Übergeordnete Aktivität verliert Daten, wenn onBackPressed() aufgerufen wird

Question

Ich habe eine Listview in Unterabschnitt Aktivität, wenn ich darauf klicke, öffnet es Tabbed-Aktivität. Wenn ich jetzt die Navigationstaste oben links drücke und zurück zur Elternaktivität gehe, wird die Listenansicht leer. Aber wenn ich die Zurück-Taste auf der Tastatur drücke, verliert die Elternaktivität ihre Daten nicht. Die Listenansicht wird mit der Datenbank gefüllt.

Bitte helfen Sie mir!

SubSectionActivity.java (Parent Aktivität)

package com.suvariyaraj.algorithms; 
import android.content.Context; 
import android.content.Intent; 
import android.content.SharedPreferences; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.support.v7.widget.ListViewCompat; 
import android.util.Log; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 
import android.widget.Toast; 
import com.suvariyaraj.algorithms.Database.DBPARAM; 
import com.suvariyaraj.algorithms.Database.ExternalDbOpenHelper; 
import java.util.ArrayList; 

public class SubSectionActivity extends AppCompatActivity { 

ListView listView; 
String[] array; 
private SQLiteDatabase database; 
DBPARAM dbparam = new DBPARAM(); 
ArrayList<String> titles; 
String section; 
public static final String MyPREFERENCES = "MyPrefsAlgorithmApp" ; 
SharedPreferences sharedPreferences; 

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

    getSupportActionBar().setDisplayHomeAsUpEnabled(true); 

    Intent i = getIntent(); 
    section = i.getStringExtra("Section"); 
    Toast.makeText(getApplicationContext(), section, Toast.LENGTH_SHORT).show(); 
    sharedPreferences = getSharedPreferences ("myprefAlgoApp", Context.MODE_PRIVATE); 
    SharedPreferences.Editor editor = sharedPreferences.edit(); 
    editor.putString ("Section",section); 
    editor.commit(); 


    ExternalDbOpenHelper dbOpenHelper = new ExternalDbOpenHelper (this, dbparam.DB_NAME); 
    database = dbOpenHelper.openDataBase(); 

    getDistinctSubSections(); 
    ArrayAdapter adapter = new ArrayAdapter(this, R.layout.single_list_view_item, titles); 
    listView = (ListView) findViewById(R.id.subsection_listview); 
    listView.setAdapter(adapter); 

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
      Intent i = new Intent(getApplicationContext(), AlgorithmActivity.class); 
      i.putExtra("Subsection", titles.get (position)); 
      i.putExtra ("Section", section); 
      startActivity (i); 
     } 


    }); 
} 

private void getDistinctSubSections() { 
    titles = new ArrayList<String>(); 
    Cursor cursor = database.query(true, dbparam.TABLE_NAME, new String[] {dbparam.COLOUMN_SUBSECTION}, dbparam.COLOUMN_SECTION+" = '"+section+"'", null, null, null, null, null); 
    if(cursor!=null) { 
     cursor.moveToFirst(); 
     if (!cursor.isAfterLast()) { 
      do { 
       String name = cursor.getString(cursor.getColumnIndex(dbparam.COLOUMN_SUBSECTION)); 
       titles.add(name); 
      } while (cursor.moveToNext()); 
     } 
    } 
    cursor.close(); 
} 
} 

AlgorithmActivity.java (Kinder Aktivität)

package com.suvariyaraj.algorithms; 

import android.content.ClipData; 
import android.content.ClipboardManager; 
import android.content.Context; 
import android.content.Intent; 
import android.content.SharedPreferences; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.graphics.Color; 
import android.graphics.drawable.ColorDrawable; 
import android.support.design.widget.TabLayout; 
import android.support.v4.widget.NestedScrollView; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.app.FragmentPagerAdapter; 
import android.support.v4.view.ViewPager; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ImageView; 
import android.widget.LinearLayout; 
import android.widget.PopupWindow; 
import android.widget.RelativeLayout; 
import android.widget.TextView; 
import android.widget.Toast; 

