Question

我是C＃和MVVM的新手，我花了一整天的时间试图在ComboBox上为我的ViewModel获取SelectionChanged的价值。我已经设法使用CallMethodAction或InvokeCommandAction使用资源：

来计算出来

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

我的问题是这两种方法在更改之前都会返回ComboBox的值。任何人都可以解释如何在更改后获得的值吗？

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。任何建议将不胜感激！

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: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); } } }

修改：我的解决方案

事实证明我并不理解Binding，而是试图以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。例如，我将TextBox绑定到SelectedIndex的{{1}}，ComboBox使用INotifyPropertyChanged进行更新。

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="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 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

为什么不采用更简单的方式

<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目的属性

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

在设置_source

时也不要忘记实现INotifyPropertyChanged接口

Answer 2

如果您只想在当前项目发生变化时收到通知，为什么不使用已经属于WPF的工具而不是所有这些依赖项。

首先获取您的集合的基础视图，并在其上使用CurrentChanged事件。

ComboBoxList = new ObservableCollection<string>();
var view = CollectionViewSource.GetDefaultView(ComboBoxList);
view.MoveCurrentTo(ComboBoxList[0]);
view.CurrentChanged += new EventHandler(ComboBoxCurrentChanged);

在你的xaml中，你只需绑定你的集合并将IsSynchronizedWithCurrentItem设置为true。

<ComboBox IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding ComboBoxList}"/>

WPF - MVVM：SelectionChanged之后的ComboBox值

2 个答案: