1 类图

在【FJU项目】1像素进程保活(二)中，涉及到的几个类的类图如下所示(仅供参考)：

实线箭头：关联

虚线箭头：依赖

重构前UML类图在上图中，OnePixelManager里面有太多的职责，违背了单一职责原则。里面还有很多地方违背了其它的设计原则，稍后通过代码进行分析。

2 代码分析

2.1 之前的OnePixelManager类源码如下：

package com.yds.jianshu.onepixel;

import android.app.Activity;

import android.content.Context;

import android.content.Intent;

import android.content.IntentFilter;

import java.lang.ref.WeakReference;

public class OnePixelManager {

private static final String TAG = "[OnePixelManager]";

private WeakReference mActivity;

private OnePixelReceiver onePixelReceiver;

/**

* 一像素广播接收者注册方法。该方法中初始化OnePixelReceiver，并添加了过滤条件

* 屏幕息屏和亮屏。然后注册该广播接收者

* @param context

*/

public void registerOnePixelReceiver(Context context){

IntentFilter filter = new IntentFilter();

filter.addAction(Intent.ACTION_SCREEN_OFF);

filter.addAction(Intent.ACTION_SCREEN_ON);

onePixelReceiver = new OnePixelReceiver();

context.registerReceiver(onePixelReceiver,filter);

}

/**

* 对广播接收者进行解注册

* @param context

*/

public void unregisterOnePixelReceiver(Context context){

if (null != onePixelReceiver){

context.unregisterReceiver(onePixelReceiver);

}

}

/**

* 开启一像素Activity

* @param context

*/

public void startOnePixelActivity(Context context){

Intent intent = new Intent();

intent.setClass(context,OnePixelActivity.class);

context.startActivity(intent);

}

/**

* 关闭一像素Activity

*/

public void finishOnePixelActivity(){

if(null!=mActivity){

Activity activity = mActivity.get();

if(null!=activity){

activity.finish();

}

mActivity = null;

}

}

/**

* 使用弱引用获取一像素的上下文

* @param activity

*/

public void setKeepAliveReference(OnePixelActivity activity){

mActivity = new WeakReference(activity);

}

}

上述代码中，总共有5个方法，但是职责却不是单一的，上述方法的作用如下：

registerOnePixelReceiver：一像素广播接收者注册方法。该方法中初始化OnePixelReceiver，并添加了过滤条件屏幕息屏和亮屏。然后注册该广播接收者

unregisterOnePixelReceiver：对广播接收者进行解注册

startOnePixelActivity：开启一像素Activity

finishOnePixelActivity：关闭一像素Activity

setKeepAliveReference：使用弱引用获取一像素的上下文

上述可以大致分为两个职责，一个是对Activity进行管理，一个是对广播接收者进行管理，但上述代码将其封装到了一个类中，不利于扩展，且耦合度比较高。所以可以将其拆分成两个管理类，一个用于管理Activity的ActivityManager，一个用于管理Receiver的ReceiverManager类。

2.2 写一个Manager接口，预留后用

package com.yds.jianshu.itf;

/**

* Created by yds

* on 2019/8/2.

*/

public interface Manager {

//预留接口

}

写一个抽象ActivityManager类

package com.yds.jianshu.manager;

import android.app.Activity;

import android.content.Context;

import com.yds.jianshu.itf.Manager;

import com.yds.jianshu.utils.ObjectUtil;

/**

* Created by yds

* on 2019/8/2.

*/

public abstract class ActivityManager implements Manager {

public abstract void startActivity(Context context);

public void finishActivity(Activity activity){

ObjectUtil.requireNonNull(activity,"activity is null");

activity.finish();

}

}

一般Activity有两种最常用的行为，一个是开启Activity，一个是关闭Activity，开启Activity可以根据其需求写具体的代码，所以这里将其设置为抽象类型，关闭Activity几乎是通用的，这里就在抽象类里实现。

2.3 具体的Activity管理类OnePixelActivityManager

package com.yds.jianshu.manager;

import android.app.Activity;

import android.content.Context;

import android.content.Intent;

import com.yds.jianshu.onepixel.OnePixelActivity;

import com.yds.jianshu.utils.ObjectUtil;

import java.lang.ref.WeakReference;

/**

* Created by yds

* on 2019/8/2.

