Open User Control in MainWindow using MVVM

Question

My MainWindow has a TabControl with several TabItem. Each TabItem has several buttons. I want to open a different UserControl in grid UserControlRowwith each button click. How to do this in MVVM?

<Grid >  
	<Grid.RowDefinitions >  
		<RowDefinition x:Name="TabControlRow" Height="90"/>  
		<RowDefinition x:Name="UserControlRow" Height="*"/>  
	</Grid.RowDefinitions>  
</Grid>  

I have started the following in my ViewModel but I don't know if it is the best/correct solution. And how to open the user control, I do not know.

public class MainWindowViewModel  
    {  
        public RelayCommand Cmd { get => new RelayCommand(CmdExec); }  
        private void CmdExec(object parameter)  
        {  
            switch (parameter.ToString())  
            {  
                case "Button1":  
					//Code  
                    break;  
                case "Button2":  
					//Code  
                    break;  
                case "ButtonX":  
					//Code  
                    break;  
                default:  
                    break;  
            }  
        }  
    }  
}  

Answer 1

You could refer to the following code to switch UserControl.
MainWindow.xaml:

<Window.DataContext>  
        <local:ViewModel/>  
    </Window.DataContext>  
    <Grid>  
        <Grid.ColumnDefinitions>  
            <ColumnDefinition Width="*"/>  
            <ColumnDefinition Width="*"/>  
        </Grid.ColumnDefinitions>  

        <Grid.RowDefinitions>  
            <RowDefinition Height="20"/>  
            <RowDefinition Height="*"/>  
        </Grid.RowDefinitions>  
        <Button Grid.Row="0" Grid.Column="0" Command="{Binding ChangeFirstViewCommand}">Change View 1</Button>  
        <Button Grid.Row="0" Grid.Column="1" Command="{Binding ChangeSecondViewCommand}">Change View 2</Button>  
        <ContentControl  Grid.Row="1" Grid.ColumnSpan="2" Content="{Binding ContentView}"></ContentControl>  
    </Grid>  

MainWindow.xaml.cs:

using System;  
using System.ComponentModel;  
using System.Windows;  
using System.Windows.Input;  

namespace ClickButtonToSwitchUserControl  
{  
  public partial class MainWindow : Window  
  {  
    public MainWindow()  
    {  
      InitializeComponent();  
    }  
  }  
  public class ViewModel: INotifyPropertyChanged  
  {  
    private FrameworkElement contentView;  
    public FrameworkElement ContentView  
    {  
      get { return contentView;}  
      set  
      {  
        contentView=value;  
        OnPropertyChanged("ContentView");  
      }  
    }  
    public ViewModel()  
    {  
      SwitchViewMessage svm=new SwitchViewMessage();  
      SwitchView(svm.ViewName);  
    }  

    public ICommand ChangeFirstViewCommand  
    {  
      get  
      {  
        return new RelayCommand(x =>  
        {  
          SwitchView("FirstView");  
        });  
      }  
    }  
    public ICommand ChangeSecondViewCommand  
    {  
      get  
      {  
        return new RelayCommand(x =>  
        {  
          SwitchView("SecondView");  
        });  
      }  
    }  
    public void SwitchView(string viewName)  
    {  
      switch (viewName)  
      {  
        case "FirstView" :  
          ContentView =new FirstView();  
          ContentView.DataContext=new FirstViewModel() { Text= "This is the first view" };  
          break;  
        default:  
          ContentView = new SecondView();  
          ContentView.DataContext = new SecondViewModel() { Text = "This is the second View" };  
          break;  
      }  
    }  
    public event PropertyChangedEventHandler PropertyChanged;  

    protected void OnPropertyChanged(string propertyName)  
    {  
      if (PropertyChanged != null)  
      {  
        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));  
      }  
    }  
  }  
  public class SwitchViewMessage  
  {  
    public string ViewName { get; set; }  
  }  
  public class RelayCommand : ICommand  
  {  
    private readonly Predicate<object> _canExecute;  
    private readonly Action<object> _execute;  

    public RelayCommand(Action<object> execute)  
       : this(execute, null)  
    {  
      _execute = execute;  
    }  

    public RelayCommand(Action<object> execute, Predicate<object> canExecute)  
    {  
      if (execute == null)  
      {  
        throw new ArgumentNullException("execute");  
      }  
      _execute = execute;  
      _canExecute = canExecute;  
    }  

    public bool CanExecute(object parameter)  
    {  
      return _canExecute == null || _canExecute(parameter);  
    }  

    public void Execute(object parameter)  
    {  
      _execute(parameter);  
    }  
    public event EventHandler CanExecuteChanged  
    {  
      add  
      {  
        CommandManager.RequerySuggested += value;  
        CanExecuteChangedInternal += value;  
      }  
      remove  
      {  
        CommandManager.RequerySuggested -= value;  
        CanExecuteChangedInternal -= value;  
      }  
    }  
    private event EventHandler CanExecuteChangedInternal;  
    public void RaiseCanExecuteChanged()  
    {  
      CanExecuteChangedInternal.Raise(this);  
    }  
  }  
  public static class EventRaiser  
  {  
    public static void Raise(this EventHandler handler, object sender)  
    {  
      if (handler != null)  
      {  
        handler(sender, EventArgs.Empty);  
      }  
    }  
  }  
}  
FirstView.xaml:(UserControl1)  

<StackPanel>  
        <Label Content="View 1" FontSize="30"/>  
        <Button  
            Content="Goto View 2"  
            Command="{Binding GotoView2Command}"            
            HorizontalAlignment="Center"                
            Margin="10,10,0,0"  
            VerticalAlignment="Center"  
            Width="75">  
        </Button>  
    </StackPanel>  

View1ViewModel:

 <StackPanel>  
        <Label>This is the first view</Label>  
        <Label Content="{Binding Text}"  FontSize="30"/>  

    </StackPanel>  

FirstViewModel:

public class FirstViewModel : INotifyPropertyChanged  
  {  

    private string _text;  
    public string Text  
    {  
      get { return _text; }  
      set  
      {  
        _text = value;  
        OnPropertyChanged("Text");  
      }  
    }  
    public event PropertyChangedEventHandler PropertyChanged;  

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

SecondView.xaml:(UserControl2)

 <StackPanel>  
        <Label>This is the second view</Label>  
        <Label Content="{Binding Text}" FontSize="30" />  

    </StackPanel>  

SecondViewModel :

public class SecondViewModel : INotifyPropertyChanged  
  {  

    private string _text;  
    public string Text  
    {  
      get { return _text; }  
      set  
      {  
        _text = value;  
        OnPropertyChanged("Text");  
      }  
    }  

    public event PropertyChangedEventHandler PropertyChanged;  

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

The result:

---

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Answer 2

Hi Imilio,
you can use ItemsControl to show UserControl like in following demo:

XAML:

<Window x:Class="WpfApp1.Window010"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp010"
        mc:Ignorable="d"
        Title="Imilio_220324" Height="450" Width="800">
  <Window.DataContext>
    <local:ViewModel/>
  </Window.DataContext>
  <Window.Resources>
    <Style TargetType="Button">
      <Setter Property="Margin" Value="5"/>
      <Setter Property="Height" Value="25"/>
      <Setter Property="Background" Value="#d0d0ff"/>
    </Style>
  </Window.Resources>
  <Grid>
    <Grid.RowDefinitions >
      <RowDefinition Height="90"/>
      <RowDefinition Height="*"/>
    </Grid.RowDefinitions>
    <TabControl Grid.Row="0">
      <TabItem Header="TabItem1">
        <StackPanel Orientation="Horizontal" Background="LightGreen">
          <Button Content="Button1" Command="{Binding}" CommandParameter="Button1"/>
          <Button Content="Button2" Command="{Binding}" CommandParameter="Button2"/>
          <Button Content="Button3" Command="{Binding}" CommandParameter="Button3"/>
        </StackPanel>
      </TabItem>
    </TabControl>
    <ItemsControl Grid.Row="1" ItemsSource="{Binding UserControls}"/>
  </Grid>
</Window>

ViewModel:

using System;
using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace WpfApp010
{
  public class ViewModel : ICommand
  {
    public ObservableCollection<FrameworkElement> UserControls { get; set; } = new ObservableCollection<FrameworkElement>();

    public event EventHandler? CanExecuteChanged;
    public bool CanExecute(object? parameter) => true;
    public void Execute(object? parameter)
    {
          UserControls.Clear();
      switch (parameter?.ToString())
      {
        case "Button1":
          UserControls.Add(GetUserControlInstance("Button1"));
          break;
        case "Button2":
          UserControls.Add(GetUserControlInstance("Button2"));
          break;
        case "Button3":
          UserControls.Add(GetUserControlInstance("Button3"));
          break;
        default:
          break;
      }
    }
    private UserControl GetUserControlInstance(string name)
    {
      Random rnd = new Random();
      UserControl ctrl = new UserControl();
      Grid grd = new Grid() { Height = 100 };
      ctrl.Content = grd;
      grd.Background = new SolidColorBrush(Color.FromArgb(255,(byte)rnd.Next(100,255), (byte)rnd.Next(100, 255), (byte)rnd.Next(100, 255)));
      grd.Children.Add(new Label() { Content= name });
      return ctrl;
    }
  }
}