运用BroadcastReceiver实现强制下线
思路:首先进入登录界面,输入账号和密码后登陆到主界面,在主界面通过点击按钮发送一条强制下线的广播,广播接收者收到广播后重新进入登陆界面。
新建项目Broadcast03。强制下线功能需要先关闭所有的活动,然后返回到登录界面。所以先创建一个ActivityCollector类用来管理所有的活动:
public class ActivityCollector {
public static List<Activity> activities = new ArrayList<Activity>();
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();
}
}
}
}
在这个类中定义了三个方法,分别用来添加活动、移除活动与关闭所有活动。然后新建一个BaseActivity类作为其他所有类的父类:
public class BaseActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActivityCollector.addActivity(this);
}
@Override
protected void onDestroy() {
super.onDestroy();
ActivityCollector.removeActivity(this);
}
}
在BaseActivity类中,调用了ActivityCollector类的addActivity()和removeActivity()方法,这样其他类继承BaseActivity类的时候就会自动重写这两个方法。
编写登录界面的布局login.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginLeft="10dp"
android:gravity="center"
android:text="account:"
android:textSize="16dp" />
<EditText
android:id="@+id/et_account"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:layout_weight="1"
android:hint="please input account" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginLeft="10dp"
android:gravity="center"
android:text="password:"
android:textSize="16dp" />
<EditText
android:id="@+id/et_password"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:layout_weight="1"
android:hint="please input password"
android:inputType="numberPassword" />
</LinearLayout>
<Button
android:id="@+id/bt_login"
android:layout_width="120dp"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="Login" />
</LinearLayout>
编写登录活动。新建LoginActivity继承自BaseActivity,实现登录的逻辑,这里设置当帐号为admin,密码为123456时才能登陆成功。
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.login);
accountEdit = (EditText) findViewById(R.id.et_account);
passwordEdit = (EditText) findViewById(R.id.et_password);
login = (Button) findViewById(R.id.bt_login);
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String account = accountEdit.getText().toString();
String password = passwordEdit.getText().toString();
if ("admin".equals(account) && "123456".equals(password)) {
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
startActivity(intent);
finish();
} else {
Toast.makeText(LoginActivity.this, "输入的帐号或者密码有误,请重新输入", Toast.LENGTH_SHORT).show();
}
}
});
}
}
登录成功会进入到MainActivity主界面,我们在activity_main布局中加入一个Button,通过点击这个按钮发送一条强制下线的广播。
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.beijing.broadcast03.MainActivity">
<Button
android:id="@+id/bt_force_offline"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Send force offline broadcast" />
</RelativeLayout>
MainActivity界面点击按钮发送广播的逻辑:
public class MainActivity extends AppCompatActivity {
private Button forceOffline;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
forceOffline = (Button) findViewById(R.id.bt_force_offline);
forceOffline.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("com.beijing.broadcast03.FORCE_OFFLINE");
sendBroadcast(intent);
}
});
}
}
这里发送了一条值为com.beijing.broadcast03.FORCE_OFFLINE的广播。创建广播接收者ForceOfflineReceiver继承自BroadcastReceiver,ForceOfflineReceiver收到广播后就会弹出一个对话框来达成强制下线的目的:
public class ForceOfflineReceiver extends BroadcastReceiver {
@Override
public void onReceive(final Context context, Intent intent) {
AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(context);
dialogBuilder.setTitle("Warning");
dialogBuilder.setMessage("您的帐号已在别处登陆,请重新登录。");
dialogBuilder.setCancelable(false);
dialogBuilder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
ActivityCollector.finishAll();//销毁所有Activity
Intent intent = new Intent(context, LoginActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(intent);//重新启动LoginActivity
}
});
AlertDialog alertDialog = dialogBuilder.create();
alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);//需要设置AlertDialog的类型,以便能够在广播接收者中正常弹出
alertDialog.show();
}
}
在此通过AlertDialog.Builder来构建一个对话框,注意一定要调用setCancelable()方法将对话框设置为不可取消(按返回键是无法退出对话框的)。接着使用setPositiveButton()方法给对话框注册确定按钮,当点击确定按钮后,就会调用ActivityCollector的finishAll()方法销毁所有活动,并重新进入到LoginActivity界面。因为是在广播接收者中启动活动,所以一定要给intent加上FLAG_ACTIVITY_NEW_TASK这个标志。最后,还要把对话框的类型设置成TYPE_SYSTEM_ALERT,不然无法在广播接收者中弹出对话框。现在还剩下在AndroidManifest.xml中进行配置的任务:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.beijing.broadcast03">
<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=".BaseActivity" />
<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"/>
<receiver android:name=".ForceOfflineReceiver">
<intent-filter>
<action android:name="com.beijing.broadcast03.FORCE_OFFLINE" />
</intent-filter>
</receiver>
</application>
</manifest>
有三点需要注意:首先,在ForceOfflineReceiver中弹出了一个系统级别的对话框,需要为其声明android.permission.SYSTEM_ALERT_WINDOW权限;其次要把LoginActivity注册为主活动;最后再注册ForceOfflineReceiver,并指定它接收com.beijing.broadcast03.FORCE_OFFLINE这条广播。
现在运行程序看看效果,先进入登录界面,并且可以输入帐号和密码:
输入帐号admin和密码123456后点击Login按钮就会进到主界面:
继续点击发送广播的按钮,就会发送一条广播。ForceOfflineReceiver收到这条广播后会弹出一个提示已被强制下线的对话框:
这时,用户将无法再做任何操作,只能点击确定按钮,重新回到登录界面。到此,通过广播接收者强制下线的目标已经完成了。