回答編集履歴

  ちょっと要望と違うのですが、各ItemTypeごとにクラスを分けてしまえばよいのではないでしょうか？（Triggerが手強かったので諦めただけですが^^;

 

  文字数制限によりコード削除（編集履歴を参照）

 

  ---

 

  追記

 

  ## 案１

  バカバカしいが全パターンを入れておいて、`Visibility`で切り替え（ボツでしょうねぇ）

  <Window

  x:Class="Questions248125.MainWindow"

  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:local="clr-namespace:Questions248125"

  Width="800"

  Height="450">

  <Grid>

  <ItemsControl

  Background="Black"

  Foreground="White"

  ItemsSource="{Binding Items}">

  <ItemsControl.Resources>

 

  <DataTemplate DataType="{x:Type local:Item}">

  <Grid>

  <Line

  Name="Line"

  Stroke="{Binding Brush}"

  StrokeThickness="3"

  X1="0"

  X2="{Binding Width}"

  Y1="0"

  Y2="0" />

  <Rectangle

  Name="Rectangle"

  Width="{Binding Width}"

  Height="{Binding Height}"

  Fill="{Binding Brush}" />

  <Ellipse

  Name="Ellipse"

  Width="{Binding Width}"

  Height="{Binding Height}"

  Fill="{Binding Brush}" />

  </Grid>

  <DataTemplate.Triggers>

  <DataTrigger Binding="{Binding ItemType}" Value="Line">

  <Setter TargetName="Line" Property="Visibility" Value="Visible" />

  <Setter TargetName="Rectangle" Property="Visibility" Value="Collapsed" />

  <Setter TargetName="Ellipse" Property="Visibility" Value="Collapsed" />

  <DataTrigger Binding="{Binding ItemType}" Value="Rectangle">

  <Setter TargetName="Line" Property="Visibility" Value="Collapsed" />

  <Setter TargetName="Rectangle" Property="Visibility" Value="Visible" />

  <Setter TargetName="Ellipse" Property="Visibility" Value="Collapsed" />

  <DataTrigger Binding="{Binding ItemType}" Value="Ellipse">

  <Setter TargetName="Line" Property="Visibility" Value="Collapsed" />

  <Setter TargetName="Rectangle" Property="Visibility" Value="Collapsed" />

  <Setter TargetName="Ellipse" Property="Visibility" Value="Visible" />

  </DataTemplate.Triggers>

  </DataTemplate>

 

  </ItemsControl.Resources>

  <ItemsControl.ItemsPanel>

  <ItemsPanelTemplate>

  <Canvas />

  </ItemsPanelTemplate>

  </ItemsControl.ItemsPanel>

  <ItemsControl.ItemContainerStyle>

  <Style>

  <Setter Property="Canvas.Top" Value="{Binding Y}" />

  <Setter Property="Canvas.Left" Value="{Binding X}" />

  </Style>

  </ItemsControl.ItemContainerStyle>

  </ItemsControl>

 

  <Button

  HorizontalAlignment="Center"

  VerticalAlignment="Top"

  Click="Button_Click"

