java - 下次运行同一应用程序时，线程是否会记住它的状态？

Question

我正在尝试将麦克风获得的音频样本传递给扬声器
这是我正在使用的代码，使用 suggestions I obtained here

public class MainActivity extends Activity {
    AudioManager am = null;
    AudioRecord record =null;
    AudioTrack track =null;
    final int SAMPLE_FREQUENCY = 44100;
    final int SIZE_OF_RECORD_ARRAY = 1024;  // 1024 ORIGINAL
    final int WAV_SAMPLE_MULTIPLICATION_FACTOR = 1;
    int i= 0;
    boolean isPlaying = true;
    class MyThread extends Thread{
        private boolean passThroughMode = true;
        /*
        @Override
        public void run(){
            recordAndPlay(passThroughMode);
        }
        */

        MyThread(){
            super();
        }

        MyThread(boolean newPTV){
            this.passThroughMode = newPTV;
        }

        @Override
        public void run(){
            short[] lin = new short[SIZE_OF_RECORD_ARRAY];
            int num = 0;
            // am = (AudioManager) this.getSystemService(Context.AUDIO_SERVICE);
            // am.setMode(AudioManager.MODE_IN_COMMUNICATION);
            record.startRecording();
            track.play();
            // while (passThroughMode) {
            while (!isInterrupted()) {
                num = record.read(lin, 0, SIZE_OF_RECORD_ARRAY);
                for(i=0;i<lin.length;i++)
                    lin[i] *= WAV_SAMPLE_MULTIPLICATION_FACTOR; 
                track.write(lin, 0, num);
            }
        }
        /*
        public void stopThread(){
            passThroughMode = false;
        }
        */
    }

    MyThread newThread;

    private void init() {
        int min = AudioRecord.getMinBufferSize(SAMPLE_FREQUENCY, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);
        record = new AudioRecord(MediaRecorder.AudioSource.VOICE_COMMUNICATION, SAMPLE_FREQUENCY, AudioFormat.CHANNEL_IN_MONO,
                                 AudioFormat.ENCODING_PCM_16BIT, min);
        int maxJitter = AudioTrack.getMinBufferSize(SAMPLE_FREQUENCY, AudioFormat.CHANNEL_OUT_MONO, AudioFormat.ENCODING_PCM_16BIT);
        track = new AudioTrack(AudioManager.MODE_IN_COMMUNICATION, SAMPLE_FREQUENCY, AudioFormat.CHANNEL_OUT_MONO,
                               AudioFormat.ENCODING_PCM_16BIT, maxJitter, AudioTrack.MODE_STREAM);
     }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setVolumeControlStream(AudioManager.MODE_IN_COMMUNICATION);
        init();
        newThread = new MyThread(true);
        newThread.start();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
/*  
    private void recordAndPlay(boolean pTM) {
        short[] lin = new short[SIZE_OF_RECORD_ARRAY];
        int num = 0;
        am = (AudioManager) this.getSystemService(Context.AUDIO_SERVICE);
        am.setMode(AudioManager.MODE_IN_COMMUNICATION);
        record.startRecording();
        track.play();
        while (pTM) {
            num = record.read(lin, 0, SIZE_OF_RECORD_ARRAY);
            for(i=0;i<lin.length;i++)
                lin[i] *= WAV_SAMPLE_MULTIPLICATION_FACTOR; 
            track.write(lin, 0, num);
        }
    }
*/  
    public void passStop(View view){
        Button playBtn = (Button) findViewById(R.id.playBtn);  
        // /*
        if(!isPlaying){
            record.startRecording();
            track.play();
            isPlaying = true;
            playBtn.setText("Pause");
        }
        else{
           record.stop();
           track.pause();
           isPlaying=false;
           playBtn.setText("Pass through");
        }
        // */
    }

/*
    @SuppressWarnings("deprecation")
    @Override
    public void onDestroy(){
        newThread.stop();
    }
    */

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // android.os.Process.killProcess(android.os.Process.myPid());
        // killProcess(android.os.Process.myPid());
        // newThread.stopThread();
        newThread.interrupt();
    }
}

