Creating and Binding to a User Control in MVVM Cross

While creating my game, I recently came across the problem of navigation. This post describes how to create a custom user control and react to the event inside.

The usual disclaimer still applies here; although this is an MVVM Cross post, the contents of it should be applicable for any MVVM Framework or, in fact, any XAML binding at all.

User Control

The user control that I’m going to use is simply a navigation bar to appear at the top of each screen.

The XAML for the user control is here:

<UserControl
    x:Name="NavigationControlRoot">
    
    <Grid DataContext="{Binding ElementName=NavigationControlRoot}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <Button Content="Home" Grid.Column="0" Command="{Binding HomeClick}" />
        <Button Content="Back" Grid.Column="1" Command="{Binding BackClick}" />
    </Grid>
</UserControl>

So, I’ve got two commands, binding to the code behind. The key point here is that the root control (grid) binds to the DataContext of the user control – effectively this binds it to the containing DataContext. Here’s the code behind:

    public sealed partial class NavigationPanel : UserControl
    {
        public static DependencyProperty BackCommandProperty =
            DependencyProperty.Register(
                "BackClick",
                typeof(ICommand),
                typeof(NavigationPanel),
                new PropertyMetadata(null));

        public static DependencyProperty HomeCommandProperty =
            DependencyProperty.Register(
                "HomeClick",
                typeof(ICommand),
                typeof(NavigationPanel),
                new PropertyMetadata(null));

        public NavigationPanel()
        {
            this.InitializeComponent();
        }
        
        public ICommand BackClick
        {
            get
            {
                return (ICommand)GetValue(BackCommandProperty);
            }

            set
            {
                SetValue(BackCommandProperty, value);
            }
        }

        public ICommand HomeClick
        {
            get
            {
                return (ICommand)GetValue(HomeCommandProperty);
            }

            set
            {
                SetValue(HomeCommandProperty, value);
            }
        }        
    }

So, you’ve now exposed two dependency properties and bound them to the XAML in the user control.

Host App

Here’s the relevant XAML for the hosting view:

<controls:NavigationPanel BackClick="{Binding BackClickCommand}"                                  
                                  HomeClick="{Binding HomeClickCommand}"/>

And that just binds to the ViewModel as you would expect.

        private IMvxCommand _homeClickCommand;
        public IMvxCommand HomeClickCommand
        {
            get
            {
                if (_homeClickCommand == null)
                {
                    _homeClickCommand = new MvxCommand(() => GoHome());
                }
                return _homeClickCommand;
            }
            set
            {
                _homeClickCommand = value;
            }
        }

        private void GoHome()
        {
            ShowViewModel<MainViewModel>();
        }

For me, this is in a base view model, so it responds to the same command in every view.

Conclusion

I think the final version of this code will interact with an IMvxPresenter in some way, which may make another post.

2 thoughts on “Creating and Binding to a User Control in MVVM Cross

  1. J4N

    I don’t see what is the relation with the “ViewModel” part of MVVM, all your logic is within the code behind. I was more thinking of having a VM for this UserControl and just having to bridge the Dependencies Property from the UserControl to the VM and vice-versa

    Reply
    1. pcmichaels Post author

      You’re absolutely right. I think this was a case of having one idea when I started the post and another half way through. Thanks for reading.

      Reply

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