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我是C＃和MVVM的新手，我花了一整天的時間嘗試將我的ViewModel的ComboBox的值設置爲SelectionChanged。我已成功使用或者CallMethodAction或InvokeCommandAction與資源弄明白：WPF - MVVM：SelectionChanged後的ComboBox值
System.Windows.Interactivity.dllMicrosoft.Expression.Interactions.dll
我的問題是，這兩種方法返回ComboBox前值已改變。任何人都可以解釋如何獲得值後的變化？
我花了數小時搜索SO和Google尋求解決方案，所以我想知道其他人是否也是如此。任何建議將被認真考慮！
我的代碼如下：
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);
}
}
}
編輯：我的解決方案
原來我不明白Binding不夠好，而是試圖實現東西在一個相當複雜的方式簡單！現在我已經使用常規綁定實現了我所需的功能，而不是使用依賴關係。作爲示例，我已將TextBox綁定到ComboBox的SelectedIndex，其使用INotifyPropertyChanged進行更新。
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 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));
}
}
}
如果我明白你想要做什麼，我認爲這將有助於http://stackoverflow.com/questions/4765362/mvvm-combobox -binding – kenny
我只想給你一個想法。那麼如何將SelectedItems屬性綁定到ViewModel中的綁定模式TwoWay？無需收聽SelectionChanged事件或創建命令。每當SelectedItems值發生變化時，您將在ViewModel中的屬性設置器中收到通知。試試看。 –