如果Java中存在旧毫秒数，如何计算提供的当前毫秒数

Question

我在Android应用中创建了一个计时器。我有一种情况，即使应用程序已关闭，我也不需要停止计时器。如果计时器正在运行并且用户关闭了该应用程序，然后在一段时间后重新打开它。他应该在计时器上看到最近的时间。但目前我无法显示最新时间。我只能显示用户杀死该应用程序的时间。我正在存储计时器的时间，当用户打开应用程序时，我会将存储的时间放回计时器。但我想显示最新时间。在这里，我到目前为止所做的一切。我正在使用精密计时器小部件。

MainActivity.class：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private static final String TAG = MainActivity.class.getSimpleName();
    Chronometer tvTextView;
    Button btnStart, btnStop;
    private int state = 0; //0 means stop state,1 means play, 2 means pause

    SharedPreferences sharedPreferences;
    private boolean running = false;
    private long pauseOffSet = -1;

    ProgressBar progressBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tvTextView = findViewById(R.id.textview);
        progressBar = findViewById(R.id.puzzleProgressBar);

        btnStart = findViewById(R.id.button1);
        btnStop = findViewById(R.id.button2);
        btnStart.setOnClickListener(this);
        btnStop.setOnClickListener(this);

        sharedPreferences = getSharedPreferences("myprefs", MODE_PRIVATE);
        state = sharedPreferences.getInt("state", 0);

        tvTextView.setOnChronometerTickListener(new Chronometer.OnChronometerTickListener() {
            @Override
            public void onChronometerTick(Chronometer chronometer) {
                long time = SystemClock.elapsedRealtime() - chronometer.getBase();
                pauseOffSet=time;
                Log.e(TAG,"pauseOffSet "+pauseOffSet);
                if (time >= 79200000) {
                    tvTextView.setBase(SystemClock.elapsedRealtime());
                    tvTextView.stop();
                    running = false;
                    progressBar.setProgress(0);
                } else {
                    chronometer.setText(setFormat(time));
                    int convertTime = (int) time;
                    progressBar.setProgress(convertTime);
                }
            }
        });

        if (state == 1) { // its in play mode
            running = true;
            tvTextView.setBase(SystemClock.elapsedRealtime() - sharedPreferences.getLong("milli", 0));
            tvTextView.start();
        } else if (state == 2) { //its in pause mode
            running = false;
            pauseOffSet = sharedPreferences.getLong("milli", -1);
            long time = SystemClock.elapsedRealtime() - pauseOffSet;
            tvTextView.setBase(time);
            int convertTime = (int) pauseOffSet;
            progressBar.setProgress(convertTime);
        } else {
            running = false;
            tvTextView.setBase(SystemClock.elapsedRealtime());
        }
    }

    public void onClick(View v) {
        if (btnStart == v) {
            if (!running) {
                if (pauseOffSet != -1) {
                    pauseOffSet = sharedPreferences.getLong("milli", -1);
                }
                tvTextView.setBase(SystemClock.elapsedRealtime() - pauseOffSet);
                tvTextView.start();
                state = 1;
                pauseOffSet = 0;
                running = true;
            }
        } else if (btnStop == v) {
            if (running) {
                tvTextView.stop();
                pauseOffSet = SystemClock.elapsedRealtime() - tvTextView.getBase();
                state = 2;
                running = false;
            }
        }
    }

    @Override
    protected void onStop() {
        super.onStop();
        sharedPreferences.edit().putLong("milli", pauseOffSet).commit();
        sharedPreferences.edit().putInt("state", state).commit();
    }

    @Override
    protected void onDestroy() {
        Log.e(TAG, "onDestroy called, state: " + state);
        super.onDestroy();
    }

    String setFormat(long time) {
        int h = (int) (time / 3600000);
        int m = (int) (time - h * 3600000) / 60000;
        int s = (int) (time - h * 3600000 - m * 60000) / 1000;
        String hh = h < 10 ? "0" + h : h + "";
        String mm = m < 10 ? "0" + m : m + "";
        String ss = s < 10 ? "0" + s : s + "";
        return hh + ":" + mm + ":" + ss;
    }
}