So I am currently developing an app which displays a json file via cards in the main activity. Depending on which tab is currently selected in my tabbed activity, a method which downloads the json file decides what json file to download (I pass an integer and there is a switch in the method).
Here is the method:
Fragment.Downloadjson(rootview,integer,context);
Now, for my tabbed Activity I have a SectionsPagerAdapter which has the usual stuff: getItem, getCount, and getPageTitle.
In getItem I am creating my new fragments:
#Override
public Fragment getItem(int position) {
View v1 = getWindow().getDecorView().getRootView();
switch (position) {
case 0:
//Fragment.Download(v1,0,getApplicationContext());
return new Fragment().f(Fragment.page.TODAY);
case 1:
//Fragment.Download(v1,1,getApplicationContext());
return new Fragment().f(Fragment.page.TOMORROW);
default:
return new Fragment();
}
}
Exception :
android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
I have found the source of this error to be the rootview parameter in my method, because it works in onCreateView with rootView as a parameter, because I define it there. Hovewer, I cannot make an if statement for the currently selected tab or currently displayed fragment there, because
a) I don't know how to get the currently selected tab
b) I'm not sure it would download the json file again after I switch the tab, because after all, the If statement would be in onCreateView
So, my question is,
how do I solve this?
Don't do it inside getItem() method. In getItem just create the fragment.
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new MyFragment0();
case 1:
return new MyFragment1();
case 2:
return new MyFragment2();
}
return null;
}
Override the method instantiateItem and in there keep a map of fragment and their position:
private ArrayMap<Integer, MyFragmentBaseClass> mPagerFragmentMap = new ArrayMap<>();
#Override
public Object instantiateItem(ViewGroup container, int position) {
MyFragmentBaseClass fragment = (MyFragmentBaseClass) super.instantiateItem(container, position);
mPagerFragmentMap.put(position, fragment);
return fragment;
}
note MyFragmentBaseClass can be a marker interface that all fragments implement.
With the code above, you can already map each fragment to its tab.
If you're using TabLayout you can now set a listener using setOnTabSelectedListener and use one of its methods onTabSelected to know when the user selects that tab and perform any operation you want.
Related
I am pretty new to Android (3 days), but I have a pretty good background in PHP (which may be the cause of my confusion in a Java based environment). I started building an Android app using Android Studio (Beta). I created the default Android Studio activity with the Navigation Drawer Activity. I edited the activity fragment part to look like this:
#Override
public void onNavigationDrawerItemSelected(int position) {
Bundle bundle = new Bundle();
bundle.putStringArrayList("contacts", arr);
bundle.putStringArrayList("messages", messages);
Fragment fragment = null;
switch (position) {
case 0:
fragment = new FriendsFragment();
break;
case 1:
fragment = new ChatsFragment();
break;
case 2:
fragment = new GroupsFragment();
break;
case 3:
fragment = new LogoutFragment();
break;
default:
break;
}
if (fragment != null) {
fragment.setArguments(bundle);
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, fragment).addToBackStack(null).commit();
}
}
As you can see I am passing a Bundle to my Fragments called "messages" and "contacts" when an item is selected in the Navigation Drawer. The "messages" bundle are XMPP messages received by the aSmack library from an OpenFire server. So basically I'm trying to create a XMPP client. When I run the app I can receive the messages in the "ChatsFragment".
Now my problem:
I have to press the "ChatsFragment" item on the drawer to have my messages updated (re-receive the bundle) everytime I feel like there are new messages received from the server. But I want this to be done automatically by the fragment.
First I would like to know if my procedure is correct (Activity listens to server, creates bundle, send bundle to fragment, bundle updates messages on receive**)
** = This part I haven't been able to understand how to implement.
1- If the procedure is correct tell me how I should get the messages to be updated by the fragment through the activity?
2- If this is not the correct way to do things in Android, recommend me a way of doing it.
