BroadcastReceiver机制

发布时间: 2025-03-22 13:11

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# BroadcastReceiver机制

本文将详细介绍Android系统中的广播机制,帮助读者理解BroadcastReceiver的工作原理和使用方法。

## 广播机制概述

### 1. 定义与作用

BroadcastReceiver是Android四大组件之一,主要用于：

- 接收系统或应用发出的广播消息
- 实现应用间的消息通信
- 监听系统状态变化
- 触发后台任务

### 2. 基本特性

- 无用户界面
- 可动态注册和注销
- 支持有序和无序广播
- 可以跨进程通信

## 广播类型

### 1. 普通广播

```java
// 发送普通广播
public void sendNormalBroadcast() {
    Intent intent = new Intent("com.example.NORMAL_ACTION");
    intent.putExtra("data", "normal broadcast");
    sendBroadcast(intent);
}

// 接收普通广播
public class NormalReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        String data = intent.getStringExtra("data");
        // 处理广播数据
    }
}
```

### 2. 有序广播

```java
// 发送有序广播
public void sendOrderedBroadcast() {
    Intent intent = new Intent("com.example.ORDERED_ACTION");
    intent.putExtra("data", "initial data");
    sendOrderedBroadcast(intent, null,
        new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                // 最终接收者处理
            }
        },
        null, Activity.RESULT_OK, null, null);
}

// 接收有序广播
public class OrderedReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        String data = getResultData();
        // 修改数据
        setResultData("modified data");
        // 终止广播
        // abortBroadcast();
    }
}
```

### 3. 粘性广播(已废弃)

```java
// 发送粘性广播(不推荐使用)
public void sendStickyBroadcast() {
    Intent intent = new Intent("com.example.STICKY_ACTION");
    intent.putExtra("data", "sticky broadcast");
    sendStickyBroadcast(intent);
}
```

### 4. 本地广播

```java
// 使用LocalBroadcastManager
public class LocalBroadcastExample {
    private LocalBroadcastManager localBroadcastManager;
    private BroadcastReceiver receiver;
    
    public void setup() {
        localBroadcastManager =
            LocalBroadcastManager.getInstance(context);
            
        receiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                // 处理本地广播
            }
        };
        
        // 注册本地广播接收器
        localBroadcastManager.registerReceiver(receiver,
            new IntentFilter("LOCAL_ACTION"));
    }
    
    public void sendLocalBroadcast() {
        Intent intent = new Intent("LOCAL_ACTION");
        localBroadcastManager.sendBroadcast(intent);
    }
    
    public void cleanup() {
        localBroadcastManager.unregisterReceiver(receiver);
    }
}
```

## 注册方式

### 1. 静态注册

```xml

<receiver
    android:name=".MyReceiver"
    android:enabled="true"
    android:exported="true">
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED" />
        <action android:name="com.example.MY_ACTION" />
    </intent-filter>
</receiver>
```

### 2. 动态注册

```java
public class DynamicRegistrationExample extends Activity {
    private BroadcastReceiver receiver;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        receiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                // 处理广播
            }
        };
        
        // 注册广播接收器
        IntentFilter filter = new IntentFilter();
        filter.addAction("com.example.MY_ACTION");
        registerReceiver(receiver, filter);
    }
    
    @Override
    protected void onDestroy() {
        super.onDestroy();
        // 注销广播接收器
        unregisterReceiver(receiver);
    }
}
```

## 广播权限

### 1. 发送广播权限

```java
// 发送带权限的广播
public void sendProtectedBroadcast() {
    Intent intent = new Intent("com.example.PROTECTED_ACTION");
    sendBroadcast(intent, "com.example.CUSTOM_PERMISSION");
}
```

