I am new to android. I've created a list view in my application. I want to add a back button on the action bar. I've tried a lot but wasn't able to to get it done. Following is the code snippet which I've used:
public class Home extends ListActivity {
private ProgressDialog pDialog;
// URL to get contacts JSON
private static String url = "http://api-11hr.anovatesoft.com/v1/list";
// JSON Node names
private static final String TAG_CONTACTS = "contacts";
private static final String TAG_USERNAME = "username";
private static final String TAG_NAME = "name";
private static final String TAG_EMAIL = "email";
private static final String TAG_ADDRESS = "address";
private static final String TAG_CONTACT_NUMBER = "contactnumber";
private static final String TAG_POSTAL_CODE = "postalcode";
private static final String TAG_IMAGE = "image";
SessionManager session;
private double latitude;
private double longitude;
private String apikey;
private String status;
GPSTracker gps;
// contacts JSONArray
JSONArray contacts = null;
// Hashmap for ListView
ArrayList<HashMap<String, String>> contactList;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.home);
ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
AlertDialog.Builder alertDialog2 = new AlertDialog.Builder(
Home.this);
// Setting Dialog Title
alertDialog2.setTitle("Too quiet?");
// Setting Dialog Message
alertDialog2.setMessage("Follow your favourite merchants and see what deals they're launching at the 11th Hour!");
// Setting Positive "Yes" Btn
alertDialog2.setPositiveButton("YES",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// Write your code here to execute after dialog
dialog.cancel();
}
});
alertDialog2 .show();
Gps_func();
// Session class instance
session = new SessionManager(getApplicationContext());
// get user data from session
HashMap<String, String> user = session.getUserDetails();
// apikey
// Calling Application class (see application tag in AndroidManifest.xml)
final GlobalClass globalVariable = (GlobalClass) getApplicationContext();
//Set name and email in global/application context
apikey = globalVariable.getApikey();
latitude = globalVariable.getLatitude();
longitude = globalVariable.getLongitude();
status = globalVariable.getStatus();
contactList = new ArrayList<HashMap<String, String>>();
ListView lv = getListView();
// Listview on item click listener
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String cost = ((TextView) view.findViewById(R.id.email))
.getText().toString();
// Starting single contact activity
Intent in = new Intent(getApplicationContext(),
Adds.class);
in.putExtra(TAG_EMAIL, cost);
startActivity(in);
}
});
// Calling async task to get json
new GetContacts().execute();
}
private void Gps_func() {
gps = new GPSTracker(Home.this);
// check if GPS enabled
if (gps.canGetLocation()) {
double latitude = gps.getLatitude();
double longitude = gps.getLongitude();
// \n is for new line
// Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
Log.d("tag", "Longitude:\n" + longitude + "\n Latitude: \n" + latitude);
} else {
// can't get location
// GPS or Network is not enabled
// Ask user to enable GPS/network in settings
gps.showSettingsAlert();
if (gps.canGetLocation()) {
double latitude = gps.getLatitude();
double longitude = gps.getLongitude();
// \n is for new line
// Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
Log.d("tag", "Longitude:\n" + longitude + "\n Latitude: \n" + latitude);
}
}
}
@Override
protected void onRestart() {
super.onRestart();
Gps_func();
}
/**
* Async task class to get json by making HTTP call
*/
private class GetContacts extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(Home.this);
pDialog.setMessage("Please wait....");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
// Creating service handler class instance
ServiceHandler1 sh = new ServiceHandler1(apikey, latitude, longitude);
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(url, ServiceHandler1.POST);
Log.d("Response: ", "> " + jsonStr);
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
// Getting JSON Array node
contacts = jsonObj.getJSONArray(TAG_CONTACTS);
// looping through All Contacts
for (int i = 0; i < contacts.length(); i++) {
JSONObject c = contacts.getJSONObject(i);
String username = c.getString(TAG_USERNAME);
String name = c.getString(TAG_NAME);
String email = c.getString(TAG_EMAIL);
String address = c.getString(TAG_ADDRESS);
String gender = c.getString(TAG_CONTACT_NUMBER);
String postalcode = c.getString(TAG_POSTAL_CODE);
// tmp hashmap for single contact
HashMap<String, String> contact = new HashMap<String, String>();
// adding each child node to HashMap key => value
contact.put(TAG_EMAIL, email);
// adding contact to contact list
contactList.add(contact);
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
Home.this, contactList,
R.layout.list_item1, new String[]{TAG_EMAIL,
}, new int[]{
R.id.email,});
setListAdapter(adapter);
}
public boolean onOptionsItemSelected(MenuItem item){
Intent myIntent = new Intent(getApplicationContext(),Home.class);
startActivityForResult(myIntent, 0);
return true;
}
}
}
It throws a NullPointerException... Please give me a perfect solution. This is the log which is shown:
Unable to start activity ComponentInfo{com.example.kmi_dev.fbloginsample/com.example.kmi_dev.fbloginsample.Home}: java.lang.NullPointerException
First of all, you will only use getSupportActionBar() if your activity is extending an ActionBarActivity, so in your case, you must use getActionBar() like you did. The problem could be in your Theme. Make sure in your AndroidManifest.xml if you aren't using something such as android:theme="@android:style/Theme.Holo.Light.NoActionBar", because it can cause nullexception.
In Addition to what you have done, you need to add
getActionBar().setHomeButtonEnabled(true);
before
getActionBar().setDisplayHomeAsUpEnabled(true);