My code for displaying the messages in fragment:
private void displayListView() {
// Messages array list
List<String> contacts = getArguments().getStringArrayList("messages");
//System.out.println("arr: " + contacts);
//create an ArrayAdaptar from the String Array
ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(getActivity(),
R.layout.url_list, contacts);
ListView listView = (ListView) getView().findViewById(R.id.listView);
// Assign adapter to ListView
listView.setAdapter(dataAdapter);
//enables filtering for the contents of the given ListView
listView.setTextFilterEnabled(true);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// Send the URL to the host activity
//mListener.onURLSelected(((TextView) view).getText().toString());
}
});
}
Thanks in advance.
Typically for long running operations in the background, like listening to a server, incoming messages, etc, you need to use Services. You do so by subclassing the Service class in Android.
Now for your problem - the design approach should be that you have a background service listening to incoming messages. Anytime a message is received (an input stream in your socket operator) you should send a "broadcast" an intent that a message was received. A custom broadcast receiver that you create should wait for this broadcast. Within the onReceive() method of this receiver, you should trigger the creation of the bundle and updating your message.
Remember you should always delegate your long running operations in Android to services. That is exactly what they are for.
So basically if you're already listening for new messages to come in your activity, then you must have some kind of callback like onMessageRecieved() or something like that.
If you do, you can then notify your fragment in this way.
Create a field (goes under your class declaration) called curFrag, so something like this:
public class MyActivity extends Activity {
private Fragment curFrag;
//other code...
}
then in the code you posted you would initialize the curFrag there, but you also need to set a tag for the current fragment. This will be based on your case statement. Make some final string variables as tags.
i.e.
public static final String CHATSTAG = "chatstag";
#Override
public void onNavigationDrawerItemSelected(int position) {
Bundle bundle = new Bundle();
bundle.putStringArrayList("contacts", arr);
bundle.putStringArrayList("messages", messages);
Fragment fragment = null;
String tag = null;
switch (position) {
case 0:
tag = FRIENDSTAG;
fragment = new FriendsFragment();
break;
case 1:
tag = CHATSTAG;... and so on through the switch statement.
fragment = new ChatsFragment();
break;
case 2:
fragment = new GroupsFragment();
break;
case 3:
fragment = new LogoutFragment();
break;
default:
break;
}
if (fragment != null) {
fragment.setArguments(bundle);
FragmentManager fragmentManager = getSupportFragmentManager();
//remember to set the tag.
if(tag != null) {
fragmentManager.beginTransaction()
.replace(R.id.container, fragment, tag).addToBackStack(null).commit();
} else {
fragmentManager.beginTransaction()
.replace(R.id.container,fragment,DEFAULTTAG).addToBackStack(null).commit();
}
//new code
curFrag = fragment;
}
}
Now in your activity when a new message comes in, check the tag of the fragment and then if it matches a certain fragment, notify the fragment that new data has come in and retrieve it in the fragment.
public void onMessageRecieved() {
if(curFrag.getTag().equalsIgnoreCase(CHATSTAG)) {
ChatsFragment frag = (ChatsFragment) curFrag;
frag.notifyDataRecieved();
}
}
Once you have a reference to your fragment in the activity, you have access to any public methods in that fragment.
If your fragment cannot access the data on its own, then you'll need to get a reference to the activity and create a method in the activity that returns the new data.
So in your activity:
public String getMessageData() {
String newData = ...//get stuff from server;
return newData;
}
then in your fragment
public void notifyNewMessage() {
try {
MyActivity activity = (MyActivity) getActivity();
} catch (ClassCastException e) {
e.printStackTrace();
} catch (NullPointerException e) {
e.printStackTrace();
}
String message = activity.getMessageData();
//do something with the message.
}
It's not necessarily pretty but it works pretty well. You should also check to make sure your fragments are attached when you do this so that you avoid null exceptions.
Hope this helps!
I am trying to show multiple fragments in a FrameLayout container. The basic idea is to use a spinner to select a different fragment to be displayed in the container. I am trying to add them programmatically and for this I have created one xml file for each day of the week which is what I am trying to show.
// Set up the spinner to select days of the week.
