【发布时间】：2010-09-24 12:24:58
【问题描述】：
对于那些喜欢良好的 WPF 绑定挑战的人：
我有一个几乎实用的示例，将CheckBox 双向绑定到标志枚举的单个位（感谢 Ian Oakes，original MSDN post）。但问题是绑定的行为好像是一种方式（UI 到 DataContext，反之亦然）。所以有效地CheckBox 不会初始化，但如果它被切换，则数据源会正确更新。 Attached 是定义一些附加依赖属性以启用基于位的绑定的类。我注意到 ValueChanged 永远不会被调用，即使我强制 DataContext 更改。
我尝试过的： 更改属性定义的顺序，使用标签和文本框来确认 DataContext 正在冒泡更新，任何合理的 FrameworkMetadataPropertyOptions (AffectsRender, BindsTwoWayByDefault)，显式设置Binding Mode=TwoWay，撞墙，将ValueProperty更改为EnumValueProperty以防冲突。
任何建议或想法将不胜感激，感谢您提供的任何东西！
枚举：
[Flags]
public enum Department : byte
{
None = 0x00,
A = 0x01,
B = 0x02,
C = 0x04,
D = 0x08
} // end enum Department
XAML 用法：
CheckBox Name="studentIsInDeptACheckBox"
ctrl:CheckBoxFlagsBehaviour.Mask="{x:Static c:Department.A}"
ctrl:CheckBoxFlagsBehaviour.IsChecked="{Binding Path=IsChecked, RelativeSource={RelativeSource Self}}"
ctrl:CheckBoxFlagsBehaviour.Value="{Binding Department}"
班级：
/// <summary>
/// A helper class for providing bit-wise binding.
/// </summary>
public class CheckBoxFlagsBehaviour
{
private static bool isValueChanging;
public static Enum GetMask(DependencyObject obj)
{
return (Enum)obj.GetValue(MaskProperty);
} // end GetMask
public static void SetMask(DependencyObject obj, Enum value)
{
obj.SetValue(MaskProperty, value);
} // end SetMask
public static readonly DependencyProperty MaskProperty =
DependencyProperty.RegisterAttached("Mask", typeof(Enum),
typeof(CheckBoxFlagsBehaviour), new UIPropertyMetadata(null));
public static Enum GetValue(DependencyObject obj)
{
return (Enum)obj.GetValue(ValueProperty);
} // end GetValue
public static void SetValue(DependencyObject obj, Enum value)
{
obj.SetValue(ValueProperty, value);
} // end SetValue
public static readonly DependencyProperty ValueProperty =
DependencyProperty.RegisterAttached("Value", typeof(Enum),
typeof(CheckBoxFlagsBehaviour), new UIPropertyMetadata(null, ValueChanged));
private static void ValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
isValueChanging = true;
byte mask = Convert.ToByte(GetMask(d));
byte value = Convert.ToByte(e.NewValue);
BindingExpression exp = BindingOperations.GetBindingExpression(d, IsCheckedProperty);
object dataItem = GetUnderlyingDataItem(exp.DataItem);
PropertyInfo pi = dataItem.GetType().GetProperty(exp.ParentBinding.Path.Path);
pi.SetValue(dataItem, (value & mask) != 0, null);
((CheckBox)d).IsChecked = (value & mask) != 0;
isValueChanging = false;
} // end ValueChanged
public static bool? GetIsChecked(DependencyObject obj)
{
return (bool?)obj.GetValue(IsCheckedProperty);
} // end GetIsChecked
public static void SetIsChecked(DependencyObject obj, bool? value)
{
obj.SetValue(IsCheckedProperty, value);
} // end SetIsChecked
public static readonly DependencyProperty IsCheckedProperty =
DependencyProperty.RegisterAttached("IsChecked", typeof(bool?),
typeof(CheckBoxFlagsBehaviour), new UIPropertyMetadata(false, IsCheckedChanged));
private static void IsCheckedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if (isValueChanging) return;
bool? isChecked = (bool?)e.NewValue;
if (isChecked != null)
{
BindingExpression exp = BindingOperations.GetBindingExpression(d, ValueProperty);
object dataItem = GetUnderlyingDataItem(exp.DataItem);
PropertyInfo pi = dataItem.GetType().GetProperty(exp.ParentBinding.Path.Path);
byte mask = Convert.ToByte(GetMask(d));
byte value = Convert.ToByte(pi.GetValue(dataItem, null));
if (isChecked.Value)
{
if ((value & mask) == 0)
{
value = (byte)(value + mask);
}
}
else
{
if ((value & mask) != 0)
{
value = (byte)(value - mask);
}
}
pi.SetValue(dataItem, value, null);
}
} // end IsCheckedChanged
/// <summary>
/// Gets the underlying data item from an object.
/// </summary>
/// <param name="o">The object to examine.</param>
/// <returns>The underlying data item if appropriate, or the object passed in.</returns>
private static object GetUnderlyingDataItem(object o)
{
return o is DataRowView ? ((DataRowView)o).Row : o;
} // end GetUnderlyingDataItem
} // end class CheckBoxFlagsBehaviour
【问题讨论】：
标签： c# wpf data-binding enums bit-manipulation