仅允许OneWayToSource绑定模式 [英] Allow only OneWayToSource binding mode

问题描述

我有 EntitiesUserControl 负责 EntitiesCount 依赖项属性：

public static readonly DependencyProperty EntitiesCountProperty = DependencyProperty.Register(
    nameof(EntitiesCount),
    typeof(int),
    typeof(EntitiesUserControl),
    new FrameworkPropertyMetadata(1, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

public int EntitiesCount
{
    get { return (int)this.GetValue(EntitiesCountProperty); }
    set { this.SetValue(EntitiesCountProperty, value); }
}

另一个（主要）控件包括 EntitiesUserControl 并通过绑定读取它的属性：

Another (primary) control include EntitiesUserControl and read it property through binding:

<controls:EntitiesUserControl EntitiesCount="{Binding CountOfEntities, Mode=OneWayToSource}" />

CountOfEntities 属性仅在视图模型中存储和计数值的过程更改：

CountOfEntities property in view model just store and process changing of count value:

private int countOfEntities;
public int CountOfEntities
{
    protected get { return this.countOfEntities; }
    set
    {
        this.countOfEntities = value;
        // Custom logic with new value...
    }
}

我需要 EntitiesUserControl 的 EntitiesCount 属性为只读（主要控件一定不要更改它，只需阅读即可），它之所以能如此工作，是因为明确声明了 Mode = OneWayToSource 。但是，如果声明 TwoWay 模式或不明确声明模式，则 EntitiesCount 可以从外部重写（至少正确绑定初始化后，因为它发生在指定的默认依赖项属性值之后。

I need EntitiesCount property of EntitiesUserControl to be read-only (primary control must not change it, just read) and it works this way only because Mode=OneWayToSource declared explicitly. But if declare TwoWay mode or don't explicitly declare mode, then EntitiesCount could be rewritten from outside (at least right after binding initialization, because it happens after default dependency property value assigned).

我不能做合法的只读依赖项属性由于绑定限制（此 answer 中有最佳描述），因此我需要防止使用<$ c $以外的方式进行绑定c> OneWayToSource 。最好在OnlyOneWayToSource 标志，例如 BindsTwoWayByDefault 值system.windows.frameworkpropertymetadataoptions％28v = vs.110％29.aspx rel = nofollow noreferrer> FrameworkPropertyMetadataOptions 枚举...

I can't do 'legal' read-only dependency property due to binding limitations (best described in this answer), so I need to prevent bindings with mode other than OneWayToSource. It would be best to have some OnlyOneWayToSource flag like BindsTwoWayByDefault value in FrameworkPropertyMetadataOptions enumeration...

有人建议如何实现这一目标吗？

Any suggestions how to achieve this?

推荐答案

这是一个有点 hacky，但是您可以创建一个 Binding 派生的类，并使用它代替 Binding ：

It's a „bit" hacky, but you can create a Binding-derived class and use that instead of Binding:

[MarkupExtensionReturnType(typeof(OneWayToSourceBinding))]
public class OneWayToSourceBinding : Binding
{
    public OneWayToSourceBinding()
    {
        Mode = BindingMode.OneWayToSource;
    }

    public OneWayToSourceBinding(string path) : base(path)
    {
        Mode = BindingMode.OneWayToSource;
    }

    public new BindingMode Mode
    {
        get { return BindingMode.OneWayToSource; }
        set
        {
            if (value == BindingMode.OneWayToSource)
            {
                base.Mode = value;
            }
        }
    }
}

在XAML：

<controls:EntitiesUserControl EntitiesCount="{local:OneWayToSourceBinding CountOfEntities}" />

名称空间映射 local 可能是其他东西

The namespace mapping local might be something else for you.

此 OneWayToSourceBinding 将 Mode 设置为 OneWayToSource 并阻止将其设置为其他任何内容。

This OneWayToSourceBinding sets the Mode to OneWayToSource and prevents setting it to anything else.

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