回答編集履歴
2
例を追記
test
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@@ -109,4 +109,123 @@
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}
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```
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---
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> やりたい事は選択した日付からn日後を計算して表示する事でしたが、WPFの基本的なところでハマっていました。
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`ViewModel`で計算したプロパティを用意するパターンと、`Converter`で計算するパターン例。
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実際は`ViewModel`レスというわけにもいかないので、この中間くらい（`ViewModel`に必要ない値は`Converter`で計算）になることが多いと思います。
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```xml
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<Window
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x:Class="Q9jmho7nu44o3nz.MainWindow"
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xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
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xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
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xmlns:local="clr-namespace:Q9jmho7nu44o3nz"
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xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
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Width="800"
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Height="450">
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<Window.DataContext>
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<local:ViewModel />
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</Window.DataContext>
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<Window.Resources>
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<local:DaysLaterConverter x:Key="DaysLaterConverter" />
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</Window.Resources>
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<UniformGrid>
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<GroupBox Header="ViewModel">
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<StackPanel>
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<DatePicker SelectedDate="{Binding SelectedDate}" />
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<xctk:IntegerUpDown Minimum="0" Value="{Binding DaysLater}" />
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<TextBlock HorizontalAlignment="Right" Text="日後" />
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<TextBox Text="{Binding SelectedDateDaysLater, StringFormat=yyyy/MM/dd, Mode=OneWay}" />
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</StackPanel>
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</GroupBox>
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<GroupBox Header="Converter">
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<StackPanel>
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<DatePicker x:Name="datePicker" SelectedDate="2023/01/01" />
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<xctk:IntegerUpDown
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x:Name="integerUpDown"
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Minimum="0"
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Value="0" />
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<TextBlock HorizontalAlignment="Right" Text="日後" />
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<TextBox>
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<TextBox.Text>
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<MultiBinding
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Converter="{StaticResource DaysLaterConverter}"
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Mode="OneWay"
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StringFormat="yyyy/MM/dd">
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<Binding ElementName="datePicker" Path="SelectedDate" />
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<Binding ElementName="integerUpDown" Path="Value" />
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</MultiBinding>
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</TextBox.Text>
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</TextBox>
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</StackPanel>
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</GroupBox>
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</UniformGrid>
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</Window>
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```
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```cs
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using System;
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using System.Globalization;
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using System.Windows;
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using System.Windows.Data;
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using CommunityToolkit.Mvvm.ComponentModel;
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namespace Q9jmho7nu44o3nz
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{
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public class ViewModel : ObservableObject
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{
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// ソースジェネレーター（LangVersion 8以上）を使えれば、もっとすっきり書けるのだが...
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// [ObservableProperty 属性 - .NET Community Toolkit | Microsoft Learn](https://learn.microsoft.com/ja-jp/dotnet/communitytoolkit/mvvm/generators/observableproperty#notifying-dependent-properties)
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public int DaysLater
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{
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get => _DaysLater;
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set
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{
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if (SetProperty(ref _DaysLater, value))
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OnPropertyChanged(nameof(SelectedDateDaysLater));
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}
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}
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private int _DaysLater;
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public DateTime? SelectedDate
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{
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get => _SelectedDate;
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set
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{
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if (SetProperty(ref _SelectedDate, value))
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OnPropertyChanged(nameof(SelectedDateDaysLater));
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}
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}
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private DateTime? _SelectedDate = DateTime.Parse("2023/01/01");
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public DateTime? SelectedDateDaysLater => SelectedDate?.AddDays(DaysLater);
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}
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class DaysLaterConverter : IMultiValueConverter // 雑いｗ
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{
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public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
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{
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if (values[0] is DateTime d && values[1] is int i)
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return d.AddDays(i);
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return null;
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}
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public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) => throw new NotImplementedException();
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}
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public partial class MainWindow : Window
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{
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public MainWindow() => InitializeComponent();
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}
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}
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```
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[NuGet Gallery | CommunityToolkit.Mvvm 8.0.0](https://www.nuget.org/packages/CommunityToolkit.Mvvm/8.0.0)
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[MVVM Toolkit の概要 - .NET Community Toolkit | Microsoft Learn](https://learn.microsoft.com/ja-jp/dotnet/communitytoolkit/mvvm/)
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[NuGet Gallery | Extended.Wpf.Toolkit 4.5.0](https://www.nuget.org/packages/Extended.Wpf.Toolkit/4.5.0)
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[IntegerUpDown · xceedsoftware/wpftoolkit Wiki](https://github.com/xceedsoftware/wpftoolkit/wiki/IntegerUpDown)
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1
xaml上で
test
CHANGED
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@@ -13,7 +13,7 @@
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[csharplang/null-conditional-assignment.md at main · dotnet/csharplang](https://github.com/dotnet/csharplang/blob/main/proposals/null-conditional-assignment.md)
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### 案２
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16
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-
単純な解決法は`TextBox`が先に来るようにする。
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単純な解決法は、xaml上で`TextBox`が先に来るようにする。
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しかし順番次第でエラーになることがあるのはやや不安が残る。
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### 案３
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