wpf – 通过MVVM绑定UserControl依赖属性

我有一个包含UserControl的MainWindow,它们都是用MVVM模式实现的.
MainWindowVM具有我想要绑定到UserControl1VM中的属性的属性.但这不起作用.

这里是一些代码(viewmodels使用某种mvvm框架,在ViewModelBase类中实现INotifyPropertyChanged,但希望没问题)：

MainWindow.xaml：

<Window x:Class="DPandMVVM.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:DPandMVVM"
    Title="MainWindow" Height="300" Width="300">
    <Grid>
        <local:UserControl1 TextInControl="{Binding Text}" />
    </Grid>
</Window>

CodeBehind MainWindow.xaml.cs：

using System.Windows;
namespace DPandMVVM
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = new MainWindowVM();
        }
    }
}

MainWindow-ViewModel MainWindowVM.cs：

namespace DPandMVVM
{
    public class MainWindowVM : ViewModelBase
    {
        private string _text;
        public string Text { get { return _text; } }

        public MainWindowVM()
        {
            _text = "Text from MainWindowVM";
        }
    }
}

在这里UserControl1.xaml：

<UserControl x:Class="DPandMVVM.UserControl1"
             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" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <TextBlock Text="{Binding TextInTextBlock}" />  
    </Grid>
</UserControl>

Codebehind UserControl1.xaml.cs：

using System.Windows.Controls;    
namespace DPandMVVM
{
    /// <summary>
    /// Interaction logic for UserControl1.xaml
    /// </summary>
    public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
            DataContext = new UserControl1VM();
        }
    }
}

和Viewmodel UserControl1VM.cs：

using System.Windows;    
namespace DPandMVVM
{
    public class UserControl1VM : DependencyObject
    {
        public UserControl1VM()
        {
            TextInControl = "TextfromUserControl1VM";
        }

        public string TextInControl
        {
            get { return (string)GetValue(TextInControlProperty); }
            set { SetValue(TextInControlProperty, value); }
        }

        public static readonly DependencyProperty TextInControlProperty =
            DependencyProperty.Register("TextInControl", typeof(string), typeof(UserControl1VM));
    }
}

使用此星座,无法在MainWindow.xaml中找到DP. 我究竟做错了什么？

 

首先,如果要从外部绑定它,则需要在UserControl1中声明DependencyProperty TextInControl.

在UserControl1中移动DP的声明.

public partial class UserControl1 : UserControl
{
    public UserControl1()
    {
        InitializeComponent();
    }

    public string TextInControl
    {
        get { return (string)GetValue(TextInControlProperty); }
        set { SetValue(TextInControlProperty, value); }
    }

    public static readonly DependencyProperty TextInControlProperty =
        DependencyProperty.Register("TextInControl", typeof(string), 
                                       typeof(UserControl1));
}

其次,你将UserControl的DataContext外部设置为UserControl1VM,

public UserControl1()
    {
        InitializeComponent();
        DataContext = new UserControl1VM(); <-- HERE (Remove this)
    }

所以WPF绑定引擎在UserControl1VM中寻找属性Text而不是MainWindowVM.删除设置DataContext并将UserControl1的XAML更新为：

<UserControl x:Class="DPandMVVM.UserControl1"
             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" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300"
             x:Name="userControl1">
    <Grid>
        <TextBlock Text="{Binding TextInTextBlock, ElementName=userControl1}" />  
    </Grid>
</UserControl>

通过在UserControl上设置x：Name,使用ElementName绑定DP.

UPDATE

如果您希望UserControl的ViewModel完好无损,则必须更新MainWindow中的绑定.

显式告诉WPF绑定引擎在MainWindow的DataContext中使用ElementName查找属性,如下所示：

<local:UserControl1 TextInControl="{Binding DataContext.Text,
                    ElementName=mainWindow}" />

为此,您需要在窗口根级别设置x：Name =“mainWindow”.

出处：http://www.voidcn.com/article/p-udpyjbsd-bue.html

注意： 在使用MVVM框架的时候，如果在vm里获取UserControl的绑定数据，需要使用双向绑定"{Binding PageIndex,Mode=TwoWay}"

======================================================================

另外在提供一个在界面上使用ContentControl控件来绑定UserControl对象的方法。

界面元素：

    <Window.DataContext>
        <localVM:BarViewModel />
    </Window.DataContext>

    <Grid>
        <StackPanel Height="30" Margin="0,300,2,105">
            <ContentControl Content="{Binding StatusBar}"></ContentControl>
        </StackPanel>
    </Grid>

对应的BarViewModel类：

    public class BarViewMod : INotifyPropertyChanged
    {
        public BarViewMod()
        {
            StatusBar = new View.UserCtrl.StatusBarView();
        }

        public object StatusBar { get; set; }

        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName]string propertyName = "")
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }

StatusBarView对于界面元素

<UserControl x:Class="WpfApp1.View.UserCtrl.StatusBarView"
             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:WpfApp1.View.UserCtrl"
             xmlns:uc="clr-namespace:WpfApp1.VM"
             mc:Ignorable="d" 
             d:DesignHeight="25" d:DesignWidth="800">
    <UserControl.DataContext>
        <uc:StatusBarViewModel></uc:StatusBarViewModel>
    </UserControl.DataContext>
    <Grid>

        <StatusBar x:Name="MyStatusBar">
            <StatusBar.ItemsPanel>
                <ItemsPanelTemplate>
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="100" />
                            <ColumnDefinition Width="Auto" />
                            <ColumnDefinition Width="*" />
                            <ColumnDefinition Width="Auto" />
                            <ColumnDefinition Width="100" />
                        </Grid.ColumnDefinitions>
                    </Grid>
                </ItemsPanelTemplate>
            </StatusBar.ItemsPanel>
            <StatusBarItem>
                <TextBlock Name="lbMsg" Text="{Binding TestMsg}" />
            </StatusBarItem>
            <Separator Grid.Column="1" />
            <StatusBarItem Grid.Column="2">
                <TextBlock Text="http://www.baidu.com/file.txt" />
            </StatusBarItem>
            <Separator Grid.Column="3" />
            <StatusBarItem Grid.Column="4">
                <ProgressBar Value="0" Width="90" Height="16" />
            </StatusBarItem>
        </StatusBar>

    </Grid>
</UserControl>

StatusBarView对应的ViewModel类：

namespace WpfApp1.VM
{
    using System.ComponentModel;
    using System.Runtime.CompilerServices;
    using System.Windows;

    public class StatusBarViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged([CallerMemberName]string propertyName = "")
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        public string TestMsg { get; set; } = "test....";

    }
}

 如果是使用了其他框架的，可以依照框架修改，如下面是使用了IOC框架的，则在主界面的VM中构造函数中创建UserControl对象：

StatusBar = _serviceProvider.GetRequiredService<UserCtrl.StatusBarViewModel>();