Spinner spinner = (Spinner) weekView.findViewById(R.id.day_selecter);
spinner.setOnItemSelectedListener(new OnItemSelectedListener(){
#Override
public void onItemSelected(AdapterView<?> parent, View view,
int pos, long id) {
// For each day of the week, create a new instance of Switches
// get an instance of FragmentTransaction from your Activity
FragmentManager fm = getFragmentManager();
FragmentTransaction fragmentTransaction = fm.beginTransaction();
Fragment frag = fm.findFragmentByTag(Integer.toString(pos));
if(frag == null) {
switch(pos) {
case 0: frag = new mondayFragment();
break;
case 1: frag = new tuesdayFragment();
break;
case 2: frag = new wednesdayFragment();
break;
case 3: frag = new thursdayFragment();
break;
case 4: frag = new fridayFragment();
break;
case 5: frag = new saturdayFragment();
break;
case 6: frag = new sundayFragment();
break;
}
fragmentTransaction.add(R.id.week_program_switches, frag, Integer.toString(pos));
}
else
fragmentTransaction.replace(R.id.week_program_switches, frag, Integer.toString(pos));
fragmentTransaction.commit();
}
#Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
The program manages to load the fragment corresponding to the first day of the week, i.e. the mondayFragment into the container. Each fragment contains textboxes and checkboxes so i need to save the view of each fragment loaded. At times the app would allow me to select a different day but the content from the previous fragment gets carried over and it eventually crashes the app with an IllegalStateException error: Day has already been added to fragment transaction. other times, simply selecting a different day in the spinner immediately crashes the app with the same error. I really need your help in this as I'm all out of ideas.
Few Notes:
1. I have not added any fragment statically into any layout. I have seen this to be the cause of many related issues.
2. I originally intended to use a single fragment and create multiple instances in a frameLayout container but i had similar issues of saving the content in each instance.
I have a problem with the FragmentPagerAdapter .
I can not save the state of the Fragment and then there is the view that within the Fragment . Whenever I use the swipe left and right , the Fragment is recreated by overriding the method getItem ( int position ) in the static class that extends the FragmentPagerAdapter .
public static class GraphicsCollectionPagerAdapter extends FragmentPagerAdapter {
final int NUM_ITEMS = 3; // number of tabs
public GraphicsCollectionPagerAdapter(FragmentManager fm) {
super(fm);
fragmentList = new AnalyzeFragmentPageListWithDate();
fragment1 = new AnalyzeFragmentPage1();
fragment2 = new AnalyzeFragmentPage2();
}
#Override
public Fragment getItem(int position) {
//Log.i(TAG, "getItem() -> New fragment at position " + position);
switch (position) {
case 0:
return fragmentList;
case 1:
return fragment1;
case 2:
return fragment2;
}
return null;
}
#Override
public int getCount() {
return 3;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Fragm1";
case 1:
return "Fragm2";
case 2:
return "Fragm3";
}
return "OBJECT " + (position + 1);
}
}
Within the method OnCreateView of each instance of the Fragment there are several steps to the SQLite database and this causes a saturation of the Database Connection Pool.
The warning found whenever change dynamically fragment is: "W / SQLiteConnectionPool (1111 ) : A SQLiteConnection object for database ' / data / data / com.myapp / databases / mydb ' was leaked ! Please fix your application to end transactions in progress properly and to close the database When it is no longer needed . "
I already tried to use the FragmentStatePagerAdapter without success.
Could you kindly tell me how to proceed ? I do not want the Fragment is regenerated each time, causing problems to the database. Have you got an example for save Fragment/View sate?
I have not found any suggestion for now .
thank you very much
use setOffscreenPageLimit property for your ViewPager object.
ViewPager pager = (ViewPager) findViewById(R.id.viewPagerId);
pager.setOffscreenPageLimit(2);
First of all create a new instance of Fragment every time the getItem() is called
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new FragmentList();
case 1:
return new AnalyzeFragmentPage1();
case 2:
return new AnalyzeFragmentPage2();
}
return null;
}
Note that FragmentPagerAdapter does not work exactly like normal Adapter meaning it does NOT use an empty vessel Fragment and then refills it with different data.
Instead it creates a new Fragment whenever it is needed. So you should pass data (if any) when the Fragment is created. Please study the example in the Android docs.
In a real time projects instead of passing current position to a new Fragment you could pass the actual ID of the entry that a Fragment should refer to.
i'm new to Android, (not programming, or even Java) so bear with me.
I'm trying to get a handle on the use of fragments.
