Question

我在wpf中玩数据绑定，遇到了问题。这是我的代码：

MainWindow.xaml

<Window x:Class="TestWpf.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:TestWpf"
        Title="MainWindow" Height="350" Width="525">    
    <StackPanel Name="stackpanel">
        <TextBox Name="tb1" Text="{Binding Path=A.Number}" />
        <TextBox Name="tb2" Text="{Binding Path=B.Number}" />
        <TextBlock Name="tbResult" Text="{Binding Path=C}" />
    </StackPanel>
</Window>

MainWindow.xaml.cs

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        MyClass myClass = new MyClass();
        myClass.A = new MySubClass();
        myClass.B = new MySubClass();
        stackpanel.DataContext = myClass;
    }
}

MyClass.cs

class MyClass : INotifyPropertyChanged
{
    private MySubClass a;
    public MySubClass A 
    {
        get { return a; }
        set
        {
            a = value;
            OnPropertyChanged("A");
            OnPropertyChanged("C");
        }
    }

    private MySubClass b;
    public MySubClass B 
    {
        get { return b; }
        set
        {
            b = value;
            OnPropertyChanged("B");
            OnPropertyChanged("C");
        }
    }

    public int C
    {
        get { return A.Number + B.Number; }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string p)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(p));
        }
    }        
}

MySubClass.cs

class MySubClass : INotifyPropertyChanged
{
    private int number;
    public int Number 
    {
        get { return number; }
        set
        {
            number = value;
            OnPropertyChanged("Number");
        }
    }

    public MySubClass()
    {
        Number = 1;
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string p)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(p));
        }
    }     
}

现在，问题是在运行应用程序后绑定工作正常。此外，值A.Number和B.Number正在更新，因为我在文本框中更改它们。但MyClass.C中的变量C仅在应用程序启动时更新，从不更新。当我更改A.Number或B.Number时，我需要更改以便C更新。感谢。

Answer 1

更新数据模型时，您是直接在MySubClass实例上更改数字还是将新的子类分配给MyClass实例？即：

myClass.A.Number = 5; // will trigger OnPropertyChanged on MySubClass, but not on MyClass

不会在A上触发OnPropertyChanged（但当然会更新A.Number）。为此，您必须执行以下操作：

MySubClass v = new MySubClass()
v.Number = 5;
myClass.A = v;  // will trigger OnPropertyChanged on MyClass

更新了答案。你可以这样做来捕捉a和b中的任何属性变化。

public MyClass()
{
    a.PropertyChanged += new PropertyChangedEventHandler(UpdateC);
    b.PropertyChanged += new PropertyChangedEventHandler(UpdateC);
}

void UpdateC(object sender, PropertyChangedEventArgs e)
{
    OnPropertyChanged("C");
}

Answer 2

我需要更改什么才能在更改A.Number或B.Number时更新C。

您需要侦听对A和B属性的更改。如果您将此代码添加到A setter：

，它应该可以工作



set
{
if (a != null)
{
 a.PropertyChanged-=NumberChanged;
}
 a = value;
 a.PropertyChanged+=NumberChanged;
 OnPropertyChanged("A");
 OnPropertyChanged("C");
}

private void NumberChanged(object sender, PropertyChangedEventArgs e)
{
  if (e.PropertyName == "Number")
  {
    OnPropertyChanged("C");
  }
}

和B setter一样。

WPF与类和子类绑定到DataContext

2 个答案: