How to handle Back Button press in android fragments
I think you can do this:
Create a generic Fragment:
public abstract class extends BaseFragment {
public abstract boolean onBackPressed();
}
In his Fragments, extends this BaseFragment, example:
public class TopStoriesFragment extends BaseFragment {
...
@Override
public boolean onBackPressed()
{
//if you return false, then it is because you have not consumed
//the event, but if it returns true, which is consumed by this event.
return false;
}
}
In his MainActivity activity, you should check in onBackPressed event, if the event was consumed or not, to decide what to do.
It is very important that you save the current tab!
public class MainActivity extends FragmentActivity implements
ActionBar.TabListener {
//It is very important that you save the current tab!
private BaseFragment currentTab;
// ... implementation
public class TabsPagerAdapter extends FragmentPagerAdapter {
public TabsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int index) {
currentTab = null;
switch (index) {
case 0:
// Top Rated fragment activity
currentTab = new TopStoriesFragment();
break;
case 1:
// Games fragment activity
return new NationalFragment();
case 2:
// Movies fragment activity
currentTab = new InternationalFragment();
break;
case 3:
// Movies fragment activity
currentTab = new SportsFragment();
break;
case 4:
// Movies fragment activity
currentTab = new TechnologyFragment();
case 5:
// Movies fragment activity
currentTab = new BusinessFragment();
break;
case 6:
// Movies fragment activity
currentTab = new EntertainmentFragment();
break;
}
return currentTab;
}
@Override
public int getCount() {
// get item count - equal to number of tabs
return 7;
}
public void stop() {
// get item count - equal to number of tabs
return;
}
}
@Override
public void onBackPressed()
{
//If the event returned false, then call the super.
if(currentTab == null || !currentTab.onBackPressed())
super.onBackPressed();
}
}
Change to your case!
![Akshat](https://i.stack.imgur.com/BkdA1.png?s=256&g=1)
Akshat
An average scoring Computer Science graduate into career in Information Technology. Working as Mobile Apps Developer in the Silicon City of India, called Bangalore. Facebook Twitter LinkedIn
Updated on June 26, 2022Comments
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Akshat about 2 years
I have a class which extends fragment. It receives a data from server and loads on the fragment layout. The data comes from AsyncTask doInBackground. But I am facing a problem that if asynctask is still doing in background and user presses back button, my app goes to another activity. But when the asynctask finishes, it does not find the needed layout and hence crashes the app. How to cancel this async task when user presses the back button in the middle of do in background, and more importantly, how to call on back pressed in fragments.
Here is my code:
TabsPagerAdapter.java
public class TabsPagerAdapter extends FragmentPagerAdapter { public TabsPagerAdapter(FragmentManager fm) { super(fm); } @Override public Fragment getItem(int index) { switch (index) { case 0: // Top Rated fragment activity return new TopStoriesFragment(); case 1: // Games fragment activity return new NationalFragment(); case 2: // Movies fragment activity return new InternationalFragment(); case 3: // Movies fragment activity return new SportsFragment(); case 4: // Movies fragment activity return new TechnologyFragment(); case 5: // Movies fragment activity return new BusinessFragment(); case 6: // Movies fragment activity return new EntertainmentFragment(); } return null; } @Override public int getCount() { // get item count - equal to number of tabs return 7; } public void stop() { // get item count - equal to number of tabs return; } }
MainActivity.java
