Android使用广播的最佳实践——强制下线功能

看了《第二行代码》一段时间了，这次按照书上的内容，用广播写个退出登录的功能。强制下线功能会关闭掉所有的活动，然后回到登录界面。
先新建一个空项目day10_BroadcastBestPractice

一、管理页

新建一个ActivityCollector类，用来管理所有的活动

public class ActivityCollector {
    private static List<Activity> activities = new ArrayList<>();

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

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

    public static void finishAll(){
        for (Activity activity : activities){
            if (!activity.isFinishing()){
                activity.finish();
            }
        }
        activities.clear();
    }
}

新建一个BaseActivity活动当所有活动的父类

public class BaseActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActivityCollector.addActivity(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        ActivityCollector.removeActivity(this);
    }
}

最后在AndroidManifest.xml把登录页设置为启动页：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.day10_broadcastbestpratice">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        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=".BaseActivity" />
        <activity android:name=".MainActivity"></activity>
    </application>

</manifest>

二、登录页

新建LoginActivity，对应的布局文件activity_login.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:orientation="horizontal">
        <TextView
            android:gravity="center"
            android:layout_width="90dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:textSize="18sp"
            android:text="用户名:"/>
        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:layout_gravity="center_vertical"
            android:id="@+id/account"
            android:hint="在这里输入用户名啊~魂淡~"/>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:orientation="horizontal">
        <TextView
            android:layout_width="90dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:gravity="center"
            android:text="密码:"
            android:textSize="18sp"/>
        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/password"
            android:inputType="textPassword"
            android:layout_gravity="center_vertical"
            android:hint="在这里输入密码啊~魂淡~"/>
    </LinearLayout>

    <Button
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:text="登录"
        android:id="@+id/login"/>

</LinearLayout>

这是它的LoginActivity，账号和密码已经锁死：

public class LoginActivity extends BaseActivity {
    private EditText accountEdit;
    private EditText passwordEdit;
    private Button login;

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

        accountEdit = findViewById(R.id.account);
        passwordEdit = findViewById(R.id.password);
        login = findViewById(R.id.login);
        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String account = accountEdit.getText().toString();
                String password = passwordEdit.getText().toString();
                if (account.equals("breathy") && password.equals("000000")){
                    Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                    startActivity(intent);
                    finish();
                }else {
                    Toast.makeText(LoginActivity.this, "账号或密码不正确", Toast.LENGTH_LONG).show();
                }
            }
        });
    }
}

三、主页

主页就是登录成功的页面，来康康他的布局：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="恭喜你登陆成功！"
        android:layout_gravity="center"
        android:gravity="center"
        android:textSize="20sp"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:text="点我注销"
        android:id="@+id/force_offline"/>

</FrameLayout>

主活动的下线按钮会发送出OKForceOffline这样一条广播

public class MainActivity extends BaseActivity {

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

        Button force_offline = findViewById(R.id.force_offline);
        force_offline.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent("OKForceOfflineReceiver");
                sendBroadcast(intent);
            }
        });
    }
}

四、广播接收器

为了使得强制下线功能不依附于任何界面，但是可以在任何时候都能弹出对话框阻塞操作，所以这个动态广播接收器应该在BaseActivity中，要点如下：

1. 完成广播接收器的注册。为了保证其能接收到下线的消息，接收广播的活动必须处于栈顶，即onResume()下
2. 响应广播的功能。弹出一个不可取消的对话框，提示下线
3. 注销广播接收器情况。为了避免重复注册广播接收器，在onPause()里注销广播接收器

代码如下：

public class BaseActivity extends AppCompatActivity {
    private ForceOfflineReceiver receiver;

    @Override
    protected void onPause() {
        super.onPause();
        if (receiver != null){
            unregisterReceiver(receiver);
            receiver = null;
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction("OKForceOfflineReceiver");
        receiver = new ForceOfflineReceiver();
        registerReceiver(receiver, intentFilter);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActivityCollector.addActivity(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        ActivityCollector.removeActivity(this);
    }

    class ForceOfflineReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(final Context context, Intent intent) {
            AlertDialog.Builder builder = new AlertDialog.Builder(context);
            builder.setTitle("提示");
            builder.setMessage("你被踢下线了。");
            builder.setCancelable(false);
            builder.setPositiveButton("行吧", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    ActivityCollector.finishAll();
                    Intent i = new Intent(context, LoginActivity.class);
                    context.startActivity(i);
                }
            });
            builder.show();
        }
    }
}

五、运行

完美！