I have an Activity with ViewPager which manage 2 Fragments using FragmentStatePagerAdapter,
The fragments have ListViews, each of the ListView shows data and I am able to go from Fragment_A to Fragment_B by swipe or item tapping on the ListView of Fragment_A.
I am also able to update the underlying data source for Fragment_B based on the item selected in Fragment_A. But when I try to notifyDataSetChanged() on the DataAdapter of Fragment_B, I am getting NullPointerException .
I want to update the data in Fragment_B according to the item selected in Fragment_A.
Here is my code
public class MyActivity extends FragmentActivity implements AdapterView.OnItemClickListener{
ViewPager viewPager = null;
int mSelectedItemPosition;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_fail_activity);
viewPager = (ViewPager) findViewById(R.id.fail_pager_VP);
viewPager.setAdapter(new pagerAdapter(getSupportFragmentManager()));
}
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
mSelectedItemPosition = position;
viewPager.setCurrentItem(1);
FragmentStatePagerAdapter fspa = (FragmentStatePagerAdapter) viewPager.getAdapter();
Fragment_B item = (Fragment_B) fspa.getItem(1);
item.setData(position);
item.refresh();
}
}
class pagerAdapter extends FragmentStatePagerAdapter {
public pagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
if (position == 0) {
fragment = new Fragment_A();
} else if (position == 1) {
fragment = new Fragment_B();
}
return fragment;
}
#Override
public int getCount() {
return 2;
}
#Override
public CharSequence getPageTitle(int position) {
String title = "";
if (position == 0) {
return "a_title";
}else if (position == 1) {
return "b_title";
}
}
}
public class Fragment_A extends android.support.v4.app.Fragment {
private ListView frag_a_listView;
DataAdapter dataAdapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
ListView frag_a_listView = (ListView) getActivity().findViewById(R.id.frag_a_LV);
frag_a_listView.setOnItemClickListener((AdapterView.OnItemClickListener) getActivity());
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View layout = inflater.inflate(R.layout.fragment_fail_main, container, false);
frag_a_listView = (ListView) layout.findViewById(R.id.frag_a_LV);
dataAdapter = new DataAdapter(getActivity(),
R.layout.data_row,
R.id.data_label_TV,
getFrag_aData());
frag_a_listView.setAdapter(dataAdapter);
return layout;
}
private List<String> getFrag_aData() {
...
return someData;
}
}
public class Fragment_B extends android.support.v4.app.Fragment {
ListView frag_b_listView;
List<String> mData;
DataAdapter dataAdapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
ListView frag_b_listView = (ListView) getActivity().findViewById(R.id.frag_b_LV);
frag_b_listView.setOnItemClickListener((AdapterView.OnItemClickListener) getActivity());
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View layout = inflater.inflate(R.layout.fragment_frag_b, container, false);
frag_b_listView = (ListView) layout.findViewById(R.id.frag_b_LV);
setData(0);
dataAdapter = new DataAdapter(getActivity(),
R.layout.data_row,
R.id.data_label_TV,
mData);
frag_b_listView.setAdapter(dataAdapter);
return layout;
}
public void setData(int position) {
...
mData = some List<String>;
}
public void refresh() {
dataAdapter.notifyDataSetChanged(); <------- this crashes the app
}
}
public class DataAdapter extends ArrayAdapter {
public DataAdapter(Context context, int resource, int textViewResourceId, List objects) {
super(context, resource, textViewResourceId, objects);
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
convertView = super.getView(position, convertView, parent);
return convertView;
}
}
here is the crash log
06-25 16:51:46.813 21537-21537/au.myCity.eight E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: au.myCity.eight, PID: 21537
java.lang.NullPointerException: Attempt to invoke virtual method 'void au.myCity.eight.dataAdapter.notifyDataSetChanged()' on a null object reference
at au.myCity.eight.fragments.Fragment_B.refresh(Fragment_B.java:56)
at au.myCity.eight.MyActivity.onItemClick(MyActivity.java:37)
at android.widget.AdapterView.performItemClick(AdapterView.java:305)
at android.widget.AbsListView.performItemClick(AbsListView.java:1146)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3053)
at android.widget.AbsListView$3.run(AbsListView.java:3860)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
After few tries with Log.d and checking some variable references.
