generic type in xaml

Question

Hi

<DataTemplate DataType="{x:Type vm:MyViewModel1}">
                <StackPanel DataContext="{Binding}">
                    <!--template-->
                </StackPanel>
            </DataTemplate>

the above code works fine except the case of generic class
examples:
MyViewModel2<T>
MyViewModel3<TAcad, TCivil>

i'm using .Net Framework 4.7 Wpf ClassLibrary project
any help will be appreciated, thanks in advance.

Answer 1

Hi,
the easiest way is to encapsulate the generic class. Try following demo:

XAML MainWindow:

Window x:Class="WpfApp1.Window034"
        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:WpfApp034"
        xmlns:view="clr-namespace:WpfControlLibrary1;assembly=WpfControlLibrary1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
  <Window.DataContext>
    <local:ViewModel/>
  </Window.DataContext>
  <StackPanel>
    <Button Content="Switch" Command="{Binding}" Width="200" Margin="5"/>
    <view:Window034UC1 DataContext="{Binding CurrentVM}"/>
  </StackPanel>
</Window>

ViewModel:

using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Input;

namespace WpfApp034
{
  public class ViewModel : ICommand, INotifyPropertyChanged
  {
    public object CurrentVM { get; set; } = new WpfControlLibrary034.MyViewModel1();

    public void Execute(object parameter)
    {
      if (CurrentVM is WpfControlLibrary034.MyViewModel2)
      {
        WpfControlLibrary034.MyViewModel1 vm = new WpfControlLibrary034.MyViewModel1();
        vm.Data.Info1 = DateTime.Now.ToString("mm:ss.fff");
        CurrentVM = vm;
      }
      else
      {
        WpfControlLibrary034.MyViewModel2 vm = new WpfControlLibrary034.MyViewModel2();
        vm.Data.Info2 = DateTime.Now.ToString("mm:ss.fff");
        CurrentVM = vm;
      }
      OnPropertyChanged(nameof(CurrentVM));
    }

    public event EventHandler CanExecuteChanged;
    public bool CanExecute(object parameter) => true;

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged([CallerMemberName] string propName = "") =>
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
  }
}

UserControl with DataTemplates

<UserControl x:Class="WpfControlLibrary1.Window034UC1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:local="clr-namespace:WpfControlLibrary1"
             xmlns:view="clr-namespace:WpfControlLibrary034"
             xmlns:vm="clr-namespace:WpfControlLibrary034"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
  <UserControl.Resources>
    <DataTemplate DataType="{x:Type vm:MyViewModel1}">
      <view:MyViewModel1View DataContext="{Binding}"/>
    </DataTemplate>
    <DataTemplate DataType="{x:Type vm:MyViewModel2}">
      <view:MyViewModel2View DataContext="{Binding}"/>
    </DataTemplate>
  </UserControl.Resources>
  <ContentControl Content="{Binding}"/>
</UserControl>

And classes:

using System;
using System.Windows.Controls;
using System.Windows.Data;

namespace WpfControlLibrary034
{
  public class MyViewModel1 : MyViewModel<ModelData1> { }
  public class MyViewModel2 : MyViewModel<ModelData2> { }

  public class MyViewModel<T>
  {
    private T d;
    public T Data
    {
      get
      {
        if (d == null) d = (T)Activator.CreateInstance(typeof(T));
        return d;
      }
    }
  }
  public class ModelData1 { public string Info1 { get; set; } }
  public class ModelData2 { public string Info2 { get; set; } }
  public class MyViewModel1View : UserControl
  {
    public MyViewModel1View()
    {
      StackPanel stp = new StackPanel();
      this.Content = stp;
      stp.Children.Add(new Label() { Content = "1. View" });
      Label lbl = new Label();
      lbl.SetBinding(Label.ContentProperty, new Binding("Data.Info1"));
      stp.Children.Add(lbl);
    }
  }
  public class MyViewModel2View : UserControl
  {
    public MyViewModel2View()
    {
      StackPanel stp = new StackPanel();
      this.Content = stp;
      stp.Children.Add(new Label() { Content = "2. View" });
      Label lbl = new Label();
      lbl.SetBinding(Label.ContentProperty, new Binding("Data.Info2"));
      stp.Children.Add(lbl);
    }
  }
}