接收广播意图时出现错误

Question

尝试使用ConnectivityManager.CONNECTIVITY_ACTION测试broadCastReceiver时，应用程序崩溃，并且logcat显示Error receiving broadcast Intent。请告诉我我错过了什么。

代码:

public class wifi_socket_01 extends Activity {

TextView tv_conn_status;
TextView tv_conn_ssid;
TextView tv_conn_speed;
TextView tv_conn_strengt;
TextView tv_conn_ip;

EditText et_ip;
ToggleButton tobBtn_connect;
EditText et_msg;
Button btn_send;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    SetUpAllViews(R.layout.activity_main);
    displayWiFiStates();

    this.registerReceiver(this.myWiFiReceiver, 
            new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION));
}

private BroadcastReceiver myWiFiReceiver = new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO Auto-generated method stub
        NetworkInfo networkInfo = intent.getParcelableExtra(ConnectivityManager.EXTRA_EXTRA_INFO);
        if (networkInfo.getType() == ConnectivityManager.TYPE_WIFI) {
            displayWiFiStates();
        }
    }
};

private void SetUpAllViews(int layout) {
    // TODO Auto-generated method stub
    setContentView(layout);

    tv_conn_status = (TextView) findViewById(R.id.tv_conn_status);
    tv_conn_ssid = (TextView) findViewById(R.id.tv_conn_ssid);
    tv_conn_speed = (TextView) findViewById(R.id.tv_conn_speed);
    tv_conn_strengt = (TextView) findViewById(R.id.tv_conn_strength);
    tv_conn_ip = (TextView) findViewById(R.id.tv_conn_ip);
    et_ip = (EditText) findViewById(R.id.et_ip);
    tobBtn_connect = (ToggleButton) findViewById(R.id.togbtn_connect);
    et_msg = (EditText) findViewById(R.id.et_msg);
    btn_send = (Button) findViewById(R.id.btn_send);
}

protected void displayWiFiStates() {
    // TODO Auto-generated method stub
    String service = Context.CONNECTIVITY_SERVICE;
    ConnectivityManager myConnManager = (ConnectivityManager) getSystemService(service);
    NetworkInfo myNetworkInfo = myConnManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
    WifiManager myWifiManager = (WifiManager)getSystemService(Context.WIFI_SERVICE);
    WifiInfo myWiFiInfo = myWifiManager.getConnectionInfo();

    if(myNetworkInfo.isConnected()) {
        tv_conn_ip.setText("IP: "+myWiFiInfo.getIpAddress());
    }else {
        tv_conn_status.setText("Disconnected");
    }
}

}

LogCat:

11-08 10:26:57.645: E/AndroidRuntime(15348): FATAL EXCEPTION: main
11-08 10:26:57.645: E/AndroidRuntime(15348): Process: com.example.wifi_socket_01, PID:   
15348
11-08 10:26:57.645: E/AndroidRuntime(15348): java.lang.RuntimeException: Error 
receiving broadcast Intent { act=android.net.conn.CONNECTIVITY_CHANGE flg=0x4000010   
(has extras) } in com.example.wifi_socket_01.MainActivity$1@4302f638
11-08 10:26:57.645: E/AndroidRuntime(15348):    at 
android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:782)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at a
ndroid.os.Handler.handleCallback(Handler.java:733)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at 
 android.os.Handler.dispatchMessage(Handler.java:95)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at 
android.os.Looper.loop(Looper.java:157)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at 
android.app.ActivityThread.main(ActivityThread.java:5293)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at  
java.lang.reflect.Method.invokeNative(Native Method)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at   
java.lang.reflect.Method.invoke(Method.java:515)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at 
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at   
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at    
dalvik.system.NativeStart.main(Native Method)
11-08 10:26:57.645: E/AndroidRuntime(15348): Caused by: java.lang.NullPointerException
11-08 10:26:57.645: E/AndroidRuntime(15348):    at 
com.example.wifi_socket_01.MainActivity$1.onReceive(MainActivity.java:48)
11-08 10:26:57.645: E/AndroidRuntime(15348):    at 
android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:772)

- LetsamrIt

---

在 AndroidManifest.xml 文件中，你被授予了哪些权限？ - Haresh Chhelana

我认为你无法使用http://developer.android.com/reference/android/net/ConnectivityManager.html#EXTRA_EXTRA_INFO检索网络信息。 - Spurdow

Answer 1

你可能在AndroidManifest中缺少正确的Android权限：

 <!-- ANDROID PERMISSIONS -->
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

- Otieno Rowland

Answer 2

尝试使用这个替代方法：

更改您的

NetworkInfo networkInfo = intent.getParcelableExtra(ConnectivityManager.EXTRA_EXTRA_INFO);

为了

ConnectivityManager cm =
        (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = cm.getActiveNetworkInfo();

从文档中得知：EXTRA_EXTRA_INFO是一个可选提供的字符串查找键，用于提供有关网络状态的额外信息。该信息可能来自较低级别的网络层，并且其含义可能特定于特定的网络类型。使用getStringExtra(String)检索它。常量值为“extraInfo”。

因此，我们发现问题的根本在于它实际上并没有返回networkInfo。这一切都与网络状态有关。

希望对您有所帮助 :)

- Spurdow

---

是的，因为您正在访问networkInfo.getType() [它是null]，所以才会抛出NPE异常。 - Spurdow

抱歉，我不明白为什么它是空的，Wi-Fi已激活。 - LetsamrIt

即使您获取了实例，除非使用该实例及其行为，否则它不会抛出NPE。现在您将获得NPE。以下是示例：Person p = null; // p仅为null p.getFirstNAme(); // 抛出异常，就像null.getFirstName() - Spurdow

让我们在聊天中继续这个讨论。 - Spurdow

也许您还想检查一下这个问题 http://stackoverflow.com/questions/26816657/the-network-states-do-not-change-synchronously-according-to-its-broadcastreceive - LetsamrIt

Answer 3

我遇到了同样的问题，最终发现是onReceive函数内部的空指针引起的，我通过修改代码解决了这个问题。

    Boolean up = cm.getActiveNetworkInfo().isConnected();

转换为

    NetworkInfo info = cm.getActiveNetworkInfo();
    boolean up = false;
    if(info != null && info.isConnected()){
        up = true;
    }

我也在使用Android N，这个问题发生在运行在UI线程上的服务中。

- Fire Crow