WPF Using TabItem and binding ViewModels

Question

My goal is have each TabItem linked to a specific viewmodel. Furthermore, after transvering through each TabItem, the user input should not be reset. I am finding solutions for this and came across a potential solution but my testing failed me.

I have searched for answers and chose to do the following as it seems it applies the MVVM concept and it looks neat! However, I have a XAML binding error. I tried to replicate Jakob Christensen's answer provided in this link. I tried to debug and I think the issue is with the type of ObservableCollection that is created. It's an object type.

Thank you for helping!

Error

This is the XAML code for my view

<TabControl>
    <TabItem DataContext="{Binding TabList[0]}" x:Name="Tab1" Header="Tab1" Margin="-2,-2,-2,2" >
            <Grid>
                <TextBox x:Name ="EnterNum1"  Margin="300,100,300,300" Text="{Binding test1, Mode =TwoWay}"/>
                <Button Name="RunBtn1" Command="{Binding Path=RunBtn1, Mode=TwoWay}" Content="RUN" HorizontalAlignment="Right" Width="180" Height="40" FontSize="18"/>
            </Grid>
        </TabItem>
    <TabItem DataContext="{Binding TabList[1]}" x:Name="Tab2" Header="Tab2" >
        <Grid>
            <TextBox x:Name ="EnterNum2"  Margin="300,100,300,300" Text="{Binding test2, Mode =TwoWay}" Grid.Column="1"/>
            <Button Name="RunBtn2" Command="{Binding Path=RunBtn2, Mode=TwoWay}" Content="RUN" HorizontalAlignment="Right" Width="180" Height="40" FontSize="18"/>
        </Grid>
    </TabItem>
</TabControl>

This is the XAML.cs for my view

public ObservableCollection<object> TabList { get; set; }
    public ImportData()
    {
        InitializeComponent();
        TabList = new ObservableCollection<object>();
        TabList.Add(new SampleViewModel1());
        TabList.Add(new SampleViewModel2());
    }

Answer 1

You should first set DataContext to TabControl or Window, then you can bind the TabItem to the viewmodel(TabList) list item

XAML

 <TabControl>
        <TabItem DataContext="{Binding TabList[0]}" x:Name="Tab1" Header="Tab1" Margin="-2,-2,-2,2" >
            <Grid>
                <TextBox x:Name ="EnterNum1"  Margin="300,100,300,240" Text="{Binding Test1, Mode =TwoWay}"/>
                <Button Name="RunBtn1" Command="{Binding Path=RunBtn1, Mode=TwoWay}" Content="RUN" HorizontalAlignment="Right" Width="180" Height="40" FontSize="18"/>
            </Grid>
        </TabItem>
        <TabItem DataContext="{Binding TabList[1]}" x:Name="Tab2" Header="Tab2" >
            <Grid>
                <TextBox x:Name ="EnterNum2"  Margin="300,100,300,240" Text="{Binding Test2, Mode =TwoWay}" Grid.Column="1"/>
                <Button Name="RunBtn2" Command="{Binding Path=RunBtn2, Mode=TwoWay}" Content="RUN" HorizontalAlignment="Right" Width="180" Height="40" FontSize="18"/>
            </Grid>
        </TabItem>
    </TabControl>

XAML.cs

   public partial class MainWindow : Window
    {
        
        public MainWindow()
        {
            InitializeComponent();

            AllViewModel allViewModel = new AllViewModel();
            allViewModel.TabList = new ObservableCollection<object>();
            allViewModel.TabList.Add(new SampleViewModel1());
            allViewModel.TabList.Add(new SampleViewModel2());

            this.DataContext = allViewModel;
        }
    }

    public class AllViewModel : INotifyPropertyChanged
    {
        private ObservableCollection<object> tabList;

        public ObservableCollection<object> TabList 
        { 
            get => tabList;
            set { tabList = value;RaiseChange("TabList"); }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        public void RaiseChange(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public class SampleViewModel1 : INotifyPropertyChanged
    {
        private string test1 = "test1";
        private ICommand runBtn1;

        public string Test1
        {
            get => test1;
            set { test1 = value;RaiseChange("Test1"); }
        }

        public ICommand RunBtn1 
        { 
            get => runBtn1;
            set { runBtn1 = value;RaiseChange("RunBtn1"); }
        }

        public SampleViewModel1()
        {
            
        }

        public event PropertyChangedEventHandler PropertyChanged;

        public void RaiseChange(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public class SampleViewModel2 : INotifyPropertyChanged
    {
        private string test2 = "test2";
        private ICommand runBtn2;

        public string Test2
        {
            get => test2;
            set { test2 = value; RaiseChange("Test2"); }
        }

        public ICommand RunBtn2
        {
            get => runBtn2;
            set { runBtn2 = value; RaiseChange("RunBtn2"); }
        }

        public SampleViewModel2()
        {

        }

        public event PropertyChangedEventHandler PropertyChanged;

        public void RaiseChange(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

run result