The problem was the reference to Fragment_B changed by the time I called dataAdapter.notifyDataSetChanged(), to fix this I used the solution suggested in SO here, thanks to the "Streets Of Boston".
Summery, In the PagerAdapter:
Save a reference to initialized fragments in a SparseArray, use getRegisteredFragment in
onItemClick instead of getItem in MyActivity.
Override instantiateItem and destroyItem as suggested in the link.
How can i start an instance of activity.
My custom activity has a constructor take some paramters.
public class CustomActivity extends Activity {
public CustomActivity(String someParameters) {
}
}
And i create an instance of it. How to start it.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
CustomActivity activity = new CustomActivity("TEST");
// how to start to the above activity from this activity
}
I am unit testing activity with Robolectric framework and getting the following error of parse initialization error.
MyActivity.java
public class WelcomeActivity extends Activity
{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// hide action bar
// Set up the action bar.
final ActionBar actionBar = getActionBar();
actionBar.hide();
//Checking Current User
ParseUser currentUser = ParseUser.getCurrentUser();
if (currentUser != null)
{
Intent i=new Intent(WelcomeActivity.this, ViewPagerStyleLandingActivity.class);
startActivity(i);
WelcomeActivity.this.finish();
}
setContentView(R.layout.actvity_welcome);
SharedPreferences pref = getSharedPreferences(Constants.SIGNUP_CHECK_PREF, MODE_PRIVATE);
SharedPreferences.Editor editor = pref.edit();
editor.putBoolean(Constants.PREF_KEY_FIRST_RUN, false);
editor.commit();
Button loginbut=(Button) findViewById(R.id.login);
Button registerbut=(Button) findViewById(R.id.register);
loginbut.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
Intent i=new Intent(WelcomeActivity.this,LoginActivity.class);
startActivity(i);
}
});
registerbut.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
Intent i=new Intent(WelcomeActivity.this,RegisterActivity.class);
startActivity(i);
}
});
}
}
and have made the test case as
#RunWith(RobolectricTestRunner.class)
public class WelcomeActivityTest {
private WelcomeActivity activity;
private Button loginbut;
#Before
public void setup() {
activity = Robolectric.buildActivity(WelcomeActivity.class).create().get();
loginbut = (Button) activity.findViewById(R.id.button);`}
#Test
public void checkActivityNotNull() throws Exception {
assertNotNull(activity);
}
#Test
public void shouldHaveButtonThatSaysAudit() throws Exception{
assertThat((String) loginbut.getText(), equalTo("Login"));
}
#Test
public void pressingLaunchButtonForSecondActivity() throws Exception {
String resultValue = "Testing Text";
assertNotNull(loginbut);
loginbut.performClick();
Intent startedIntent = shadowOf(activity).getNextStartedActivity();
assertThat(resultValue, equalTo(startedIntent.getStringExtra("result")));
}
private ShadowContextWrapper shadowOf(WelcomeActivity activity2) {
return null;
}
#After
public void tearDown() throws Exception {
// Nothing Here
}
}
now getting the error
when running with jUnit
I have a viewpager with an adapter that extends FragmentStatePagerAdapter, this has to show some fragment that always repeats the same layout (in whic there is a listView) for every page ... now the problem is how can I update the listView that is currently visible by clicking on a button that is outside of the Fragment? I can refresh only the ones that are in the not visible pages,but not the ones that are displayed or adjacent...