  Content="ChangeShapes" />

  </Grid>

  </Window>

  ```

 

  using System;

  using System.Collections.ObjectModel;

  using System.ComponentModel;

  using System.Runtime.CompilerServices;

  using System.Windows;

  using System.Windows.Media;

 

  namespace Questions248125

  {

  public enum ItemType { Line, Rectangle, Ellipse, }

 

  public class Item : INotifyPropertyChanged

  {

  public int X { get; }

  public int Y { get; }

  public int Width { get; }

  public int Height { get; }

  public SolidColorBrush Brush { get; }

  public ItemType ItemType { get => _ItemType; set => Set(ref _ItemType, value, null); }

  public ItemType _ItemType;

 

  private static readonly Random r = new Random();

  private static readonly Array types = Enum.GetValues(typeof(ItemType));

 

  public Item()

  X = r.Next(700);

  Y = r.Next(350);

  Width = r.Next(400);

  Height = r.Next(300);

  Brush = new SolidColorBrush(Color.FromRgb((byte)r.Next(255), (byte)r.Next(255), (byte)r.Next(255)));

  ItemType = (ItemType)types.GetValue(r.Next(types.Length));

 

  public void ChangeShape() => ItemType = (ItemType)types.GetValue(r.Next(types.Length));

 

  #region INotifyPropertyChanged

  public event PropertyChangedEventHandler PropertyChanged;

  protected bool Set<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)

  if(Equals(storage, value)) return false;

  storage = value;

  OnPropertyChanged(propertyName);

  return true;

  protected void OnPropertyChanged([CallerMemberName] string propertyName = null)

  => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

  #endregion

  }

 

  public partial class MainWindow : Window

  {

  public ObservableCollection<Item> Items { get; }

 

  public MainWindow()

  InitializeComponent();

 

  DataContext = this;

  Items = new ObservableCollection<Item>

  {

  };

  private void Button_Click(object sender, RoutedEventArgs e)

  foreach(var item in Items) item.ChangeShape();

  }

  }

  ```

 

  ## 案２

  1段間に挟まってしまうが、`DataTemplate.Trigger`で`ControlTemplate`を切り替える。

  <Window

  x:Class="Questions248125.MainWindow"

  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:local="clr-namespace:Questions248125"

  Width="800"

  Height="450">

  <Grid>

  <ItemsControl

  Background="Black"

  Foreground="White"

  ItemsSource="{Binding Items}">

  <ItemsControl.Resources>

  <ControlTemplate x:Key="Line">

  <Line

  Name="Line"

  Stroke="{Binding Brush}"

  StrokeThickness="3"

  X1="0"

  X2="{Binding Width}"

  Y1="0"

  Y2="0" />

  </ControlTemplate>

  <ControlTemplate x:Key="Rectangle">

  <Rectangle

  Name="Rectangle"

  Width="{Binding Width}"

  Height="{Binding Height}"

  Fill="{Binding Brush}" />

  </ControlTemplate>

  <ControlTemplate x:Key="Ellipse">

  <Ellipse

  Name="Ellipse"

  Width="{Binding Width}"

  Height="{Binding Height}"

  Fill="{Binding Brush}" />

  </ControlTemplate>

  <DataTemplate DataType="{x:Type local:Item}">

  <Control Name="Control" />

  <DataTemplate.Triggers>

  <DataTrigger Binding="{Binding ItemType}" Value="Line">

  <Setter TargetName="Control" Property="Template" Value="{StaticResource Line}" />

  <DataTrigger Binding="{Binding ItemType}" Value="Rectangle">

  <Setter TargetName="Control" Property="Template" Value="{StaticResource Rectangle}" />

  <DataTrigger Binding="{Binding ItemType}" Value="Ellipse">

  <Setter TargetName="Control" Property="Template" Value="{StaticResource Ellipse}" />

  </DataTemplate.Triggers>

  </DataTemplate>

 

  </ItemsControl.Resources>

  <ItemsControl.ItemsPanel>

  <ItemsPanelTemplate>

  <Canvas />

  </ItemsPanelTemplate>

  </ItemsControl.ItemsPanel>

  <ItemsControl.ItemContainerStyle>

  <Style>

  <Setter Property="Canvas.Top" Value="{Binding Y}" />

  <Setter Property="Canvas.Left" Value="{Binding X}" />

  </Style>

  </ItemsControl.ItemContainerStyle>

  </ItemsControl>

 

  <Button

  HorizontalAlignment="Center"

  VerticalAlignment="Top"

  Click="Button_Click"

  Content="ChangeShapes" />

  </Grid>

  </Window>

  ```

  C#コードは同じ

 

  ## 案３

  いっそのこと`DependencyProperty`で`ItemType`を持った専用コントロールを作ってしまう。

  これも方向性が違うのでコードは省略。