安卓强制下线

强制下线功能比较常见，很多应用程序都具备这个功能。例如你的QQ号在别处登录了，就会将你强制挤下线。其实实现强行挤下线的思路很简单，只需要在界面上弹出一个对话框，让用户无法进行其他操作。必须要点到对话框中的确定按钮，然后回到登录界面即可。

1.强制下线功能需要先关闭所有的活动，然后回到登录界面，此时我们先建一个ActivityCollector类用于管理所有活动的功能：

package com.example.myapplication;

import android.app.Activity;

import java.util.ArrayList;
import java.util.List;

public class ActivityCollector {
    public static List<Activity> activitys=new ArrayList<>();//存放活动的集合
    //添加活动
    public static void addActivity(Activity activity){
        activitys.add(activity);
    }
    //移除活动
    public static void remove(Activity activity){
        activitys.remove(activity);
    }
    //关闭所有活动
    public static void finshAll(){
        for(Activity activity:activitys){
            if(!activity.isFinishing()){
                activity.finish();
            }
        }
        activitys.clear();
    }
}

2.然后创建一个BaseActivity类作为所有活动的父类，此父类会动态注册一个广播接收器：

package com.example.myapplication;

import android.content.BroadcastReceiver;
import android.content.ComponentName;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.WindowManager;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

public class BaseActivity extends AppCompatActivity {
    private ForceOfflineReceiver receiver;

    @Override
    protected void onResume() {
        super.onResume();
        //注册广播
        IntentFilter intentFilter=new IntentFilter();
        intentFilter.addAction("com.example.My Application.FORCE_OFFLINE");
        receiver=new ForceOfflineReceiver();
        registerReceiver(receiver,intentFilter);
    }

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

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

    class ForceOfflineReceiver extends BroadcastReceiver{

        @Override
        public void onReceive(final Context context, Intent intent) {
            AlertDialog.Builder builder=new AlertDialog.Builder(context);
            builder.setTitle("警告");
            builder.setMessage("你被迫下线，请再次登录！");
            builder.setCancelable(false);
            builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    ActivityCollector.finshAll();//销毁所有活动
                    Intent i=new Intent(context,LoginActivity.class);
                    startActivity(i);//重新启动登录界面
                }
            });
            AlertDialog alertDialog=builder.create();
            alertDialog.show();

        }
    }
}

3.登录界面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:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="60dp">
        <TextView
            android:layout_width="90dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:textSize="18sp"
            android:text="用户名："/>
        <EditText
            android:id="@+id/username"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:layout_gravity="center_vertical"/>
    </LinearLayout>

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="60dp">
        <TextView
            android:layout_width="90dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:textSize="18sp"
            android:text="密码："/>
        <EditText
            android:id="@+id/password"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:layout_gravity="center_vertical"/>
    </LinearLayout>
    <Button
        android:id="@+id/login"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:text="登录"/>


</LinearLayout>

4.修改MainActivity.java，发送下线广播

package com.example.myapplication;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.content.BroadcastReceiver;
import android.content.ComponentName;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends BaseActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button forceOffline=(Button)findViewById(R.id.force_offline);
        forceOffline.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent("com.example.My Application.FORCE_OFFLINE");
                sendBroadcast(intent);
            }
        });

    }

}

activity_main.xml代码非常简单，只需要一个发送按钮就行：

<?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">

    <Button
        android:id="@+id/force_offline"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="发生强制下线广播"/>


</LinearLayout>

最后，修改AndroidManifest.xml,将登录界面设置为主活动

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapplication">
    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>
    <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=".MainActivity">

        </activity>
    </application>

</manifest>

结果：