在第一次运行期间，程序运行良好，麦克风的声音传递到扬声器，当我按下返回按钮时，线程似乎也停止了，因此当应用程序退出时，传递停止。但是，如果我再次运行该应用程序，则不会发生传递。是否

newThread = new MyThread(true);
newThread.start();  

每次执行应用程序时(即调用 onCreate() )启动一个新线程，或者是否由于某种原因记住旧线程的状态？我怎样才能完全重置这个应用程序，以便每次执行时都会启动一个全新的应用程序？

--- 编辑 ---

无中断的替代版本:

public class MainActivity extends Activity {
    AudioManager am = null;
    AudioRecord record =null;
    AudioTrack track =null;
    final int SAMPLE_FREQUENCY = 44100;
    final int SIZE_OF_RECORD_ARRAY = 1024;  // 1024 ORIGINAL
    final int WAV_SAMPLE_MULTIPLICATION_FACTOR = 1;
    int i= 0;
    boolean isPlaying = true;
    class MyThread extends Thread{
        private volatile boolean passThroughMode = true;
         /*
        @Override
        public void run(){
            recordAndPlay(passThroughMode);
        }
        // */


        // /*
        MyThread(){
            super();
        }

        MyThread(boolean newPTV){
            this.passThroughMode = newPTV;
        }
        // */

        // /*
        @Override
        public void run(){
            short[] lin = new short[SIZE_OF_RECORD_ARRAY];
            int num = 0;
            // am = (AudioManager) this.getSystemService(Context.AUDIO_SERVICE);
            // am.setMode(AudioManager.MODE_IN_COMMUNICATION);
            record.startRecording();
            track.play();
            while (passThroughMode) {
            // while (!isInterrupted()) {
                num = record.read(lin, 0, SIZE_OF_RECORD_ARRAY);
                for(i=0;i<lin.length;i++)
                    lin[i] *= WAV_SAMPLE_MULTIPLICATION_FACTOR; 
                track.write(lin, 0, num);
            }
            record.stop();
            track.stop();
            record.release();
            track.release();
        }
        // */

        // /*
        public void stopThread(){
            passThroughMode = false;
        }
        // */
    }

    MyThread newThread;

    private void init() {
        int min = AudioRecord.getMinBufferSize(SAMPLE_FREQUENCY, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);
        record = new AudioRecord(MediaRecorder.AudioSource.VOICE_COMMUNICATION, SAMPLE_FREQUENCY, AudioFormat.CHANNEL_IN_MONO,
                                 AudioFormat.ENCODING_PCM_16BIT, min);
        int maxJitter = AudioTrack.getMinBufferSize(SAMPLE_FREQUENCY, AudioFormat.CHANNEL_OUT_MONO, AudioFormat.ENCODING_PCM_16BIT);
        track = new AudioTrack(AudioManager.MODE_IN_COMMUNICATION, SAMPLE_FREQUENCY, AudioFormat.CHANNEL_OUT_MONO,
                               AudioFormat.ENCODING_PCM_16BIT, maxJitter, AudioTrack.MODE_STREAM);
     }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setVolumeControlStream(AudioManager.MODE_IN_COMMUNICATION);
        init();
        Log.d("MYLOG", "onCreate() called");

        //Toast.makeText(getApplicationContext(), "HERE", Toast.LENGTH_SHORT).show();
        // newThread = new MyThread(true); // -> Moved this to onResume();
        // newThread = new MyThread();
        // newThread.start(); // -> Moved this to onResume()
        // newThread.run();
    }

    @Override
    protected void onResume(){
        super.onResume();
        // newThread.stopThread();
        Log.d("MYLOG", "onResume() called");
        newThread = new MyThread(true);
        newThread.start(); 
    }

    @Override
    protected void onPause(){
        super.onPause();
        Log.d("MYLOG", "onPause() called");
        newThread.stopThread();
        // android.os.Process.killProcess(android.os.Process.myPid());
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