*/

public class OnePixelActivityManager extends ActivityManager {

private WeakReference mActivity;

/**

* 将{@link OnePixelActivity}的引用保存起来，用于后面监测到屏幕亮时关闭{@link OnePixelActivity}，

* 使用弱引用，是因为如果O{@link OnePixelActivity}被回收了，那么就不需要再保存该对象的引用用于

* finish了

* @param activity

*/

public void registerActivityReference(Activity activity){

ObjectUtil.requireNonNull(activity,"activity is null");

mActivity = new WeakReference(activity);

}

@Override

public void startActivity(Context context) {

ObjectUtil.requireNonNull(context,"context is null");

Intent intent = new Intent();

intent.setClass(context, OnePixelActivity.class);

context.startActivity(intent);

}

public void finishOnePixelActivity(){

ObjectUtil.requireNonNull(mActivity,"mActivity is null");

Activity activity = mActivity.get();

ObjectUtil.requireNonNull(activity,"activity is null");

finishActivity(activity);

mActivity = null;

}

}

2.4 用于管理BroadcastReceiver的类

package com.yds.jianshu.manager;

import android.content.BroadcastReceiver;

import android.content.Context;

import com.yds.jianshu.itf.Manager;

/**

* Created by yds

* on 2019/8/2.

*/

public abstract class ReceiverManager implements Manager {

public BroadcastReceiver receiver;

public abstract void register(Context context);

public abstract void unregister(Context context);

public void createReceiver(BroadcastReceiver receiver){

this.receiver = receiver;

}

}

广播接收者一般有两个行为，一个是注册，一个是取消注册。因为注册和取消注册，都需要创建具体的Receiver实例，所以可以将其提取到父类中。

2.5 用于管理1像素receiver的OnePixelReceiverManager

package com.yds.jianshu.manager;

import android.content.Context;

import android.content.Intent;

import android.content.IntentFilter;

import com.yds.jianshu.onepixel.OnePixelReceiver;

import com.yds.jianshu.utils.ObjectUtil;

/**

* Created by yds

* on 2019/8/2.

*/

public class OnePixelReceiverManager extends ReceiverManager {

public OnePixelReceiverManager(){

createReceiver(new OnePixelReceiver());

}

@Override

public void register(Context context) {

ObjectUtil.requireNonNull(context,"context is null");

ObjectUtil.requireNonNull(receiver,"receiver is null");

IntentFilter filter = new IntentFilter();

filter.addAction(Intent.ACTION_SCREEN_OFF);

filter.addAction(Intent.ACTION_SCREEN_ON);

context.registerReceiver(receiver,filter);

}

@Override

public void unregister(Context context) {

ObjectUtil.requireNonNull(context,"context is null");

ObjectUtil.requireNonNull(receiver,"receiver is null");

context.unregisterReceiver(receiver);

}

}

上述代码符合单一职责原则，单一职责原则有如下定义：

单一职责原则：一个对象应该只包含单一的职责，并且该职责被完整封装在一个类中。

上述OnePixelReceiverManager符合单一职责，它主要是对OnePixelReceiver进行相关操作管理；OnePixelActivityManager 也符合单一职责，它主要是对OnePixelActivity进行相关管理。

上述代码中，有这么一段代码：

public class OnePixelReceiverManager extends ReceiverManager {

public OnePixelReceiverManager(){

createReceiver(new OnePixelReceiver());

}

}

public abstract class ReceiverManager implements Manager {

public BroadcastReceiver receiver;

public void createReceiver(BroadcastReceiver receiver){

this.receiver = receiver;

}

}

ReceiverManager 的createReceiver的参数是BroadcastReceiver ，在ReceiverManager的子类OnePixelReceiverManager 中调用createReceiver时，用OnePixelReceiver实例化了BroadcastReceiver，这符合里氏代换原则，其定义如下：

里氏代换原则：所有引用基类的地方必须能透明地使用其子类的对象。

在里氏代换原则中，应该将父类设计为抽象类或者接口，让子类继承父类或实现父接口，并实现在父类中声明方法，在运行时子类实例替换父类实例。更详细可参考【设计模式】里氏代换原则

设计ActivityManager和ReceiverManager是为了让代码符合开闭原则，因为这两个管理类中都提取了Activity和Receiver的共性方法，如果需要增加其它具体的Activity和Receiver管理类，只需创建一个新的具体类，而不需要修改ActivityManager和ReceiverManager代码，符合开闭原则，开闭原则定义如下：

