使用 Android AudioRecord 时出现 java.lang.NullPointerException

Question

我是 Android 新手，正在学习 Android AudioRecord 示例。目的是在单击按钮 btnStart 时将音频录制到文件中，并在单击按钮 btnStop 时停止录制。代码如下:

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);
    }
}

我收到以下异常:

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)

我做错了什么？

提前谢谢你。

Answer 1

当您使用 try block 时，您打算将依赖于其中创建的对象的所有内容放入 block 内。

所以，当你有这个的时候:

FileOutputStream os = null;
try {
    os = new FileOutputStream(filePath);
} catch (FileNotFoundException e) {
    e.printStackTrace();
}

...如果无法创建 os，当您稍后尝试取消引用它时(您这样做)，它将为 null。检查您的路径是否正确。

这可能是这样的。您还可以将 close 调整为 finally 条件，以便始终保证在初始化时关闭它。

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();
        }
    }
}