Question

我正在使用MVVM模式构建应用程序。点击其中一个元素后，我想看到这个元素的详细信息。我写了这个：

XAML

<phone:LongListSelector ItemsSource="{Binding Data}" 
                        Margin="0,0,0,158"
                        SelectedItem="{Binding SelectedItem}">
    <phone:LongListSelector.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <Button>
                <!-- Command="{Binding ShowDetailsAction}"-->
                    <Button.Template>
                        <ControlTemplate>
                            <TextBlock Text="{Binding Text}"></TextBlock>
                        </ControlTemplate>
                    </Button.Template>
                </Button>
            </StackPanel>
        </DataTemplate>
    </phone:LongListSelector.ItemTemplate>
</phone:LongListSelector>

视图模型：

public IEnumerable SelectedItem
{
    get { return _itemsControl; }
    set
    {
        if (_itemsControl == value)
            return;
        _itemsControl = value;

        // Test
        _mss.ErrorNotification("fd");
    }
}

我也试过使用一个也不起作用的命令。

这是命令部分：

public ICommand ShowDetailsCommand { get; private set; }

public ViewModel()
{
    _loadDataCommand = new DelegateCommand(LoadDataAction);
    SaveChangesCommand = new DelegateCommand(SaveChangesAction);
    ShowDetailsCommand = new DelegateCommand(ShowDetailsAction);
}

private void ShowDetailsAction(object p)
{
    _mss.ErrorNotification("bla bla");
}

修改

视图模型

private IEnumerable _itemsControl;
public IEnumerable Data
{
  get
  {
    return _itemsControl;
  }
  set
  {
    _itemsControl = value;
    RaisePropertyChanged("Data");
  }
}

protected void RaisePropertyChanged(string propertyName)
{
  PropertyChangedEventHandler handler = PropertyChanged;
  if (handler != null)
    {
      handler(this, new PropertyChangedEventArgs(propertyName));
    }
}

模型

public string Text { get; set; }
public DateTimeOffset Data { get; set; }

EDIT2

private MobileServiceCollection<ModelAzure, ModelAzure> _items;
        private readonly IMobileServiceTable<ModelAzure> _todoTable = App.MobileService.GetTable<ModelAzure>();


private async void RefreshTodoItems()
{
   try
    {
        _items = await _todoTable.ToCollectionAsync();
    }
   catch (MobileServiceInvalidOperationException e)
     {
          _mss.ErrorNotification(e.ToString());
     }
   Data = _items;
}

Answer 1

在ViewModel中，您有：

public IEnumerable SelectedItem
{
get { return _itemsControl; }
set
{
    if (_itemsControl == value)
        return;
    _itemsControl = value;

    // Test
    _mss.ErrorNotification("fd");
}

}

为什么您的SelectItem是IEnumerable？它不应该是“模型”类型吗？您的列表绑定到“Data”，它应该是ObservableList，而不是IEnumerable。它将提供自己的更改通知，因此您不需要。

列表将在选中时设置SelectedItem，但如果类型错误，则不会设置。

格雷格

Answer 2

您的Data属性看起来像

private MobileServiceCollection<ModelAzure, ModelAzure> _itemsControl;
public MobileServiceCollection<ModelAzure, ModelAzure> Data
{
  get
  {
    return _itemsControl;
  }
  set
  {
    _itemsControl = value;
    RaisePropertyChanged("Data");
  }
}

<强>被修改

似乎SelectedItem property from LongListSelector cannot be bound in WP8。你能做的是：

使用上面链接中提供的派生和固定自定义LongListSelector而不是默认值，如下所示：

public class LongListSelector : Microsoft.Phone.Controls.LongListSelector
{
    public LongListSelector()
    {
        SelectionChanged += LongListSelector_SelectionChanged;
    }

    void LongListSelector_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        SelectedItem = base.SelectedItem;
    }

    public static readonly DependencyProperty SelectedItemProperty =
        DependencyProperty.Register(
            "SelectedItem",
            typeof(object),
            typeof(LongListSelector),
            new PropertyMetadata(null, OnSelectedItemChanged)
        );

    private static void OnSelectedItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var selector = (LongListSelector)d;
        selector.SelectedItem = e.NewValue;
    }

    public new object SelectedItem
    {
        get { return GetValue(SelectedItemProperty); }
        set { SetValue(SelectedItemProperty, value); }
    }
}

从LongListSelector注册SelectionChanged事件，并在关联的处理程序/回调中自行调用ViewModel：

在您看来

：

<phone:LongListSelector x:Name="YourLongListSelectorName"
                        ItemsSource="{Binding Data}" 
                        Margin="0,0,0,158"
                        SelectionChanged="OnSelectedItemChanged">

在您的代码中：

private void OnSelectedItemChanged(object sender, SelectionChangedEventArgs selectionChangedEventArgs e)
{
    ((YourViewModel)this.DataContext).NewSelectedItemMethodOrWhateverYouWant((ModelAzure)this.YourLongListSelectorName.SelectedItem);
    //or
    ((YourViewModel)this.DataContext).SelectedItem = (ModelAzure)this.YourLongListSelectorName.SelectedItem;
}

最后，您的Button命令无法正常工作，因为当您使用DataTemplate时，Ambiant DataContext就是项目本身。这意味着它正在查找您的Command个Model个实例，而不是ViewModel个实例。

希望这有帮助

如何使用MVVM模式在LongListSelector中选择一个项目？

2 个答案: