如果有人能在我發瘋之前幫助我。我有一個包含 ListBox 的用戶控制元件我想將 SelectedItem 的屬性添加到 UserControl，以便父級可以獲取它。所以我使用了 DependencyProperty

用戶控制元件（VersionList.xaml）：

<UserControl
    x:Class="PcVueLauncher.Controls.VersionsList"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:converters="clr-namespace:PcVueLauncher.Converters"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:PcVueLauncher.Controls"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    d:Background="white"
    d:DesignHeight="450"
    d:DesignWidth="800"
    mc:Ignorable="d">
    <FrameworkElement.Resources>
        <ResourceDictionary>
            <converters:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter" />
        </ResourceDictionary>
    </FrameworkElement.Resources>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <TextBlock
            Grid.Row="0"
            Padding="10"
            Text="Versions" />
        <ListBox
            Grid.Row="1"
            d:ItemsSource="{d:SampleData ItemCount=5}"
            ItemsSource="{Binding Versions}"
            SelectedItem="{Binding SelectedVersion}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*" />
                            <ColumnDefinition Width="auto" />
                        </Grid.ColumnDefinitions>
                        <TextBlock
                            Grid.Column="0"
                            Margin="5,5,10,5"
                            Text="{Binding VersionName}" />
                        <Button
                            Grid.Column="1"
                            Padding="5"
                            Command="{Binding RemoveVersionCommand}"
                            Content="Remove"
                            Visibility="{Binding CanBeRemoved, Converter={StaticResource BoolToVisibilityConverter}}" />
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>

        </ListBox>
    </Grid>
</UserControl>

UserControl 關聯的 ViewModel (VersionListViewModel)

namespace PcVueLauncher.ViewModels.Controls
{
    public class VersionsListViewModel : ViewModelBase
    {

        private List<VersionPcVue> _versions;
        public List<VersionPcVue> Versions
        {
            get
            {
                return _versions;
            }
            set
            {
                _versions = value;
                OnPropertyChanged(nameof(Versions));
            }
        }

        private VersionPcVue _selectedVersion;
        public VersionPcVue SelectedVersion
        {
            get
            {
                return _selectedVersion;
            }
            set
            {
                _selectedVersion = value;
                OnPropertyChanged(nameof(SelectedVersion));
            }
        }


        public ICommand RemoveVersionCommand { get; }


        public VersionsListViewModel()
        {
            List<VersionPcVue> versionPcVues = new()
            {
                new VersionPcVue{VersionName="V15"},
                new VersionPcVue{VersionName="V12"}
            };
            Versions = versionPcVues;
        }
    }
}

用戶控制元件背后的代碼（VersionList.cs）：

public partial class VersionsList : UserControl
{
    public VersionsList()
    {
        InitializeComponent();
    }

    public VersionPcVue SelectedVersion
    {
        get { return (VersionPcVue)GetValue(SelectedVersionProperty); }
        set { SetValue(SelectedVersionProperty, value); }
    }

    //Using a DependencyProperty as the backing store for SelectedVersion.This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SelectedVersionProperty =
        DependencyProperty.Register("SelectedVersion",
            typeof(VersionPcVue),
            typeof(VersionsList),
            new FrameworkPropertyMetadata(
        defaultValue: null,
        flags: FrameworkPropertyMetadataOptions.AffectsMeasure,
        propertyChangedCallback: new PropertyChangedCallback(OnSelectionChanged)));


    private static void OnSelectionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        d.CoerceValue(SelectedVersionProperty);
    }
}


    // Register a dependency property with the specified property name,
    // property type, owner type, property metadata, and callbacks.
    public static readonly DependencyProperty SelectedVersionProperty = DependencyProperty.Register(
    name: "SelectedVersion",
    propertyType: typeof(VersionPcVue),
    ownerType: typeof(VersionsList),
    typeMetadata: new FrameworkPropertyMetadata(
        defaultValue: null,
        flags: FrameworkPropertyMetadataOptions.AffectsMeasure,
        propertyChangedCallback: new PropertyChangedCallback(OnSelectionChanged)
    ));



    private static void OnSelectionChanged(DependencyObject depObj, DependencyPropertyChangedEventArgs e)
    {
        depObj.CoerceValue(SelectedVersionProperty);
    }

在包含 UserControl 的 HomeView 中，我有這個：

<UserControl
    x:Class="PcVueLauncher.Views.HomeView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:Controls="clr-namespace:PcVueLauncher.Controls"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:PcVueLauncher.Views"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:system="clr-namespace:System;assembly=netstandard"
    xmlns:viewmodels="clr-namespace:PcVueLauncher.ViewModels"
    d:Background="White"
    d:DataContext="{d:DesignInstance Type=viewmodels:HomeViewModel}"
    d:DesignHeight="450"
    d:DesignWidth="800"
    mc:Ignorable="d">
    <Grid>

