Android-广播机制

广播机制

android中每个应用程序都可以对自己感兴趣的广播进行注册，这些广播可能是来源于系统也可能来源于其他应用程序，接收广播的方法则需要引入一个新概念——广播接收器 Broadcast Receiver

广播类型

1、标准广播

在广播发出后所有的广播接收器几乎同时接收到这条广播消息，因此没有先后之分，这种广播效率比较高也就意味着它是无法被截断的。

2、有序广播

广播发出后同一时刻只有一个广播接收器可以接收到这条广播消息，当这个广播接收器的逻辑执行完毕后，广播才会继续传播，优先级高的广播接收器就可以先接收到广播消息，而且还可以截断正在传播的广播，而后面的广播则不能收到广播消息。  

静态注册实现开机

new->Other->Broadcast Receiver

public class BootCompleteReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.

        Toast.makeText(context,"Boot Complete",Toast.LENGTH_SHORT).show();
    }
}

添加

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

与

<intent-filter>

<action android:name="android.intent.action.BOOT_COMPLETED"/>

</intent-filter>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.wangkangli.broadcast">
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
    <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=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

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

</manifest>重启即可启动

发送自定义广播

1、发送标准广播

先定义一个广播接收器准备接收此广播

public class MyBroadcastReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        Toast.makeText(context,"receiver in MyBroadcastReceiver",Toast.LENGTH_SHORT).show();
    }
}

在AndroidManifest.xml中修改广播接收器

<receiver
            android:name=".MyBroadcastReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="com.wangkangli.broadcast.MY_BROADCAST" />
            </intent-filter>
        </receiver>

设置点击事件发送广播

public class MainActivity extends AppCompatActivity {

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

2、发送有序广播

新建project->新建AnotherBroadcastReceiver

public class AnotherBroadcastReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        Toast.makeText(context,"received in AnotherBroadcastReceiver",Toast.LENGTH_SHORT).show();
    }
}

<receiver
            android:name=".AnotherBroadcastReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="com.wangkangli.broadcast.MY_BROADCAST" />
            </intent-filter>
        </receiver>

现在还是标准广播可以收到两个Toast提示

现在更改为有序广播更改MainActivity

 button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent("com.wangkangli.broadcast.MY_BROADCAST");
                sendOrderedBroadcast(intent,null);
            }
        });

使用sendOrderedBroadcast

如何设定先后顺序呢，在注册时

 <receiver
            android:name=".MyBroadcastReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="100">
                <action android:name="com.wangkangli.broadcast.MY_BROADCAST" />
            </intent-filter>
        </receiver>

priority = "100"优先级即比其他接收器高

现在截断这条广播使用abortBroadcast()

public class MyBroadcastReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        Toast.makeText(context,"receiver in MyBroadcastReceiver",Toast.LENGTH_SHORT).show();
        abortBroadcast();
    }
}

3、使用本地广播

前面发送和接收的都属于系统全局广播，关键性数据广播会被截断，其他程序会不断的向我们发送垃圾广播，这样就需要使用本地广播处理这些安全问题 LocalBroadcast对广播进行管理

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
    private LocalBroadcastManager localBroadcastManager;
    private LocalReceiver localReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        localBroadcastManager = LocalBroadcastManager.getInstance(this); //获取实例
        Button button = findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent("com.wangkangli.broadcast.LOCAL_BROADCAST");
                localBroadcastManager.sendBroadcast(intent); //发送本地广播
            }
        });
        intentFilter = new IntentFilter();
        intentFilter.addAction("com.wangkangli.broadcast.LOCAL_BROADCAST");
        localReceiver = new LocalReceiver();
        localBroadcastManager.registerReceiver(localReceiver,intentFilter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        localBroadcastManager.unregisterReceiver(localReceiver);
    }
}
class LocalReceiver extends BroadcastReceiver{
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context,"received local broadcast",Toast.LENGTH_SHORT).show();
    }
}

4、广播的最佳实践-实现强制下线功能

创建活动管理器

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();
            }
        }
    }
}

创建继承AppCompatActivity的BaseActivity

public class BaseActivity extends AppCompatActivity {
    private ForceOfflineReceiver receiver;

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

登陆界面

<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="Account:"/>
        <EditText
            android:id="@+id/account"
            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="Password:"/>
        <EditText
            android:id="@+id/password"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:layout_gravity="center_vertical"
            android:inputType="textPassword"/>
    </LinearLayout>

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

接收输入信息

public class LoginActivity extends BaseActivity {
private EditText accountEdit,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("admin")&&password.equals("123456")){
                    Intent intent = new Intent(LoginActivity.this,MainActivity.class);
                    startActivity(intent);
                    finish();
                }else{
                    Toast.makeText(LoginActivity.this,"account or password is invalid",Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

修改MainActivity

public class MainActivity extends BaseActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button forceOffine = findViewById(R.id.forcew_offline);
        forceOffine.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent("com.wangkangli.mylogicreceiver.FORCE_OFFLINE");
                sendBroadcast(intent);
            }
        });
    }
}

修改BaseActivity

public class BaseActivity extends AppCompatActivity {
    private ForceOfflineReceiver receiver;

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

    @Override
    protected void onResume() {
        super.onResume();
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction("com.wangkangli.mylogicreceiver.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.Please try to login again.");
        builder.setCancelable(false);
        builder.setPositiveButton("ok", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
           ActivityCollector.finishAll();
           Intent intent = new Intent(context,LoginActivity.class);
           context.startActivity(intent);
            }
        });
        builder.show();
    }
}

修改AndroidManifest.xml

        <activity android:name=".LoginActivity">
            <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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