将子数据汇总到父级进行绑定

Question

此帖子已完全修改，以提供更加可靠的示例和简化的问题

我希望将子更改的结果反映在Parent中，尤其是字段NumberOfChildrenWithDegrees。如果您同时选中HasUniversityDegree和HasHighSchoolDegree的绑定框，则在子视图更新中选中HasTwoDegrees。我想要的是在父虚拟机中反映HasTwoDegrees的孩子数。

我认为这很简单，但事实证明它不起作用 - 检查两个框在父视图中没有任何变化（<TextBlock Text="{Binding NumberOfChildrenWithDegrees,Mode=TwoWay,UpdateSourceTrigger=Explicit}"/>区域。 怎么能我让这个数字更改实时发生？

我已经为Windows Phone创建了一个小样本，可以直接插入名为 TestPage 的页面。只需将XAML放在内容网格中，然后将代码放在代码隐藏（VB）中。

XAML：

    <Grid x:Name="ContentPanel" Background="{StaticResource PhoneChromeBrush}" Grid.Row="1">
        <ListBox x:Name="parentLB" Margin="12,12,12,12" HorizontalContentAlignment="Stretch">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Vertical" Margin="0,12,0,0">
                        <StackPanel Orientation="Horizontal">
                            <TextBlock Text="Parent Name: "/>
                            <TextBlock Text="{Binding Name}"/>
                        </StackPanel>
                        <StackPanel Orientation="Horizontal">
                            <TextBlock Text="Number of Children with Degrees: "/>
                            <TextBlock Text="{Binding NumberOfChildrenWithDegrees,Mode=TwoWay,UpdateSourceTrigger=Explicit}"/>
                        </StackPanel>
                        <ListBox Margin="12,0,0,0" x:Name="group2" ItemsSource="{Binding Children,Mode=TwoWay}">
                            <ListBox.ItemTemplate>
                                <DataTemplate>
                                    <StackPanel>
                                        <StackPanel Orientation="Horizontal">
                                            <TextBlock Text="Child Name: "/>
                                            <TextBlock Text="{Binding Name}"/>
                                        </StackPanel>
                                            <CheckBox Content="Has High School Degree:" IsChecked="{Binding HasHighSchoolDegree,Mode=TwoWay}"/>
                                            <CheckBox Content="Has University Degree: " IsChecked="{Binding HasUniversityDegree,Mode=TwoWay}"/>
                                            <CheckBox Content="Has Two Degrees? " IsEnabled="False" IsChecked="{Binding HasTwoDegrees}"/>
                                    </StackPanel>
                                </DataTemplate>
                            </ListBox.ItemTemplate>
                        </ListBox>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>

代码隐藏：

Imports System.Collections.ObjectModel
Imports System.ComponentModel

Partial Public Class TestPage
    Inherits PhoneApplicationPage

    Public Sub New()
        InitializeComponent()
        parentLB.ItemsSource = Grandparent1.ParentGroups
    End Sub
    Public Function Grandparent1() As GrandParent
        Dim ParentGroups As New List(Of Parent)
        ParentGroups.Add(Parent1)
        ParentGroups.Add(Parent2)
        Dim gp As New GrandParent
        gp.ParentGroups = ParentGroups
        Return gp
    End Function
    Public Function Parent2() As Parent
        Dim p As New Parent With {.Name = "Tom"}
        Dim c1 As New Child With {.Name = "Tammy"}
        Dim c2 As New Child With {.Name = "Timmy"}
        Dim children As New List(Of Child)
        children.Add(c1)
        children.Add(c2)
        p.Children = children
        Return p
    End Function

    Public Function Parent1() As Parent
        Dim p As New Parent With {.Name = "Carol"}
        Dim c1 As New Child With {.Name = "Carl"}
        c1.HasHighSchoolDegree = True
        c1.HasUniversityDegree = True
        Dim c2 As New Child With {.Name = "Karla"}
        Dim children As New List(Of Child)
        children.Add(c1)
        children.Add(c2)
        p.Children = children
        Return p
    End Function
End Class

