev, Mar 31 '15 at 07:05
The type `ViewModel` that your `MainWindowViewModel` is inheriting has no parameterless constructor. You need to add a default constructor to your `MainWindowViewModel` that calls the base’s constructor correctly. Also, finish the implementation of your view model or nothing will work. — poke, Mar 31 '15 at 07:07
I've edited my code by adding constructor to my viewmodel but for base constructor i've confused how to give value, It's showing error like ''System.Waf.Applications.ViewModel' does not contain a constructor that takes 0 arguments D:\MajorApps\SampleApp\MajorApps.Application\ViewModels\MainWindowViewModel.cs' — nag, Mar 31 '15 at 07:13
@nag you can [edit](http://stackoverflow.com/posts/29362189/edit) your question and include that information. You are still not showing the constructor for MainWindowViewModel. — default, Mar 31 '15 at 08:16

score 0 · Accepted Answer · answered Mar 31 '15 at 06:50

The base class for MainWindowViewModel does not contain a parameterless constructor. You would have to call one of the ones that it has defined, something like:

public class MainWindowViewModel:ViewModel<IMainWindowView>, IMainWindowViewModel
{
    public MainWindowViewModel()
        : base(/* something here */)
    {
    }

    // ....
}

WPF MVVM Navigation

1 Answers1