当UI元素数据发生更改时，WPF OneTime数据绑定将脱离

问题描述

| 我正在尝试在Numericupdown的value属性和CS对象的属性之间建立数据绑定。 Numericupdown在“模态”对话框中，因此我只希望在用户按下“确定”按钮时更新数据绑定。此Numericupdown位于PropertyGrid中，该属性在非Modal对话框情况下可以正常工作，因此我不想修改最初创建数据绑定的XAML。我也不想重复XAML只是为了更改数据绑定。因此，我正在尝试复制和修改Modal对话框的Loaded事件处理程序中的数据绑定。 在这里，我复制和修改最初在XAML中创建的数据绑定。

    void OnLoad(object sender,RoutedEventArgs e)
    {
        GetBindings(DialogPropPanel);
    }  

    private void GetBindings(FrameworkElement root)
   {
      FieldInfo[] infos = root.GetType().GetFields(BindingFlags.Public | BindingFlags.FlattenHierarchy |
         BindingFlags.Instance | BindingFlags.Static);

      foreach(FieldInfo field in infos)
      {
         if(field.FieldType == typeof(DependencyProperty))
         {
            DependencyProperty dp = (DependencyProperty)field.GetValue(null);
            BindingExpression ex = root.GetBindingExpression(dp);
            if(ex != null)
            {
               PropertyElement elem = FindBoundElement(ex.DataItem,GroupContainer.PropertyGroups);
               if(elem != null)
               {
                  Binding bd = ex.ParentBinding;
                  if(bd.Mode == BindingMode.Default || bd.Mode == BindingMode.TwoWay)
                  {
                     // copy the binding an change mode.
                     Binding newBinding = CreateOneTimeBinding(bd,ex.DataItem);
                     BindingOperations.ClearBinding(root,dp);
                     BindingOperations.SetBinding(root,dp,newBinding);
                     BindingExpression nuExp = root.GetBindingExpression(dp);
                     m_bindings.Add(nuExp);
                  }
               }
            }
         }
      }

      int children = VisualTreeHelper.GetChildrenCount(root);
      for(int i = 0; i < children; i++)
      {
         FrameworkElement child = VisualTreeHelper.GetChild(root,i) as FrameworkElement;

         if(child != null)
            GetBindings(child);
      }
   }

在这里，我将模式更改为OneTime，将UpdateSourceTrigger更改为Explicit。

    public static Binding CreateOneTimeBinding(Binding binding,object source)
    {
      var result = new Binding
      {
        Source = source,AsyncState = binding.AsyncState,BindingGroupName = binding.BindingGroupName,BindsDirectlyToSource = binding.BindsDirectlyToSource,Converter = binding.Converter,ConverterCulture = binding.ConverterCulture,ConverterParameter = binding.ConverterCulture,//ElementName = binding.ElementName,FallbackValue = binding.FallbackValue,IsAsync = binding.IsAsync,Mode = BindingMode.OneWay,NotifyOnSourceUpdated = binding.NotifyOnSourceUpdated,NotifyOnTargetUpdated = binding.NotifyOnTargetUpdated,NotifyOnValidationError = binding.NotifyOnValidationError,Path = binding.Path,//RelativeSource = binding.RelativeSource,StringFormat = binding.StringFormat,TargetNullValue = binding.TargetNullValue,UpdateSourceExceptionFilter = binding.UpdateSourceExceptionFilter,UpdateSourceTrigger = UpdateSourceTrigger.Explicit,ValidatesOnDataErrors = binding.ValidatesOnDataErrors,ValidatesOnExceptions = binding.ValidatesOnExceptions,XPath = binding.XPath,};

      foreach(var validationRule in binding.ValidationRules)      
        result.ValidationRules.Add(validationRule);      

      return result;
    }

当用户通过Numericupdown更改目标值时，BindingExpression的DataItem属性将设置为null。然后，当我在那个BindingExpression上调用下面的UpdateSource（）时，抛出一个异常，该异常是：\“当绑定分离时，无法执行此操作。\”

void ApplyClicked(object sender,RoutedEventArgs e)
{
  foreach(BindingExpression express in m_bindings)
    express.UpdateSource();
}

我究竟做错了什么？     

解决方法

        我发现了问题。数据绑定需要具有TwoWay（或OneWayToSource）模式才能更新源。因此，在上面的代码中，唯一需要更改的是将OneWay更改为TwoWay。