Android 数据绑定：为什么将变量传递给 ViewStubs 不像包含布局那样工作？

Question

使用 Android 数据绑定可以在包含的布局上设置变量，如下所示（来自文档）：

    <?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:bind="http://schemas.android.com/apk/res-auto">
   <data>
       <variable name="user" type="com.example.User"/>
   </data>
   <LinearLayout
       android:orientation="vertical"
       android:layout_width="match_parent"
       android:layout_height="match_parent">
       <include layout="@layout/name"
           bind:user="@{user}"/>
       <include layout="@layout/contact"
           bind:user="@{user}"/>
   </LinearLayout>
</layout>

我试过在使用 ViewStub 时做同样的事情来传递变量，但它不起作用。为什么 ViewStub 不像包含布局那样工作？

Answer 1

ViewStub 在 Data Binding Library documentation 中被称为不同。

ViewStubs

ViewStubs are a little different from normal Views. They start off invisible and when they either are made visible or are explicitly told to inflate, they replace themselves in the layout by inflating another layout.

Because the ViewStub essentially disappears from the View hierarchy, the View in the binding object must also disappear to allow collection. Because the Views are final, a ViewStubProxy object takes the place of the ViewStub, giving the developer access to the ViewStub when it exists and also access to the inflated View hierarchy when the ViewStub has been inflated.

When inflating another layout, a binding must be established for the new layout. Therefore, the ViewStubProxy must listen to the ViewStub's ViewStub.OnInflateListener and establish the binding at that time. Since only one can exist, the ViewStubProxy allows the developer to set an OnInflateListener on it that it will call after establishing the binding.

Answer 2

向 ViewStubs 传递数据按预期工作。您定义命名空间并在该命名空间中传递变量，并在 ViewStub 布局中将其作为常规 <variable> 接受，如下所示：

main_layout.xml:

<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:my-namespace="http://schemas.android.com/apk/res-auto">
    <data>
        <variable name="myData" type="com.example.SomeModel" />
    </data>

    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">

        <ViewStub
            android:id="@+id/view_stub"
            android:inflatedId="@+id/view"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout="@layout/another_layout"
            my-namespace:data="@{myData}"
            />
    </RelativeLayout>
</layout>

another_layout.xml:

<layout xmlns:android="http://schemas.android.com/apk/res/android">
<!-- No need to declare my-namespace here -->
    <data>
        <variable name="data" type="com.example.SomeModel" />
    </data>

    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{data.someValue}" />

    </RelativeLayout>
</layout>

Android 数据绑定：为什么将变量传递给 ViewStubs 不像包含布局那样工作？

Android Data Binding: Why doesn't passing in variable to ViewStubs work like include layouts?

android

android-layout

android-databinding