Android廣播機(jī)制原理與開發(fā)

更新時間：2023年02月23日 09:08:43 作者：Godams

Android廣播機(jī)制就是在Android中，有一些操作完成以后，會發(fā)送廣播，比如說發(fā)出一條短信，或打出一個電話，如果某個程序接收了這個廣播，就會做相應(yīng)的處理

廣播機(jī)制簡介

標(biāo)準(zhǔn)廣播：完全異步執(zhí)行，廣播發(fā)出后，所有廣播接收器幾乎都同一時刻收到這條廣播（無法被截斷）
有序廣播：同步執(zhí)行，廣播發(fā)出后同一時刻只會有一個廣播接收器能收到這條廣播消息，前面的接收器可以截斷正在傳遞的廣播

接收系統(tǒng)廣播

廣播接收器可在代碼中注冊和AndroidManifest.xml中注冊，前者為動態(tài)注冊，后者被稱為靜態(tài)注冊。

動態(tài)注冊監(jiān)聽網(wǎng)絡(luò)變化

示例代碼：

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
    private NetworkChangeReceiver networkChangeReceiver;
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView((R.layout.activity_main));
        intentFilter= new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_VHANGE");
        networkChangeReceiver = new NetworkChangeReceiver();
        registerReceiver(networkChangeReceiver, intentFilter);
    }
    @Override
    protected void onDestroy(){
        super.onDestroy();
        unregisterReceiver(networkChangeReceiver);
    }
    class NetworkChangeReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent){
            ConnectivityManager connectionManager = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo = connectionManager.getActiveNetworkInfo();
            if(networkInfo != null && networkInfo.isAvailable()){
                Toast.makeText(context, "network is available", Toast.LENGTH_SHORT).show();
            }else {
                Toast.makeText(context, "network is unavailable", Toast.LENGTH_SHORT).show();
            }
            Toast.makeText(context, "network changes", Toast.LENGTH_SHORT).show();
        }
    }
}

靜態(tài)注冊實(shí)現(xiàn)開機(jī)啟動

<receiver
            android:name=".BootCompleteReceiver"
            android:enabled="true"
            android:exported="true"></receiver>

Export屬性表示是否允許這個廣播接收器接收本程序以外的廣播，enable表示是否使用這個廣播接收器。

<receiver
            android:name=".BootCompleteReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED"/>
            </intent-filter>
        </receiver>

添加了filter就可以過濾了

可以通過左鍵新建-》其它來新建靜態(tài)注冊廣播

廣播接收器中不允許開線程，當(dāng)onReceive方法運(yùn)行較長時間而沒結(jié)束時，程序就會報錯，所以其中不能添加過多的邏輯或任何耗時操作。

發(fā)送自定義廣播

發(fā)送標(biāo)準(zhǔn)廣播

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

通過點(diǎn)擊按鈕發(fā)送廣播

public class myBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "receiverd in myBroadcastReceiver", Toast.LENGTH_SHORT).show();
    }
}

這里是自定義的接收器

<receiver
            android:name=".myBroadcastReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="com.example.broadcasttest.MY_BROADCAST"/>
            </intent-filter>
        </receiver>

在xml中定義過濾的廣播類型

發(fā)送有序廣播

廣播是一種跨進(jìn)程的通信方式

protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView((R.layout.activity_main));
        Button button = (Button)findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                Intent intent = new Intent("com.example.broadcasttest.MY_BROADCAST");
                sendOrderedBroadcast(intent, null);
            }
        });
    }

只需要修改一行代碼 sendOrederedBroadcast即可發(fā)送有序廣播，同時在接收器的xml文件中可以設(shè)置優(yōu)先級

<receiver
            android:name=".myBroadcastReceiver"
            android:enabled="true"
            android:exported="true">
<!--            在這里設(shè)置優(yōu)先級-->
            <intent-filter android:priority="100">
                <action android:name="com.example.broadcasttest.MY_BROADCAST"/>
            </intent-filter>
        </receiver>

如果想要在接收到廣播之后就讓廣播停止繼續(xù)傳遞呢，修改onReceive的代碼即可

public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "receiverd in myBroadcastReceiver", Toast.LENGTH_SHORT).show();
//        停止繼續(xù)傳遞
        abortBroadcast();
    }

使用本地廣播

前面我們發(fā)送和接收的廣播全部屬于系統(tǒng)全局廣播,即發(fā)出的廣播可以被其他任何應(yīng)用程序接收到,并且我們也可以接收來自于其他任何應(yīng)用程序的廣播。這樣就很容易引起安全性的問題,比如說我們發(fā)送的一些攜帶關(guān)鍵性數(shù)據(jù)的廣播有可能被其他的應(yīng)用程序截獲,或者其他的程序不停地向我們的廣播接收器里發(fā)送各種垃圾廣播。