One possible solution is to reset the adapter, but it doesn't seems to be right one, because it' s slow... could you please help me?
public class MainActivity extends FragmentActivity implements OnClickListener{
#Override
protected void onCreate(Bundle arg0) {
// TODO Auto-generated method stub
super.onCreate(arg0);
setContentView(R.layout.layout1);
pagerAdapter = new AdapterPager(getSupportFragmentManager());
ctx=this;
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(pagerAdapter);
pagerTab=(PagerTabStrip) findViewById(R.id.pager_tab_strip);
mViewPager.setCurrentItem(paginaCentrale);
modifica=(ImageView)findViewById(R.id.modifica);
modifica.setOnClickListener(this);
}
#Override
public void onClick(View arg0) {
// TODO onClick
switch (arg0.getId()){
case R.id.modifica:
//here I would like to call the method caricaLista() of the fragment
break;
}
}
public static class AdapterPager extends FragmentStatePagerAdapter {
public AdapterPager(FragmentManager fm) {
super(fm);
}
#Override
public int getItemPosition(Object object) {
// TODO Auto-generated method stub
return super.getItemPosition(object);
}
#Override
public Fragment getItem(int i) {
Fragment fragment;
Bundle args = new Bundle();
args.putInt("position", i);
fragment=new Fragment1();
fragment.setArguments(args);
return fragment;
}
#Override
public int getCount() {
return 1000;}
#Override
public CharSequence getPageTitle(int i) {
String title=String.valueOf(i);
return title;
}
}
public static class Fragment1 extends Fragment implements OnItemClickListener{
int fragmentPosition;
ListView lv;
List<Lista> lista= new ArrayList<Lista>();
public Fragment1(){
}
public static Fragment1 newInstance(){
return new Fragment1();
}
#Override
public void onResume() {
// TODO Auto-generated method stub
super.onResume();
caricaLista("")}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle
savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment1, container, false);
lv=(ListView) rootView.findViewById(R.id.listViewCompiti);
Bundle args = getArguments();
int position= args.getInt("position");
fragmentPosition=position;
lv.setOnItemClickListener(this);
homeListAdapter= new HomeListAdapterWithCache(ctx,R.layout.list_item_home,lista);
lv.setAdapter(homeListAdapter);
return rootView;
}
You have to store the Current Fragment into your MainActivity , and change every time the page changes.
So you call the method of the current fragments.
Check out how your MainActivity should look like:
public class MainActivity extends FragmentActivity implements OnClickListener{
&Fragment mCurrentFragment;*
protected void onCreate(Bundle arg0) {
super.onCreate(arg0);
setContentView(R.layout.layout1);
pagerAdapter = new AdapterPager(getSupportFragmentManager());
ctx=this;
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(pagerAdapter);
pagerTab=(PagerTabStrip) findViewById(R.id.pager_tab_strip);
mViewPager.setCurrentItem(paginaCentrale);
modifica=(ImageView)findViewById(R.id.modifica);
modifica.setOnClickListener(this);
*mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
mCurrentFragment = pagerAdapter.getItem(position);
}*
});
#Override
public void onClick(View arg0) {
// TODO onClick
switch (arg0.getId()){
case R.id.modifica:
*mCurrentFragment.caricaLista();*
break;
}
}
}
I'm pretty new to programming but here is a code I have. I'm trying to develop an app and I want it to open the camera feature right away. This is what I'm working with. It's asking me to add more details so I figure I should type more... Any help would be appreciated. This is my only grade for a class that is taught very poorly
import android.content.Context;
import android.hardware.Camera;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class CameraSurfaceView extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder sHolder;
public Camera camera= null;{
}
public CameraSurfaceView(Context context) {
super(context);
sHolder= getHolder();
sHolder .addCallback(this);
// TODO Auto-generated constructor stub
}
#Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
// TODO Auto-generated method stub
Camera.Parameters params= camera.getParameters();
params.setPreviewSize(width, height);
camera.setParameters(params);
camera.startPreview();
}
#Override
public void surfaceCreated(SurfaceHolder holder) {
camera = Camera.open();
try{
camera.setPreviewDisplay(sHolder);
}catch(Exception e){
}
// TODO Auto-generated method stub
}
#Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
camera.stopPreview();
camera= null;
}
public void capture (Camera.PictureCallback jpegHandler){
camera.takePicture(null, null, jpegHandler);
}
}