利用Broadcast实现强制下线

一、设想
强制下线：当另一处有同一用户登录，本地用户被强退到登录页面，结束当前页面。
1、用ActivityCollector类实现关闭全部Activity的功能
2、用静态注册广播接收器实现强制下线
3、用MainActivity触发广播发送，模拟另一用户登录

二、实现
ActivityCollector类：

/**
 * 活动管理器类：实现关闭所有的活动的功能
 */
public class ActivityCollector {

    public static List<Activity> activities = new ArrayList<>();

    public static void addActivity(Activity activity) {
        activities.add(activity);
    }

    public static void removeActivity(Activity activity) {
        activities.remove(activity);
    }

    /**
     * 关闭所有的活动
     */
    public static void finishAll() {
        for(Activity activity : activities) {
            if(!activity.isFinishing()) {
                activity.finish();
            }
        }
    }
}

BaseActivity类：作为所有活动的基类

/**
 * 所有Activity的父类
 */
public class BaseActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //每当有活动创建，就加入活动管理器
        ActivityCollector.addActivity(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //从活动管理器移除
        ActivityCollector.removeActivity(this);
    }
}

LoginActivity类：登录页面，强退时也回退到这一页面

public class LoginActivity extends BaseActivity {
//用两个输入框和一个按钮简单模拟了一个登录页面
    private EditText account;

    private EditText pwd;

    private Button login;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        account = (EditText) findViewById(R.id.account);
        pwd = (EditText) findViewById(R.id.pwd);
        login = (Button) findViewById(R.id.button);
        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            //简单模拟登录逻辑
                if(account.getText().toString().equals("barbara") &&
                        pwd.getText().toString().equals("12345")) {
                    Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                    startActivity(intent);
                } else {
                    Toast.makeText(LoginActivity.this, "wrong", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

MainActivity类：模拟app登录后的主页面，模拟触发强制下线

/**
 * 登陆后的程序主页面
 */
public class MainActivity extends BaseActivity {

    private Button button;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        button = (Button) findViewById(R.id.buttonExit);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //发送一个广播,模拟触发强制下线
                Intent intent = new Intent("com.example.barbara.broadcastbestpractice.FORCE_OFFLINE");
                sendBroadcast(intent);
            }
        });
    }
}

ForceOfflineReceiver类：强制下线广播接收器

/**
 * 强制下线接收器
 */
public class ForceOfflineReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(final Context context, Intent intent) {//接收到广播后，显示提醒框，强制关闭所有Activity，返回登录界面
        AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(context);
        dialogBuilder.setTitle("Warning");
        dialogBuilder.setMessage("Force offline!");
        dialogBuilder.setCancelable(false);
        dialogBuilder.setPositiveButton("OK",
                new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        ActivityCollector.finishAll();
                        Intent intent = new Intent(context, LoginActivity.class);
                        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        context.startActivity(intent);
                    }
                });
        AlertDialog dialog = dialogBuilder.create();
        dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
        dialog.show();
    }
}

在Manifest文件中静态注册此接收器：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.barbara.broadcastbestpractice">

    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".LoginActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".MainActivity">
        </activity>
        <!-- 注册接收器-->
        <receiver android:name=".ForceOfflineReceiver">
            <intent-filter>
                <action android:name="com.example.barbara.broadcastbestpractice.FORCE_OFFLINE"/>
            </intent-filter>
        </receiver>
        <!-- 注册完成-->
    </application>

</manifest>