        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="2*" />
        </Grid.ColumnDefinitions>


        <Controls:VersionsList
            x:Name="test"
            Grid.Column="0"
            DataContext="{Binding VersionsListViewModel}"
            SelectedVersion="{Binding DataContext.SelectedVersion, RelativeSource={RelativeSource FindAncestor, AncestorLevel=1, AncestorType={x:Type UserControl}}, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />


    </Grid>
</UserControl>

并在關聯的 ViewModel (HomeViewModel)

   public class HomeViewModel : ViewModelBase
    {
        private IProjectService _projectService;

        private VersionPcVue _selectedVersion;
        public VersionPcVue SelectedVersion
        {
            get
            {
                return _selectedVersion;
            }   
            set
            {
                _selectedVersion = value;
                OnPropertyChanged(nameof(SelectedVersion));
            }
        }

        private VersionPcVue _test1;
        public VersionPcVue Test1
        {
            get
            {
                return _test1;
            }
            set
            {
                _test1 = value;
                OnPropertyChanged(nameof(Test1));
            }
        }

        private string _test;
        public string Test
        {
            get
            {
                return _test;
            }
            set
            {
                _test = value;
                OnPropertyChanged(nameof(Test));
            }
        }

        private VersionsListViewModel versionsListViewModel;
        public VersionsListViewModel VersionsListViewModel
        {
            get
            {
                return versionsListViewModel;
            }
            set
            {
                versionsListViewModel = value;
                OnPropertyChanged(nameof(VersionsListViewModel));
            }
        }

        public HomeViewModel(IProjectService projectService)
        {

            _projectService = projectService;

            VersionsListViewModel = new();
        }
    }

當我更改用戶控制元件中的選定項時，HomeViewModel 中沒有任何反應。我想到了一個系結錯誤，但為了嘗試，我改變了這個

   SelectedVersion="{Binding DataContext.SelectedVersionnnnnnn, RelativeSource={RelativeSource FindAncestor, AncestorLevel=1, AncestorType={x:Type Grid}}, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />

Visual Studio 告訴我 HomeViewModel 中不存在 SelectedVersionnnnn。

為什么我不能將 Selected Item 回傳到我的 HomeViewModel 的 SelectedVersion 屬性。

非常感謝你的幫助

uj5u.com熱心網友回復：

您需要解決幾個問題：

不要DependencyObject.CoerceValue從屬性更改的回呼中顯式呼叫。它由依賴屬性系統自動呼叫 - 在屬性更改回呼之前。
您的財產不會影響布局。為了更好的性能，不要設定FrameworkPropertyMetadataOptions.AffectsMeasure標志，因為它會在每次屬性更改時強制執行完整的布局傳遞，這在您的情況下是不必要的。對控制元件的ListBox.SelectedItem布局沒有影響。相反，您應該考慮通過設定FrameworkPropertyMetadataOptions.BindsTwoWayByDefault標志將屬性配置為默認系結兩種方式。
a) 將 a 的內部結構系結Control到控制元件的屬性，而不是系結到DataContext. 否則您的控制元件將變得不便處理（和撰寫）。例如，如果您更改DataContext或重命名回傳的物件的屬性DataContext，您將被迫重寫內部系結以處理新的物件結構/屬性名稱。

b) 這意味著您必須洗掉所有內部 DataContext系結并為每個系結引入一個依賴屬性。例如，洗掉對屬性的ListBox.ItemsSource系結VersionsListViewModel.Versions并改為引入一個VersionsItemsSource依賴屬性。
例如HomeView：定義所有DataContext與Binding實際DataContext的UserControl（或FrameworkElement一般情況下）相關的，而不是開始遍歷（使用）來查找與系結目標相同Binding.RelativeSource的父級。沒有意義，只能說明你還沒有理解Binding的作業原理。DataContextDataContext