I've got a project that I've created using the default swipe/actionbar. I've extended this further to handle the settings i want.... however i don't quite understand what's going on/how to fix this.
/**
* 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 DummySectionFragment (defined as a static inner class
// below) with the page number as its lone argument.
Fragment fragment = new DummySectionFragment();
Bundle args = new Bundle();
args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
fragment.setArguments(args);
return fragment;
}
#Override
public int getCount() {
// Show 8 total pages.
return 8;
}
#Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.title_section1).toUpperCase(l);
case 1:
return getString(R.string.title_section2).toUpperCase(l);
case 2:
return getString(R.string.title_section3).toUpperCase(l);
case 3:
return getString(R.string.title_section4).toUpperCase(l);
case 4:
return getString(R.string.title_section5).toUpperCase(l);
case 5:
return getString(R.string.title_section6).toUpperCase(l);
case 6:
return getString(R.string.title_section7).toUpperCase(l);
case 7:
return getString(R.string.title_section8).toUpperCase(l);
}
return null;
}
}
/**
* A dummy fragment representing a section of the app, but that simply
* displays dummy text.
*/
public class DummySectionFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
public String ARG_SECTION_NUMBER = "section_number";
public DummySectionFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
int position;
position = getArguments().getInt(ARG_SECTION_NUMBER)-1;
View rootView;
TextView dummyTextView;
I don't really want anything static or final here, and I've got it mostly worked out but I don't understand the following line or how to fix it. I kinda get what it's doing.
args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
The error is: cannot make a static reference to the non-static field DummySectionFragment.ARG_SECTION_NUMBER
There is probably a simple fix for this, i just am unfamiliar enough with Android and Java, as my current job i spend all my time in SQL Server.
-- EDITED ADDITIONS
i'm not opposed to anything static or final etc. the problem i'm not quite understanding is when i want to DO something in each of those fragments. I have a textview on each of those layouts and i want to be able to manipulate them say in a loop. I think i'm stuck in a circle and can't figure my way out... lol.
For example below the code I put above is
case 4:
rootView = inflater.inflate(R.layout.fragment_main_location,container, false);
dummyTextView= (TextView) rootView .findViewById(R.id.section_label);
// location
Button btnShowLocation = (Button) rootView.findViewById(R.id.btnShowLocation);
Button btnShowDBLocList = (Button) rootView.findViewById(R.id.btnShowDBLocList);
Button btnLocationsCount = (Button) rootView.findViewById(R.id.btnLocationsCount);
Button btnTruncateDBLocationsTable = (Button) rootView.findViewById(R.id.btnTruncateDBLocationsTable);
btnTruncateDBLocationsTable.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Activity activity = getActivity();
int intCount = 0;
/*if (activity != null) {
//dummyTextView.setText("");
try {
locationDatabaseHandler.truncateLocationTable();
intCount = locationDatabaseHandler.getLocationCount();
} catch (Exception e){
//dummyTextView.append(e.toString());
}
//dummyTextView.append("Count:" + intCount + "\n\n");
Toast.makeText(activity, "toast_you_just_clicked_a_fragment btnTruncateDBLocationsTable button", Toast.LENGTH_LONG).show();
}*/
}
});
dummyTextView = (TextView) rootView .findViewById(R.id.section_label);
dummyTextView.append("\nLocation Stuff\n");
break;
//dummyTextView.append("Count:" + intCount + "\n\n");
I run into a circle where if I dummyTextView try to use the dummmyText w/in the onClick event, it says that i need to make it static (quick fix) with a complaining error of : cannot refer to a non-final variable dummy7Text inside an indder class defined in a different method.
I've added a variables to handle this inside the onCreate that get filled for (LayoutInflater and Viewgroup, and then reference them w/in the onclick (not shown), but when i go in and instansiate ... nothing happens with the textviews...
There is something i'm not quite getting here, and once i get by that hurdle, i'll have this by the balls, and will be able to make it do what i want.
I don't really want anything static or final here
Why? They will not negatively impact performance, nor are they a sign of poor coding practices.
I don't understand the following line
Every Fragment can be created with a Bundle containing any number of key-value pairs. DummySectionFragment.ARG_SECTION_NUMBER is a the key (a String), and position + 1 is the value. Thus this code is telling the new DummySectionFragment which section of content the Fragment should show.
