WPF - MVVM：SelectionChanged后的ComboBox值 [英] WPF - MVVM: ComboBox value after SelectionChanged

问题描述

我是新的C＃和MVVM，我花了一整天试图获得 ComboBox 的价值到我的ViewModel在 SelectionChanged 。我已经设法使用 CallMethodAction 或 InvokeCommandAction 与资源：

• System.Windows.Interactivity.dll


• Microsoft.Expression.Interactions.dll

我的问题是这两个方法都返回 ComboBox 。

我花了几个小时搜索SO和Google的解决方案，所以我想知道如果别人也是。

我的代码如下：

MainWindow.xaml

 < Window x：Class =SelectionChange.MainWindow
 xmlns =http： 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 =MainWindowWidth =300Height =300> 
< Window.DataContext> 
< vm：ViewModel /> 
< /Window.DataContext> 
< Grid> 
< ComboBox Name =SelectBoxVerticalAlignment =TopSelectedIndex =0> 
< i：Interaction.Triggers> 
< i：EventTrigger EventName =SelectionChanged> 
< si：CallMethodAction MethodName =SelectionChangedTargetObject ={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

 命名空间SelectionChange 
 {
 using System; 
使用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

 命名空间SelectionChange 
 {
 using System; 
使用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）; 
} 
} 
} 
  

修改：我的解决方案

原来我不明白绑定足够好，而是试图以一种相当复杂的方式实现一个简单的东西！而不是使用依赖，我现在已经实现了我需要使用常规绑定。例如，我已经将 TextBox 绑定到 ComboBox 的 SelectedIndex code>，使用 INotifyPropertyChanged 更新。

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 =MainWindowWidth =300Height =300> 
< Window.DataContext> 
< vm：ViewModel /> 
< /Window.DataContext> 
< Grid> 
< Grid.ColumnDefinitions> 
< ColumnDefinition Width =Auto/> 
< ColumnDefinition Width =*/> 
< /Grid.ColumnDefinitions> 
 
< ComboBox SelectedItem ={Binding SelectedItem}SelectedIndex =0Grid.Column =0VerticalAlignment =Top> 
< ComboBoxItem Content =Item 1/> 
< ComboBoxItem Content =Item 2/> 
< ComboBoxItem Content =Item 3/> 
< / ComboBox> 
 
<！ -  TextBox显示ComboBox的SelectedIndex  - > 
< TextBox Text ={Binding selectedIndex}Grid.Column =1VerticalAlignment =Top/> 
< / Grid> 
< / Window> 
  

ViewModel.cs

 命名空间SelectionChange 
 {
 using System; 
 using System.ComponentModel; 
 using System.Windows.Controls; 
 
 public class ViewModel：INotifyPropertyChanged 
 {
 public ViewModel（）
 {
} 
 
 //存储/检索ComboBox的SelectedIndex 
 private int _SelectedIndex; 
 public int SelectedIndex {get;组; } 
 
 //绑定到ComboBox的SelectedItem的属性
 private ComboBoxItem _SelectedItem; 
 public ComboBoxItem SelectedItem 
 {
 get {return _SelectedItem; } 
 set 
 {
 _SelectedItem = value; 
 
 // SelectedItem的内容
 string Content =（string）value.Content; 
 
 // SelectedItem的父级（即ComboBox）
 ComboBox SelectBox =（ComboBox）value.Parent; 
 
 // ComboBox的SelectedIndex 
 int Index = SelectBox.SelectedIndex; 
 
 //在属性
中存储SelectedIndex SelectedIndex = Index; 
 
 //使用存储属性的名称提高PropertyChanged 
 RaisePropertyChanged（SelectedIndex）; 
} 
} 
 
 // INotifyPropertyChanged 
 public event PropertyChangedEventHandler PropertyChanged; 
 private void RaisePropertyChanged（string PropertyName）
 {
 if（PropertyChanged！= null）
 PropertyChanged（this，new PropertyChangedEventArgs（PropertyName））; 
} 
} 
} 
  

解决方案>

为什么不用更简单的方法

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

在您的ViewModel中声明组合框项目并使用属性Source将其返回视图

 列表< string& _source = new List< string> {Item 1，Item 2，Item 3}; 
 public List< string>源
 {
 get {return _source; } 
} 
  

然后定义一个保存所选项目的属性

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

同时不要忘记实现INotifyPropertyChanged接口_source

I am new to C# and MVVM, and I've spent all day trying to get the value of a ComboBox to my ViewModel on SelectionChanged. I have managed to figure it out using either CallMethodAction or InvokeCommandAction with the resources:

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

My problem is that both these methods return the value of the ComboBox before it has changed. Could anyone explain how to get the value after the change?

I have spent hours searching through SO and Google for a solution, so I wonder if others are too. Any advice will be appreciated!

My code is below:

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);
        }
    }
}

Edit: My Solution

It turns out I didn't understand Binding well enough and instead was trying to implement something simple in a rather complicated way! Instead of using dependencies, I have now achieved what I needed using regular bindings. As an example, I've bound a TextBox to the SelectedIndex of the ComboBox, which gets updated using 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));
        }
    }
}

解决方案

Why not do it the simpler way

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

In your ViewModel declare the combo box items and use a property "Source" to return it to the view

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

Then define one property which holds the selected item

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

Also don't forget to implement the INotifyPropertyChanged interface while setting the _source

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