kotlin ViewModel SavedStateHandle临时保存数据

教程使用kotlin语言，使用了Jetpack库中的ViewModel，LiveData,DataBindeing等组件

自己模拟app被后台杀死得情况，开发者选项中勾选不保留活动测试

1.build.gradle（app）中添加

android {
    dataBinding {
        enabled = true
    }
}

2.activity_main.xml

<?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">
 
    <data>
 
        <variable
            name="viewModel"
            type="com.renchunlin.databindingkt.MyViewModel" />
    </data>
 
    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">
 
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="32dp"
            android:text="@{String.valueOf(viewModel.getContentNumber())}"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
 
        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="150dp"
            android:onClick="@{()->viewModel.add()}"
            android:text="Button"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
 
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

3.MyViewModel.kt

package com.renchunlin.databindingkt
 
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.SavedStateHandle
import androidx.lifecycle.ViewModel
 
/*
 * class title: 
 * Author by RenChunLin, Email 18957806320@163.com, Date on 2021/8/18.
 * PS: Not easy to write code, please indicate.
 */
class MyViewModel(private val handle: SavedStateHandle) : ViewModel() {
 
    companion object {
        const val KEY_NUMBER = "key"
    }
 
    private val number: Int = 0
 
    fun getContentNumber(): MutableLiveData<Int> {
        if (!handle.contains(KEY_NUMBER)) {
            handle.set(KEY_NUMBER, number)
        }
        return handle.getLiveData(KEY_NUMBER)
    }
 
    fun add() {
        getContentNumber().value = getContentNumber().value?.plus(1)
    }
}

4.MainActivity.kt

package com.renchunlin.databindingkt
 
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.lifecycle.ViewModelProvider
import com.renchunlin.databindingkt.databinding.ActivityMainBinding
 
class MainActivity : AppCompatActivity() {
 
    private val myViewModel by lazy {
        ViewModelProvider(this).get(MyViewModel::class.java)
    }
    private lateinit var binding: ActivityMainBinding
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        binding.viewModel = myViewModel
        binding.lifecycleOwner = this
    }
}