This method is preferable to putting these arguments in a constructor because your custom constructor for a Fragment isn't guaranteed to be called. There are many ways for Android to generate Fragments, so this lowers the possibility of problems such as NullPointerExceptions.
the error is: cannot make a static reference to the non-static field DummySectionFragment.ARG_SECTION_NUMBER
As you seem to know, DummySectionFragment.ARG_SECTION_NUMBER is referring to a static field within the DummySectionFragment class called ARG_SECTION_NUMBER. By making this field non-static, you can no longer reference this constant value without a DummySectionFragment instance.
Another option (if you really don't want a static field) would be to hardcode the String. Thus your code would be:
args.putInt("section_number", position + 1);
However, a public static field is a much better coding practice and will prevent silly mistakes with typos in your Strings.
I run into a cirle where if i dummyTextView try to use the dummmyText w/in the onClick event, it says that i need to make it static (quick fix) with a complaining error of : cannot refer to a non-final variable dummy7Text inside an indder class defined in a different method.
Instead of using an anonymous inner class, I would let your Fragment implement OnClickListener.
For example:
public class MyFragment extends Fragment implements OnClickListener {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// ...
Button btnTruncateDBLocationsTable = (Button) rootView.findViewById(R.id.btnTruncateDBLocationsTable);
btnTruncateDBLocationsTable.setOnClickListener(this);
// ...
}
#Override
public void onClick(View v) {
// You can reference dummyTextView here without any problems
}
}
that means that ARG_SECTION_NUMBER should be declared as public static. Better if it declared as public static final
I am using android DrawerLayout from Support Library to show slide menu.I am using a single activity and 5-6 fragments to show them upon selection in DrawerLayout menu.But I have a small problem which is "How do I check which fragment is currently visible so if user selected the menu item which corresponds to already opened fragment. Currently it creating the Fragment again and displaying it which is not good.The function that triggers when clicked on menu item is:
private void selectItem(int position) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
// Locate Position
switch (position) {
case 0:
ft.replace(R.id.content_frame, fragment1);
break;
case 1:
ft.replace(R.id.content_frame, fragment2);
break;
case 2:
ft.replace(R.id.content_frame, fragment3);
break;
}
ft.commit();
mDrawerList.setItemChecked(position, true);
// Close drawer
mDrawerLayout.closeDrawer(mDrawerList);
}
How do I check if the requested fragment is already opened so not to create it again?Is their any method to check this through FragmentManager?
I would add to #Plato's answer.
Check get currently displayed fragment question if you haven't already.
The answer says that when you add the fragment in your transaction, you can use a tag to represent a particular fragment. Something like:
ft.replace(android.R.id.content, fragment, "MY_FRAGMENT");
Later if you want to check if that fragment is visible, you can do something like:
RequestedFragment fragment = (RequestedFragment)getFragmentManager().findFragmentByTag("MY_FRAGMENT"); //"My_FRAGMENT" is its tag
if (fragment.isVisible()) {
// add your code here
}
Hope this helps.
the simplest approach would be to store last used position and compare next time. Just make your selectItem method like:
int lastPosition = -1;
private void selectItem(int position) {
if( position != lastPosition ) {
[ old method body here ]
lastPostion = position;
}
}
Assign different tags to each one of your fragments and call findFragmentByTag() of the FragmentManager to check if each one is already present.
You can also use the findFragmentById() of the FragmentManager for the same purpose and use the ids of your fragments.
If you are absolutely sure that each of fragment1, fragment2, fragment3 cannot be visible at the same time and if you reuse the same fragments (i.e. do not create a new fragment each time you change position) then the method isVisible() from the class Fragment should tell you if that fragment is currently visible.
Your switch should look like:
switch (position) {
case 0:
if(!fragment1.isVisible()) {
ft.replace(R.id.content_frame, fragment1);
}
break;
case 1:
if(!fragment2.isVisible()) {
ft.replace(R.id.content_frame, fragment2);
}
break;
case 2:
if(!fragment3.isVisible()) {
ft.replace(R.id.content_frame, fragment3);
}
break;
}