I define a CustomView with one Bindable Property. To make things clearer, I removed all code unnessesary to understand my problem.
This is my XAML:

我定义了一个具有一个可绑定属性的CustomView。为了让事情更清楚，我删除了理解我的问题所需的所有代码。这是我的XAML：

<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:vm="clr-namespace:Packer.ViewModels"
             x:DataType="vm:ContainerItemViewModel"
             x:Class="Packer.CustomViews.ContainerView">
    <ContentView.BindingContext>
        <vm:ContainerItemViewModel/>
    </ContentView.BindingContext>
    <StackLayout Orientation="Vertical">
        <Label Text="Hello World!" />
    </StackLayout>
</ContentView>

...and this is my code behind:

...这是我后面的代码：

using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace Packer.CustomViews
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class ContainerView : ContentView
    {
        public static readonly BindableProperty ItemIdProperty =
            BindableProperty.Create(nameof(ItemId), typeof(int), typeof(ContainerView), -1);
 
        public ContainerView()
        {
            InitializeComponent();
        }

        public int ItemId
        {
            get => (int)GetValue(ItemIdProperty);
            set
            {
                SetValue(ItemIdProperty, value);
            }
        }
    }
}

With xmlns:custom="clr-namespace:Packer.CustomViews" This CustomView is called as follows:

使用xmlns:custom=“clr-namespace:Packer.CustomViews”时，此自定义视图的调用方式如下：

<StackLayout Orientation="Horizontal">
     <custom:ContainerView HorizontalOptions="FillAndExpand" ItemId="{Binding ItemId}" />
     <Label Text="{Binding ItemId}" />
</StackLayout>

Debugging this app as UWP, I can't see property ItemId being hit. However, the label following the Custom View is displayed properly, as well as the "Hello World" Label defined in the Custom View.

将此应用程序调试为UWP，我看不到属性ItemID被命中。但是，可以正确显示自定义视图后面的标签以及在自定义视图中定义的“Hello World”标签。

This is my configuration:

这是我的配置：

Updates:

最新情况：

When you set this in xaml:

在XAML中设置此项时：

<ContentView.BindingContext>
    <vm:ContainerItemViewModel/>
</ContentView.BindingContext>

It just like you set this in page:

就像你在第页中设置的一样：

<custom:ContainerView BindingContext=ContainerViewModel HorizontalOptions="FillAndExpand" ItemId="{Binding ItemId}" />

Of course we could not get the ItemId property change because we maually set the BindingContext to ContainerViewModel (We know that ItemId is not in it).

当然，我们无法更改Itemid属性，因为我们主要将BindingContext设置为ContainerViewModel(我们知道Itemid不在其中)。

But when I set

但当我把

Content.BindingContext = new ContainerItemViewModel();

It means we just set the BindingContext for the ContainerView's Content. We could also receive the changes of ItemId.

这意味着我们只为ContainerView的内容设置了BindingContext。我们也可以收到伊特米德的变化。

If you want to Detect property changes for BindableProperty, you could use a callback method instead of adding some logic in Setter.

如果要检测BindableProperty的属性更改，可以使用回调方法，而不是在Setter中添加一些逻辑。

public static readonly BindableProperty ItemIdProperty =
           BindableProperty.Create(nameof(ItemId), typeof(int), typeof(ContainerView), -1,propertyChanged:OnItemIdPropertyChanged);

private static void OnItemIdPropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
    var a = (int)newValue;
}

I don't know why you use a ContainerItemViewModel for ContainerView. Because the BindingContext can inherit from the parent page. If you still want to do so, you could delete:

我不知道您为什么对ContainerView使用ContainerItemViewModel。因为BindingContext可以从父页继承。如果您仍想这样做，您可以删除：

<!--<ContentView.BindingContext>
    <vm:ContainerItemViewModel/>
</ContentView.BindingContext>-->

And set it in code-behind like this:

并在代码隐藏中设置它，如下所示：

public ContainerView()
{
    InitializeComponent();
    // Notice here, please set Content.BindingContext here
    Content.BindingContext = new ContainerItemViewModel();
}

Now if you set a breakpoint in OnItemIdPropertyChanged method, and it will hit the code. If you still have any question, feel free to ask.

现在，如果您在OnItemIdPropertyChanged方法中设置断点，它将命中代码。如果你还有任何问题，请随时提问。

Hope it helps!

希望它能帮上忙！

Solution:

解决方案：

Liqun Shen-MSFT's answer solves my problem.

沈立群的回答解决了我的问题。

However, the breakpoint in the ItemId setter is not hit but event OnItemIdChanged:

但是，未命中Itemid setter中的断点，而是事件OnItemIdChanged：

public static readonly BindableProperty ItemIdProperty =
    BindableProperty.Create(nameof(ItemId), typeof(int), typeof(ContainerView), propertyChanged:OnItemIdChanged);

private static void OnItemIdChanged(BindableObject bindable, object oldValue, object newValue)
{
}

This is a strange behaviour that I did not expect.

这是一种我没想到的奇怪行为。