Question

我目前在底部导航中有3个片段。片段之一包含一个计时器。当您启动计时器，更改片段并返回到计时器片段时，就会出现问题。重置。

主要活动

public class MainActivity extends AppCompatActivity implements BottomNavigationView.OnNavigationItemSelectedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        loadFragment(new TimerFragment());

        BottomNavigationView navigation = findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(this);

    }

    private boolean loadFragment (Fragment fr) {
        if (fr != null){
            getSupportFragmentManager()
                    .beginTransaction()
                    .replace(R.id.fragContainer,fr)
                    .commit();
            return true;
        }
        return false;
    }

   public boolean onNavigationItemSelected (@NonNull MenuItem item) {
        Fragment fr = null;

        switch (item.getItemId()){
            case R.id.navigation_home:
                fr = new TimerFragment();
                break;

            case R.id.navigation_dashboard:
                fr = new ListFragment();
                break;

            case R.id.navigation_notifications:
                fr = new RemindFragment();
                break;
        }

        return loadFragment(fr);
   }


}

计时器片段

public class TimerFragment extends Fragment {

    TextView tvTimer;
    long startTime = 0;
    Handler timerHandler = new Handler();
    Runnable timerRunnable = new Runnable() {
        @Override
        public void run() {
            long millis = System.currentTimeMillis() - startTime;
            int seconds = (int)(millis/1000);
            int minutes = seconds / 60;
            seconds = seconds % 60;
            tvTimer.setText(String.format("%d:%02d", minutes, seconds));
            timerHandler.postDelayed(this,500);
        }
    };



    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.frag_timer, null);

        tvTimer = (TextView)view.findViewById(R.id.tvTimer);
        Button btn = (Button)view.findViewById(R.id.btn1);

        btn.setText("Start");
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Button b = (Button) v;

                if (b.getText().equals("Stop")){
                    timerHandler.removeCallbacks(timerRunnable);
                    b.setText("Start Monitoring");
                }

                else {
                    startTime = System.currentTimeMillis();
                    timerHandler.postDelayed(timerRunnable, 0);
                    b.setText("Stop");
                    Toast.makeText(getActivity(),"Monitoring started.",Toast.LENGTH_SHORT).show();
                }
            }
        });
        return view;
    }
}

我试图做的一件事是add而不是replace的片段。它不会在更改片段时重置计时器，而是将片段彼此叠放在一起，看起来像一团混乱。返回TimerFragment将创建另一个计时器，现在有两个计时器。知道该怎么办吗？我该如何编码，以使片段发生变化时计时器不会重置？

我认为hide和show可以在这里工作，但是我不确定在有3个片段要切换的情况下如何应用。

Answer 1

当选择导航时，也许会创建一个新的计时器片段 onNavigationItemSelected中的片段。那是我的猜测。

Answer 2

我认为捉迷藏可以在这里工作，但我不确定如何申请在我要切换三个片段的情况下。

您是对的，请按照以下示例将其应用于您的代码。

public class MainActivity extends AppCompatActivity implements BottomNavigationView.OnNavigationItemSelectedListener {

    private final Fragment mTimerFragment = new TimerFragment();
    private final Fragment mListFragment = new ListFragment();
    private final Fragment mReminderFragment = new RemindFragment();

    private Fragment mActiveFragment = mTimerFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        getSupportFragmentManager().beginTransaction()
                .add(R.id.fragContainer, mReminderFragment, "TimerFragment")
                .hide(mReminderFragment)
                .commit();
        getSupportFragmentManager().beginTransaction()
                .add(R.id.fragContainer, mListFragment, "ListFragment")
                .hide(mListFragment)
                .commit();
        getSupportFragmentManager().beginTransaction()
                .add(R.id.fragContainer, mTimerFragment, "ReminderFragment")
                .commit();

        BottomNavigationView navigation = findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(this);
    }

    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_home:
                getSupportFragmentManager().beginTransaction()
                        .hide(mActiveFragment)
                        .show(mTimerFragment)
                        .commit();
                mActiveFragment = mTimerFragment;
                return true;
            case R.id.navigation_dashboard:
                getSupportFragmentManager().beginTransaction()
                        .hide(mActiveFragment)
                        .show(mListFragment)
                        .commit();
                mActiveFragment = mListFragment;
                return true;
            case R.id.navigation_notifications:
                getSupportFragmentManager().beginTransaction()
                        .hide(mActiveFragment)
                        .show(mReminderFragment)
                        .commit();
                mActiveFragment = mReminderFragment;
                return true;
        }

        return false;
    }
}

片段更改时计时器重置，add（）将片段彼此堆叠

2 个答案: