How to set Multiple Datacontext in a window in wpf

Question

In the application I wanted to bind data from 2 different viewmodels. Which is I have to set datacontext to two different viewmodels.

When I did with two different viewmodels, only the last set datacontext is taking precedence.

Hence, I have a CombinedDataContext class with other viewmodel classes.

I could able to update to viewmodel, but it is not getting displayed onto views.

ViewModel1

public class Data1 : INotifyPropertyChanged
    {
        private string _string1;

        public string String1
        {
            get { return _string1; }
            set { _string1 = value; onPropertyChnaged("String1"); }
        }

        private void onPropertyChnaged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

    }

ViewModel2

public class Data2 : INotifyPropertyChanged
    {
        private string _string2;

        public string String2
        {
            get { return _string2; }
            set { _string2 = value; onPropertyChnaged("String2");}
        }

        private void onPropertyChnaged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

    }

Views:

public partial class MainWindow : Window
    {
        Data12 d12 = new Data12 { };
        public MainWindow()
        {
            InitializeComponent();
            DataContext = d12;
        }

        private void button_Click(object sender, RoutedEventArgs e)
        {
            ViewModel_1();
            ViewModel_2();
        }

        private void ViewModel_1()
        {
            var viewmodel = DataContext as Data12;
            viewmodel.Data1.String1 = textBox.Text;
        }
        private void ViewModel_2()
        {
            var viewmodel = DataContext as Data12;
            viewmodel.Data1.String1 = textBox.Text;
        }
}

Combined ViewModel:

class Data12
    {
        public Data1 Data1 = new Data1();
        public Data2 Data2= new Data2();
    }

Xaml file:

<Grid>

        <Label x:Name="label" HorizontalAlignment="Left" Margin="92,61,0,0" VerticalAlignment="Top" Content="{Binding Data1.String1}"  />

        <Label x:Name="label1" Content="{Binding Data2.String2}" HorizontalAlignment="Left" Margin="349,61,0,0" VerticalAlignment="Top" />
        <TextBox x:Name="textBox" HorizontalAlignment="Left" Height="23" Margin="65,153,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
        <TextBox x:Name="textBox1" HorizontalAlignment="Left" Height="23" Margin="360,153,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
        <Button x:Name="button" Content="Button" HorizontalAlignment="Left" Margin="205,246,0,0" VerticalAlignment="Top" Width="75" Click="button_Click" />
</Grid>

There is no Nullreference, but binding is not working. I tried even by instantiating inner properties, but did not work. Please help me on this.

Answer 1

You can't bind on Fields, so just turn them into properties and it should work:

class Data12
{
    public Data12()
    {
        this.Data1 = new Data1();
        this.Data2 = new Data2();
    }
    public Data1 Data1 { get; private set; }
    public Data2 Data2 { get; private set; }
}

As @Clemens commented, this can be shortened to

class Data12
{
    public Data1 Data1 { get; } = new Data1();
    public Data2 Data2 { get; } = new Data2();
}