I'm new to Android and i'm following an Android AudioRecord example. The aim is to record audio to a file when button btnStart is clicked and stop recording when the button btnStop is clicked. The code is as follows:
package com.example.blaqx.audio_record;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import android.app.Activity;
import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.widget.Button;
import com.example.blaqx.audio_record.R;
public class Audio_Record extends Activity {
private static final int RECORDER_SAMPLERATE = 8000;
private static final int RECORDER_CHANNELS = AudioFormat.CHANNEL_IN_MONO;
private static final int RECORDER_AUDIO_ENCODING = AudioFormat.ENCODING_PCM_16BIT;
private AudioRecord recorder = null;
private Thread recordingThread = null;
private boolean isRecording = false;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
setButtonHandlers();
enableButtons(false);
int bufferSize = AudioRecord.getMinBufferSize(RECORDER_SAMPLERATE,
RECORDER_CHANNELS, RECORDER_AUDIO_ENCODING);
}
private void setButtonHandlers() {
((Button) findViewById(R.id.btnStart)).setOnClickListener(btnClick);
((Button) findViewById(R.id.btnStop)).setOnClickListener(btnClick);
}
private void enableButton(int id, boolean isEnable) {
((Button) findViewById(id)).setEnabled(isEnable);
}
private void enableButtons(boolean isRecording) {
enableButton(R.id.btnStart, !isRecording);
enableButton(R.id.btnStop, isRecording);
}
int BufferElements2Rec = 1024; // want to play 2048 (2K) since 2 bytes we use only 1024
int BytesPerElement = 2; // 2 bytes in 16bit format
private void startRecording() {
recorder = new AudioRecord(MediaRecorder.AudioSource.MIC,
RECORDER_SAMPLERATE, RECORDER_CHANNELS,
RECORDER_AUDIO_ENCODING, BufferElements2Rec * BytesPerElement);
recorder.startRecording();
isRecording = true;
recordingThread = new Thread(new Runnable() {
public void run() {
writeAudioDataToFile();
}
}, "AudioRecorder Thread");
recordingThread.start();
}
//Conversion of short to byte
private byte[] short2byte(short[] sData) {
int shortArrsize = sData.length;
byte[] bytes = new byte[shortArrsize * 2];
for (int i = 0; i < shortArrsize; i++) {
bytes[i * 2] = (byte) (sData[i] & 0x00FF);
bytes[(i * 2) + 1] = (byte) (sData[i] >> 8);
sData[i] = 0;
}
return bytes;
}
private void writeAudioDataToFile() {
// Write the output audio in byte
String filePath = "/sdcard/8k16bitMono.pcm";
short sData[] = new short[BufferElements2Rec];
FileOutputStream os = null;
try {
os = new FileOutputStream(filePath);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
while (isRecording) {
// gets the voice output from microphone to byte format
recorder.read(sData, 0, BufferElements2Rec);
System.out.println("Short writing to file" + sData.toString());
try {
// writes the data to file from buffer stores the voice buffer
byte bData[] = short2byte(sData);
os.write(bData, 0, BufferElements2Rec * BytesPerElement);
} catch (IOException e) {
e.printStackTrace();
}
}
try {
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
private void stopRecording() {
// stops the recording activity
if (null != recorder) {
isRecording = false;
recorder.stop();
recorder.release();
recorder = null;
recordingThread = null;
}
}
private View.OnClickListener btnClick = new View.OnClickListener() {
public void onClick(View v) {
switch (v.getId()) {
case R.id.btnStart: {
enableButtons(true);
startRecording();
break;
}
case R.id.btnStop: {
enableButtons(false);
stopRecording();
break;
}
}
}
};
// onClick of backbutton finishes the activity.
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
finish();
}
return super.onKeyDown(keyCode, event);
}
}
I'm getting the following exception:
java.lang.NullPointerException
at com.example.blaqx.audio_record.Audio_Record.writeAudioDataToFile(Audio_Record.java:118)
at com.example.blaqx.audio_record.Audio_Record.access$000(Audio_Record.java:23)
at com.example.blaqx.audio_record.Audio_Record$1.run(Audio_Record.java:77)
at java.lang.Thread.run(Thread.java:841)
What i'm I doing wrong?
Thank you in advance.
When you use a try block, you're intended to put everything that depends on the objects created within it inside of the block.
So, while you have this:
FileOutputStream os = null;
try {
os = new FileOutputStream(filePath);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
...if os can't be created, it'll be null when you attempt to dereference it later (which you do). Check that your path is correct.
Here's how that might look. You can also adjust your close to be a finally condition so that you're always guaranteed to close it out if it's initialized.
FileOutputStream os = null;
try {
os = new FileOutputStream(filePath);
while (isRecording) {
// gets the voice output from microphone to byte format
recorder.read(sData, 0, BufferElements2Rec);
System.out.println("Short writing to file" + sData.toString());
try {
// writes the data to file from buffer stores the voice buffer
byte bData[] = short2byte(sData);
os.write(bData, 0, BufferElements2Rec * BytesPerElement);
} catch (IOException e) {
e.printStackTrace();
}
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} finally {
if(os != null) {
try {
os.close();
} catch(IOException e) {
e.printStackTrace();
}
}
}