Android 数据绑定 &MVVM - 对不同布局文件夹中的布局文件使用相同的名称 [英] Android DataBinding & MVVM - Using same name for layout files in different layout folders

问题描述

我一直在开发具有数据绑定功能的应用程序MVVM.

I've been developing an app with data binding & MVVM.

我正在尝试在横向模式下为我的应用程序使用替代布局.我有:

I'm trying to use an alternative layout for my app on landscape mode. I have:

layout/fragment_content.xml
layout-land/fragment_content.xml

两种布局都有相同的视图，但外观不同，并从相同的视图模型中获取提要，如下所示:

Both layouts have same views with different look, and get feeds from same view models, like this:

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

<data class="MyBinding">

    <variable
        name="viewModel"
        type="com.myapp.package.viewModel.VMFirst"/>

    <variable
        name="controlModel"
        type="com.myapp.package.viewModel.VMSecond"/>
</data>

<DIFFERENT CONTENT HERE>

所有的视图和 ID 都存在于两种布局中.

All the views and id's exist in both layouts.

好吧，问题是，它不能编译，错误只是找不到符号方法 getViewModel" 和另一个变量的 getter.

Well, problem is, it doesn't compile, error is simply "cannot find symbol method getViewModel" and getter for the other variable.

到目前为止我尝试过的:

What I tried so far:

1. 使用 layout 和 layout-land 文件夹(失败，上面解释了错误)

1. Using layout and layout-land folders ( Failed, error is explained above )

使用布局别名使用布局别名，我在这里找到了问题 199344:数据绑定不适用于布局别名.尝试这种方法时，我没有更改 xml 文件中的任何内容.这也失败了，错误是 Could not write to com.myapp.package.databinding.MyBinding

Using layout aliases Use Layout Aliases which I found here Issue 199344: Data binding does not work with layout aliases. I didn't change anything in xml files while trying this approach. This also failed, error is Could not write to com.myapp.package.databinding.MyBinding

是否不能在多个布局文件中使用数据绑定 data 标签?在使用数据绑定时，我应该使用什么来为不同的状态使用不同的布局?谢谢！

Is it not possible to use data binding data tag in multiple layout files ? What should I use to use different layouts for different states while using data binding ? Thanks !

删除 class="MyBinding" 没有改变错误.

deleting class="MyBinding" did not change errors.

推荐答案

如果有人搜索这个问题，2 年后我尝试做同样的事情，我发现现在一切正常.

If anyone searches for this question, after 2 years I tried to do the same, and I saw it's working all fine now.

我在 layout 和 layout_sw600dp 下创建了一个布局文件 activity_main.这是layout资源下的布局:

I created a layout file activity_main under layout and layout_sw600dp. Here's the layout under layout resources:

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <variable
        name="small_variable"
        type="Integer"/>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/myRoot"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <View
            android:id="@+id/small_square"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:background="@android:color/holo_blue_bright"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

这是layout_sw600dp文件夹下的布局:

<?xml version="1.0" encoding="utf-8"?>

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <variable
        name="big_variable"
        type="Long"/>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/myRoot"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <View
            android:id="@+id/big_square"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:background="@android:color/holo_blue_bright"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

两者都有一个视图，但每个视图都有不同的 id:small_square 和 big_square.

Both has a view but it has different id in each: small_square and big_square.

我在电话上运行该项目 &药片.以下是我的发现:

I run the project on phone & tablet. Here are my findings:

• DataBinding 创建一个实现，其中包含不同布局文件夹中所有同名布局文件下的ALL 视图和变量.
• 存在于所有布局中的视图不可为空，所有其他布局均可为空.在上述 XML 中，myRoot 在使用 Kotlin 绑定时不是可空视图，而 big_square 和 small_square > 可以为空 视图.无论是否存在于所有布局中，变量都是可为空的(这是预期的行为).
• 您不能在每个文件中命名不同的绑定类.它必须是相同的(MainBinding 在上面的例子中，或者如果你没有定义它 LayoutResourceName + Binding 默认情况下).
• 绑定实现上的视图和变量的名称是驼峰式的.所以我的 small_variable &small_square 是代码端的 binding.smallVariable 和 binding.smallSquare.
• 使用 Kotlin，您可以只使用像 binding.bigSquare?.operation 这样的视图，这很棒，您无需事先检查它是平板电脑还是手机或视图是否为空.
• 提示一下，即使不使用它们所在的布局，您也可以分配 binding 字段.您仍然可以在代码上说 binding.smallVariable = 3 ，它会进行分配并保存值.我认为小心点很好.

• DataBinding creates an implementation that contains ALL views and variables under all layout files of same name in different layout folders.
• Views that exists in all layouts are not nullable, all others are nullable. In above XML's, myRoot is not a nullable view when using binding from Kotlin, while big_square and small_square are nullable views. Variables are nullable whether or not they exists in all layouts ( which is expected behaviour ).
• You cannot name binding classes different in each file. It has to be same ( MainBinding in above examples, or if you don't define it LayoutResourceName + Binding by default ).
• Names for views and variables on binding implementation are camel case. So my small_variable & small_square was binding.smallVariable and binding.smallSquare on code side.
• With Kotlin, you can just use views like binding.bigSquare?.operation, which is great that you don't need to check if it's tablet or phone or view is null or not beforehand.
• Just a tip, you can assign binding fields even if layout that they are in won't be used. You can still say binding.smallVariable = 3 on code and it'll do the assignment and save the value. I think it's good to be careful.

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