回答編集履歴

1 流れの説明

TN8001 score 4229

2020/08/15 16:55  投稿

> 選択されているというのが重要な情報の場合（ファイルに選択情報も保存して次回復元する等）は、別の手のほうがいいかもしれません。

> Taskクラスにbool IsSelectedプロパティを用意して、lst_TitleではListBoxItemのIsSelectedにバインドし、lst_DetailではListBoxItemのVisibilityにバインドします。

> どちらのListBoxもTaskListがソースですが、lst_Detailでは未選択のものは無いように見えます。

> ちょっとずるいようですが、割とポピュラーな手段だと思います。もし気になるようでしたら追記しますので言ってください。

１万字に収まらなかったのでこちらで失礼します。

IsSelectedにバインドパターン

```xaml

<Window

x:Class="Questions284783.Views.MainWindow"

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

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

xmlns:controls="clr-namespace:System.Windows.Controls;assembly=PresentationFramework"

xmlns:prism="http://prismlibrary.com/"

Width="525"

Height="350"

prism:ViewModelLocator.AutoWireViewModel="True">

<Window.Resources>

<BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter" />

</Window.Resources>

<Grid>

<Grid.ColumnDefinitions>

<ColumnDefinition />

<ColumnDefinition Width="2*" />

</Grid.ColumnDefinitions>

<Grid.RowDefinitions>

<RowDefinition Height="Auto" />

<RowDefinition />

</Grid.RowDefinitions>

<Grid>

<Grid.ColumnDefinitions>

<ColumnDefinition Width="Auto" />

<ColumnDefinition />

</Grid.ColumnDefinitions>

<Label

Margin="5"

VerticalAlignment="Center"

Content="表題" />

<TextBox

Grid.Column="1"

Margin="5"

VerticalAlignment="Center"

Text="{Binding Txt_Title, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"

TextWrapping="Wrap" />

</Grid>

<Grid Grid.Column="1">

<Grid.ColumnDefinitions>

<ColumnDefinition Width="Auto" />

<ColumnDefinition />

<ColumnDefinition Width="Auto" />

</Grid.ColumnDefinitions>

<Label

Margin="5"

VerticalAlignment="Center"

Content="Memo" />

<TextBox

Grid.Column="1"

Margin="5"

VerticalAlignment="Center"

Text="{Binding Txt_Memo, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"

TextWrapping="Wrap" />

<Button

Grid.Column="2"

MinWidth="56"

Margin="5"

Command="{Binding ExecuteCommand}"

Content="追加" />

</Grid>

<Grid Grid.Row="1">

<Grid.RowDefinitions>

<RowDefinition Height="Auto" />

<RowDefinition />

</Grid.RowDefinitions>

<ComboBox

x:Name="comboBox"

Margin="5"

SelectedIndex="0">

<controls:SelectionMode>Single</controls:SelectionMode>

<controls:SelectionMode>Multiple</controls:SelectionMode>

<controls:SelectionMode>Extended</controls:SelectionMode>

</ComboBox>

<ListBox

x:Name="lst_Title"

Grid.Row="1"

Margin="5"

DisplayMemberPath="Title"

IsSynchronizedWithCurrentItem="True"

ItemsSource="{Binding TaskList}"

SelectionMode="{Binding SelectedValue, ElementName=comboBox}">

<ListBox.ItemContainerStyle>

<Style TargetType="ListBoxItem">

<Setter Property="IsSelected" Value="{Binding IsSelected}" />

</Style>

</ListBox.ItemContainerStyle>

</ListBox>

</Grid>

<ListBox

Grid.Row="1"

Grid.Column="1"

Margin="5"

ItemsSource="{Binding TaskList}">

<ListBox.ItemContainerStyle>

<Style TargetType="ListBoxItem">

<Setter Property="Visibility" Value="{Binding IsSelected, Converter={StaticResource BooleanToVisibilityConverter}}" />

</Style>

</ListBox.ItemContainerStyle>

<ListBox.ItemTemplate>

<DataTemplate>

<StackPanel>

<TextBlock FontWeight="Bold" Text="{Binding Title}" />

<TextBlock Text="{Binding Detail}" />

</StackPanel>

</DataTemplate>

</ListBox.ItemTemplate>

</ListBox>

</Grid>

</Window>

```

```C#

using System.Collections.ObjectModel;

using Prism.Commands;

using Prism.Mvvm;

namespace Questions284783.ViewModels

{

public class MainWindowViewModel : BindableBase

{

private string txt_Title;

public string Txt_Title

{

get => txt_Title;

set { if(SetProperty(ref txt_Title, value)) ExecuteCommand.RaiseCanExecuteChanged(); }

}

private string txt_Memo;

public string Txt_Memo

{

get => txt_Memo;

set { if(SetProperty(ref txt_Memo, value)) ExecuteCommand.RaiseCanExecuteChanged(); }

}

public ObservableCollection<Task> TaskList { get; } = new ObservableCollection<Task>();

public DelegateCommand ExecuteCommand { get; private set; }

public MainWindowViewModel()

{

TaskList.Add(new Task { Title = "aaa", Detail = "111" });

TaskList.Add(new Task { Title = "bbb", Detail = "222" });

TaskList.Add(new Task { Title = "ccc", Detail = "333" });

ExecuteCommand = new DelegateCommand(Execute, CanExecute);

}

private void Execute()

{

TaskList.Add(new Task { Title = Txt_Title, Detail = Txt_Memo });

Txt_Title = "";

Txt_Memo = "";

ExecuteCommand.RaiseCanExecuteChanged();

}

private bool CanExecute() => !string.IsNullOrEmpty(Txt_Title);

}

public class Task : BindableBase

{

public string Title { get; set; }

public string Detail { get; set; }

private bool isSelected;

public bool IsSelected { get => isSelected; set => SetProperty(ref isSelected, value); }

}

}

```