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POLogcat: NullPointerException
 

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    <p>I am making an app that sends some bytes to a Lego NXT. I had a previous app working with the same code. When i run it, i get this in the LogCat:</p> <pre><code>10-29 12:35:12.691: I/ENTRE(14494): ONCREATE 10-29 12:35:12.721: I/Excelente(14494): BT ACTIVADO 10-29 12:35:12.721: I/Excelente(14494): ENTRE A BT ACTIVAR 10-29 12:35:12.721: V/BluetoothSocket.cpp(14494): initSocketNative 10-29 12:35:12.721: V/BluetoothSocket.cpp(14494): ...fd 40 created (RFCOMM, lm = 26) 10-29 12:35:12.721: V/BluetoothSocket.cpp(14494): initSocketFromFdNative 10-29 12:35:12.751: D/BluetoothUtils(14494): isSocketAllowedBySecurityPolicy start : device null 10-29 12:35:13.442: V/BluetoothSocket.cpp(14494): connectNative 10-29 12:35:14.153: V/BluetoothSocket.cpp(14494): ...connect(40, RFCOMM) = 0 (errno 115) 10-29 12:35:14.163: I/CONECTE(14494): CONEXION EXITOSA 10-29 12:35:14.163: I/Excelente(14494): CONEXION EXITOSA 10-29 12:35:14.163: I/Exelente(14494): ENTRE A MOTOR 10-29 12:35:14.163: I/Excelente(14494): ENTRE A WRITE 10-29 12:35:14.163: D/AndroidRuntime(14494): Shutting down VM 10-29 12:35:14.163: W/dalvikvm(14494): threadid=1: thread exiting with uncaught exception (group=0x4114e2a0) 10-29 12:35:14.163: E/AndroidRuntime(14494): FATAL EXCEPTION: main 10-29 12:35:14.163: E/AndroidRuntime(14494): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wordpress.sochidev.NXTControl/com.wordpress.sochidev.NXTControl.NXT}: java.lang.NullPointerException 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2092) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2117) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.app.ActivityThread.access$700(ActivityThread.java:134) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1218) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.os.Handler.dispatchMessage(Handler.java:99) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.os.Looper.loop(Looper.java:137) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.app.ActivityThread.main(ActivityThread.java:4867) 10-29 12:35:14.163: E/AndroidRuntime(14494): at java.lang.reflect.Method.invokeNative(Native Method) 10-29 12:35:14.163: E/AndroidRuntime(14494): at java.lang.reflect.Method.invoke(Method.java:511) 10-29 12:35:14.163: E/AndroidRuntime(14494): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007) 10-29 12:35:14.163: E/AndroidRuntime(14494): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774) 10-29 12:35:14.163: E/AndroidRuntime(14494): at dalvik.system.NativeStart.main(Native Method) 10-29 12:35:14.163: E/AndroidRuntime(14494): Caused by: java.lang.NullPointerException 10-29 12:35:14.163: E/AndroidRuntime(14494): at com.wordpress.sochidev.NXTControl.BT_comm.writeMessage(BT_comm.java:96) 10-29 12:35:14.163: E/AndroidRuntime(14494): at com.wordpress.sochidev.NXTControl.Motor.motor(Motor.java:41) 10-29 12:35:14.163: E/AndroidRuntime(14494): at com.wordpress.sochidev.NXTControl.NXT.onCreate(NXT.java:27) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.app.Activity.performCreate(Activity.java:5047) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094) 10-29 12:35:14.163: E/AndroidRuntime(14494): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2056) 10-29 12:35:14.163: E/AndroidRuntime(14494): ... 11 more 10-29 12:40:22.040: I/Process(14494): Sending signal. PID: 14494 SIG: 9 </code></pre> <p>Main Activity:</p> <pre><code>package com.wordpress.sochidev.NXTControl; import com.wordpress.sochidev.NXTControl.BT_comm; import com.wordpress.sochidev.NXTControl.Motor; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.view.Menu; import android.view.View; import android.widget.EditText; public class NXT extends Activity { boolean connection = false; BT_comm BT = new BT_comm(); Motor MT = new Motor(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_nxt); Log.i("ENTRE", "ONCREATE"); BT.enableBT(); Log.i("Excelente", "BT ACTIVADO"); BT.connectToNXTs(); Log.i("Excelente", "CONEXION EXITOSA"); MT.motor(2,(byte) 0x64, false, true, false); connection = true; } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.nxt, menu); return true; } } </code></pre> <p>Motor Class:</p> <pre><code>package com.wordpress.sochidev.NXTControl; import android.util.Log; public class Motor { BT_comm BT = new BT_comm(); public void motor(int motor, byte power, boolean speedReg, boolean motorSync, boolean brake) { Log.i("Exelente","ENTRE A MOTOR"); byte[] data = { (byte) 0x0c, (byte) 0x00, (byte) 0x80, (byte) 0x04, (byte) 0xFF, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x20, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00 }; switch (motor) { case 0: data[4] = (byte) 0xFF; break; case 1: data[4] = (byte) 0x00; break; case 2: data[4] = (byte) 0x01; break; case 3: data[4] = (byte) 0x02; break; } data[5] = power; if (speedReg) { data[7] = 0x01; } if (motorSync) { data[7] = 0x02; } if (brake) { data [6] = 0x02; } try { BT.writeMessage (data); } catch (InterruptedException e) { // TODO Auto-generated catch block Log.i("FAILED","SEND DATA"); } } } </code></pre> <p>BT_comm class:</p> <pre><code>package com.wordpress.sochidev.NXTControl; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.OutputStream; import java.io.OutputStreamWriter; import java.util.UUID; import com.wordpress.sochidev.NXTControl.NXT; import com.wordpress.sochidev.NXTControl.Motor; import android.bluetooth.BluetoothAdapter; import android.bluetooth.BluetoothDevice; import android.bluetooth.BluetoothSocket; import android.util.Log; public class BT_comm { //Target NXTs for communication final String nxt1 = "00:16:53:15:4D:66"; BluetoothAdapter localAdapter; BluetoothSocket socket_nxt1; boolean success=false; BluetoothSocket mmSocket; InputStream mmInStream; OutputStream mmOutStream; //Enables Bluetooth if not enabled public void enableBT(){ localAdapter=BluetoothAdapter.getDefaultAdapter(); //If Bluetooth not enable then do it if(localAdapter.isEnabled()==false){ localAdapter.enable(); while(!(localAdapter.isEnabled())){ } } } //connect to both NXTs public boolean connectToNXTs(){ //get the BluetoothDevice of the NXT BluetoothDevice nxt_1 = localAdapter.getRemoteDevice(nxt1); Log.i("Excelente", "ENTRE A BT ACTIVAR"); //try to connect to the nxt try { socket_nxt1 = nxt_1.createRfcommSocketToServiceRecord(UUID .fromString("00001101-0000-1000-8000-00805F9B34FB")); socket_nxt1.connect(); success = true; } catch (IOException e) { Log.i("Bluetooth","Err: Device not found or cannot connect"); success=false; } if (success) { Log.i("CONECTE","CONEXION EXITOSA"); } return success; } public void writeMessage(byte[] msg) throws InterruptedException{ //BluetoothSocket connSock; Log.i("Excelente","ENTRE A WRITE"); // connSock=socket_nxt1; try { // OutputStreamWriter out =new OutputStreamWriter(connSock.getOutputStream()); // mmOutStream.write(msg); // out.flush(); OutputStream outputStream = socket_nxt1.getOutputStream(); Log.i("Excelente","Asigne socket"); outputStream.write(msg); Log.i("Excelente","COMANDO EXITOSO"); Thread.sleep(100); } catch (IOException e) { // TODO Auto-generated catch block Log.i("PROBLEMA","ERROR DE DATOS"); } } public byte [] readMessage(){ byte[] buffer = new byte[64]; Log.i("Excelente","Entre a readmessage"); try { InputStream inputstream = socket_nxt1.getInputStream(); inputstream.read(buffer); //mmInStream.read(buffer); Log.i("Excelente","Lei los datos"); for (int index = 0; index &lt; buffer.length; index++){ Log.i("RECIBIDO:", String.format("0x%20x", buffer[index])); } Log.i("Excelente","Recibi datos y los escribi"); return buffer; } catch (IOException e) { // TODO Auto-generated catch block Log.i("PROBLEMA","ERROR DE DATOS AL RECIBIR"); return null; } } } </code></pre> <p>I guess it is I am new to android dev so i dont know what the error means. Any ideas?</p> <p>Thanks.</p>
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    1. COsomething is null at BT_comm.java: line no.96
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    2. COI know, socket_nxt1 is null but it should be equal to nxt_1.createRfcommSocketToServiceRecord(UUID .fromString("00001101-0000-1000-8000-00805F9B34FB")); socket_nxt1.connect(); At connectToNXTs()
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    3. COThen why don't you `catch` that exception?
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