StatusBar Bind to property in UserControl in active tab of TabControl

Question

I made this Minimal, Complete, and Verifiable example of the challenge I'm facing. It works but is definitely not MVVM and is nothing more than a hack.

It updates the status bar based on some property changing in the user control. It also updates when the user changes the tab. For the real deal, it will be displaying a records count (how many data rows are displayed in each tab).

There must be a cleaner way of doing this...

How can this be done using MVVM?

Note: In my actual implementation, the data context for each user control is different. So if someone has a suggestion for binding that involves a similar data context, please take that into consideration.

Main Window XAML

User Control XAML

Main Window Code Behind

namespace TabControlStatusBarBinding
{
    public partial class MainWindow : Window
    {
        public static DependencyProperty dp_StatusBarText = DependencyProperty.Register("DP_StatusBarText", typeof(string), typeof(MainWindow));
        public string DP_StatusBarText
        {
            get { return (string)GetValue(dp_StatusBarText); }
            set { SetValue(dp_StatusBarText, value); }
        }
        public MainWindow()
        {
            InitializeComponent();

            DP_StatusBarText = "Main window loaded";

            UC1_A.StatusUpdated += MyEventHandlerFunction_StatusUpdated;
            UC1_B.StatusUpdated += MyEventHandlerFunction_StatusUpdated;
            UC1_C.StatusUpdated += MyEventHandlerFunction_StatusUpdated;
        }
        public void MyEventHandlerFunction_StatusUpdated(object sender, EventArgs e)
        {
            DP_StatusBarText = (string)sender;
        }
    }
}

User Control Code Behind

namespace TabControlStatusBarBinding
{
    public partial class UserControl1 : UserControl
    {
        public event EventHandler StatusUpdated;
    
        public UserControl1()
        {
            InitializeComponent();
        }

        private void RaiseStatusUpdatedEvent(string SendText)
        {
            if (this.StatusUpdated != null)
                this.StatusUpdated(SendText, new EventArgs());
        }

        private void UC1_TextChanged(object sender, TextChangedEventArgs e)
        {
            RaiseStatusUpdatedEvent(UC1.Text);
        }

        private void MyUserControl_GotFocus(object sender, RoutedEventArgs e)
        {
            RaiseStatusUpdatedEvent(UC1.Text);
        }
    }
}

Evk · Accepted Answer

Well your example only uses views - no models, no viewmodels, so not very clear what are your problems with MVVM :) But I'll try to help you introducing some data in your example.

First, just simple data item.

public class TestDataItem : INotifyPropertyChanged {
    public int ID { get; set; }
    private string _text;
    public string Text
    {
        get { return _text; }
        set
        {
            if (value == _text) return;
            _text = value;
            OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

UserControl1. Just binds textbox Text to model Text property. Codebehind is empty.

Window. Tabs in tab control are now bound to a list of data items. Tab content is just UserControl1 (it will inherit data context).

Window code-behind:

public partial class MainWindow : Window {
    public MainWindow() {
        InitializeComponent();
        this.DataContext = new MainViewModel();
    }
}

View model:

 public class MainViewModel : INotifyPropertyChanged {
    public IEnumerable Items => new[] {
            new TestDataItem() {ID = 100, Text = "item1"},
            new TestDataItem() {ID = 200, Text = "item2"},
            new TestDataItem() {ID = 300, Text = "item3"}
        };

    private string _statusText = "No data selected";
    public string StatusText
    {
        get { return _statusText; }
        set
        {
            if (value == _statusText) return;
            _statusText = value;
            OnPropertyChanged();
        }
    }

    private TestDataItem _selectedItem;
    public TestDataItem SelectedItem
    {
        get { return _selectedItem; }
        set
        {
            if (Equals(value, _selectedItem)) return;
            _selectedItem = value;
            OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

So we just bind status to SelectedItem.Text and done.