How to update textblock text of an inactive window from main window

Question

I have two windows; main window and a sub window. I need to update some text in a textblock which is on sub window. But the text is not updates, when I put that textblock on main window, it updates the text.

I tried the following code:

Main Window QPlayer.XAML (Active Window)

<Window x:Class="AlQuran.Views.QPlayer"
        xmlns:ViewModel="clr-namespace:AlQuran.ViewModel"
        Width="300" Height="306" WindowStyle="None"
        ResizeMode="NoResize" BorderThickness="0" Foreground="White" AllowsTransparency="True" MouseDown="Window_MouseDown" SnapsToDevicePixels="True" Loaded="Window_Loaded">
    <Window.Background>
        <ImageBrush ImageSource="../Resources/AlQuran_Window.png"/>
    </Window.Background>
    <Window.DataContext>
        <ViewModel:QuranViewModel/>
    </Window.DataContext>
    <Grid >
                <Image x:Name="BtnPlay" Grid.Column="0" MouseDown="BtnPlay_MouseDown" HorizontalAlignment="Center" VerticalAlignment="Center" Width="79" Height="79">
                    <Image.Style>
                        <Style TargetType="{x:Type Image}">
                            <Setter Property="Source" Value="../Resources/BtnPlay.png"/>
                            <Style.Triggers>
                                <Trigger Property="IsMouseOver" Value="True">
                                    <Setter Property="Source" Value="../Resources/BtnPlay_Over.png"/>
                                </Trigger>
                            </Style.Triggers>
                        </Style>
                    </Image.Style>
                    <Image.InputBindings>
                        <MouseBinding Gesture="LeftClick" Command="{Binding Play_Btn, Mode=OneTime}" />
                    </Image.InputBindings>
                </Image>

        <TextBlock Grid.Column="1" Grid.Row="6" Text="{Binding TxtAyah, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Height="47" Background="#FF38ECEC" FontSize="16" />

Info Window AyahWindow.xaml (Inactive window)

<Window x:Class="AlQuran.Views.AyahWindow"
        xmlns:local="clr-namespace:AlQuran"
        xmlns:ViewModel="clr-namespace:AlQuran.ViewModel"
        Width="900" Height="630"  WindowStartupLocation="CenterScreen" WindowStyle="None"
        ResizeMode="NoResize" BorderThickness="0" Foreground="White" Opacity=".94" AllowsTransparency="True" MouseDown="Window_MouseDown" >

    <Window.Resources>
        <ViewModel:QuranViewModel x:Key="QViewModel"/>
    </Window.Resources>
    <Window.DataContext>
        <ViewModel:QuranViewModel />
    </Window.DataContext>
    <Grid >
         <TextBlock Grid.Column="1" Grid.Row="1" ScrollViewer.CanContentScroll="True"
            Text="{Binding TxtAyah, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
            x:Name="AyahLine" TextWrapping="Wrap" Background="#FFF51E1E" 
            FontFamily="Futura Md BT" FontSize="36" TextAlignment="Right"/>
    </Grid>

InfoWindow AyahWindow.XAML.CS (Inactive)

        public InfoWindow()
        {
            InitializeComponent();
        }
        public string txt;
        public InfoWindow(string txt)
        {
            InitializeComponent();
            TxtToShow.Text = txt;
        }

ViewModel Class QuranViewModel.CS

namespace AlQuran.ViewModel
{
    public class QuranViewModel : INotifyPropertyChanged
    {

        public ICommand Play_Btn { get; set; }

        public QuranViewModel()
        {
            Play_Btn = new RelayCommand(PlayMethod, CanExecuteMyMethod);
        }

        private string _txtAyah;

        public string TxtAyah
        {
            get { return _txtAyah; }
            set { _txtAyah = value; OnPropertyChanged("TxtAyah"); }
        }

        private void PlayMethod(object parameter)
        {
            TxtAyah =new Random().Next(5,999999).ToString() ;

            AyahWindow aw = new AyahWindow(TxtAyah);
            aw.txt = TxtAyah;

        }

    }
}

Please help, I am really stuck at this point.

and here is my project image to get better understanding enter image description here

Answer 1

And never handle view controls or classes in you view model. Create and show the InfoWindow from the buttons's event handler from your code-behind. MainWindow.xaml:

<Window x:Class="MainWindow"
        DataContext="{StaticResource ProjViewModel}">
  <Grid>
      <Button Click="ShowWindow_OnClick"/>
      <TextBox Text="{Binding TextToShow, UpdateSourceTrigger=PropertyChanged}"/>
  </Grid>
</Window>

MainWindow.xaml.cs:

public partial class MainWndow
{
    private void ShowWindow_OnClick(object sender, RoutedEventArgs e)
    {
      new InfoWindow().Show();
    }
}

InfoWindow.xaml

<Window x:Class="InfoWindow" 
        DataContext="{StaticResource ProjViewModel}">
  <Grid>
        <TextBlock Text="{Binding TextToShow}"/>
    </Grid>
</Window>

App.xaml:

View model:

class ProjViewModel : INotifyPropertyChanged
{
    public ProjViewModel()
    {
    }

    private string _texttoshow;
    public string TextToShow
    {
        get { return _txttoshow; }
        set { _txttoshow= value; OnPropertyChanged("TxtToShow"); }
    }
}