一、前言：
Lifecycle-aware components生命周期感知组件执行操作，以响应另一个组件生命周期状态的更改，例如Activity和Fragment。这些组件可以帮助您生成更有组织、更容易维护的轻量级代码。
注意：LifecycleObserver -过时了，新版本必须引入包。
// DefaultLifecycleObserver - 引入新包
implementation "android.arch.lifecycle:common-java8:1.1.1"
1、没有生命周期感知组件，你的代码可能是这样的
class MyLocationListener {
public MyLocationListener(Context context, Callback callback) {
// ...
}
void start() {
// connect to system location service
}
void stop() {
// disconnect from system location service
}
}
class MyActivity extends AppCompatActivity {
private MyLocationListener myLocationListener;
@Override
public void onCreate(...) {
myLocationListener = new MyLocationListener(this, (location) -> {
// update UI
});
}
@Override
public void onStart() {
super.onStart();
myLocationListener.start();
// manage other components that need to respond
// to the activity lifecycle
}
@Override
public void onStop() {
super.onStop();
myLocationListener.stop();
// manage other components that need to respond
// to the activity lifecycle
}
}
Android框架中定义的大多数应用程序组件都具有附加的生命周期。生命周期由运行在流程中的操作系统或框架代码管理。它们是Android工作原理的核心，您的应用程序必须尊重它们。
不这样做可能会引发内存泄漏，甚至应用程序崩溃。
二、lifecycle使用
1、让需要感知生命周期的组件实现LifecycleObserver接口（老的版本，有过时方法）
import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.OnLifecycleEvent;
//老的版本
public class MyLocationListener implements LifecycleObserver {
private Context context;
public MyLocationListener(Context context) {
this.context = context;
}
@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
void onCreate() {
showLog("onCreate");
}
@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
void onDestroy() {
showLog("onDestroy");
}
@OnLifecycleEvent(Lifecycle.Event.ON_START)
void onStart() {
showLog("onStart");
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
void onStop() {
showLog("onStop");
}
@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
void onResume() {
showLog("onResume");
}
@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
void onPause() {
showLog("onPause");
}
private void showLog(String msg) {
Log.e("===MyLocationListener", msg);
}
}
//2、新版本
/**
* 自定义View 监听Activity 或者Fragment的生命周期
* LifecycleObserver -过时了
* DefaultLifecycleObserver - 需要导入新包 implementation "android.arch.lifecycle:common-java8:1.1.1"
*/
class MyLocationListener2(context: Context) : DefaultLifecycleObserver {
private val context: Context
init {
this.context = context
}
@SuppressLint("LongLogTag")
override fun onCreate(owner: LifecycleOwner) {
showLog("onCreate")
}
@SuppressLint("LongLogTag")
override fun onStart(owner: LifecycleOwner) {
showLog("onStart")
}
@SuppressLint("LongLogTag")
override fun onStop(owner: LifecycleOwner) {
showLog("onStop")
}
@SuppressLint("LongLogTag")
override fun onResume(owner: LifecycleOwner) {
showLog("onResume")
}
@SuppressLint("LongLogTag")
override fun onPause(owner: LifecycleOwner) {
showLog("onPause")
}
@SuppressLint("LongLogTag")
override fun onDestroy(owner: LifecycleOwner) {
showLog("onDestroy")
}
private fun showLog(msg: String) {
Log.e("===MyLocationListener", msg)
}
}
对应的activity或者fragment实现LifecycleOwner，并调用getLifecycle().addObserverLifecycle().addObserver添加观察者
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
var btnNext = findViewById<Button>(R.id.btn_next)
btnNext.setOnClickListener {
//老的版本调用
getLifecycle().addObserver( MyLocationListener(this))
//新的版本调用
getLifecycle().addObserver( MyLocationListener2(this))
}
}
}
打印结果
2019-09-01 14:53:13.956 22701-22701/com.mengk.lifecyclerdemo E/===MyLocationListener: onCreate
2019-09-01 14:53:13.960 22701-22701/com.mengk.lifecyclerdemo E/===MyLocationListener: onStart
2019-09-01 14:53:13.968 22701-22701/com.mengk.lifecyclerdemo E/===MyLocationListener: onResume
2019-09-01 14:53:16.678 22701-22701/com.mengk.lifecyclerdemo E/===MyLocationListener: onPause
2019-09-01 14:53:17.282 22701-22701/com.mengk.lifecyclerdemo E/===MyLocationListener: onStop
2019-09-01 14:53:19.258 22701-22701/com.mengk.lifecyclerdemo E/===MyLocationListener: onDestroy
2、自定义生命周期组件
如果你有一个自定义类，你想让它成为LifecycleOwner，你可以使用LifecycleRegistry类，但是你需要将事件转发到该类中，如下面的代码示例所示:
package com.example.myapplication.utils
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.LifecycleRegistry
class MyCommpont : LifecycleOwner {
private val lifecycleRegistry: LifecycleRegistry
init {
lifecycleRegistry = LifecycleRegistry(this)
}
fun onCreate() {
//过时方法
//lifecycleRegistry.markState(Lifecycle.State.CREATED)
lifecycleRegistry.setCurrentState(Lifecycle.State.CREATED)
}
fun onStart() {
lifecycleRegistry.setCurrentState(Lifecycle.State.STARTED)
}
fun onResume() {
lifecycleRegistry.setCurrentState(Lifecycle.State.RESUMED)
}
fun onKillApp() {
lifecycleRegistry.setCurrentState(Lifecycle.State.DESTROYED)
}
override fun getLifecycle(): Lifecycle {
return lifecycleRegistry
}
}
调用
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
var btnNext = findViewById<Button>(R.id.btn_next)
btnNext.setOnClickListener {
val myCommpont = MyCommpont()
myCommpont.onCreate()
myCommpont.onStart()
myCommpont.lifecycle.addObserver(MyLocationListener2(this))
}
}
}
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