DialogHost in MVVM pattern "No loaded DialogHost instances"

[meilleur102]

Hi! I have some trouble using the DialogHost.
Ive copy a code from my old software(where it's working) but in the new one I have the error No loaded DialogHost.

The navigation is not exactly the same but I don't really get why it's not working.

Here's my main windows (You can see the RootDialog at the end of the code

 <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/materialdesigntheme.dialoghost.xaml"/>
            </ResourceDictionary.MergedDictionaries>
            <DataTemplate DataType="{x:Type modelDN:DnErrorModel}">
            <StackPanel Margin="20">
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto"></ColumnDefinition>
                        <ColumnDefinition Width="Auto"></ColumnDefinition>
                    </Grid.ColumnDefinitions>
                    <md:PackIcon Kind="{Binding PackIconKind}"
                                 Height="48"
                                 Width="48"
                                 Margin="20, 25, 20, 20"
                                 Grid.Column="0" />
                    <StackPanel Margin="20"
                                Grid.Column="1"
                                MinWidth="300">
                        <TextBlock Text="{Binding Title}"/>
                        <TextBlock Text="{Binding Message}" Margin="0,20,0,0"/>
                    </StackPanel>
                </Grid>
                <Button Content="OK" Command="{x:Static md:DialogHost.CloseDialogCommand}"
                        Style="{StaticResource MaterialDesignRaisedAccentButton}"
                        HorizontalAlignment="Right" Margin="0 0 50 0"/>
            </StackPanel>
        </DataTemplate>
   
        <DataTemplate DataType="{x:Type vm:TextViewModel}">
            <v:TextView/>
        </DataTemplate>
        <DataTemplate DataType="{x:Type vm:StudViewModel}">
            <v:StudView/>
        </DataTemplate>
        <DataTemplate DataType="{x:Type vm:HomeViewModel}">
            <v:HomeView/>
        </DataTemplate>
        <DataTemplate DataType="{x:Type vmQm:FormProdViewModel}">
            <vQm:FormProdView/>
        </DataTemplate>
        </ResourceDictionary>
    </Window.Resources>
    
    <Grid>
    <md:DialogHost Identifier="MainDialog">
      
        <md:DrawerHost IsLeftDrawerOpen="{Binding IsMenuOpen}">
        <md:DrawerHost.LeftDrawerContent>
            <DockPanel MinWidth="220">
                <ToggleButton 
                        Style="{StaticResource MaterialDesignHamburgerToggleButton}" 
                        DockPanel.Dock="Top"
                        HorizontalAlignment="Right" 
                        Margin="16"
                        IsChecked="{Binding IsMenuOpen}"/>
                
                <ListBox 
                        Margin="0 16 0 16"
                        SelectedItem="{Binding SelectedViewModel, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
                        ItemsSource="{Binding MenuItems}"
                        Style="{StaticResource MaterialDesignNavigationPrimaryListBox}">
                    <ListBox.Resources>
                        <Style TargetType="ScrollBar" BasedOn="{StaticResource MaterialDesignScrollBarMinimal}"/>
                    </ListBox.Resources>
                    <i:Interaction.Triggers>
                        <i:EventTrigger EventName="SelectionChanged">
                            <i:InvokeCommandAction Command="{Binding NewViewModelCommand}"/>
                        </i:EventTrigger>
                    </i:Interaction.Triggers>
                    <ListBox.ItemTemplate>
                        <DataTemplate DataType="vm:ViewModelBase">
                            <TextBlock Text="{Binding Title}" Margin="24 4 0 4" />
                        </DataTemplate>
                    </ListBox.ItemTemplate>
                </ListBox>
            </DockPanel>
        </md:DrawerHost.LeftDrawerContent>

        <DockPanel>
            <md:ColorZone
                    Padding="16"
                    md:ShadowAssist.ShadowDepth="Depth2"
                    Mode="PrimaryMid"
                    DockPanel.Dock="Top">
                <Grid>
                    <ToggleButton Style="{StaticResource MaterialDesignHamburgerToggleButton}"
                                  HorizontalAlignment="Left"
                                  IsChecked="{Binding IsMenuOpen}"/>

                    <TextBlock
                            HorizontalAlignment="Center"
                            VerticalAlignment="Center"
                            FontSize="22"
                            Text="Camsoft"/>
                    
                    <md:PopupBox PlacementMode="BottomAndAlignRightEdges"
                                 StaysOpen="False"
                                 DockPanel.Dock="Right"
                                 HorizontalAlignment="Right">
                        <StackPanel>
                            <StackPanel Orientation="Horizontal"
                                        HorizontalAlignment="Center"
                                        Margin="10">
                                <TextBlock Text="Light" Margin="0 0 10 0"/>
                                <ToggleButton Command="{Binding ChangeThemeCommand}"
                                              IsChecked="{Binding IsDarkIsChecked, Mode=TwoWay}"/>
                                <TextBlock Text="Dark" Margin="10 0 0 0"/>
                            </StackPanel>
                        </StackPanel>
                    </md:PopupBox>
                </Grid>
               
            </md:ColorZone>
            <ScrollViewer
                md:ScrollViewerAssist.IsAutoHideEnabled="True"
                HorizontalScrollBarVisibility="Auto"
                VerticalScrollBarVisibility="Auto">
                <ContentControl Content="{Binding CurrentViewModel}"/>
            </ScrollViewer>
        </DockPanel>
     </md:DrawerHost>
    </md:DialogHost>
        
        <md:DialogHost Identifier="RootDialog" 
                       CloseOnClickAway="False" />


    </Grid>
</Window>

And in a viewModel I used to just call the DialogHost.Show and I had my Dialog

     _nav.ErrMsg.Message = "Test";
            await DialogHost.Show(_nav.ErrMsg, "RootDialog");
        

Now I have the Error.
The _nav is pass with dependency injection in the App.xaml.cs in both case.
Thanks.

[meilleur102]

By Creating a View and ViewModel of the Dialog, it works. Well Ill use this form for now.