WPF - MVVM:SelectionChanged之后的ComboBox值

Question

我是C#和MVVM的新手,我花了一整天的时间来尝试获取ComboBox我的ViewModel 的值SelectionChanged.我已设法使用其中一个CallMethodAction或InvokeCommandAction与资源一起计算出来:

• System.Windows.Interactivity.dll
• Microsoft.Expression.Interactions.dll

我的问题是这两个方法都返回ComboBox它更改之前的值.任何人都可以解释如何在变更后获得价值吗？

我花了几个小时搜索SO和Google的解决方案,所以我想知道其他人是否也是如此.任何建议将被认真考虑!

我的代码如下:

MainWindow.xaml

<Window x:Class="SelectionChange.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        xmlns:si="clr-namespace:Microsoft.Expression.Interactivity.Core;assembly=Microsoft.Expression.Interactions"
        xmlns:vm="clr-namespace:SelectionChange"
        Title="MainWindow" Width="300" Height="300">
    <Window.DataContext>
        <vm:ViewModel />
    </Window.DataContext>
    <Grid>
        <ComboBox Name="SelectBox" VerticalAlignment="Top" SelectedIndex="0">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="SelectionChanged">
                    <si:CallMethodAction MethodName="SelectionChanged" TargetObject="{Binding}" />
                    <!--<i:InvokeCommandAction Command="{Binding SelectionChangedCommand}" CommandParameter="{Binding ElementName=SelectBox, Path=Text}" />-->
                </i:EventTrigger>
            </i:Interaction.Triggers>
            <ComboBoxItem Content="Item 1" />
            <ComboBoxItem Content="Item 2" />
            <ComboBoxItem Content="Item 3" />
        </ComboBox>
    </Grid>
</Window>

ViewModel.cs

namespace SelectionChange
{
    using System;
    using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Input;

    public class ViewModel
    {
        public ViewModel()
        {
            SelectionChangedCommand = new SelectionChangedCommand();
        }

        public ICommand SelectionChangedCommand
        {
            get;
            set;
        }

        public void SelectionChanged(object sender, EventArgs e)
        {
            ComboBox SelectBox = (ComboBox)sender;
            MessageBox.Show("Called SelectionChanged: " + SelectBox.Text);
        }
    }
}

SelectionChangedCommand.cs

namespace SelectionChange
{
    using System;
    using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Input;

    public class SelectionChangedCommand : ICommand
    {
        public SelectionChangedCommand()
        {
        }

        public event EventHandler CanExecuteChanged;

        public bool CanExecute(object parameter)
        {
            return true;
        }

        public void Execute(object parameter)
        {
            MessageBox.Show("Executed SelectionChangedCommand: " + parameter);
        }
    }
}

编辑:我的解决方案

事实证明,我不太了解Binding,而是试图以一种相当复杂的方式实现简单的事情!我没有使用依赖项,而是使用常规绑定实现了我所需要的功能.举个例子,我已经绑定一个TextBox到SelectedIndex的ComboBox,它获取更新使用INotifyPropertyChanged.

MainWindow.xaml

<Window x:Class="SelectionChange.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:SelectionChange"
        Title="MainWindow" Width="300" Height="300">
    <Window.DataContext>
        <vm:ViewModel />
    </Window.DataContext>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>

        <ComboBox SelectedItem="{Binding SelectedItem}" SelectedIndex="0" Grid.Column="0" VerticalAlignment="Top">
            <ComboBoxItem Content="Item 1" />
            <ComboBoxItem Content="Item 2" />
            <ComboBoxItem Content="Item 3" />
        </ComboBox>

        <!-- TextBox to display the ComboBox's SelectedIndex -->
        <TextBox Text="{Binding SelectedIndex}" Grid.Column="1" VerticalAlignment="Top" />
    </Grid>
</Window>

ViewModel.cs

namespace SelectionChange
{
    using System;
    using System.ComponentModel;
    using System.Windows.Controls;

    public class ViewModel : INotifyPropertyChanged
    {
        public ViewModel()
        {   
        }

        // Property to store / retrieve ComboBox's SelectedIndex
        private int _SelectedIndex;
        public int SelectedIndex { get; set; }

        // Property to bind to ComboBox's SelectedItem
        private ComboBoxItem _SelectedItem;
        public ComboBoxItem SelectedItem
        {
            get { return _SelectedItem; }
            set
            {
                _SelectedItem = value;

                // SelectedItem's Content
                string Content = (string)value.Content;

                // SelectedItem's parent (i.e. the ComboBox)
                ComboBox SelectBox = (ComboBox)value.Parent;

                // ComboBox's SelectedIndex
                int Index = SelectBox.SelectedIndex;

                // Store the SelectedIndex in the property
                SelectedIndex = Index;

                // Raise PropertyChanged with the name of the stored property
                RaisePropertyChanged("SelectedIndex");
            }
        }

        // INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged;
        private void RaisePropertyChanged(string PropertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
        }
    }
}

Answer 1

为什么不以更简单的方式做到这一点

<ComboBox MaxHeight="25" 
          ItemsSource="{Binding Source}" 
          SelectedItem="{Binding TheSelectedItem, Mode=TwoWay}" />

在ViewModel中声明组合框项目并使用属性"Source"将其返回到视图

List<string> _source = new List<string>{"Item 1", "Item 2", "Item 3"};
public List<string> Source 
{ 
    get { return _source; } 
}

然后定义一个包含所选项的属性

string _theSelectedItem = null;
public string TheSelectedItem 
{ 
    get { return _theSelectedItem; } 
    set { _theSelectedItem = value; } // NotifyPropertyChanged
}

另外,在设置_source时不要忘记实现INotifyPropertyChanged接口