[英]How to select an item in LongListSelector using the MVVM-pattern?
我正在使用MVVM模式构建应用程序。 单击其中一个元素后,我想查看该元素的详细信息。 我这样写:
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>
ViewModel:
public IEnumerable SelectedItem
{
get { return _itemsControl; }
set
{
if (_itemsControl == value)
return;
_itemsControl = value;
// Test
_mss.ErrorNotification("fd");
}
}
我也尝试使用一个命令,但该命令也不起作用。
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");
}
编辑
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; }
编辑2
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;
}
在ViewModel中,您具有:
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”类型的吗? 您的列表绑定到“数据”,该数据应该是ObservableList,而不是IEnumerable。 它将提供自己的更改通知,因此您不需要。
列表将在被选择时设置SelectedItem,但如果类型错误,则不会设置。
格雷格
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");
}
}
已编辑
看来LongListSelector的SelectedItem属性不能在WP8中绑定 。 您可以执行以下任一操作:
使用上面链接中提供的派生和固定的自定义LongListSelector,而不是默认的自定义LongListSelector,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中注册SelectionChanged事件,并在关联的处理程序/回调内部自己调用ViewModel:
在您看来:
<phone:LongListSelector x:Name="YourLongListSelectorName"
ItemsSource="{Binding Data}"
Margin="0,0,0,158"
SelectionChanged="OnSelectedItemChanged">
在您后面的代码中:
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;
}
最终,您的Button
命令无法正常工作,因为当您使用DataTemplate
,周围的DataContext就是项本身。 这意味着它是在Model
实例而不是ViewModel
实例中寻找Command
。
希望这可以帮助
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