在 WPF 中使用 StringFormat 通过 Multibinding 通知和更新源

Question

请分析以下代码sn-p：

<TextBox x:Name="TxtBox_CommandInfo"  Style="{DynamicResource MetroTextBox}"
    IsReadOnly="True" Controls:TextBoxHelper.Watermark="This is a textbox" 
    HorizontalAlignment="Left" Margin="0,236,0,0" TextWrapping="Wrap"
    VerticalAlignment="Top" Height="154" Width="780" 
    ScrollViewer.HorizontalScrollBarVisibility="Auto" 
    ScrollViewer.VerticalScrollBarVisibility="Auto">
  <TextBox.Text>
    <MultiBinding StringFormat="{}{0} {1} {2}" NotifyOnTargetUpdated="True">
      <Binding  Path="A" />
      <Binding  Path="B" />
      <Binding  Path="C"/>
      <Binding Path="D" Mode="TwoWay" NotifyOnTargetUpdated="True"
          UpdateSourceTrigger="PropertyChanged"/>
    </MultiBinding>
  </TextBox.Text>
</TextBox>

如您所见TxtBox_CommandInfo 文本框文本（目标）值将仅由 A,B,C 修改/格式化，但更新后的文本应通过 binding.Model 通知D，如下所示：

A,B,C => [TexBox.Text] => D

问题是当TxtBox_CommandInfo.Text 发生更改时，C# 端的各个源 D 不会得到通知和更新。

1. 没有任何Converters如何实现这个问题的解决方案？
2. 我是否错误地配置了Multibinding 设置？

它确实需要StringFormat 功能，因此在不注入转换的情况下，我们有任何替代StringFormat 的方法吗？

Answer 1

我还是一头雾水。不明白你的意思：

我试图在 cmets 中解释的内容，这里有一个解决方案。

XAML：

 <Grid>
    <StackPanel>
        <ComboBox ItemsSource="{Binding Path=MyTexts}" SelectedItem="{Binding Path=A}" Margin="10"/>
        <ComboBox ItemsSource="{Binding Path=MyTexts}" SelectedItem="{Binding Path=B}" Margin="10"/>
        <ComboBox ItemsSource="{Binding Path=MyTexts}" SelectedItem="{Binding Path=C}" Margin="10"/>

        <TextBox Height="80" Margin="10" Text="{Binding Path=D, Mode=OneWay}" IsReadOnly="True" AcceptsReturn="True" TextWrapping="Wrap">
        </TextBox>
    </StackPanel>
</Grid>

C#：（视图模型）

 public class MyViewModel : INotifyPropertyChanged
{
    private string _a;
    private string _b;
    private string _c;

    public string A
    {
        get => _a;
        set
        {
            _a = value;
            OnPropertyChanged(nameof(A));
            OnPropertyChanged(nameof(D));
        }
    }
    public string B
    {
        get => _b;
        set
        {
            _b = value;
            OnPropertyChanged(nameof(B));
            OnPropertyChanged(nameof(D));
        }
    }
    public string C
    {
        get => _c;
        set
        {
            _c = value;
            OnPropertyChanged(nameof(C));
            OnPropertyChanged(nameof(D));
        }
    }
    public string D => $"{A} {B} {C}";

    public List<string> MyTexts { get; }

    public MyViewModel()
    {
        MyTexts = new List<string>() { "FHAKWEFJ AWKEEF AWEKF LAEWKF LAWEF", "AAAAAAAAAAAAAAAAAAAAAA", "BBBBBBBBBBBBBBBBBBBBBBBBB", "EEEEEEEEEEEEEEEEEEEEEEEEE", "GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG", "GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG" };
    }

    #region INotifyPropertyChanged
    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion
}

没有黑客，没有魔法，没有事件。纯 MVVM

编辑： 我想这就是你想要的（只显示对上面代码的修改）：

<TextBox Height="80" Margin="10" TextChanged="TextBoxBase_OnTextChanged" IsReadOnly="True" AcceptsReturn="True" TextWrapping="Wrap">
   <TextBox.Text>
                <MultiBinding StringFormat="{}{0} {1} {2}" NotifyOnTargetUpdated="True" Mode="OneWay">
                    <Binding  Path="A" Mode="OneWay"/>
                    <Binding  Path="B"  Mode="OneWay"/>
                    <Binding  Path="C" Mode="OneWay"/>
                </MultiBinding>
            </TextBox.Text>
 </TextBox>

C#：

private void TextBoxBase_OnTextChanged(object sender, TextChangedEventArgs e)
{
    if (this.DataContext is MyViewModel dataContext)
        dataContext.D = ((TextBox) sender).Text;
}

C#（虚拟机）：

    private string _d;

    public string D
    {
        get => _d;
        set
        {
            _d = value;
            OnPropertyChanged(nameof(D));
        }
    }