### 2. 接收广播权限

```xml

<permission
    android:name="com.example.CUSTOM_PERMISSION"
    android:protectionLevel="signature" />

<uses-permission android:name="com.example.CUSTOM_PERMISSION" />

<receiver
    android:name=".ProtectedReceiver"
    android:permission="com.example.CUSTOM_PERMISSION">
    <intent-filter>
        <action android:name="com.example.PROTECTED_ACTION" />
    </intent-filter>
</receiver>
```

## 实现原理

### 1. 广播分发机制

```java
// 广播分发流程示意
public class BroadcastQueue {
    private final ArrayList<BroadcastRecord> mParallelBroadcasts =
        new ArrayList<>();
    private final ArrayList<BroadcastRecord> mOrderedBroadcasts =
        new ArrayList<>();
        
    public void enqueueBroadcastLocked(Intent intent,
                                      ProcessRecord callerApp,
                                      String callerPackage,
                                      int callingUid,
                                      boolean ordered) {
        BroadcastRecord r = new BroadcastRecord(intent,
            callerApp, callerPackage, callingUid,
            ordered ? mOrderedBroadcasts : mParallelBroadcasts);
            
        if (ordered) {
            mOrderedBroadcasts.add(r);
        } else {
            mParallelBroadcasts.add(r);
        }
        
        scheduleBroadcastsLocked();
    }
}
```

### 2. 接收器调用

```java
// 接收器调用流程
public final class ReceiverDispatcher {
    private final BroadcastReceiver mReceiver;
    private final Context mContext;
    private final Handler mActivityThread;
    private final Instrumentation mInstrumentation;
    private final boolean mRegistered;
    
    public void performReceive(Intent intent,
                             int resultCode,
                             String data,
                             Bundle extras,
                             boolean ordered,
                             boolean sticky,
                             int sendingUser) {
        // 准备接收环境
        Args args = new Args(intent, resultCode,
            data, extras, ordered,
            sticky, sendingUser);
            
        if (intent == null) {
            return;
        }
        
        // 调用接收器的onReceive方法
        mActivityThread.post(() -> {
            try {
                mReceiver.onReceive(mContext, intent);
            } catch (Exception e) {
                // 处理异常
            }
        });
    }
}
```

## 最佳实践

### 1. 广播使用建议

1. 选择合适的广播类型
   - 一般场景用普通广播
   - 需要顺序处理用有序广播
   - 应用内通信用本地广播

2. 注册方式选择
   - 需要常驻后台用静态注册
   - 和组件生命周期同步用动态注册
   - 注意及时注销避免内存泄漏

3. 安全性考虑
   - 使用权限控制
   - 避免敏感信息
   - 验证广播来源

### 2. 性能优化

1. 避免耗时操作
   - onReceive方法中不做耗时工作
   - 使用Service处理后台任务
   - 合理使用WakeLock

2. 减少广播次数
   - 合并相似广播
   - 使用其他通信方式
   - 避免频繁发送

### 3. 调试技巧

```java
// 广播调试辅助类
public class BroadcastDebugHelper {
    public static void logBroadcast(Context context,
                                   Intent intent,
                                   String tag) {
        // 记录广播信息
        Log.d(tag, "Action: " + intent.getAction());
        Log.d(tag, "Package: " + context.getPackageName());
        Log.d(tag, "Time: " + System.currentTimeMillis());
        
        // 打印Extra数据
        Bundle extras = intent.getExtras();
        if (extras != null) {
            for (String key : extras.keySet()) {
                Log.d(tag, "Extra: " + key + " = " +
                    extras.get(key));
            }
        }
    }
}
```

## 总结

BroadcastReceiver机制的关键点：

1. 多种广播类型
   - 普通广播
   - 有序广播
   - 本地广播

2. 灵活的注册方式
   - 静态注册
   - 动态注册
   - 权限控制

3. 系统级通信
   - 跨进程通信
   - 系统事件监听
   - 应用间交互

通过合理使用广播机制,开发者可以：

1. 实现组件间通信
2. 监听系统状态
3. 触发后台任务
4. 实现应用解耦

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