开闭原则： 软件实体应该对扩展开放，对修改关闭。

设计Manager接口也是如此，该接口是预留接口，后续可能会用到。

2.6 再看看OnePixelActivity里修改部分

package com.yds.jianshu.onepixel;

import android.app.Activity;

import android.os.Bundle;

import android.support.annotation.Nullable;

import android.util.Log;

import android.view.Gravity;

import android.view.Window;

import android.view.WindowManager;

import com.yds.jianshu.manager.OnePixelActivityManager;

public class OnePixelActivity extends Activity{

private static final String TAG = "[OnePixelActivity]";

private OnePixelActivityManager manager;

@Override

protected void onCreate(@Nullable Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setWindowAttributes();

initData();

Log.e(TAG,"onCreate");

}

private void initData(){

manager = new OnePixelActivityManager();

manager.registerActivityReference(this);//将引用传给OnePixelActivityManager

}

private void setWindowAttributes(){

Window window = getWindow();

window.setGravity(Gravity.LEFT|Gravity.TOP);

WindowManager.LayoutParams params = window.getAttributes();

params.x = 0;

params.y = 0;

params.height = 1;

params.width = 1;

window.setAttributes(params);

}

@Override

protected void onDestroy() {

super.onDestroy();

Log.e(TAG,"onDestroy");

}

@Override

protected void onStop() {

super.onStop();

Log.e(TAG,"onStop");

}

@Override

protected void onPause() {

super.onPause();

Log.e(TAG,"onPause");

}

@Override

protected void onStart() {

super.onStart();

Log.e(TAG,"onStart");

}

@Override

protected void onResume() {

super.onResume();

Log.e(TAG,"onResume");

}

}

2.7 OnePixelReceiver源码

package com.yds.jianshu.onepixel;

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;

import com.yds.jianshu.manager.OnePixelActivityManager;

public class OnePixelReceiver extends BroadcastReceiver {

private static final String TAG = "[OnePixelReceiver]";

private OnePixelActivityManager manager;

@Override

public void onReceive(Context context, Intent intent) {

String action = intent.getAction();

manager = new OnePixelActivityManager();

if (Intent.ACTION_SCREEN_ON.equals(action)){//如果亮屏，则关闭1像素Activity

manager.finishOnePixelActivity();

}else if(Intent.ACTION_SCREEN_OFF.equals(action)){//如果息屏，则开启1像素Activity

manager.startActivity(context);

}

}

}

2.8 OnePixelService源码部分

package com.yds.jianshu.onepixel;

import android.app.Service;

import android.content.Intent;

import android.os.IBinder;

import com.yds.jianshu.manager.OnePixelReceiverManager;

import com.yds.jianshu.manager.ReceiverManager;

public class OnePixelService extends Service {

private ReceiverManager manager;

public OnePixelService() {

}

@Override

public IBinder onBind(Intent intent) {

// TODO: Return the communication channel to the service.

throw new UnsupportedOperationException("Not yet implemented");

}

@Override

public int onStartCommand(Intent intent, int flags, int startId) {

manager = new OnePixelReceiverManager();//符合里氏代换原则

manager.register(this);//注册广播接收者

return START_STICKY;

}

@Override

public void onDestroy() {

manager.unregister(this);

}

}

在上述代码中，使用了OnePixelReceiverManager来实例化ReceiverManager ，符合里氏代换原则。

2.9 MainActivity代码

package com.yds.jianshu.mobile;

import android.content.Intent;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import com.example.myapplication.R;

import com.yds.jianshu.onepixel.OnePixelService;

public class MainActivity extends AppCompatActivity{

private static final String TAG = "[MainActivity]";

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

initData();

}

private void initData(){

startOnePixelService();

}

private void startOnePixelService(){

Intent intent = new Intent();

intent.setClass(MainActivity.this, OnePixelService.class);

startService(intent);

}

@Override

protected void onDestroy() {

super.onDestroy();

}

}

该部分代码基本不变。

在此基础上，还增加了一个工具类，用于对对象判空

package com.yds.jianshu.utils;

/**

* Created by yds

* on 2019/8/2.

*/

public class ObjectUtil {

public static T requireNonNull(T object,String message){

if(object == null){

throw new NullPointerException(message);

}

return object;

}

}

3 重构后的UML图

暂时不提供

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