OnPropertyChanged()仅由手动编辑TextBox触发

Question

我需要一个绑定到ClassA的TextBox，它显示来自ClassB中两个Object的变量的和。只有当我尝试手动编辑TextBox时，它才会更改其值。我的问题是，我不知道如何在ClassA中实现一个方法，如果ClassB中的变量发生了变化，该方法就会列出。我试图让ClassB从ClassA变成SubClass，但后来我得到了StackOverflowException，所以这不起作用。

---

MainWindow.xaml

---

<Window x:Class="INPCTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:INPCTest"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Window.DataContext>
<local:ClassA/>
</Window.DataContext>
<Grid x:Name="BaseGrid" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="10"/>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="10" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="10"/>
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<TextBox x:Name="TextBoxClassA" Grid.Row="1" Grid.Column="1" Text="{Binding Sum, UpdateSourceTrigger=PropertyChanged}" />
<TextBox x:Name="TextBox1ClassB" Grid.Row="2" Grid.Column="1" Text="{Binding MyClassB1.Var, UpdateSourceTrigger=PropertyChanged}" />
<TextBox x:Name="TextBox2ClassB" Grid.Row="2" Grid.Column="2" Text="{Binding MyClassB2.Var, UpdateSourceTrigger=PropertyChanged}" />
</Grid>
</Window>

---

ClassA.cs

---

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace INPCTest
{
public class ClassA : ObservableObject
{
private decimal _sum;

public decimal Sum
{
get { _sum = MyClassB1.Var + MyClassB2.Var; return _sum; }
set { _sum = value; OnPropertyChanged();}
}

public ClassB MyClassB1 { get; set; } = new ClassB(1);
public ClassB MyClassB2 { get; set; } = new ClassB(2);
}
}

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ClassB.cs

---

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace INPCTest
{
public class ClassB : ObservableObject
{
private decimal _var;
public ClassB(decimal var)
{
_var = var;
}
public decimal Var
{
get { return _var; }
set { _var = value; OnPropertyChanged();}
}

}
}

---

ObservableObject.cs

---

using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
namespace INPCTest
{
public class ObservableObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler? PropertyChanged;
public void OnPropertyChanged([CallerMemberName] string propertyname = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyname));
}
}
}

Answer 1

您可以从Action使用。

A类：

public class ClassA : ObservableObject
{
private decimal _sum;
public ClassA()
{
MyClassB1 = new ClassB(1) {OnVarChanged = OnVarChange};
MyClassB2 = new ClassB(2) {OnVarChanged = OnVarChange};
}
public decimal Sum
{
get { _sum = MyClassB1.Var + MyClassB2.Var; return _sum; }
set { _sum = value; OnPropertyChanged(); }
}

public ClassB MyClassB1 { get; set; }
public ClassB MyClassB2 { get; set; }
private void OnVarChange() => OnPropertyChanged(nameof(Sum));
}

B类：

public class ClassB : ObservableObject
{
private decimal _var;
public ClassB(decimal var)
{
_var = var;
}
public Action OnVarChanged { get; set; }
public decimal Var
{
get { return _var; }
set
{
_var = value;
OnPropertyChanged();
OnVarChanged?.Invoke();
}
}
}

Answer 2

使用INotifyPropertyChanged和WPFPropertyChangedEventManager使ClassA侦听其每个ClassB对象。当任一Var属性发生更改时，ClassA可以为其Sum属性引发PropertyChanged事件。例如，您可以为类a编写一个构造函数来完成

public ClassA()
{
PropertyChangedEventManager.AddHandler(
MyClassB1,
(_,_) => OnPropertyChanged(nameof(Sum)),
nameof(ClassB.Var));
PropertyChangedEventManager.AddHandler(
MyClassB2,
(_,_) => OnPropertyChanged(nameof(Sum)),
nameof(ClassB.Var));
}

但有一个问题：您有一个ClassA.Sum的公共setter。如果Sum应该是每两个ClassB.Var值的相加，那么这怎么可能起作用呢？你怎么往另一个方向走？

每次有人设置ClassA.Sum时，你都必须以某种方式将新的Sum除以两个ClassB，或者下次有人调用getter时，值就会变回来。

我不知道怎么办。