pass specific ID to MVVM

Thre's something I don't get. If i have for instance a profile.xaml page and 开发者_开发百科I have a ProfileViewModel with a user instance. How do I tell the ProfileViewModel with a User property to load user with an id that I want?

I mean : How do I pass a userid to the profileviewmodel when I click a button in another page to open that page?

For Instance

Userlist.xaml has a list of users. One is clicked and an instance of Profile.Xaml is loaded, but how do I pass the userId onto the viewmodel? Won't i need some dependencyproperty in profile.xaml and then pass it on?

Please tell me if this makes sense to you :)

You should consider binding your list of users in Userlist.xaml to a collection of ProfileViewModel instances, then you can just provide the specific ProfileViewModel to the profile.xaml.

In this example, your Userlist.xaml would include:

<UserControl Name="userView">
    <!-- other stuff -->
    <ItemsControl ItemsSource={Binding Users}>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding UserName}" />
                    <Button Content="View User Profile"
                    Command="{Binding ElementName=userView, Path=DataContext.ViewUserProfileCommand}"
                    CommandParameter="{Binding}" />
                </StackPanel>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
    <!-- other stuff -->
</UserControl>

And your UserlistViewModel would include:

    #region Users Property

    public const string UsersPropertyName = "Users";

    private ObservableCollection<IProfileViewModelViewModel> _users;

    public ObservableCollection<IProfileViewModelViewModel> Users
    {
        get { return _users; }
        set
        {
            if (_users == value)
                return;

            _users = value;
            RaisePropertyChanged(UsersPropertyName);
        }
    }

    #endregion

    public RelayCommand<IProfileViewModel> ViewUserProfileCommand
        = new RelayCommand<IProfileViewModel>(ViewUserProfileCommandExecute);

    private void ViewUserProfileCommandExecute(IUserProfileViewModel userProfileViewModel)
    {
        // display your profile view here
    }

As Reed mentioned above, one way to pass the user profile view model to your other page would be MVVM Light Toolkit's messaging.

There are multiple options, here.

If you're working from within a "parent" ViewModel, you can potentially construct a new ProfileViewModel with the specific user ID, and set it to a property that is picked up by your View directly. This is the approach I used in my MVVM article.

Alternatively, if you have a single ProfileViewModel (and ProfileView) and it's not "connected" to the screen/view where you're picking the user directly, the best option is typically to use some form of messaging service. This is the approach MVVM Light uses.