SocketService.java：
public class SocketService extends Service {
int mStartMode;
IBinder mBinder = new LocalBinder();
boolean mAllowRebind;
String IPValue;
String PortValue;
Socket socket;
byte data[];
public class LocalBinder extends Binder {
public SocketService getServerInstance() {
return SocketService.this;
}
}
@Override
public void onCreate() {
System.out.println("SERVICE CREATED");
SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
IPValue = sharedPreferences.getString("IPValue", "NA");
PortValue = sharedPreferences.getString("PortValue", "NA");
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
System.out.println("SERVICE ONSTARTCOMMAND");
return mStartMode;
}
@Override
public IBinder onBind(Intent intent) {
System.out.println("SERVICE BOUND");
try {
InetAddress serverAddr = null;
serverAddr = InetAddress.getByName(IPValue);
int serverPort = Integer.parseInt(PortValue);
System.out.println(serverAddr.getHostAddress() + serverPort);
socket = new Socket(serverAddr, serverPort);
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return mBinder;
}
public void send_mesage(String msg) {
PrintWriter out = null;
try {
out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
socket.getOutputStream())), true);
out.println(msg);
} catch (IOException e) {
e.printStackTrace();
}
}
}
我已经在 中获取了 IP 和端口onCreate，并在 中建立了套接字连接onBind。
现在在我的活动中：
public class MainActivity extends Activity {
public String IPValue;
public String PortValue;
public Socket socket;
boolean mBounded;
SocketService mServer;
ServiceConnection mConnection = new ServiceConnection() {
public void onServiceDisconnected(ComponentName name) {
Toast.makeText(MainActivity.this, "Service is disconnected", 1000).show();
mBounded = false;
mServer = null;
}
public void onServiceConnected(ComponentName name, IBinder service) {
Toast.makeText(MainActivity.this, "Service is connected", 1000).show();
mBounded = true;
SocketService.LocalBinder mLocalBinder = (SocketService.LocalBinder)service;
mServer = mLocalBinder.getServerInstance();
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Intent mIntent = new Intent(this, SocketService.class);
bindService(mIntent, mConnection, BIND_AUTO_CREATE);
}
这完美地工作，我的 TCP 服务器显示连接为 created。
现在我想访问send_message()里面的方法SocketService。所以我只是mServer.send_mesage("HELLO WORLD!");在我的活动中添加bindService(mIntent, mConnection, BIND_AUTO_CREATE);了。onCreate()
但这会导致一切崩溃。我的服务器和应用程序 FC 上没有建立我的连接。以下是日志：
10-21 15:37:33.945 9125-9125/com.example.myfirstapp D/dalvikvm﹕ GC_EXTERNAL_ALLOC freed 54K, 50% free 2694K/5379K, external 0K/0K, paused 313ms
10-21 15:37:48.985 9125-9125/com.example.myfirstapp D/AndroidRuntime﹕ Shutting down VM
10-21 15:37:48.985 9125-9125/com.example.myfirstapp W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x40018560)
10-21 15:37:49.015 9125-9125/com.example.myfirstapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1768)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
at android.app.ActivityThread.access$1500(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3835)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:864)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.myfirstapp.MainActivity.onCreate(MainActivity.java:57)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
at android.app.ActivityThread.access$1500(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3835)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:864)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)
at dalvik.system.NativeStart.main(Native Method)
NullPointerException 就在我刚刚添加的新行上！
我不明白是什么导致了这个问题！甚至奇怪的是，显然这次甚至没有调用服务的onCreateandonBind方法，因为我没有看到我在每个语句中放入的 print 语句的输出。
有什么帮助吗？