import com.getbase.floatingactionbutton.FloatingActionButton; 
import com.getbase.floatingactionbutton.FloatingActionsMenu; 
import com.suvariyaraj.algorithms.Database.DBPARAM; 
import com.suvariyaraj.algorithms.Database.ExternalDbOpenHelper; 

import org.w3c.dom.Text; 

import java.util.ArrayList; 

public class AlgorithmActivity extends AppCompatActivity { 

/** 
* The {@link android.support.v4.view.PagerAdapter} that will provide 
* fragments for each of the sections. We use a 
* {@link FragmentPagerAdapter} derivative, which will keep every 
* loaded fragment in memory. If this becomes too memory intensive, it 
* may be best to switch to a 
* {@link android.support.v4.app.FragmentStatePagerAdapter}. 
*/ 
private SectionsPagerAdapter mSectionsPagerAdapter; 

private static SQLiteDatabase database; 
static DBPARAM dbparam = new DBPARAM(); 
ArrayList<String> titles; 
static ArrayList<String> array; 
static String section; 
static String subsection; 

/** 
* The {@link ViewPager} that will host the section contents. 
*/ 
private ViewPager mViewPager; 
String title; 

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


    Intent i = getIntent(); 
    subsection = i.getStringExtra("Subsection"); 
    section = i.getStringExtra("Section"); 

    ExternalDbOpenHelper dbOpenHelper = new ExternalDbOpenHelper (this, dbparam.DB_NAME); 
    database = dbOpenHelper.openDataBase(); 

    //Toast.makeText(getApplicationContext(), title, Toast.LENGTH_SHORT).show(); 

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 
    getSupportActionBar().setDisplayHomeAsUpEnabled(true); 
    getSupportActionBar().setHomeButtonEnabled(true); 
    // Create the adapter that will return a fragment for each of the three 
    // primary sections of the activity. 
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 

    // Set up the ViewPager with the sections adapter. 
    mViewPager = (ViewPager) findViewById(R.id.container); 
    if (mViewPager != null) { 
     mViewPager.setAdapter(mSectionsPagerAdapter); 
    } 

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs); 
    if (tabLayout != null) { 
     tabLayout.setupWithViewPager(mViewPager); 
    } 

    FloatingActionButton fab_copy = (FloatingActionButton) findViewById (R.id.fab_copy); 
    FloatingActionButton fab_share = (FloatingActionButton) findViewById (R.id.fab_share); 
    FloatingActionButton fab_doubt = (FloatingActionButton) findViewById (R.id.fab_doubt); 
    final FloatingActionsMenu fab_menu = (FloatingActionsMenu) findViewById (R.id.fab_menu); 

    if (fab_copy != null) { 
     fab_copy.setOnClickListener (new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       String s = "C Code : \n"+array.get(1).replace ("~~", "")+ "\n\nJava Code : \n"+array.get(2).replace ("~~", ""); 
       ClipboardManager clipboard = (ClipboardManager) getSystemService(CLIPBOARD_SERVICE); 
       ClipData clip = ClipData.newPlainText("Shared Content", s); 
       clipboard.setPrimaryClip(clip); 
       Toast.makeText (getApplicationContext(),"Content Copied",Toast.LENGTH_SHORT).show(); 
       if (fab_menu != null) { 
        fab_menu.collapse(); 
       } 
      } 
     }); 
    } 

    if (fab_share != null) { 
     fab_share.setOnClickListener (new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       String s = "Algorithm Name : "+subsection+"\n\nC Code : \n"+array.get(1).replace ("~~", "")+ "\n\nJava Code : \n"+array.get(2).replace ("~~", ""); 
       if (fab_menu != null) { 
        fab_menu.collapse(); 
       } 
       Intent sendIntent = new Intent(); 
       sendIntent.setAction(Intent.ACTION_SEND); 
       sendIntent.putExtra(Intent.EXTRA_TEXT, s); 
       sendIntent.setType("text/plain"); 
       startActivity(Intent.createChooser(sendIntent, "Share using...")); 
      } 
     }); 
    } 

    if (fab_doubt != null) { 
     fab_doubt.setOnClickListener (new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       Intent i = new Intent (getApplicationContext(), DoubtActivity.class); 
       i.putExtra ("Title", title); 
       if (fab_menu != null) { 
        fab_menu.collapse(); 
       } 
       startActivity (i); 
      } 
     }); 
    } 
} 



@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_algorithm, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 
    //if (item.getItemId() == android.R.id.home) { 
    // onBackPressed(); 
    //} 

    return super.onOptionsItemSelected(item); 
} 

/** 
* A placeholder fragment containing a simple view. 
*/ 
public static class PlaceholderFragment extends Fragment { 
    /** 
    * The fragment argument representing the section number for this 
    * fragment. 
    */ 
    private static final String ARG_SECTION_NUMBER = "section_number"; 

    public PlaceholderFragment() { 
    } 

    /** 
    * Returns a new instance of this fragment for the given section 
    * number. 
    */ 
    public static PlaceholderFragment newInstance(int sectionNumber) { 
     PlaceholderFragment fragment = new PlaceholderFragment(); 
     Bundle args = new Bundle(); 
     args.putInt(ARG_SECTION_NUMBER, sectionNumber); 
     fragment.setArguments(args); 
     return fragment; 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 

     View rootView = inflater.inflate(R.layout.fragment_algorithm, container, false); 
     TextView textView = (TextView) rootView.findViewById(R.id.section_label); 
     array = new ArrayList<String>(); 
     array.add ("Hi from description"); 
     array.add ("Hi from C"); 
     array.add ("Hi from JAVA"); 
     getInformation(); 

     NestedScrollView scrollView = (NestedScrollView) rootView.findViewById(R.id.abcscrollView); 

     LinearLayout linearLayout = new LinearLayout (rootView.getContext()); 
     LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT); 
     linearLayout.setLayoutParams (params); 
     params.bottomMargin=10; 
     linearLayout.setOrientation (LinearLayout.VERTICAL); 

     if(getArguments().getInt(ARG_SECTION_NUMBER)-1==0) { 
      String temparray[] = array.get(0).split("~~"); 
      //array.set (0, ""); 
      for (int i = 0; i < temparray.length; i++) { 
       if (temparray[i].startsWith("Image:")) { 
        ImageView iv = new ImageView(rootView.getContext()); 
        iv.setId(i+1); 
        int itd = this.getResources().getIdentifier(temparray[i].substring(6), "drawable", getActivity().getPackageName()); 
        iv.setImageResource(itd); 
        linearLayout.addView (iv); 

       } else { 
        TextView tv = new TextView(rootView.getContext()); 
        tv.setText(temparray[i]); 
        tv.setTextSize (24); 
        tv.setId(i+1); 
        linearLayout.addView (tv); 
       } 
      } 
     } 

     if(getArguments().getInt(ARG_SECTION_NUMBER)-1==1) { 
      String temparray[] = array.get(1).toString().split("~~"); 
      for (int i = 0; i < temparray.length; i++) { 
       if (temparray[i].startsWith("Output:")) { 
        TextView tv = new TextView(rootView.getContext()); 
        tv.setText(temparray[i]); 
        //tv.setTextSize (24); 
        tv.setId(i+100); 
        tv.setBackgroundColor (Color.GRAY); 

        linearLayout.addView (tv,params); 
       } else if (temparray[i].startsWith("Input:")) { 
        TextView tv = new TextView (rootView.getContext()); 
        tv.setText (temparray[i]); 
        //tv.setTextSize (24); 
        tv.setId (i+100); 
        tv.setBackgroundColor (Color.GRAY); 
        linearLayout.addView (tv, params); 
       }else { 
        if (temparray[i].trim().equals ("")){ 
         continue; 
        } 
        TextView tv = new TextView(rootView.getContext()); 
        tv.setText(temparray[i].trim()); 
        //tv.setTextSize (24); 
        tv.setId(i+100); 
        linearLayout.addView (tv); 
       } 
      } 
     } 

