如何从ContentView获取ContentPage的BindingContext? [英] How to get ContentPage's BindingContext from ContentView?

问题描述

我有以下Contentpage.content，在其中设置了某些绑定上下文.

<StackLayout>
    <local:Post />  
    <local:Comments />
</StackLayout>

在Post.xaml.cs(ContentView)中，我试图以这种方式获取ContentPage的绑定上下文，但是它不起作用.

BindingContext = (PostViewModel)Parent.BindingContext;

如果我站在ContentView中，如何获取ContentPage的绑定上下文?

解决方案

在调用构造函数时，BindingContext可能尚未初始化.

因此，您应该等待BindingContext被更改以对其执行操作.

我认为答案是OnBindingContextChanged事件. https://developer.xamarin.com/api/member/Xamarin .Forms.View.OnBindingContextChanged()

小样

        protected override void OnBindingContextChanged ()
        {
            base.OnBindingContextChanged ();

            //BindingContext should not be null at this point
            // and you may add your code here.
        }

注意: 如果您在ContentPage中有一个ContentView，除非由另一个控件(例如，将ItemTemplate用于ListView)或您的代码明确设置，否则ContentView的BindingContext与ContentPage相同.

因此，不必称呼父母".

让我知道是否需要进一步澄清.

I have the following Contentpage.content, where I set certain binding context.

<StackLayout>
    <local:Post />  
    <local:Comments />
</StackLayout>

In Post.xaml.cs (ContentView), I've tried to get the binding context of the ContentPage this way but it doesn't work.

BindingContext = (PostViewModel)Parent.BindingContext;

How can I get the binding context of the ContentPage if I'm standing in a ContentView?

解决方案

By the time your constructor is called, the BindingContext might not be initialised yet.

So, you should wait for the BindingContext being changed to perform operations on it.

I think the answer is OnBindingContextChanged event. https://developer.xamarin.com/api/member/Xamarin.Forms.View.OnBindingContextChanged()

Little sample:

        protected override void OnBindingContextChanged ()
        {
            base.OnBindingContextChanged ();

            //BindingContext should not be null at this point
            // and you may add your code here.
        }

Note: If you have a ContentView inside a ContentPage, unless explicitly set by another Control (like when using an ItemTemplate for a ListView) or by your code, the BindingContext of the ContentView is the same as the ContentPage.

So, it shouldn't be necessary to call "Parent".

Let me know if more clarification is needed.

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