android – 为什么我会在这种状态下获得NPE

我正在尝试从设备录制音频.

我创建了一个AudioRecord对象,并在活动周期中对其进行管理.

当我的应用程序转到后台时,它会停止,而当它在前台时会继续.

录音运行时,我想将录音机中的样本转换为字节数组

这是我用来做的代码：

private void startRecorder() {
    Log.d(TAG, "before start recording");
    myBuffer = new byte[2048];
    audioManager.setMode(AudioManager.MODE_IN_COMMUNICATION);
    audioManager.requestAudioFocus(mAudioFocusListener, AudioManager.STREAM_DTMF, AudioManager.AUDIOFOCUS_GAIN_TRANSIENT);
    myRecorder = new AudioRecord(MediaRecorder.AudioSource.MIC, 8000, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, 2048);

    myThread = new Thread() {
        public void run() {
            while (true) {
                if (myRecorder != null && myRecorder.getState() == AudioRecord.RECORDSTATE_RECORDING) {
                    myRecorder.read(myBuffer, 0, 2048);
                    recordingSampleNumber++;
                    if (recordingSampleNumber % 10 == 0) {
                        Log.d(TAG, "recording sample number:" + recordingSampleNumber);
                    }
                }
            }
        }
    };
    myThread.setPriority(Thread.MAX_PRIORITY);

    myRecorder.startRecording();
    myThread.start();
    Log.d(TAG, "after start recording");
}

我的问题是：每隔一段时间我就会收到以下错误：

06-22 11:44:21.057: E/AndroidRuntime(17776): Process: com.example.microphonetestproject2, PID: 17776
06-22 11:44:21.057: E/AndroidRuntime(17776): java.lang.NullPointerException: Attempt to invoke virtual method 'int android.media.AudioRecord.getState()' on a null object reference
06-22 11:44:21.057: E/AndroidRuntime(17776):    at com.example.microphonetestproject2.MicrophoneTestApp$3.run(MicrophoneTestApp.java:108)

我的问题是：为什么我在myRecorder.getState()上获得一个NPE,而在我写“if myRecorder！= null”之前只有半行

解决方法:

这看起来像一个并发问题.

似乎在检查myRecorder！= null之后,该变量实际上在另一个线程中设置为null,这是可能的,因为您可能知道并行运行的线程.

我建议您锁定对象并执行循环.然后,没有人会不合时宜地访问它.

while (true) {
    synchronized (myRecorder) {
        if (myRecorder != null && myRecorder.getState() == AudioRecord.RECORDSTATE_RECORDING) {
            myRecorder.read(myBuffer, 0, 2048);
            recordingSampleNumber++;
            if (recordingSampleNumber % 10 == 0) {
                Log.d(TAG, "recording sample number:" + recordingSampleNumber);
            }
        }
    }
}

虽然这可能会解决您的问题,但您应该以其他方式处理它,例如：而不是将变量设置为null以取消线程,使用内置中断和连接方法：

private Thread mRecorderThread;

private void startRecorder() {
    myRecorder = new AudioRecord(MediaRecorder.AudioSource.MIC, 8000,
            AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, 2048);

    mRecorderThread = new Thread() {
        public void run() {
            while (true) {
                if (!isInterrupted() && myRecorder.getState() == AudioRecord
                        .RECORDSTATE_RECORDING) {
                    myRecorder.read(myBuffer, 0, 2048);
                    recordingSampleNumber++;
                    if (recordingSampleNumber % 10 == 0) {
                        Log.d(TAG, "recording sample number:" + recordingSampleNumber);
                    }
                }
            }
        }
    };
    mRecorderThread.setPriority(Thread.MAX_PRIORITY);
    myRecorder.startRecording();
    mRecorderThread.start();
    Log.d(TAG, "after start recording");
}

private void stopRecorder() {
    mRecorderThread.interrupt();
    // Wait for the thread to finish (for the interruption to take effect)
    try {
        mRecorderThread.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    myRecorder.stop();
}

你可能已经了解了interrupt(),中断了线程,但它并没有立即杀死它.在join()的帮助下,您可以在中断线程后等待线程完成.

标签：android,audiorecord
来源： https://codeday.me/bug/20190708/1400130.html