问题
I have a listview in subsection activity when I click on it, it opens up tabbed activity. Now when I press up navigation button on top left corner and go back to parent activity, the listview becomes empty. But when I press back button on the keypad the parent activity does not lose its data. The listview is populated using the database.
Please help me!
SubSectionActivity.java (Parent Activity)
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 (child activity)
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;
}
}
}
回答1:
This may solve your problem
Put this in your AlgorithmActivity.java and remove your code.
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
onBackPressed();
return true;
}
return super.onOptionsItemSelected(item);
}
来源：https://stackoverflow.com/questions/37642676/parent-activity-loses-data-when-onbackpressed-is-called