WPF 上下文菜单未绑定到正确的数据绑定项 [英] WPF Context menu doesn't bind to right databound item

问题描述

在标签页上的用户控件的上下文菜单中绑定命令时遇到问题.我第一次使用菜单(右键单击选项卡)时效果很好，但如果我切换选项卡，命令将使用第一次使用的数据绑定实例.

I have a problem when binding a command in a context menu on a usercontrol that is on a tab page. The first time I use the menu (right-click on the tab) it works great, but if I switch tab the command will use the databound instance that was used the first time.

如果我在用户控件中放置一个绑定到命令的按钮，它会按预期工作...

If I put a button that is bound to the command in the usercontrol it works as expected...

谁能告诉我我做错了什么??

Can someone please tell me what I'm doing wrong??

这是一个暴露问题的测试项目:

This is a test project that exposes the problem:

App.xaml.cs:

App.xaml.cs:

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        CompanyViewModel model = new CompanyViewModel();
        Window1 window = new Window1();
        window.DataContext = model;
        window.Show();
    }
}

Window1.xaml:

Window1.xaml:

<Window x:Class="WpfApplication1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:vw="clr-namespace:WpfApplication1"
Title="Window1" Height="300" Width="300">

  <Window.Resources>
    <DataTemplate x:Key="HeaderTemplate">
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="{Binding Path=Name}" />
        </StackPanel>
    </DataTemplate>
    <DataTemplate DataType="{x:Type vw:PersonViewModel}">
        <vw:UserControl1/>
    </DataTemplate>

</Window.Resources>
<Grid>
    <TabControl ItemsSource="{Binding Path=Persons}" 
                ItemTemplate="{StaticResource HeaderTemplate}"
                IsSynchronizedWithCurrentItem="True" />
</Grid>
</Window>

UserControl1.xaml:

UserControl1.xaml:

<UserControl x:Class="WpfApplication1.UserControl1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    MinWidth="200">
    <UserControl.ContextMenu>
        <ContextMenu >
            <MenuItem Header="Change" Command="{Binding Path=ChangeCommand}"/>
        </ContextMenu>
    </UserControl.ContextMenu>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="100" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <Label Grid.Column="0">The name:</Label>
        <TextBox Grid.Column="1" Text="{Binding Path=Name, UpdateSourceTrigger=PropertyChanged}" />
    </Grid>
</UserControl>

公司视图模型.cs:

public class CompanyViewModel
{
    public ObservableCollection<PersonViewModel> Persons { get; set; }
    public CompanyViewModel()
    {
        Persons = new ObservableCollection<PersonViewModel>();
        Persons.Add(new PersonViewModel(new Person { Name = "Kalle" }));
        Persons.Add(new PersonViewModel(new Person { Name = "Nisse" }));
        Persons.Add(new PersonViewModel(new Person { Name = "Jocke" }));
    }
}

PersonViewModel.cs:

PersonViewModel.cs:

public class PersonViewModel : INotifyPropertyChanged
{
    Person _person;
    TestCommand _testCommand;

    public PersonViewModel(Person person)
    {
        _person = person;
        _testCommand = new TestCommand(this);
    }
    public ICommand ChangeCommand 
    {
        get
        {
            return _testCommand;
        }
    }
    public string Name 
    {
        get
        {
            return _person.Name;
        }
        set
        {
            if (value == _person.Name)
                return;
            _person.Name = value;
            OnPropertyChanged("Name");
        }
    }
    void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
        {
            var e = new PropertyChangedEventArgs(propertyName);
            handler(this, e);
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
}

TestCommand.cs:

TestCommand.cs:

public class TestCommand : ICommand
{
    PersonViewModel _person;
    public event EventHandler CanExecuteChanged;

    public TestCommand(PersonViewModel person)
    {
        _person = person;
    }
    public bool CanExecute(object parameter)
    {
        return true;
    }
    public void Execute(object parameter)
    {
        _person.Name = "Changed by command";
    }
}

Person.cs:

public class Person
{
    public string Name { get; set; }
}

推荐答案

这里要记住的关键是上下文菜单不是可视化树的一部分.

因此，它们不会继承与它们所属的用于绑定的控件相同的源.处理这个的方法是绑定到ContextMenu本身的放置目标.

Therefore they don't inherit the same source as the control they belong to for binding. The way to deal with this is to bind to the placement target of the ContextMenu itself.

<MenuItem Header="Change" Command="{Binding 
    Path=PlacementTarget.ChangeCommand, 
    RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContextMenu}}}"
/>

这篇关于WPF 上下文菜单未绑定到正确的数据绑定项的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！