android:viewmodel的例子

一，引入lifecycle相关库

1,在项目根目录下的build.gradle中配置脚本，增加:

buildscript{
    ext {
        lifecycle = "2.5.1"
    }
}

编辑app下的build.gradle,增加:

    // lifecycle相关
    api "androidx.lifecycle:lifecycle-livedata-core-ktx:${rootProject.ext.lifecycle}"
    api "androidx.lifecycle:lifecycle-livedata-ktx:${rootProject.ext.lifecycle}"
    api "androidx.lifecycle:lifecycle-runtime-ktx:${rootProject.ext.lifecycle}"
    api "androidx.lifecycle:lifecycle-viewmodel-ktx:${rootProject.ext.lifecycle}"

然后点击Sync Now

二，代码

1,viewmodel类

package com.example.okdemo1.viewmodel

import androidx.lifecycle.LiveData
import androidx.lifecycle.ViewModel
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.delay
import kotlinx.coroutines.launch

class CounterViewModel : ViewModel() {
    // MutableLiveData 用于修改数据
    private val _counter = MutableLiveData(0)
    val counter: LiveData<Int> get() = _counter

    // 在后台线程模拟耗时操作
    fun increment() {
        viewModelScope.launch(Dispatchers.Default) {
            delay(1000) // 模拟耗时操作
            _counter.postValue(_counter.value?.plus(1))
        }
    }

    // 普通数据操作（无耗时）
    fun reset() {
        _counter.value = 0
    }
}

2,activity代码

package com.example.okdemo1.activity

import android.os.Bundle
import android.view.View
import androidx.activity.enableEdgeToEdge
import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity
import androidx.core.view.ViewCompat
import androidx.core.view.WindowInsetsCompat
import com.example.okdemo1.R
import com.example.okdemo1.databinding.ActivityMainBinding
import com.example.okdemo1.databinding.ActivityVmBinding
import com.example.okdemo1.viewmodel.CounterViewModel

class VmActivity : AppCompatActivity() {

    private lateinit var binding: ActivityVmBinding
    private val viewModel: CounterViewModel by viewModels() // 委托初始化

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()

        binding = ActivityVmBinding.inflate(layoutInflater)
        setContentView(binding.root)

        // 监听 LiveData 变化（仅当 Activity 处于 STARTED/RESUMED 状态时触发）
        viewModel.counter.observe(this) { count ->
            binding.tvCount.text = "Count: $count"
            binding.progressBar.visibility = if (count > 5) View.VISIBLE else View.GONE
        }

        //增加
        binding.btnIncrement.setOnClickListener {
            viewModel.increment()
        }

        //重置
        binding.btnReset.setOnClickListener {
            viewModel.reset()
        }

    }
}

activity xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".activity.VmActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="30dp"
        android:orientation="vertical">

        <TextView
            android:id="@+id/tvCount"
            android:text="Count: 0"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="44sp"/>

        <ProgressBar
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/progressBar"
            android:visibility="gone" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/btnIncrement"
            android:textSize="44sp"
            android:text="增长"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/btnReset"
            android:textSize="44sp"
            android:text="重置"/>

    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

三，测试效果: