c# - UWP 自定义控件，不能使用绑定(bind)，只有 x :Bind, 如何适配？

Question

我在 UWP 中创建了一个自定义控件，但我在 Microsoft 提供的自定义控件上也存在这个问题，因此我将使用 UWP Community Toolkit OrbitView 作为示例。以下 3 个绑定(bind)工作:

<Grid>
    <TextBlock Text="{Binding MyProperty}"/>
    <TextBlock Text="{x:Bind PageViewModel.MyProperty, Mode=OneWay}"/>
    <Toolkit:OrbitView MinItemSize="{x:Bind PageViewModel.MyProperty, Mode=OneWay}" />
</Grid>

标准控件 (TextBlock) 使用 Binding 或 x:Bind。但是如果我想在自定义控件上使用 Binding:

<Toolkit:OrbitView MinItemSize="{Binding MyProperty}" />

事实并非如此。在这里和网络上搜索我正在努力弄清楚发生了什么以及为什么。一般的解决方案似乎是只使用 x:Bind。但是我想将我的自定义控件放在 UserControl 中，因为我希望在运行时使用 XamlReader 从外部 Xaml 文件加载它的选项。我的理解是你不能在这种情况下使用 x:Bind，因为它需要在编译时存在。有什么解决方案可以实现我在 UWP 中的目标吗？

Answer 1

好吧，如果你在 setter 中运行其他代码，这就是为什么它不工作的原因，以及如何让它工作。

下面是实现依赖属性并在 setter 上执行代码的正确方法。这是在 UWP 项目中完成的，因为您的问题是 UWP，但对任何项目类型的所有依赖属性具有完全相同的原则。

public sealed partial class MainPage : Page
{
    public MainPage() => InitializeComponent();        

    public int SomeValue
    {
        get => (int)GetValue(SomeValueProperty);
        set => SetValue(SomeValueProperty, value);
    }

    public static readonly DependencyProperty SomeValueProperty = //Notice this is static. It's bound to an internal static hash table of some sort; I use to know exactly but forgot.
        DependencyProperty.Register(
            nameof(SomeValue), /*The name of the property to register against. 
                               * The static version is always the name of the property ended with Property
                               * i.e. SomeValue property is SomeValueProperty dependency property */                                                 
            typeof(int), //This is the type used to describe the property.
            typeof(MainPage), //This is the type the dependency property relates to. 

            /* Below this is the magic. It's where we supply the property meta data and can be delivered different ways.
            * For this example I will supply only the default value and the event we want to use when the value is changed.
            * Note: 
            * The event we supply is fired ONLY if the value is changed. This event is what we need to use to handle changes in the setter to cover binding operations as well. */
            new PropertyMetadata(default(int),  /* This is the default value the dependency property will have. 
                                                * It can be whatever you decide but make sure it works with the same type or you'll most likely get an error. */

                /* This is the event fired when the value changes.
                 * Note: Dependency properties binding and events always operate on the UI thread. Cross threading will throw exceptions. */
                new PropertyChangedCallback((s, e) =>
                {
                    var mainPage = s as MainPage; //The sender of the callback will always be of the type it's from.

                    /* The values given from the e argument for OldValue and NewValue should be of type int in this example...
                     * but since we can't gaurantee the property is setup properly before here I always add a check. */
                    if (e.OldValue is int oldValue) { }
                    if (e.NewValue is int newValue) 
                    { 
                         /* Now do what you want with the information.  This is where you need to do custom work instead of using the setter.
                          * Note: If you need to work on something in the MainPage remember this is a static event and you'll need to refer to the sender or s value in this case.
                          * I've converted s to the variable mainPage for easy referencing here. */
                         mainPage.MyCustomControl.Value = newValue;  //Note: The custom control should bind to this as well via XAML making this pointless. I set the value here just for educational purposes.
                    }
                })));

}

依赖属性不应该看起来这么可怕，实际上也不是，但我添加了很多注释来帮助您更轻松地浏览它。希望这会有所帮助:)