Activity class field behavior after screen rotation

There is a simple project (full listing below).

In project,

• There is an Activity with ListView. Each element of the list is a button - clicking on which brings up the context menu.

• in the MainActivity class there is a tagButton field that remembers the position of the element whose button was pressed.

• The adapter is custom, menu items are drawn inside the adapter, and the Tag field of the button is assigned the position of a specific item in the list.

• When you rotate the screen, the adapter is saved with a fragment

Before the screen rotates, everything works (pressing the button -> saving the position in the tagButton -> menu display -> getting the correct tagButton).

But if you turn the screen, it turns out something incomprehensible to me: pressing the button -> saving the correct position in tagButton -> displaying the menu -> getting the wrong tagButton ?!

What happens between “storing the correct position in the tagButton” and “getting the wrong tagButton”?

Ps. If you wrap the tagButton into a simple class and change / get the value using the setter / getter and at the same time save an instance of the class through a fragment (when you turn the screen), then everything is fine.

Pps. Algorithm for receiving errors:

1. Run the application.
2. Press any button (for example, 3), a menu appears. Logs: Tag before: 3
3. Select a menu item. In Tag after logs: 3
4. Turn over the screen.
5. Press any button (for example, 2), a menu appears. Logs: Tag before: 2
6. Select a menu item. Tag after logs: -1

MainActivity code:

import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.util.Log; import android.view.ContextMenu; import android.view.MenuItem; import android.view.View; import android.widget.Button; import android.widget.ListView; import layout.SaveFragment; public class MainActivity extends AppCompatActivity { int tagButton = -1; LvAdapter adapter; SaveFragment saveStateFragment; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); saveStateFragment = (SaveFragment) getSupportFragmentManager().findFragmentByTag("SAVE"); if (saveStateFragment != null) { adapter = saveStateFragment.getAdapter(); } else { saveStateFragment = new SaveFragment(); getSupportFragmentManager() .beginTransaction() .add(saveStateFragment, "SAVE") .commit(); adapter = new LvAdapter(this); } tagButton = -1; ((ListView) findViewById(R.id.lv1)).setAdapter(adapter); } @Override public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) { tagButton = (int) ((Button) v).getTag(); Log.d("err", "Tag before: " + String.valueOf(tagButton)); menu.add("Получить Tag"); } @Override public boolean onContextItemSelected(MenuItem item) { Log.d("err", "Tag after: " + String.valueOf(tagButton)); return super.onContextItemSelected(item); } @Override protected void onPause() { saveStateFragment.setAdapter(adapter); super.onPause(); } } 

Adapter code:

 import android.app.Activity; import android.content.Context; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.Button; public class LvAdapter extends BaseAdapter { int count = 100; Context ctx; LayoutInflater lInflater; public LvAdapter (Context context) { ctx = context; lInflater = (LayoutInflater) ctx .getSystemService(Context.LAYOUT_INFLATER_SERVICE); } @Override public int getCount() { return count; } @Override public Integer getItem(int i) { return i; } @Override public long getItemId(int i) { return i; } @Override public View getView(int i, View convertView, ViewGroup viewGroup) { View view = convertView; if (view == null) { view = lInflater.inflate(R.layout.item, viewGroup, false); } final Button btn = (Button) view.findViewById(R.id.btn); btn.setText(String.valueOf(i)); btn.setTag(i); btn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Activity activity = (Activity) ctx; activity.registerForContextMenu(btn); activity.openContextMenu(btn); } }); return view; } } 

Fragment code:

 import android.os.Bundle; import android.support.v4.app.Fragment; import biz.temp.LvAdapter; public class SaveFragment extends Fragment { LvAdapter adapter; public LvAdapter getAdapter() { return adapter; } public void setAdapter(LvAdapter adapter) { this.adapter = adapter; } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setRetainInstance(true); } } 

Activity Markup:

 <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="horizontal"> <ListView android:id="@+id/lv1" android:layout_width="match_parent" android:layout_height="match_parent"/> </LinearLayout> 

The layout of the list item:

 <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <Button android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/btn"/> </LinearLayout>