     /* 
    private void recordAndPlay(boolean pTM) {
        short[] lin = new short[SIZE_OF_RECORD_ARRAY];
        int num = 0;
        am = (AudioManager) this.getSystemService(Context.AUDIO_SERVICE);
        am.setMode(AudioManager.MODE_IN_COMMUNICATION);
        record.startRecording();
        track.play();
        while (pTM) {
            num = record.read(lin, 0, SIZE_OF_RECORD_ARRAY);
            for(i=0;i<lin.length;i++)
                lin[i] *= WAV_SAMPLE_MULTIPLICATION_FACTOR; 
            track.write(lin, 0, num);
        }
    }
// */   
    public void passStop(View view){
        Button playBtn = (Button) findViewById(R.id.playBtn);  
        // /*
        if(!isPlaying){
            record.startRecording();
            track.play();
            isPlaying = true;
            playBtn.setText("Pause");
        }
        else{
           record.stop();
           track.pause();
           isPlaying=false;
           playBtn.setText("Pass through");
        }
        // */
    }

     /*
    @SuppressWarnings("deprecation")
    @Override
    public void onDestroy(){
        // newThread.stop();
        newThread.stopThread();
    }
    // */

    // /*
    @Override
    protected void onDestroy() {
        super.onDestroy();
        newThread.stopThread();
        // android.os.Process.killProcess(android.os.Process.myPid());
        // killProcess(android.os.Process.myPid());
        // newThread.interrupt();
         Log.d("MYLOG", "onDestroy() called");
    }
    // */
}  

---编辑2---

08-20 20:57:58.266: D/MYLOG(21936): onResume() called
08-20 20:57:58.266: W/dalvikvm(21936): threadid=11: thread exiting with uncaught exception (group=0x416f5700)
08-20 20:57:58.266: E/AndroidRuntime(21936): FATAL EXCEPTION: Thread-897
08-20 20:57:58.266: E/AndroidRuntime(21936): java.lang.IllegalStateException: startRecording() called on an uninitialized AudioRecord.
08-20 20:57:58.266: E/AndroidRuntime(21936):    at android.media.AudioRecord.startRecording(AudioRecord.java:517)
08-20 20:57:58.266: E/AndroidRuntime(21936):    at com.example.mypassthrough.MainActivity$MyThread.run(MainActivity.java:54)
08-20 20:57:58.286: D/MYLOG(21936): onPause() called
08-20 20:57:58.366: D/MYLOG(21936): onDestroy() called

Answer 1

不，Activity 实例之间的 Thread 对象没有状态持久性。 但是，您错误地假设每次运行应用程序时都会获得一个新的 Activity。 Activity 将持续存在，直到 Android 操作系统决定删除它们。只有当您再次进入应用程序时，才会创建一个新实例 - 否则，您将获得与之前相同的 Activity，并且在这种情况下不会再次调用 onCreate()。

换句话说，您应该使用 onResume() 和 onPause() 来进行 init/deinit。请查看lifecycle page了解更多详情。

编辑:另一个问题是您使用interrupt()来控制线程的流程。这并不总是一个好主意，因为 interrupt() 有 several side effects and may not even set the interrupt status to true depending on what's going with the thread 。您应该使用“shouldStop”字段来代替，因为那时语义是由您设置的。

请注意，这个“shouldStop”字段应该是一个字段，将其作为参数传递将不起作用。您应该在 MyThread 中有类似这样的内容:

    @Override
    public void run(){
        short[] lin = new short[SIZE_OF_RECORD_ARRAY];
        int num = 0;
        record.startRecording();
        track.play();
        while (passThroughMode) {
            num = record.read(lin, 0, SIZE_OF_RECORD_ARRAY);
            for(i=0;i<lin.length;i++)
                lin[i] *= WAV_SAMPLE_MULTIPLICATION_FACTOR; 
            track.write(lin, 0, num);
        }
    }

并且，在onPause()中:

@Override
protected void onPause() {
    super.onPause();
    newThread.stopThread();
}

如果线程仍然没有停止，则表明调用正在阻塞它，这对于 I/O 操作来说是典型的。

编辑2:还有一个问题是你没有stop()和release()你的AudioTrack code> 和 AudioRecord 当播放器线程关闭时(在 while 循环之后)。 使用与 I/O 相关的内容时的经验法则是，它通常附加到“ native ”资源，这些资源需要显式“手动”释放(有时还需要分配)。在这些情况下，您应该始终检查类 API 的情况。

编辑 3: ...MyThread 实例以及所有其他资源应该在 中完全初始化>onResume()，包括在其中创建新实例，而不是在 onCreate() 中创建。