修復

1 & 2 & 3b

版本串列.xaml.cs

public partial class VersionsList : UserControl
{
    public VersionPcVue SelectedVersionItem
    {
        get => (VersionPcVue)GetValue(SelectedVersionItemProperty); 
        set => SetValue(SelectedVersionItemProperty, value); 
    }
    
    public static readonly DependencyProperty SelectedVersionItemProperty = DependencyProperty.Register(
        "SelectedVersionItem",
        typeof(VersionPcVue),
        typeof(VersionsList),
        new FrameworkPropertyMetadata(default(VersionPcVue), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnSelectedVersionChanged));

    public IList VersionsItemsSource
    {
        get => (IList)GetValue(VersionsItemsSourceProperty); 
        set => SetValue(VersionsItemsSourceProperty, value); 
    }
    
    public static readonly DependencyProperty VersionsItemsSourceProperty = DependencyProperty.Register(
        "VersionsItemsSource",
        typeof(IList),
        typeof(VersionsList),
        new PropertyMetadata(default));

    public VersionsList()
    {
        InitializeComponent();
    }

    private static void OnSelectedVersionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {        
    }
}

3a

VersionList.xaml
創作 a 時Control，始終系結到控制元件的屬性，而不是系結到的屬性DataContext：

<UserControl>
    <FrameworkElement.Resources>
        <ResourceDictionary>
            <converters:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter" />
        </ResourceDictionary>
    </FrameworkElement.Resources>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <TextBlock
            Grid.Row="0"
            Padding="10"
            Text="Versions" />
        <ListBox Grid.Row="1"
                 d:ItemsSource="{d:SampleData ItemCount=5}"
                 ItemsSource="{Binding RelativeSource={RelativeSource AncestorType=UserControl}, Path=VersionsItemsSource}"
                 SelectedItem="{Binding RelativeSource={RelativeSource AncestorType=UserControl}, Path=SelectedVersionItem}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*" />
                            <ColumnDefinition Width="auto" />
                        </Grid.ColumnDefinitions>
                        <TextBlock
                            Grid.Column="0"
                            Margin="5,5,10,5"
                            Text="{Binding VersionName}" />
                        <Button
                            Grid.Column="1"
                            Padding="5"
                            Command="{Binding RemoveVersionCommand}"
                            Content="Remove"
                            Visibility="{Binding CanBeRemoved, Converter={StaticResource BoolToVisibilityConverter}}" />
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</UserControl>

4個

HomeView.xaml
請注意，DataContext控制元件VersionsList的參考了一個VersionsListViewModel實體。您必須相應地調整所有系結：

<UserControl>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="2*" />
        </Grid.ColumnDefinitions>

        <Controls:VersionsList x:Name="test"
                               Grid.Column="0"
                               DataContext="{Binding VersionsListViewModel}"
                               VersionsItemsSource="{Binding Versions}"
                               SelectedVersionItem="{Binding SelectedVersion}" />
    </Grid>
</UserControl>

鑒于您當前的類設計和控制元件配置，您的VersionsList控制元件將系結到該VersionsListViewModel.SelectedVersion屬性。目前尚不清楚您真正想要什么。要么通過讓偵聽屬性更改來
手動委托值，要么從中洗掉相關屬性并直接系結到。大多數情況下，每個視圖/控制元件一個視圖模型類將導致錯誤的類設計/代碼。創建單獨的類應該基于不同的考慮，比如職責。然后你總是想避免重復代碼（如屬性和邏輯）：而不是復制你將代碼移動到單獨的類。HomeViewModelVersionsListViewModel.SelectedVersionVersionsListViewModelHomeViewModel.SelectedVersion

uj5u.com熱心網友回復：

在VersionList.xaml：

<ListBox SelectedItem="{Binding SelectedVersion}" ...

這只系結ListBox.SelectedItem到{DataContext}.SelectedVersion. Then when a item is selected, the dependency property VersionList.SelectedVersionisn't updated.

解決方案 1：通過視圖模型（無依賴屬性）

我認為您混淆了，因為您嘗試使用復雜的依賴屬性。一種簡單的方法是直接使用沒有依賴屬性的視圖模型。

在VersionsList.cs中，洗掉SelectedVersionProperty和SelectedVersion成員。

保持VersionList.xaml：

<UserControl x:Class="PcVueLauncher.Controls.VersionsList" />
...
    <ListBox
        ...
        ItemsSource="{Binding Versions}"
        SelectedItem="{Binding SelectedVersion}">
...
</UserControl>

ListBox.SelectedItem系結到也是如此ListBox.DataContext.SelectedVersion。如果ListBox.DataContext是VersionsListViewModel，則ListBox.SelectedItem系結到VersionsListViewModel.SelectedVersion。

在父控制元件HomeView中，只需要將a傳遞VersionsListViewModel給VersionList.DataContext：

<UserControl x:Class="PcVueLauncher.Views.HomeView"
...
    <Controls:VersionsList DataContext="{Binding VersionsListViewModel}" />
...
</UserControl>

HomeView.VersionsList.ListBox.SelectedItem系結也是如此HomeView.DataContext.VersionsListViewModel.SelectedVersion。如果HomeView.DataContext是HomeViewModel，那么HomeView.VersionsList.ListBox.SelectedItem就是系結HomeViewModel.VersionsListViewModel.SelectedVersion。

最后，您可以洗掉該成員HomeViewModel.SelectedVersion并使用HomeViewModel.VersionsListViewModel.SelectedVersion.

