# Passing Data Between ViewModels (ISupportParameter) | WPF Controls | DevExpress Documentation The [ViewModelBase](/WPF/17351/mvvm-framework/viewmodels/viewmodelbase) class implements the [ISupportParameter](/CoreLibraries/DevExpress.Mvvm.ISupportParameter) interface. This interface provides the [Parameter](/CoreLibraries/DevExpress.Mvvm.ISupportParameter.Parameter) property, that you can use to pass initial data to View Models. Note The [POCO](/WPF/17352/mvvm-framework/viewmodels/runtime-generated-poco-viewmodels) mechanism does not generate the [ISupportParameter](/CoreLibraries/DevExpress.Mvvm.ISupportParameter) interface implementation automatically, but you can implement this interface in your POCO View Model manually. The following code demonstrates how to set the [ISupportParameter.Parameter](/CoreLibraries/DevExpress.Mvvm.ISupportParameter.Parameter) property in code-behind when a Detail View Model is created from the Main View Model. - C# - VB.NET

public class MainViewModel : ViewModelBase {
    public DetailViewModel DetailViewModel { get; private set; }
    public MainViewModel() {
        DetailViewModel = new DetailViewModel();
        ((ISupportParameter)DetailViewModel).Parameter = "Document 1";
    }
}

Public Class MainViewModel
    Inherits ViewModelBase
    Dim _DetailViewModel As DetailViewModel
    Public ReadOnly Property DetailViewModel As DetailViewModel
        Get
            Return _DetailViewModel
        End Get
    End Property
    Public Sub New()
        _DetailViewModel = New DetailViewModel()
        DirectCast(_DetailViewModel, ISupportParameter).Parameter = "Document 1"
    End Sub
End Class

When the [Parameter](/CoreLibraries/DevExpress.Mvvm.ISupportParameter.Parameter) property is set, the **ViewModelBase.OnParameterChanged** virtual method is invoked. You can override the **ViewModelBase.OnParameterChanged** virtual method to process passed data. - C# - VB.NET

public class DetailViewModel : ViewModelBase {
    protected override void OnParameterChanged(object parameter) {
        base.OnParameterChanged(parameter);
        if(IsInDesignMode) {
            //...
        } else {
            //...
        }
    }
}

Public Class DetailViewModel
    Inherits ViewModelBase
    Protected Overrides Sub OnParameterChanged(parameter As Object)
        MyBase.OnParameterChanged(parameter)
        If IsInDesignMode Then
            '...
        Else
            '...
        End If
    End Sub
End Class

## Passing Data Between Loosely Coupled Main and Detail View Model You can implement passing data from a Main to a Detail View Model when these View Models are loosely coupled, i.e., when View Models do not know about each other. In this case, you should set the **ViewModelExtensions.Parameter** attached property in XAML. The diagram below illustrates how it works. ![ISupportParameter-scheme](/WPF/images/isupportparameter-scheme19443.png) Here, the Main View contains an instance of a Detail View. The Views’ **DataContext**s are the *MainViewModel* and *DetailViewModel* respectively. To pass data from the Main View/Main ViewModel to the Detail ViewModel, assign the data to the **ViewModelExtensions.Parameter** attached property on the Detail View instance. - XAML

<UserControl x:Class="Example.View.MainView" ...
    xmlns:ViewModel="clr-namespace:Example.ViewModel"
    xmlns:View="clr-namespace:Example.View"
    xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm">
    <UserControl.DataContext>
        <ViewModel:MainViewModel/>
    </UserControl.DataContext>
    <Grid x:Name="LayoutRoot">
        ...
        <!-- It is necessary to use the ElementName binding mode, 
        because the DetailView's DataContext is a DetailViewModel object. 
        That is why the following regular binding cannot be used 
        in this case: dxmvvm:ViewModelExtensions.Parameter="{Binding}"
        Instead, use one of the following constructions:-->
        <View:DetailView dxmvvm:ViewModelExtensions.Parameter="{Binding DataContext, ElementName=LayoutRoot}"/>
        <ContentControl>
            <ContentControl.ContentTemplate>
                <DataTemplate>
                    <View:DetailView dxmvvm:ViewModelExtensions.Parameter="{Binding DataContext, Source={x:Reference LayoutRoot}}"/>
                </DataTemplate>
            </ContentControl.ContentTemplate>
        </ContentControl>
        ...
    </Grid>
</UserControl>

