1 ActivityLifecycleCallbacks用来监听所有Activity的生命周期回调
Activity 的每一个生命周期都对应 ActivityLifecycleCallbacks 接口中的一个方法，比如 onActivityCreated 回调是在 Activity 的 onCreate 方法中调用 getApplication().dispatchActivityCreated(this, savedInstanceState) 完成对 Activity 生命周期跟踪监听。
public interface ActivityLifecycleCallbacks {
void onActivityCreated(Activity activity, Bundle savedInstanceState);
void onActivityStarted(Activity activity);
void onActivityResumed(Activity activity);
void onActivityPaused(Activity activity);
void onActivityStopped(Activity activity);
void onActivitySaveInstanceState(Activity activity, Bundle outState);
void onActivityDestroyed(Activity activity);
}
2 ActivityLifecycleCallbacks使用
/**
* 要求 API 14+
*/
public class MainApplication extends Application {
@Override
public void onCreate() {
super.onCreate();
// AppLifecycleCallback实现ActivityLifecycleCallbacks接口方法
this.registerActivityLifecycleCallbacks(new CustomActivityLifecycleCallback());
}
}
3 探究在Android中的应用
- 判断应用在前后台
- 管理Activity页面栈
- 获取当前Activity页面
- 保存恢复状态值 savedInstanceState
- 应用新开进程假重启处理（低内存回收、修改权限）
- 页面分析统计埋点
3.1 判断应用在前后台
判断应用是否在后台运行，针对前后台运行会做一些处理，比如：实现从后台任务恢复启动（热启动）、提示用户应用运行在后台、以及应用前后台切换回调通知等。业务场景非常多，对于开发而言就是提供稳定可靠的检测前后台方法，避免出现机型不兼容问题。
/**
* 自定义生命周期回调，判断是否从后台任务恢复启动（以实现从后台任务恢复启动为例）
*/
public class CustomActivityLifecycleCallback implements Application.ActivityLifecycleCallbacks {
private static final String TAG = "CustomActivityLifecycleCallback";
/**
* 处于后台5分钟 跳到启动页
*/
private static long JUMP_SPLASH_GAP = 5 * 60 * 1000;
private final Object mActivityLock = new Object();
/**
* 记录Started +1、Stopped -1后是否等0，判断是否退出到后台
*/
private int mStartStopedCount = 0;
/**
* 是否是推送等其他的冷启动
*/
private boolean mIsOtherStart = false;
private long mLastEndAppTime;
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
}
@Override
public void onActivityStarted(Activity activity) {
if (activity == null) {
return;
}
synchronized (mActivityLock) {
// 排除：正常冷启动、热启动、推送等其他冷启动，才是：从后台任务恢复的启动
if (!(activity instanceof SplashActivity) && mIsOtherStart && mStartStopedCount == 0) {
checkNeedStartSplashActivity(activity);
}
mStartStopedCount++;
}
}
private void checkNeedStartSplashActivity(Activity activity) {
if (mStartStopedCount == 0 && mIsOtherStart && (System.currentTimeMillis() - mLastEndAppTime) > JUMP_SPLASH_GAP) {
SplashHotActivity.actionStart(activity);
}
}
@Override
public void onActivityResumed(Activity activity) {
}
@Override
public void onActivityPaused(Activity activity) {
}
@Override
public void onActivityStopped(Activity activity) {
synchronized (mActivityLock) {
mStartStopedCount--;
if (mStartStopedCount == 0) {
// 下次启动时，从后台恢复
mIsOtherStart = true;
mLastEndAppTime = System.currentTimeMillis();
}
}
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
}
@Override
public void onActivityDestroyed(Activity activity) {
}
}
/**
* 后台任务恢复启动闪屏页，区别于SplashActivity页面的神策统计
*/
public class SplashHotActivity extends SplashActivity {
public static void actionStart(Context context) {
if (context == null) {
return;
}
Intent intent = new Intent(context, SplashHotActivity.class);
intent.putExtra(BUNDLE_KEY_START_FROM_BACK, true);
context.startActivity(intent);
}
}
3.2 管理Activity页面栈
Activity页面栈，最常用的实现就是用来完全退出应用。ActivityLifecycleCallbacks和Stack来管理所有的Activity，不仅方便集中管理存储Activity实例，也不容易造成内存泄露。监听回调方法onActivityCreated和 onActivityDestroyed 添加删除Actvity实例。
// CustomActivityLifecycleCallback.java
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
ActivityStackManager.getInstance().addActivity(activity);
}
@Override
public void onActivityDestroyed(Activity activity) {
ActivityStackManager.getInstance().removeActivity(activity);
}
// ActivityStackManager.java
public void addActivity(Activity activity){
if (activities == null) {
activities = new Stack<Activity>();
}
if (activities.search(activity) == -1) {
activities.push(activity);
}
}
public void removeActivity(Activity activity){
if (activities != null && activities.size()>0){
activities.remove(activity);
}
}
3.3 获取当前Activity页面
经常需要获取当前的 TopActivity 实例，用来弹出安全键盘、RN接口通信等。关于获取当前Activity的一些思考，结合具体实现，推荐两个实现思路：** 弱引用持有当前Activity实例和Activity页面栈方式。**
（1）CustomActivityLifecycleCallback.java
// CustomActivityLifecycleCallback.java
@Override
public void onActivityResumed(Activity activity) {
// 弱引用持有当前 Activity 实例
ActivityStackManager.getInstance().setCurrentActivity(activity);
// Activity 页面栈方式
ActivityStackManager.getInstance().setTopActivity(activity);
}
（2）为什么Activity页面栈方式还需要在onActivityResumed中设置当前Activity页面？
答疑：当关闭B页面返回A页面时，首先A页面的onResume会先执行，然后才会调用 B 页面的onDestroy。
（3）ActivityStackManager获取当前Activity页面
// ActivityStackManager.java
private WeakReference<Activity> sCurrentActivityWeakRef;
public Activity getCurrentActivity() {
Activity currentActivity = null;
if (sCurrentActivityWeakRef != null) {
currentActivity = sCurrentActivityWeakRef.get();
}
return currentActivity;
}
public void setCurrentActivity(Activity activity) {
sCurrentActivityWeakRef = new WeakReference<Activity>(activity);
}
public Activity getTopActivity(){
if (activities != null && activities.size() > 0) {
return activities.peek();
}
return null;
}
public void setTopActivity(Activity activity){
if (activities != null && activities.size() > 0) {
if (activities.search(activity) == -1) {
activities.push(activity);
return;
}
int location = activities.search(activity);
if (location != 1) {
activities.remove(activity);
activities.push(activity);
}
}
}
3.4 保存恢复状态值savedInstanceState
// CustomActivityLifecycleCallback.java
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
if (savedInstanceState != null && savedInstanceState.getBoolean("saveStateKey", false)) {
Log.e(TAG, "localTime --> " + savedInstanceState.getLong("localTime"));
}
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
outState.putBoolean("saveStateKey", true);
outState.putLong("localTime", System.currentTimeMillis());
}