如何使用 sharedpreferences 保存计时器时间并在另一个活动中检索它

Question

I have a chronometer in Mainactivity.java I wanted to save the starting time using SharedPreferences and get the starting time show it in another activity but I can't figure out how to do so.I've tried Service which allows it running in the background but it failed as it can't pass the variable to another activity and people suggested using SharedPreferences would be easier. So does anyone knows how to save the starting time and get the value in another activity? Here's the code.

MainActivity.java

public class MainActivity extends AppCompatActivity{
private Chronometer chronometer;
protected FirebaseAuth firebaseauth = FirebaseAuth.getInstance();

 @Override
      protected void onStart(){
        super.onStart();
          chronometer.setBase(SystemClock.elapsedRealtime());
          final long startTime = (SystemClock.elapsedRealtime() - chronometer.getBase());
          final SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(this);
          final SharedPreferences.Editor editor = pref.edit();   
              @Override
              public void onDataChange (DataSnapshot dataSnapshot){
                    String status = dataSnapshot.getValue(String.class);

                   if (status.equals ("occupied")) {

                        chronometer.start();
                        editor.putLong("time",startTime);
                       editor.commit();

                   }
                   else
                       mValueView1.setBackgroundColor(Color.parseColor("#66d983"));

              }
              @Override
              public void onCancelled (DatabaseError databaseError){

              }

          });

SecondActivity.java

@Override
    protected void onStart() {
        super.onStart();

        final SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(this);
        mChildReference1.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                String status = dataSnapshot.getValue(String.class);
                // firebase status is occupied start chronometer
                if(status.equals("occupied")) {
                   savedTime = pref.getLong("time",01);

                    chronometer.setBase(savedTime);
                    chronometer.getBase();
                    chronometer.setVisibility(View.VISIBLE);


                }

                if(!status.equals("occupied")){
                        chronometer.setBase(SystemClock.elapsedRealtime());
                        pauseOffset = 0;
                        chronometer.stop();

                    }
                }


            @Override
            public void onCancelled(DatabaseError databaseError) {

            }

        });
    }

Answer 1

if you are using the sharedpreference only in one activity it's ok to use getDefaultSharedPreferences() or getPreferences() methods on your activity.but in your case(as mentioned in the documentation) which is using one sharedPreference for multiple activities, you should assign a name to the sharedpreference.
this way the activity knows to get which of your sharedpreferences. just change this in your code

SharedPreferences pref = getSharedPreferences("chornometer", Context.MODE_PRIVATE);

for more information read the documentation