对于喜欢WPF绑定挑战的人:
我有一个近乎功能的例子,双向绑定一个复选框到一个标志枚举的单个位(感谢Ian Oakes,原始的MSDN帖子).但问题是绑定的行为就好像它是一种方式(UI到DataContext,反之亦然).因此,复选框不会初始化,但如果切换,则数据源会正确更新.Attached是定义一些附加依赖项属性的类,以启用基于位的绑定.我注意到,即使我强制DataContext更改,也永远不会调用ValueChanged.
我尝试过的:更改属性定义的顺序,使用标签和文本框确认DataContext正在冒泡更新,任何合理的FrameworkMetadataPropertyOptions(AffectsRender,BindsTwoWayByDefault),显式设置绑定模式= TwoWay,敲打墙头,改变如果发生冲突,请将ValueProperty添加到EnumValueProperty.
任何建议或想法将非常感谢,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:
///
/// A helper class for providing bit-wise binding.
///
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
///
/// Gets the underlying data item from an object.
///
/// The object to examine.
/// The underlying data item if appropriate, or the object passed in.
private static object GetUnderlyingDataItem(object o)
{
return o is DataRowView ? ((DataRowView)o).Row : o;
} // end GetUnderlyingDataItem
} // end class CheckBoxFlagsBehaviour
PaulJ.. 45
您可以使用值转换器.这是目标枚举的一个非常具体的实现,但不难看出如何使转换器更通用:
[Flags]
public enum Department
{
None = 0,
A = 1,
B = 2,
C = 4,
D = 8
}
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
this.DepartmentsPanel.DataContext = new DataObject
{
Department = Department.A | Department.C
};
}
}
public class DataObject
{
public DataObject()
{
}
public Department Department { get; set; }
}
public class DepartmentValueConverter : IValueConverter
{
private Department target;
public DepartmentValueConverter()
{
}
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
Department mask = (Department)parameter;
this.target = (Department)value;
return ((mask & this.target) != 0);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
this.target ^= (Department)parameter;
return this.target;
}
}
然后在XAML中使用转换器:
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