Public Class GrandParent
    Inherits BindableBase
    Public Property ParentGroups As List(Of Parent)
End Class
Public Class Parent
    Inherits BindableBase
    Public Property Name As String

    Private _children As List(Of Child)
    Public Property Children As List(Of Child)
        Get
            Return Me._children
        End Get
        Set(value As List(Of Child))
            Me.SetProperty(Me._children, value)
        End Set
    End Property

    Private _numberOfChildrenWithDegrees As Integer
    Public Property NumberOfChildrenWithDegrees As Integer
        Get
            Return Children.Where(Function(f) f.HasTwoDegrees).Count
        End Get
        Set(value As Integer)
            Me.SetProperty(Me._numberOfChildrenWithDegrees, value)
        End Set
    End Property
End Class
Public Class Child
    Inherits BindableBase
    Public Property Name As String

    Public ReadOnly Property HasTwoDegrees As Boolean
        Get
            Return HasHighSchoolDegree AndAlso HasUniversityDegree
        End Get
    End Property

    Private _hasUniversityDegree As Boolean
    Public Property HasUniversityDegree As Boolean
        Get
            Return Me._hasUniversityDegree
        End Get
        Set(value As Boolean)
            Me.SetProperty(Me._hasUniversityDegree, value)
            OnPropertyChanged("HasTwoDegrees")
        End Set
    End Property

    Private _hasHighSchoolDegree As Boolean
    Public Property HasHighSchoolDegree As Boolean
        Get
            Return Me._hasHighSchoolDegree
        End Get
        Set(value As Boolean)
            Me.SetProperty(Me._hasHighSchoolDegree, value)
            OnPropertyChanged("HasTwoDegrees")
        End Set
    End Property
End Class
Public MustInherit Class BindableBase
    Implements INotifyPropertyChanged
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
    Protected Function SetProperty(Of T)(ByRef storage As T, value As T,
                                    Optional propertyName As String = Nothing) As Boolean

        If Object.Equals(storage, value) Then Return False

        storage = value
        Me.OnPropertyChanged(propertyName)
        Return True
    End Function
    Protected Sub OnPropertyChanged(Optional propertyName As String = Nothing)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub

End Class

Answer 1

由于您的子元素是引发PropertyChangeEvent的元素，并且count与父属性绑定，因此您需要在父元素中订阅每个子元素的PropertyChangedEvent。然后，您需要在父元素中引发自己的属性更改事件，并将PropertyName绑定到UI元素。

引发PropertyChangedEvent时执行的操作只是调用传递了OnPropertyChanged()字符串的NumberOfChildrenWithDegrees方法。如果你有一个更复杂的对象，你可能想要执行一个基于事件args中的PropertyName的ChildOnPropertyChanged()方法中的case语句。我在代码中留下了一个注释示例。下面是完整的C＃代码，我不需要更改XAML。请注意，我还更改了列表的创建和添加方式，以便在将每个子项的属性更改事件添加到列表中时对其进行订阅。

using System.Linq;
using Microsoft.Phone.Controls;
using System.Collections.Generic;
using System.ComponentModel;

namespace PhoneApp1
{



public partial class TestPage : PhoneApplicationPage
{

    public TestPage()
    {
        InitializeComponent();
        this.parentLB.ItemsSource = Grandparent1().ParentGroups;
    }
    public GrandParent Grandparent1()
    {
        List<Parent> ParentGroups = new List<Parent>();
        ParentGroups.Add(Parent1());
        ParentGroups.Add(Parent2());
        GrandParent gp = new GrandParent();
        gp.ParentGroups = ParentGroups;
        return gp;
    }
    public Parent Parent2()
    {
        Parent p = new Parent { Name = "Tom" };
        Child c1 = new Child { Name = "Tammy" };
        Child c2 = new Child { Name = "Timmy" };
        p.AddChild(c1);
        p.AddChild(c2);

