Question

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位于“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。这个NumericUpDown在一个PropertyGrid中，在非Modal对话框的情况下工作正常，所以我不想修改最初创建数据绑定的XAML。我也不想仅仅为了更改数据绑定而复制XAML。所以，我试图在Modal对话框的Loaded事件处理程序中复制和修改数据绑定。

这里我复制并修改最初在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);
      }
   }

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BindingExpression上调用下面的UpdateSource（）时，抛出一个异常，说：“分离绑定时无法执行此操作。”

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

我做错了什么？

Answer 1

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，唯一需要改变的是将OneWay更改为TwoWay。

当UI元素数据发生更改时，WPF OneTime数据绑定会分离

1 个答案: