androidx 与 Spinner 和自定义对象的数据绑定

Question

如何使用 androidx 数据绑定库用自定义对象列表填充 Spinner (app:entries)？以及如何为 Spinner (app:onItemSelected) 创建适当的 selection 回调？

我的布局：

<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">

<data>

    <variable
        name="viewModel"
        type=".ui.editentry.EditEntryViewModel" />
</data>

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.editentry.EditEntryActivity">

        <Spinner
            android:id="@+id/spClubs"
            android:layout_width="368dp"
            android:layout_height="25dp"
            app:entries="@{viewModel.projects}"
            app:onItemSelected="@{viewModel.selectedProject}"
             />

</FrameLayout>

</layout>

EditEntryViewModel.kt

class EditEntryViewModel(repository: Repository) : ViewModel() {

    /** BIND SPINNER DATA TO THESE PROJECTS **/
    val projects : List<Project> = repository.getProjects()

    /** BIND SELECTED PROJECT TO THIS VARIABLE **/
    val selectedProject: Project;
}

Project.kt

data class Project(
    var id: Int? = null,
    var name: String = "",
    var createdAt: String = "",
    var updatedAt: String = ""
)

Spinner 应该显示每个项目的名称，当我 select 一个项目时，它应该保存在 viewModel.selectedProject 中。 LiveData 的使用是可选的。

我想我必须为 app:entries 编写一个@BindingAdapter 并为 app:onItemSelected 编写一个@InverseBindingAdapter。但是如果不为 Spinneradapter 编写通常的样板代码，我无法弄清楚如何实现它们...

Answer 1

你可以在fragment里面设置

            binding.spinnerState.adapter = ArrayAdapter(
                context!!,
                R.layout.simple_spinner_item_1line,
                viewModel.projects?.map { it.name }!!
            )

请注意项目应该是

 MutableLiveData<List<Projects>>()

Answer 2

好的，我想出了一个妥善的解决办法。这是带有一些解释的代码：

layout.xml

<Spinner
    android:id="@+id/spProjects"
    android:layout_width="368dp"
    android:layout_height="wrap_content"
    android:layout_marginStart="16dp"
    android:layout_marginTop="8dp"
    android:layout_marginEnd="16dp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/spActivities"
    app:projects="@{viewModel.projects}"
    app:selectedProject="@={viewModel.entry.project}" />

app:projects 在我的 ViewModel

中绑定到 val projects: List<Project>

app:selectedProject 绑定到 val entry: Entry，这是一个 class 具有 Project 作为属性.

所以这是我的 ViewModel 的一部分：

class EditEntryViewModel() : ViewModel() {
    var entry: MutableLiveData<Entry> = MutableLiveData()
    var projects : List<Project> = repository.getProjects()
}

现在缺少的是实现以下功能的 BindingAdapter 和 InverseBindingAdapter：

Spinner 应该列出来自 repsitory 的所有项目
Spinner 应该预先 select select 当前 entry
select编辑新项目时，应自动将其设置为entry

绑定适配器

    /**
     * fill the Spinner with all available projects.
     * Set the Spinner selection to selectedProject.
     * If the selection changes, call the InverseBindingAdapter
     */
    @BindingAdapter(value = ["projects", "selectedProject", "selectedProjectAttrChanged"], requireAll = false)
    fun setProjects(spinner: Spinner, projects: List?, selectedProject: Project, listener: InverseBindingListener) {
        if (projects == null) return
        spinner.adapter = NameAdapter(spinner.context, android.R.layout.simple_spinner_dropdown_item, projects)
        setCurrentSelection(spinner, selectedProject)
        setSpinnerListener(spinner, listener)
    }

您可以将 BindingAdapter 放在空文件中。它不必是任何 class 的一部分。重要的是它的参数。它们由 BindingAdapters values 扣除。在本例中，值为 projects、selectedProject 和 selectedProjectAttrChanged。前两个参数对应我们自己定义的两个layout-xml属性。 last/third 参数是 DataBinding 过程的一部分：对于每个具有双向数据绑定的布局-xml 属性（即@={），都会生成一个值名字 <attribute-name>AttrChanged

这个特殊情况的另一个重要部分是 NameAdapter，它是我自己的 SpinnerAdapter，它能够将我的项目作为项目保存，并且只在 name 属性中显示它们=88=]。这样我们总是可以访问整个项目实例，而不是只能访问一个字符串（默认的 SpinnerAdapter 通常是这种情况）。

这是我的自定义 Spinner 适配器的代码：

名称适配器

class NameAdapter(context: Context, textViewResourceId: Int, private val values: List<Project>) : ArrayAdapter<Project>(context, textViewResourceId, values) {

    override fun getCount() = values.size
    override fun getItem(position: Int) = values[position]
    override fun getItemId(position: Int) = position.toLong()

    override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
        val label = super.getView(position, convertView, parent) as TextView
        label.text = values[position].name
        return label
    }

    override fun getDropDownView(position: Int, convertView: View?, parent: ViewGroup): View {
        val label = super.getDropDownView(position, convertView, parent) as TextView
        label.text = values[position].name
        return label
    }
}

现在我们有了一个保存整个项目信息的 Spinner，InverseBindingAdapter 就很简单了。它用于告诉 DataBinding 库应该设置什么值，从 UI 到实际的 class 属性 viewModel.entry.project:

InverseBindingAdapter

    @InverseBindingAdapter(attribute = "selectedProject")
    fun getSelectedProject(spinner: Spinner): Project {
        return spinner.selectedItem as Project
    }

就是这样。所有的工作都很顺利。需要提及的一件事是，如果您的 List 包含大量数据，则不推荐使用此方法，因为所有这些数据都存储在适配器中。在我的例子中，它只是一些字符串字段，所以应该没问题。

为了完成，我想从 BindingAdapter 添加两个方法：

private fun setSpinnerListener(spinner: Spinner, listener: InverseBindingListener) {
    spinner.onItemSelectedListener = object : AdapterView.OnItemSelectedListener {
        override fun onItemSelected(parent: AdapterView<*>?, view: View?, position: Int, id: Long) = listener.onChange()
        override fun onNothingSelected(adapterView: AdapterView<*>) = listener.onChange()
    }
}

private fun setCurrentSelection(spinner: Spinner, selectedItem: HasNameField): Boolean {
    for (index in 0 until spinner.adapter.count) {
        if (spinner.getItemAtPosition(index) == selectedItem.name) {
            spinner.setSelection(index)
            return true
        }
    }
    return false
}

Answer 3

这个问题和回复对我过去几天努力解决类似问题非常有帮助。本着分享的精神，这里是我所有的文件：

MainActivity.kt

package com.mandal.mvvmspinnerviewbindingexample

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.ViewModelProvider
import com.mandal.mvvmspinnerviewbindingexample.databinding.ActivityMainBinding
import com.mandal.mvvmspinnerviewbindingexample.viewmodel.UserViewModel


class MainActivity : AppCompatActivity()  {
    /**
     * Lazily initialize our [UserViewModel].
     */
   private val viewModel: UserViewModel by lazy {
       ViewModelProvider(this).get(UserViewModel::class.java)
   }
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    enter code here
     val binding: ActivityMainBinding =
            DataBindingUtil.setContentView(this, R.layout.activity_main)

        // Allows Data Binding to Observe LiveData with the lifecycle of this Activity
        binding.lifecycleOwner = this

        // Giving the binding access to the UserViewModel
       binding.viewModel = viewModel

    }
}

User.kt

package com.mandal.mvvmspinnerviewbindingexample.model

data class User(
    val id: Int,
    val name: String,
) {
    override fun toString(): String = name
}

Entry.kt

package com.mandal.mvvmspinnerviewbindingexample.model

data class Entry (var user: User)

NameAdapter.kt

package com.mandal.mvvmspinnerviewbindingexample.adapter

import android.content.Context
import android.view.View
import android.view.ViewGroup
import android.widget.ArrayAdapter
import android.widget.TextView
import com.mandal.mvvmspinnerviewbindingexample.model.User

class NameAdapter(context: Context, textViewResourceId: Int, private val values: List<User>) : ArrayAdapter<User>(context, textViewResourceId, values) {

    override fun getCount() = values.size
    override fun getItem(position: Int) = values[position]
    override fun getItemId(position: Int) = position.toLong()

    override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
        val label = super.getView(position, convertView, parent) as TextView
        label.text = values[position].name
        return label
    }

    override fun getDropDownView(position: Int, convertView: View?, parent: ViewGroup): View {
        val label = super.getDropDownView(position, convertView, parent) as TextView
        label.text = values[position].name
        return label
    }
}

UserViewModel.kt

package com.mandal.mvvmspinnerviewbindingexample.viewmodel

import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import com.mandal.mvvmspinnerviewbindingexample.model.Entry
import com.mandal.mvvmspinnerviewbindingexample.model.User

class UserViewModel: ViewModel (){

    var users : List<User> = getUserList()
    var entry: MutableLiveData<Entry> = MutableLiveData()

    /**
     * Sets the value of the status LiveData to the Mars API status.
     */
    private fun getUserList() : List<User>{
        //Setup Users
        val user1 = User(1, "John")
        val user2 = User(2, "Mary")
        val user3 = User(2, "Patrick")
        val user4 = User(2, "Amanda")
        //Setup User List
        val list = arrayListOf<User>(user1, user2, user3, user4)
        return list
    }

}

BindingAdapters.kt

package com.mandal.mvvmspinnerviewbindingexample

import android.R
import android.view.View
import android.widget.AdapterView
import android.widget.Spinner
import android.widget.Toast
import androidx.databinding.BindingAdapter
import androidx.databinding.InverseBindingAdapter
import androidx.databinding.InverseBindingListener
import com.mandal.mvvmspinnerviewbindingexample.adapter.NameAdapter
import com.mandal.mvvmspinnerviewbindingexample.model.User

/**
 * fill the Spinner with all available projects.
 * Set the Spinner selection to selectedProject.
 * If the selection changes, call the InverseBindingAdapter
 */
@BindingAdapter(value = ["users", "selectedUser", "selectedUserAttrChanged"], requireAll = false)
fun setUsers(spinner: Spinner, users: List<User>?, selectedUser: User?, listener: InverseBindingListener) {
    if (users == null) return
    spinner.adapter = NameAdapter(spinner.context, R.layout.simple_spinner_dropdown_item, users)
    setCurrentSelection(spinner, selectedUser)
    setSpinnerListener(spinner, listener)
}


@InverseBindingAdapter(attribute = "selectedUser")
fun getSelectedUser(spinner: Spinner): User {
    Toast.makeText(
        spinner.context,
        (spinner.selectedItem as User).name,
        Toast.LENGTH_LONG
    )
        .show()
    return spinner.selectedItem as User
}

private fun setSpinnerListener(spinner: Spinner, listener: InverseBindingListener) {
    spinner.onItemSelectedListener = object : AdapterView.OnItemSelectedListener {
        override fun onItemSelected(parent: AdapterView<*>?, view: View?, position: Int, id: Long)  = listener.onChange()
        override fun onNothingSelected(adapterView: AdapterView<*>) = listener.onChange()
    }
}

private fun setCurrentSelection(spinner: Spinner, selectedItem: User?): Boolean {
    for (index in 0 until spinner.adapter.count) {
        if (spinner.getItemAtPosition(index) == selectedItem?.name) {
            spinner.setSelection(index)
            return true
        }
    }
    return false
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    >
<data>

    <variable name="viewModel"
        type="com.mandal.mvvmspinnerviewbindingexample.viewmodel.UserViewModel" />
</data>
    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

    <!--Spinner widget-->
    <Spinner
        android:id="@+id/userSpinner"
        android:layout_width="160dp"
        android:layout_height="50dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.17"
        app:users="@{viewModel.users}"
        app:selectedUser="@={viewModel.entry.user}"
     />

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

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mandal.mvvmspinnerviewbindingexample" >

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme" >
        <activity android:name="com.mandal.mvvmspinnerviewbindingexample.MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>
        </activity>

    </application>

</manifest>

androidx 与 Spinner 和自定义对象的数据绑定

androidx databinding with Spinner and custom objects

android

android-spinner

android-databinding

android-viewmodel