        return p;
    }

    public Parent Parent1()
    {
        Parent p = new Parent { Name = "Carol" };
        Child c1 = new Child { Name = "Carl" };
        c1.HasHighSchoolDegree = true;
        c1.HasUniversityDegree = true;
        Child c2 = new Child { Name = "Karla" };
        p.AddChild(c1);
        p.AddChild(c2);

        return p;
    }
}

public class GrandParent : BindableBase
{
    public List<Parent> ParentGroups { get; set; }
}
public class Parent : BindableBase
{
    public string Name { get; set; }



    private List<Child> _children;
    public List<Child> Children
    {
        get { return this._children; }
        set { _children = value; }
    }

    public Parent()
    {
        _children = new List<Child>();
    }

    public void AddChild(Child child)
    {
        child.PropertyChanged += ChildOnPropertyChanged;
        _children.Add(child);
    }

    private void ChildOnPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
    {
        //if(propertyChangedEventArgs.PropertyName == "HasUniversityDegree");
        OnPropertyChanged("NumberOfChildrenWithDegrees");
    }

    private int _numberOfChildrenWithDegrees;
    public int NumberOfChildrenWithDegrees
    {
        get { return Children.Where(f => f.HasTwoDegrees).Count(); }
        set { _numberOfChildrenWithDegrees = value; }
    }
}
public class Child : BindableBase
{
    public string Name { get; set; }

    public bool HasTwoDegrees
    {
        get { return HasHighSchoolDegree && HasUniversityDegree; }
    }

    private bool _hasUniversityDegree;
    public bool HasUniversityDegree
    {
        get { return this._hasUniversityDegree; }
        set
        {
            _hasUniversityDegree = value;
            OnPropertyChanged("HasTwoDegrees");
        }
    }

    private bool _hasHighSchoolDegree;
    public bool HasHighSchoolDegree
    {
        get { return this._hasHighSchoolDegree; }
        set
        {
            _hasHighSchoolDegree = value;
            OnPropertyChanged("HasTwoDegrees");
        }
    }
}
public abstract class BindableBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    protected bool SetProperty<T>(ref T storage, T value, string propertyName = null)
    {

        if (object.Equals(storage, value))
            return false;

        storage = value;
        this.OnPropertyChanged(propertyName);
        return true;
    }
    protected void OnPropertyChanged(string propertyName = null)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

}
}

Answer 2

我希望这听起来不像广告。使用BCL的工具，您只有机会完成@jmshapland所说的内容。对于这个简单的聚合，这可能不是太糟糕，但如果聚合变得更复杂，代码会变得更加复杂。但是，有一些工具可以为您提供支持，特别是我自己的工具：NMF Expressions（开源）

这个工具基本上允许你创建一个可观察的表达式并听取它的更新。

 public class Parent
 {
      private INotifyValue<bool> _allTwoDegrees;
      public Parent()
      {
          _allTwoDegrees = Observable.Expression(() => Children.WithUpdates().All(child => child.HasTwoDegrees));
          _allTwoDegrees.ValueChanged += (o,e) => OnPropertyChanged("AllTwoDegrees");
      }
      public bool AllTwoDegrees
      {
          get
          {
              return _allTwoDegrees.Value;
          }
      }
      ...
 }

支持许多聚合，包括Sum，Count，Average，Min，Max，All和Any。此外，您几乎可以使用所有标准查询运算符。然而，这种灵活性是有代价的，因为目前的实施基于反射。

如果使用直接实现INotifyEnumerable的VM类，则可以删除“WithUpdates（）”方法，如ObservableCollection上的薄层所做。

Answer 3

我一直试图解决你的问题一段时间我必须承认，我最终得到了与@jmshapland非常相似的解决方案 - 原理是一样的：订阅孩子的PropertyChanged。在这种情况下，我想知道是否写这个答案 - 最后我决定这样做，但把这个答案视为对@ jmshapland解决方案的更大评论。这是代码：

Bindable类 - 更容易实现INotify：

public abstract class Bindable : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    protected bool SetProperty<T>(ref T storage, T value, [CallerMemberName] String property = null)
    {
        if (object.Equals(storage, value)) return false;
        storage = value;
        this.OnPropertyChanged(property);
        return true;
    }

    protected void OnPropertyChanged([CallerMemberName] string property = null)
    {
        if (this.PropertyChanged != null)
            this.PropertyChanged(this, new PropertyChangedEventArgs(property));
    }
}

Child课程 - 可能没什么新内容：

public class Child : Bindable
{
    private string name;
    public string Name
    {
        get { return name; }
        set { SetProperty(ref name, value); }
    }

    public bool HasTwoDegrees { get { return HasHighSchoolDegree && HasUniversityDegree; } }

    private bool hasUniversityDegree;
    public bool HasUniversityDegree
    {
        get { return this.hasUniversityDegree; }
        set
        {
            SetProperty(ref hasUniversityDegree, value);
            OnPropertyChanged("HasTwoDegrees");
        }
    }

    private bool hasHighSchoolDegree;
    public bool HasHighSchoolDegree
    {
        get { return this.hasHighSchoolDegree; }
        set
        {
            SetProperty(ref hasHighSchoolDegree, value);
            OnPropertyChanged("HasTwoDegrees");
        }
    }
}

Parent类 - 这里有一些改进 - 我使用一种方法订阅CollectionChanged事件，该方法添加/删除对添加/删除项目的订阅。订阅方法item_PropertyChanged检查是否允许调用它的属性更新Parent的属性。如果是，则为每个已定义的OnPropertyChanged引发bindingNames事件。我认为只要查看代码就会更容易：

public class Parent : Bindable
{       
    private string[] bindingNames;
    private string[] allowedProperties;

    private string name;
    public string Name
    {
        get { return name; }
        set { SetProperty(ref name, value); }
    }

    private ObservableCollection<Child> children = new ObservableCollection<Child>();
    public ObservableCollection<Child> Children
    {
        get { return this.children; }
        set { children = value; }
    }

    public Parent()
    {
        this.children.CollectionChanged += children_CollectionChanged;
        bindingNames = new string[] { "NumberOfChildrenWithDegrees" };
        allowedProperties = new string[] { "HasUniversityDegree", "HasHighSchoolDegree" };
    }

    private void children_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.NewItems != null)
            foreach (Object item in e.NewItems)
                if (item is INotifyPropertyChanged)
                    (item as INotifyPropertyChanged).PropertyChanged += item_PropertyChanged;
        if (e.OldItems != null)
            foreach (Object item in e.OldItems)
                (item as INotifyPropertyChanged).PropertyChanged -= item_PropertyChanged;
    }

    private void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (bindingNames != null)
            foreach (string item in bindingNames)
                if (allowedProperties.Contains(e.PropertyName))
                    OnPropertyChanged(item);
    }

    public int NumberOfChildrenWithDegrees
    {
        get { return Children.Where(f => f.HasTwoDegrees).Count(); }
    }
}

MainPage类:(我没有更改xaml文件）

public partial class MainPage : PhoneApplicationPage
{
    ObservableCollection<Parent> parentGroups = new ObservableCollection<Parent>();

    public ObservableCollection<Parent> ParentGroups
    {
        get { return parentGroups; }
        set { parentGroups = value; }
    }

    public MainPage()
    {
        InitializeComponent();
        this.parentLB.DataContext = this;
        FillParents();
    }

    public void FillParents()
    {
        Parent p = new Parent { Name = "Tom" };
        Child c1 = new Child { Name = "Tammy" };
        Child c2 = new Child { Name = "Timmy" };
        p.Children.Add(c1);
        p.Children.Add(c2);
        ParentGroups.Add(p);
        p = new Parent { Name = "Carol" };
        c1 = new Child { Name = "Carl" };
        c1.HasHighSchoolDegree = true;
        c1.HasUniversityDegree = true;
        c2 = new Child { Name = "Karla" };
        p.Children.Add(c1);
        p.Children.Add(c2);
        ParentGroups.Add(p);
    }
}

也许它会有所帮助。