**How it works.** When the **Parameter** attached property is set on the Detail View, the **ViewModelExtensions** class identifies whether the View’s DataContext is a ViewModelBase descendant. To be more precise, the **ViewModelExtensions** class identifies whether the DataContext is an object that implements the **ISupportParameter** interface. If so, the **ViewModelExtensions** class passes the new **Parameter** value to the Detail View’s ViewModel: the new value is assigned to the ViewModel’s **ISupportParameter.Parameter** private property. When the **Parameter** private property is changed, the Detail ViewModel calls its **OnParameterChanged** protected method. You can manually override the **OnParameterChanged** protected method to access and use the new parameter value. ## Example [View Example](https://github.com/DevExpress-Examples/wpf-mvvm-framework-pass-data-between-view-models-through-the-isupportparameter-interface) - MainWindow.xaml - MainViewModel.cs - ChildViewModelBase.cs - ChildView1.xaml - MainView.xaml - ChildView2.xaml - ChildPOCOViewModel.cs

<Window x:Class="Example.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:View="clr-namespace:Example.View"
        Title="MainWindow" Height="600" Width="800">
    <Grid>
        <View:MainView/>
    </Grid>
</Window>

namespace Example.ViewModel {
    public class MainViewModel {
        public virtual string Parameter1 { get; set; }
        public virtual string Parameter2 { get; set; }
        public void ChangeParameter1() {
            counter1++;
            Parameter1 = "Parameter #" + counter1.ToString();
        }
        public void ChangeParameter2() {
            counter2++;
            Parameter2 = "Parameter #" + counter2.ToString();
        }

        int counter1 = 0;
        int counter2 = 0;
    }
}

using DevExpress.Mvvm;

namespace Example.ViewModel {
    public class ChildViewModelBase : ViewModelBase {
        IMessageBoxService MessageBoxService { get { return GetService<IMessageBoxService>(ServiceSearchMode.PreferParents); } }
        protected override void OnParameterChanged(object parameter) {
            base.OnParameterChanged(parameter);
            if(parameter is string)
                MessageBoxService.Show("ChildViewModelBase: Parameter = " + (string)parameter);
        }
    }
}

<UserControl x:Class="Example.View.ChildView1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:ViewModel="clr-namespace:Example.ViewModel"
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.DataContext>
        <ViewModel:ChildViewModelBase/>
    </UserControl.DataContext>
    <Grid>
        <TextBlock Text="This View has a ViewModel derived from the ViewModelBase class" TextWrapping="Wrap"/>
    </Grid>
</UserControl>

<UserControl x:Class="Example.View.MainView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:ViewModel="clr-namespace:Example.ViewModel"
    xmlns:View="clr-namespace:Example.View"
    xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
    xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d" d:DesignHeight="500" d:DesignWidth="600"
    DataContext="{dxmvvm:ViewModelSource ViewModel:MainViewModel}">

    <dxmvvm:Interaction.Behaviors>
        <dx:DXMessageBoxService/>
    </dxmvvm:Interaction.Behaviors>

    <Grid x:Name="LayoutRoot" Background="White">
        <StackPanel Orientation="Vertical">
            <StackPanel Orientation="Horizontal">
                <Button Content="Change Parameter1" Command="{Binding ChangeParameter1Command}"/>
                <Button Content="Change Parameter2" Command="{Binding ChangeParameter2Command}"/>
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <Border BorderThickness="1" BorderBrush="Black" Margin="10" Width="300" Height="100">
                    <View:ChildView1 dxmvvm:ViewModelExtensions.ParentViewModel="{Binding DataContext, ElementName=LayoutRoot}"
                                     dxmvvm:ViewModelExtensions.Parameter="{Binding DataContext.Parameter1, ElementName=LayoutRoot}"/>
                </Border>
            </StackPanel>
            <StackPanel Orientation="Horizontal">
                <Border BorderThickness="1" BorderBrush="Black" Margin="10" Width="300" Height="100">
                    <View:ChildView2 dxmvvm:ViewModelExtensions.ParentViewModel="{Binding DataContext, ElementName=LayoutRoot}"
                                     dxmvvm:ViewModelExtensions.Parameter="{Binding DataContext.Parameter2, ElementName=LayoutRoot}"/>
                </Border>
            </StackPanel>
        </StackPanel>
    </Grid>
</UserControl>

<UserControl x:Class="Example.View.ChildView2"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:ViewModel="clr-namespace:Example.ViewModel"
             xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300"
             DataContext="{dxmvvm:ViewModelSource ViewModel:ChildPOCOViewModel}">
    <Grid>
        <TextBlock Text="This View has a POCO ViewModel" TextWrapping="Wrap"/>
    </Grid>
</UserControl>

using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;

namespace Example.ViewModel {
    public class ChildPOCOViewModel : ISupportParameter {
        [ServiceProperty(SearchMode=ServiceSearchMode.PreferParents)]
        protected virtual IMessageBoxService MessageBoxService { get { return null; } }
        public virtual object Parameter { get; set; }

        protected virtual void OnParameterChanged() {
            if(Parameter is string)
                MessageBoxService.Show("ChildPOCOViewModel: Parameter = " + (string)Parameter);
        }
    }
}