c# - 如何调试未触发的 INPC 属性 setter ？

Question

概述:我已经使用 INPC 设置了一个属性，它在 MainViewModel 后面的 View 代码中调用页面导航。此属性绑定(bind)到绑定(bind) View 中 ListView 的 SelectedItem 属性。

INPC 实现继承自 ViewModelBase 类，实现如下，https://gist.github.com/BrianJVarley/4a0890b678e037296aba

问题:

当我从 ListView 中选择一个项目时，属性 SelectedCouncilItem setter 不会触发。此属性绑定(bind)到 ListView 的 SelectedItem 属性。

调试步骤:

• 检查 ListView 属性中 SelectedItem 的绑定(bind)名称，该名称与 MainViewModel 中的属性名称相同。
• 运行解决方案并检查输出窗口中是否存在任何绑定(bind)错误，没有发现任何错误。
• 在 SelectedCouncilItem 上放置了一个断点，当我从 ListView 中选择时它不会被触发。
• 检查了 View 的数据上下文设置，确认 View 已设置为 MainViewModel 的数据上下文。

问题:

有谁知道我可以采取哪些其他步骤来调试问题，或者问题可能是什么？

代码:

主页 - ( ListView )

    <Grid x:Name="ContentPanel"
          Grid.Row="1"
          Margin="12,0,12,0">
        <phone:LongListSelector x:Name="MainLongListSelector"
                                Margin="0,0,-12,0"
                                ItemsSource="{Binding Items}"
                                SelectedItem="{Binding SelectedCouncilItem}">
            <phone:LongListSelector.ItemTemplate>
                <DataTemplate>
                    <StackPanel Margin="0,0,0,17">
                        <TextBlock Style="{StaticResource PhoneTextExtraLargeStyle}"
                                   Text="{Binding CouncilAcronym}"
                                   TextWrapping="Wrap" />
                        <TextBlock Margin="12,-6,12,0"
                                   Style="{StaticResource PhoneTextSubtleStyle}"
                                   Text="{Binding CouncilFullName}"
                                   TextWrapping="Wrap" />
                    </StackPanel>
                </DataTemplate>
            </phone:LongListSelector.ItemTemplate>
        </phone:LongListSelector>
    </Grid>

MainViewModel -(摘要)

namespace ParkingTagPicker.ViewModels
{
    public class MainViewModel : ViewModelBase
    {


        //Dependency Injection private instances
        private INavigationCallback _navCallBack = null;

        public MainViewModel()
        {
            this.Items = new ObservableCollection<ItemViewModel>();

        }




        /// <summary>
        /// Creates and adds a few ItemViewModel objects into the Items  collection.
        /// </summary>
        public void LoadCouncilNamesData()
        {
            this.Items.Add(new ItemViewModel() { ID = "6", CouncilAcronym = "WTC", CouncilFullName = "Wicklow Town Council"});
            this.Items.Add(new ItemViewModel() { ID = "7", CouncilAcronym = "TS", CouncilFullName = "Tallaght Stadium" });
            this.Items.Add(new ItemViewModel() { ID = "8", CouncilAcronym = "GS", CouncilFullName = "Greystones" });

            this.IsDataLoaded = true;
        }



        public ObservableCollection<ItemViewModel> Items { get; private set; }

        public bool IsDataLoaded { get; private set; }

        private ItemViewModel _selectedCouncilItem;
        public ItemViewModel SelectedCouncilItem
        {          
            get
            {
                return this._selectedCouncilItem;
            }
            set
            {
                this.SetProperty(ref this._selectedCouncilItem, value, () => this._selectedCouncilItem);

                if (_selectedCouncilItem != null)
                {
                    _navCallBack.NavigateTo(_selectedCouncilItem.ID);
                }
            }
        }


        public INavigationCallback NavigationCallback
        {
            get { return _navCallBack; }
            set { _navCallBack = value; }
        }


    }
}

ViewModelBase -(详细说明 INPC 实现)

namespace ParkingTagPicker.ViewModels
{
    public abstract class ViewModelBase : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected void RaisePropertyChanged(string propertyName)
        {
            var propertyChanged = this.PropertyChanged;

            if (propertyChanged != null)
            {
                propertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        protected bool SetProperty<T>(ref T backingField, T Value, Expression<Func<T>> propertyExpression)
        {
            var changed = !EqualityComparer<T>.Default.Equals(backingField, Value);

            if (changed)
            {
                backingField = Value;
                this.RaisePropertyChanged(ExtractPropertyName(propertyExpression));
            }

            return changed;
        }

        private static string ExtractPropertyName<T>(Expression<Func<T>> propertyExpression)
        {
            var memberExp = propertyExpression.Body as MemberExpression;

            if (memberExp == null)
            {
                throw new ArgumentException("Expression must be a MemberExpression.", "propertyExpression");
            }

            return memberExp.Member.Name;
        }


    }
}

Answer 1

控制有问题。请尝试使用自定义 LongListSeletor

public class ExtendedLongListSelector : Microsoft.Phone.Controls.LongListSelector
{
    public ExtendedLongListSelector()
    {
        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); }
    }
}

并在 XAML 中用现有列表替换它。

   xmlns:controls="clr-namespace:ProjectName.FolderName"

   <controls:ExtendedLongListSelector  x:Name="MainLongListSelector"
                                Margin="0,0,-12,0"
                                ItemsSource="{Binding Items}"
                                SelectedItem="{Binding SelectedCouncilItem}">
   </controls:ExtendedLongListSelector>