当我切换活动或关闭应用时，Android中的共享首选项无法保存

Question

我检查了类似的问题，注意似乎有效。我无法弄清楚似乎是什么问题。每次应用重启或活动切换后，值都会变为0。

//just parts of code from activity1
            SharedPreferences pref;
            SharedPreferences.Editor editor;
// On create....
            pref = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
            editor = pref.edit();
            max=pref.getInt("mxtime", 0);

//If something>something...
            editor.putInt("mxtime", max);
            editor.commit();

在第一部分中，我在主Activity中声明了SharedPreferences。我将它保存在“max”int中，并且在启动时始终为0，因为如果空值为0.在第二个活动中，我有一个按钮，在点击它时应该从SharedPreferences中清空值。

活动2：

public class settings extends AppCompatActivity {
private Button myButton;
private Button myButton2;
private Button myButton3;
//sharedPrefs
SharedPreferences pref;
SharedPreferences.Editor editor;

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

    pref = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
    editor = pref.edit();
    myButton = (Button) findViewById(R.id.button3);
    myButton2 = (Button) findViewById(R.id.button4);
    myButton3 = (Button) findViewById(R.id.button5);

    myButton.setOnClickListener(new View.OnClickListener(){
        public void onClick(View v) {
            Intent i = new Intent(getApplicationContext(),MainActivity.class);
            startActivity(i);


        }
    });
    myButton2.setOnClickListener(new View.OnClickListener(){
        public void onClick(View v) {
            //sharedPrefs
            editor.remove("mxtime");
            editor.commit();


        }
    });
}

}