public class MainActivity extends FragmentActivity implements ActionBar.TabListener { private ViewPager viewPager; private TabsPagerAdapter mAdapter; private ActionBar actionBar; // Tab titles private String[] tabs = { "Top Stories", "National", "International", "Sports", "Technology", "Business", "Entertainment"}; @SuppressLint("NewApi") @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); viewPager = (ViewPager) findViewById(R.id.pager); actionBar = getActionBar(); mAdapter = new TabsPagerAdapter(getSupportFragmentManager()); viewPager.setAdapter(mAdapter); actionBar.setHomeButtonEnabled(false); actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); // Adding Tabs for (String tab_name : tabs) { actionBar.addTab(actionBar.newTab().setText(tab_name) .setTabListener(this)); } /** * on swiping the viewpager make respective tab selected * */ viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() { @Override public void onPageSelected(int position) { // on changing the page // make respected tab selected actionBar.setSelectedNavigationItem(position); } @Override public void onPageScrolled(int arg0, float arg1, int arg2) { } @Override public void onPageScrollStateChanged(int arg0) { } }); } @Override public void onTabReselected(Tab tab, FragmentTransaction ft) { } @Override public void onTabSelected(Tab tab, FragmentTransaction ft) { // on tab selected // show respected fragment view viewPager.setCurrentItem(tab.getPosition()); } @Override public void onTabUnselected(Tab tab, FragmentTransaction ft) { } }
BusinessFragment.java
public class BusinessFragment extends Fragment { public String thehindu = "xxxxx"; public String toi = "xxxxx"; public String hindustantimes = "xxxxx"; public String indianexpress = "xxxxxx"; public String reuters = "xxxxxxx"; public String dainikjagaran = "xxxxxx"; public String dainikbhaskar = "xxxxx"; public String amarujala = "xxxxxx"; public String currenturl; AlertDialog levelDialog; public LayoutInflater inflater; ListView listView; int mCurCheckPosition; SharedPreferences sp; String papername; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View rootView = inflater.inflate(R.layout.fragment_data, container, false); sp = getActivity().getSharedPreferences("myfile", getActivity().MODE_PRIVATE); papername = sp.getString("Newspaper_name", null); feedTitle = (TextView) rootView.findViewById(R.id.feedtitle); feedDescribtion = (TextView) rootView .findViewById(R.id.feeddescribtion); getCurrentURL(); listView = (ListView) rootView.findViewById(android.R.id.list); listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View v, int position, long id) { Intent intent = new Intent(getActivity(), ShowDetails.class); Bundle bundle = new Bundle(); bundle.putString("keyTitle", myRssFeed.getItem(position) .getTitle()); bundle.putString("keyDescription", myRssFeed.getItem(position) .getDescription()); bundle.putString("keyLink", myRssFeed.getItem(position) .getLink()); bundle.putString("keyPubdate", myRssFeed.getItem(position) .getPubdate()); intent.putExtras(bundle); startActivity(intent); } }); startReadRss(); return rootView; } public class RssLoadingTask extends AsyncTask<Void, Void, Void> { @Override protected void onPostExecute(Void result) { // TODO Auto-generated method stub displayRss(); } @Override protected void onPreExecute() { // TODO Auto-generated method stub preReadRss(); } @Override protected void onProgressUpdate(Void... values) { // TODO Auto-generated method stub // super.onProgressUpdate(values); } @Override protected Void doInBackground(Void... arg0) { // TODO Auto-generated method stub readRss(); return null; } } private RSSFeed myRssFeed = null; TextView feedTitle; TextView feedDescribtion; // TextView feedPubdate; // TextView feedLink; public class MyCustomAdapter extends ArrayAdapter<RSSItem> { public MyCustomAdapter(Context context, int textViewResourceId, List<RSSItem> list) { super(context, textViewResourceId, list); } @Override public View getView(int position, View convertView, ViewGroup parent) { // TODO Auto-generated method stub // return super.getView(position, convertView, parent); View row = convertView; if (row == null) { inflater = LayoutInflater.from(getActivity()); row = inflater.inflate(R.layout.row, parent, false); } TextView listTitle = (TextView) row.findViewById(R.id.listtitle); listTitle.setText(myRssFeed.getList().get(position).getTitle()); TextView listPubdate = (TextView) row .findViewById(R.id.listpubdate); listPubdate.setText(myRssFeed.getList().get(position).getPubdate()); return row; } } private void startReadRss() { new RssLoadingTask().execute(); } private void getCurrentURL() { if (papername.equalsIgnoreCase("The Times of India")) { currenturl = toi; } else if (papername.equalsIgnoreCase("The Hindu")) { currenturl = thehindu; } else if (papername.equalsIgnoreCase("The Hindustan Times")) { currenturl = hindustantimes; } else if (papername.equalsIgnoreCase("The Indian Express")) { currenturl = indianexpress; } else if (papername.equalsIgnoreCase("Reuters")) { currenturl = reuters; } else if (papername.equalsIgnoreCase("दैनिक जागरण")) { currenturl = dainikjagaran; } else if (papername.equalsIgnoreCase("दैनिक भास्कर")) { currenturl = dainikbhaskar; } else if (papername.equalsIgnoreCase("अमर उजाला")) { currenturl = amarujala; } // else if(papername.equalsIgnoreCase("Times of India")) // { // // } // else if(papername.equalsIgnoreCase("Times of India")) // { // // } // } private void preReadRss() { feedTitle.setText("--- wait ---"); feedDescribtion.setText(""); // feedPubdate.setText(""); // feedLink.setText(""); listView.setAdapter(null); // Toast.makeText(getActivity(), "Reading RSS, Please wait.", // Toast.LENGTH_LONG) // .show(); } private void readRss() { try { URL rssUrl = new URL(currenturl); SAXParserFactory mySAXParserFactory = SAXParserFactory .newInstance(); SAXParser mySAXParser = mySAXParserFactory.newSAXParser(); XMLReader myXMLReader = mySAXParser.getXMLReader(); RSSHandler myRSSHandler = new RSSHandler(); myXMLReader.setContentHandler(myRSSHandler); InputSource myInputSource = new InputSource(rssUrl.openStream()); myXMLReader.parse(myInputSource); myRssFeed = myRSSHandler.getFeed(); } catch (MalformedURLException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (ParserConfigurationException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SAXException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } private void displayRss() { if (myRssFeed != null) { Calendar c = Calendar.getInstance(); // String strCurrentTiime = "\n(Time of Reading - " // + c.get(Calendar.HOUR_OF_DAY) // + " Hrs. : " // + c.get(Calendar.MINUTE) + " Mins.)\n" +c.get(Calendar.AM_PM); SimpleDateFormat sdf = new SimpleDateFormat( "MMMM-dd-yyyy HH:mm:ss a"); String strCurrentTiime = sdf.format(c.getTime()); feedTitle.setText(papername); feedDescribtion.setText(strCurrentTiime); // feedPubdate.setText(myRssFeed.getPubdate()); // feedLink.setText(myRssFeed.getLink()); MyCustomAdapter adapter = new MyCustomAdapter(getActivity(), R.layout.row, myRssFeed.getList()); listView.setAdapter(adapter); } } }
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Akshat almost 10 yearsWhat is current tab here.? Can you please show how to declare it.? And also how to create that generic class you have mentioned above.?
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Cícero Moura almost 10 yearsYou must create this BaseFragment extends Fragment . See it requires the implementation of onBackPressed method. Your adapter will keep the current tab! In this methodology, you will be using polymorphism. Note that its main activity has a global variable BaseFragment. In its adapter are assigning the instance of the current tab. When he presses the Back button, you check if the onBackPressed the Fragment method was consumed. If so, then do nothing, but if not, then perform the standard procedure.
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Admin almost 10 yearscan you please explain How to create that generic fragment.?
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Cícero Moura almost 10 yearsYou simply create a class BaseFragment that extends Fragment. It is generic in the sense of serving as a basis for any fragment that you create. That way, you ensure polymorphism for all of them. Ententa generic used in this case as in all the fragments, which may be polymorphism in all cases. Generic here is not the concept of programming languages, like Java itself, which implements this methodology in lists, etc.. Genéirco here is the concept of the same word. You can see the setting in the code example above.