Android笔记（二十六）广播实践——实现强制下线功能

强制下线功能需要先关闭掉所有的活动，然后回到登录界面。先创建一个 ActivityCollector 类用于管理所有的活动，代码如下所示：

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

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

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

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

然后创建 BaseActivity 类作为所有活动的父类，代码如下所示：

public class BaseActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        ActivityCollector.addActivity(this);
    }

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

}

创建登录界面的布局

<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:stretchColumns="1" >

    <TableRow>

        <TextView
            android:layout_height="wrap_content"
            android:text="Account:" />

        <EditText
            android:id="@+id/account"
            android:layout_height="wrap_content"
            android:hint="Input your account" />
    </TableRow>

    <TableRow>

        <TextView
            android:layout_height="wrap_content"
            android:text="Password:" />

        <EditText
            android:id="@+id/password"
            android:layout_height="wrap_content"
            android:inputType="textPassword" />
    </TableRow>

    <TableRow>

        <Button
            android:id="@+id/login"
            android:layout_height="wrap_content"
            android:layout_span="2"
            android:text="Login" />
    </TableRow>

</TableLayout>

登录界面活动LoginActivity

public class LoginActivity extends BaseActivity {
    private EditText usernameet;
    private EditText passwordet;
    private Button button;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);
        usernameet=(EditText) findViewById(R.id.username);
        passwordet=(EditText) findViewById(R.id.password);
        button=(Button) findViewById(R.id.login);
        button.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String username=usernameet.getText().toString();
                String password=passwordet.getText().toString();
                //账号android密码123
                if(username.equals("android")&&password.equals("123")){
                    Intent intent =new Intent(LoginActivity.this,SecondActivity.class);
                    startActivity(intent);
                    finish();
                }else{
                    Toast.makeText(LoginActivity.this, "账号或密码错误", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }   
}

跳转界面布局

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <Button
        android:id="@+id/force_offline"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Send force offline broadcast" />

</LinearLayout>

跳转界面活动

public class SecondActivity extends BaseActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second);
        Button button=(Button) findViewById(R.id.force_offline);
        button.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent intent=new Intent("com.example.another.FORCE_OFFLINE");
                sendBroadcast(intent);
            }
        });
    }
}

强制下线接收器

public class ForceOfflineReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(final Context context, Intent intent) {
        // TODO Auto-generated method stub
        AlertDialog.Builder dialog=new AlertDialog.Builder(context);
        dialog.setTitle("Warning");
        dialog.setMessage("此账号已在别处登录，您已被强制下线");
        dialog.setCancelable(false);
        dialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub
                ActivityCollector.finishAll();
                Intent intent=new Intent(context,LoginActivity.class);
                intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                context.startActivity(intent);
            }
        }); 
        AlertDialog alertDialog=dialog.create();
        alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
        alertDialog.show();

    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.another"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="16" />

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

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".LoginActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".SecondActivity" >
        </activity>

        <receiver android:name=".ForceOfflineReceiver" >

            <intent-filter>
                <action android:name="com.example.another.FORCE_OFFLINE" />
            </intent-filter>
        </receiver>
    </application>

</manifest>

注意：当时在LoginActivity中忘了加载布局文件，导致整个应用无错误，但是一打开应用就崩。
setContentView(R.layout.login);