使用本地廣播則發(fā)出的廣播只能在應(yīng)用程序內(nèi)部傳遞，并且接收器也只能接收來自本應(yīng)用程序發(fā)出的廣播。

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
    private LocalReceiver localReceiver;
    private LocalBroadcastManager localBroadcastManger;
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView((R.layout.activity_main));
        localBroadcastManger = LocalBroadcastManager.getInstance(this); //獲取實(shí)例
        Button button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent("com.example.broadcasttest.LOCAL_BROADCAST");
                localBroadcastManger.sendBroadcast(intent); //發(fā)送本地廣播
            }
        });
        intentFilter = new IntentFilter();
        intentFilter.addAction("com.example.broadcasttest.LOCAL_BROADCAST");
        localReceiver = new LocalReceiver();
        localBroadcastManger.registerReceiver(localReceiver, intentFilter); //注冊本地廣播監(jiān)聽器
    }
    @Override
    protected void onDestroy(){
        super.onDestroy();
        localBroadcastManger.unregisterReceiver(localReceiver);
    }
    class LocalReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent){
            Toast.makeText(context, "received local broadcast", Toast.LENGTH_SHORT).show();
        }
    }
}

代碼的不同主要在于需要首先獲取實(shí)例，然后還要有注冊。

需要注意的是，本地廣播無法通過靜態(tài)注冊來接收。

使用廣播實(shí)現(xiàn)強(qiáng)制下線功能

強(qiáng)制下線功能首先需要實(shí)現(xiàn)下關(guān)閉所有的活動的功能，新建一個ActivityCollector類管理所有的活動

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

然后創(chuàng)建baseActivity類作為活動的父類，代碼如下：

public class BaseActivity extends AppCompatActivity {
    private ForceOfflineReceiver receiver;
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        ActivityCollector.addActivity(this);
    }
    @Override
    protected void onResume(){
        super.onResume();
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction("com.example.broadcastbestpractice.FORCE_OFFLINE");
        receiver = new ForceOfflineReceiver();
        registerReceiver(receiver, intentFilter);
    }
    @Override
    protected void onPause(){
        super.onPause();
        if(receiver != null){
            unregisterReceiver(receiver);
            receiver = null;
        }
    }
    @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("warning");
            builder.setMessage("You are forced to be offline");
            builder.setCancelable(false);
            builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int which) {
                    ActivityCollector.finishAll(); //銷毀所有活動
                    Intent intent = new Intent(context, LoginActivity.class);
                    context.startActivity(intent); //重新啟動loginActivity
                }
            });
            builder.show();
        }
    }
}

我們可以注意到，之前編寫注冊和銷毀接收器的時候是在onCreate和onDestroy這兩個函數(shù)里的，但是上面代碼中卻寫在了onResume和onPause里面，這是因為我們每次都只需要在棧頂?shù)幕顒咏邮諒V播，非棧頂活動沒必要接收這條廣播。

除此之外，我們創(chuàng)建一個登陸的活動，在活動頁面上放置輸入框，并編寫登錄邏輯

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".ui.login.LoginActivity">
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        tools:ignore="MissingConstraints">
        <TextView
            android:layout_width="90dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:textSize="18sp"
            android:text="Account:"/>
        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:id="@+id/account"
            android:layout_weight="1"
            android:layout_gravity="center_horizontal"/>
    </LinearLayout>
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        tools:ignore="MissingConstraints">
        <TextView
            android:layout_width="90dp"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:textSize="18sp"
            android:text="password:"/>
        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:id="@+id/password"
            android:layout_weight="1"
            android:layout_gravity="center_horizontal"/>
    </LinearLayout>
    <Button
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:id="@+id/login"
        android:text="Login"
        tools:ignore="MissingConstraints"></Button>
</androidx.constraintlayout.widget.ConstraintLayout>

public class LoginActivity extends AppCompatActivity {
    private EditText accountEdit;
    private EditText passwordEdit;
    private Button login;
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        accountEdit = (EditText) findViewById(R.id.account);
        passwordEdit = (EditText) findViewById(R.id.password);
        login = (Button) 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();
                //如果賬號是admin 且密碼是123456則登錄成功
                if(account.equals("admin") && password.equals("123456")){
                    Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                    startActivity(intent);
                    finish();
                }else {
                    Toast.makeText(LoginActivity.this, "account is invalid", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

這樣就模擬了登錄的窗口，然后在mainActivity中加入觸發(fā)強(qiáng)制下線的代碼

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.broadcastbestpractice.FROCE_OFFLINE");
                sendBroadcast(intent);
            }
        });
    }
}

這樣邏輯就差不多了，下面去AndroidManifest.xml中修改下程序入口即可：

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