     if(getArguments().getInt(ARG_SECTION_NUMBER)-1==2) { 
      String temparray[] = array.get(2).toString().split("~~"); 
      //array.set (2, ""); 
      for (int i = 0; i < temparray.length; i++) { 
       if (temparray[i].startsWith("Output:")) { 
        TextView tv = new TextView(rootView.getContext()); 
        tv.setText(temparray[i]); 
        //tv.setTextSize (24); 
        tv.setId(i+100); 
        tv.setBackgroundColor (Color.GRAY); 

        linearLayout.addView (tv,params); 
       } else if (temparray[i].startsWith("Input:")) { 
        TextView tv = new TextView (rootView.getContext()); 
        tv.setText (temparray[i]); 
        //tv.setTextSize (24); 
        tv.setId (i+100); 
        tv.setBackgroundColor (Color.GRAY); 
        linearLayout.addView (tv, params); 
       }else { 
        if (temparray[i].trim().equals ("")){ 
         continue; 
        } 
        TextView tv = new TextView(rootView.getContext()); 
        tv.setText(temparray[i].trim()); 
        //tv.setTextSize (24); 
        tv.setId(i+100); 
        linearLayout.addView (tv); 
       } 
      } 
     } 

     NestedScrollView.LayoutParams params2 = new NestedScrollView.LayoutParams (NestedScrollView.LayoutParams.MATCH_PARENT, NestedScrollView.LayoutParams.MATCH_PARENT); 
     scrollView.addView (linearLayout,params2); 

     //textView.setText (array.get(getArguments().getInt (ARG_SECTION_NUMBER) - 1)); 
     return rootView; 
    } 

    private void getInformation() { 
     Cursor cursor = database.query(true, dbparam.TABLE_NAME, new String[] {dbparam.COLOUMN_DESCRIPTION, dbparam.COLOUMN_CODEC, dbparam.COLOUMN_CODEJAVA}, dbparam.COLOUMN_SECTION+"='"+section+"' AND "+dbparam.COLOUMN_SUBSECTION+"='"+subsection+"'", null, null, null, null, null); 
     if(cursor!=null) { 
      cursor.moveToFirst(); 
      if (!cursor.isAfterLast()) { 
       do { 
        String discription = cursor.getString(cursor.getColumnIndex(dbparam.COLOUMN_DESCRIPTION)); 
        array.set(0, discription); 
        String codeC = cursor.getString(cursor.getColumnIndex(dbparam.COLOUMN_CODEC)); 
        array.set(1, codeC); 
        String codeJAVA = cursor.getString(cursor.getColumnIndex(dbparam.COLOUMN_CODEJAVA)); 
        array.set(2, codeJAVA); 
       } while (cursor.moveToNext()); 
      } 
      cursor.close(); 
     } 
    } 
} 

/** 
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to 
* one of the sections/tabs/pages. 
*/ 
public class SectionsPagerAdapter extends FragmentPagerAdapter { 

    public SectionsPagerAdapter(FragmentManager fm) { 
     super(fm); 
    } 

    @Override 
    public Fragment getItem(int position) { 
     // getItem is called to instantiate the fragment for the given page. 
     // Return a PlaceholderFragment (defined as a static inner class below). 
     return PlaceholderFragment.newInstance(position + 1); 
    } 

    @Override 
    public int getCount() { 
     // Show 3 total pages. 
     return 3; 
    } 

    @Override 
    public CharSequence getPageTitle(int position) { 
     switch (position) { 
      case 0: 
       return "Description"; 
      case 1: 
       return "C"; 
      case 2: 
       return "Java"; 
     } 
     return null; 
    } 


} 
} 

Answer 1

Dies kann Ihr Problem

dies in Ihrem AlgorithmActivity.java Setzen Sie lösen und entferne deinen Code.

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    switch (item.getItemId()) { 
     case android.R.id.home: 
      onBackPressed(); 
      return true; 
    } 
    return super.onOptionsItemSelected(item); 
}