如果你想保留成員HomeViewModel.SelectedVersion，那么你需要重定向HomeViewModel.SelectedVersion到HomeViewModel.VersionsListViewModel.SelectedVersionin HomeViewModel.cs：

public class HomeViewModel : ViewModelBase
{
    private VersionsListViewModel versionsListViewModel;
    public VersionsListViewModel VersionsListViewModel
    {
        get
        {
            return versionsListViewModel;
        }
        set
        {
            if(versionsListViewModel != null)
                versionsListViewModel.PropertyChanged -= VersionsListViewModel_PropertyChanged;
            versionsListViewModel = value;
            if(versionsListViewModel != null)
                versionsListViewModel.PropertyChanged  = VersionsListViewModel_PropertyChanged;
            OnPropertyChanged(nameof(VersionsListViewModel));
        }
    }

    public VersionPcVue SelectedVersion
    {
        get
        {
            return versionsListViewModel.SelectedVersion;
        }   
        set
        {
            versionsListViewModel.SelectedVersion = value;
            OnPropertyChanged(nameof(SelectedVersion));
        }
    }

    void VersionsListViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        //Propagate the property changed SelectedVersion
        if(string.IsNullOrEmpty(e.PropertyName) || e.PropertyName == nameof(VersionsListViewModel.SelectedVersion))
            OnPropertyChanged(nameof(SelectedVersion));
    }
}

訣竅是什么時候HomeViewModel.VersionsListViewModel.SelectedVersion改變了，也通知HomeViewModel.SelectedVersion改變了。

解決方案 2：通過依賴屬性

總而言之，您希望在選擇一個專案時將所選專案設定為VersionsList.SelectedVersion，然后您只需要系結ListBox.SelectedItem到VersionsList.SelectedVersion.

SelectedVersion首先，添加依賴屬性VersionList.cs：

public partial class VersionsList : UserControl
{
    public VersionsList()
    {
        InitializeComponent();
    }

    public VersionPcVue SelectedVersion
    {
        get { return (VersionPcVue)GetValue(SelectedVersionProperty); }
        set { SetValue(SelectedVersionProperty, value); }
    }

    public static readonly DependencyProperty SelectedVersionProperty =
        DependencyProperty.Register(
            "SelectedVersion",
            typeof(VersionPcVue),
            typeof(VersionsList),
            new FrameworkPropertyMetadata(
                defaultValue: null,
                flags: FrameworkPropertyMetadataOptions.AffectsMeasure
            )
        );

    public List<VersionPcVue> Versions
    {
        get { return (List<VersionPcVue>)GetValue(VersionsProperty); }
        set { SetValue(VersionsProperty, value); }
    }
 
    public static readonly DependencyProperty VersionsProperty =
        DependencyProperty.Register(
            "Versions",
            typeof(List<VersionPcVue>),
            typeof(VersionsList),
            new FrameworkPropertyMetadata(
                defaultValue: null,
                flags: FrameworkPropertyMetadataOptions.AffectsMeasure
            )
        );
}

在VersionList.xaml：

<UserControl x:Class="PcVueLauncher.Controls.VersionsList" />
...
    <ListBox
        ...
        ItemsSource="{Binding Versions}, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"
        SelectedItem="{Binding SelectedVersion, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}">
...
</UserControl>

{RelativeSource TemplatedParent}指示系結參考模板所指向的元素，此處為VersionsList。

要使用控制元件：

<UserControl x:Class="PcVueLauncher.Views.HomeView"
...
    <Controls:VersionsList
        Versions="{Binding VersionsListViewModel.Versions}" 
        SelectedVersion="{Binding SelectedVersion}"/>
...
</UserControl>

版本也發生了變化，以協調系結策略。

最后，您可以洗掉該成員VersionsListViewModel.SelectedVersion（或使用下面的技巧）。

選擇什么？

使用依賴屬性，控制元件不會鏈接到視圖模型類。我將使用它來開發一個庫以在許多應用程式中重用。

使用視圖模型，控制元件需要資料背景關系中的特定成員。我將在應用程式解決方案中使用它。

轉載請註明出處，本文鏈接：https://www.uj5u.com/qianduan/537149.html

標籤：C＃wpf

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修復

1 & 2 & 3b

3a

4個

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