Android：如何防止手机旋转后创建新线程

Question

我编写了一个 android 程序来检测房间是否嘈杂。但是每当我旋转手机时，短信和图像将不再更新，并且会打印噪音分贝 - 无穷大及其正确值。我认为每次我旋转手机时都会创建一个新线程。因为如果我旋转手机，将再打印一次幅值 Db 量，其值为 - 无穷大。我怎样才能防止这种情况发生？如何在每次旋转手机时不生成新线程的情况下保持初始线程运行？

这是我的代码

public class EnvironmentalNoise extends AppCompatActivity {

Context mContext;
private MediaRecorder mRecorder = null;
double soundLevel;
SoundMeter sm;
ImageView noiseImage;
TextView noiseTv;
double amplitudeDb;
boolean mediaRecorderExist;
boolean isTreadRunning;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_environmental_noise);
    noiseImage = findViewById(R.id.noiseImage);
    noiseTv = findViewById(R.id.noiseTv);
    mContext = getApplicationContext();
    PackageManager PM= this.getPackageManager();
    sm = new SoundMeter();
    final boolean microphone = PM.hasSystemFeature(PackageManager.FEATURE_MICROPHONE);
    amplitudeDb =0;
    mediaRecorderExist = false;
    isTreadRunning =false;
    if (microphone){
        sm.start();
    }
    else{
        noiseTv.setText("Sorry !!! This device is not equipped to microphone to detect environmental noise");
    }

}


@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    Log.d("SaveState", "onSaveInstanceState called");

    //save current amplitudeDb value in bundle key - value
    outState.putDouble("SAVED_STATE_COUNT_KEY", amplitudeDb);
    outState.putBoolean("MEDIA_RECORDER_EXIST",mediaRecorderExist);
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    Log.d("SaveState", "onRestoreInstanceState called");

    //retrieve current counter value from bundle based on key
    int retrievedNoiseDecibel = savedInstanceState.getInt("SAVED_STATE_COUNT_KEY");
    boolean retrievedMediaRecorder = savedInstanceState.getBoolean("MEDIA_RECORDER_EXIST");
    if(retrievedMediaRecorder){
        retrievedMediaRecorder = false;
    }

    //update text view
    if(retrievedNoiseDecibel>60){
        noiseTv.setText("This room is noisy!!!");
        noiseImage.setBackgroundResource(R.drawable.noise);
    }
    else{
        noiseTv.setText("This room is quiet!!!");
        noiseImage.setBackgroundResource(R.drawable.quiet);
    }


    Log.d("SaveState", "retrieved counter value:" + retrievedNoiseDecibel);
    //Toast.makeText(this, "retrieved counter value:" + retrievedCounter, Toast.LENGTH_LONG).show();

    amplitudeDb = retrievedNoiseDecibel; //update total number of clicks
    mediaRecorderExist = retrievedMediaRecorder;
}


//start of refrencing
// found this piece of code from here : https://stackoverflow.com/questions/31305163/getmaxamplitude-always-returns-0
public class SoundMeter {

    private MediaRecorder mRecorder = null;

    public void start() {
        if(mediaRecorderExist){
            mRecorder.stop();
            mRecorder.release();
            mRecorder = null;
        }
        if (mRecorder == null) {
            mRecorder = new MediaRecorder();
            mediaRecorderExist =true;
            mRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
            mRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
            mRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
            Timer timer = new Timer();
            //timer.schedule(new EnvironmentalNoise.RecorderTask(mRecorder), 0);
            timer.scheduleAtFixedRate(new RecorderTask(mRecorder), 0, 500);
            mRecorder.setOutputFile("/dev/null");
            try {
                mRecorder.prepare();
                mRecorder.start();
            } catch (IOException e) {
                e.printStackTrace();
            }
            catch (RuntimeException e){
                e.printStackTrace();
            }
        }
    }

private class RecorderTask extends TimerTask {
    //TextView sound = (TextView) findViewById(R.id.decibel);
    private MediaRecorder recorder;

    public RecorderTask(MediaRecorder recorder) {
        this.recorder = recorder;
    }

    public void run() {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    int peakAmplitude = recorder.getMaxAmplitude();
                    //double amplitudeDb = 20 * Math.log10((double)Math.abs(peakAmplitude));
                    amplitudeDb = 20 * Math.log10((double)Math.abs(peakAmplitude));
                    Log.i("sound","amplitudeDb" + amplitudeDb);
                    if (amplitudeDb>60){
                        noiseTv.setText("This room is noisy!!!");
                        noiseImage.setBackgroundResource(R.drawable.noise);
                    }
                    else{
                        noiseTv.setText("This room is quiet!!!");
                        noiseImage.setBackgroundResource(R.drawable.quiet);
                    }
                }
            });
        }
    }
}// end of referencing

Answer 1

您可以在 AndroidManifest 中为此活动添加 android:configChanges="orientation|screenSize"。在这种情况下，将不会重新创建活动，并且不会再次创建您的线程

Answer 2

设置android:configChanges="orientation|screenSize" 有效（在您的情况下），但不是一个好的解决方案，也不是应采用的惯用方式。

这是因为如果您有不同的纵向和横向布局，当您旋转手机时，它们将无法正确加载。

这里有一些选项：

1. 按照@toshkinl 的建议执行并使用服务。这样做的好处是即使应用程序关闭，线程也会运行。但是，这可能超出了您的应用的范围。

2. 将线程放入您的Application 类并在活动中访问它：

   MyApplication app = (MyApplication) getApplication();

   这样做的好处是易于实现，并且您的线程将在配置更改和活动更改后继续存在。请注意，android 操作系统可能会在您的应用不使用时将其杀死，因此当您的应用重新启动时，线程引用将在您的应用程序类中设置为null，在这种情况下您只需重新创建线程。