OneWayToSource从XAML中的readonly属性绑定 [英] OneWayToSource binding from readonly property in XAML

问题描述

我试图绑定一个 Readonly 属性与 OneWayToSource 作为模式，但似乎这不能在XAML中完成：

I'm trying to bind to a Readonly property with OneWayToSource as mode, but it seems this cannot be done in XAML:

<controls:FlagThingy IsModified="{Binding FlagIsModified, 
                                          ElementName=container, 
                                          Mode=OneWayToSource}" />

我得到：

属性FlagThingy.IsModified无法设置，因为它没有可访问的集合访问器。

The property 'FlagThingy.IsModified' cannot be set because it does not have an accessible set accessor.

IsModified 是 FlagThingy 中的只读 DependencyProperty 。我想将该值绑定到容器上的 FlagIsModified 属性。

IsModified is a readonly DependencyProperty on FlagThingy. I want to bind that value to the FlagIsModified property on the container.

要清楚：

FlagThingy.IsModified --> container.FlagIsModified
------ READONLY -----     ----- READWRITE --------

是否可以使用XAML？

Is this possible using just XAML?

更新： 嗯，我通过在容器上设置绑定而不是在 FlagThingy 上来修复这种情况。但是我仍然想知道这是否可行。

Update: Well, I fixed this case by setting the binding on the container and not on the FlagThingy. But I'd still like to know if this is possible.

推荐答案

OneWayToSource的一些研究成果...

Some research results for OneWayToSource...

1。

// Control definition
public partial class FlagThingy : UserControl
{
    public static readonly DependencyProperty IsModifiedProperty = 
            DependencyProperty.Register("IsModified", typeof(bool), typeof(FlagThingy), new PropertyMetadata());
}

<controls:FlagThingy x:Name="_flagThingy" />

// Binding Code
Binding binding = new Binding();
binding.Path = new PropertyPath("FlagIsModified");
binding.ElementName = "container";
binding.Mode = BindingMode.OneWayToSource;
_flagThingy.SetBinding(FlagThingy.IsModifiedProperty, binding);

选项＃2

// Control definition
public partial class FlagThingy : UserControl
{
    public static readonly DependencyProperty IsModifiedProperty = 
            DependencyProperty.Register("IsModified", typeof(bool), typeof(FlagThingy), new PropertyMetadata());

    public bool IsModified
    {
        get { return (bool)GetValue(IsModifiedProperty); }
        set { throw new Exception("An attempt ot modify Read-Only property"); }
    }
}

<controls:FlagThingy IsModified="{Binding Path=FlagIsModified, 
    ElementName=container, Mode=OneWayToSource}" />

选项＃3（True只读依赖属性）

Option # 3 (True read-only dependency property)

System.ArgumentException：'IsModified'属性不能被数据绑定。

System.ArgumentException: 'IsModified' property cannot be data-bound.

// Control definition
public partial class FlagThingy : UserControl
{
    private static readonly DependencyPropertyKey IsModifiedKey =
        DependencyProperty.RegisterReadOnly("IsModified", typeof(bool), typeof(FlagThingy), new PropertyMetadata());

    public static readonly DependencyProperty IsModifiedProperty = 
        IsModifiedKey.DependencyProperty;
}

<controls:FlagThingy x:Name="_flagThingy" />

// Binding Code
Same binding code...

反射器给出答案：

internal static BindingExpression CreateBindingExpression(DependencyObject d, DependencyProperty dp, Binding binding, BindingExpressionBase parent)
{
    FrameworkPropertyMetadata fwMetaData = dp.GetMetadata(d.DependencyObjectType) as FrameworkPropertyMetadata;
    if (((fwMetaData != null) && !fwMetaData.IsDataBindingAllowed) || dp.ReadOnly)
    {
        throw new ArgumentException(System.Windows.SR.Get(System.Windows.SRID.PropertyNotBindable, new object[] { dp.Name }), "dp");
    }
 ....

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