Develop Reference

Innerclass AsyncTask Static or by WeakReference?

I have a question regarding this simple frequently occurring situation in android .
I have an activity that will invoke the async task and async task will draw values from SQLite database and update on the UI. I used Async task to make the UI reponsive and fast.
This is the code I have been working on.
SqlHandler sqlHandler;
#BindView(R.id.list) ListView listView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity1);
ButterKnife.bind(this);
sqlHandler = new SqlHandler(this);
new DisplayAll(this).execute();
listView.setOnItemClickListener((AdapterView<?> parent, View view,
int position, long id) -> {
Intent i = new Intent(getApplicationContext(), Activity2.class);
String text = textView.getText().toString();
startActivity(i);
});
}
private class DisplayAll extends AsyncTask<Void, Void, Void> {
int null_val;
final ArrayList<listRow=> myList = new ArrayList<>();
private WeakReference<Activity> mActivity;
public DisplayAll(Activity activity) {
mActivity = new WeakReference<>(activity);
}
#Override
protected Void doInBackground(Void... params) {
myList.clear();
String query = " ...";
Cursor c1 =sqlHandler.selectQuery(query);
if (c1 != null && c1.getCount() != 0) {
if (c1.moveToFirst()) {
do {
.....
} while (c1.moveToNext());
}
}
try {
null_val = Objects.requireNonNull(c1).getCount();
c1.close();
}
catch (NullPointerException e)
{
Log.e("NPE", "" + e);
}
return null;
}
#Override
protected void onPostExecute(Void param) {
// get a reference to the activity if it is still there
Activity activity = mActivity.get();
if (activity == null || activity.isFinishing()) return;
ProgressBar prgBar=findViewById(R.id.prgbar);
listAdapter Adapter;
prgBar.setVisibility(View.GONE);
Adapter = new listAdapter(getApplicationContext(), myList);
listView.setAdapter(Adapter);
}
}
I had checked this question also.I have added the weak reference to my class now. But still Android Studio warns me about the memory leak.
I tried to change it to static, but changing the sqlhandler as static also causes memory leak. To change the async task to a top-level class is not good for me. I have many async tasks in different activities.
So anyone have any idea how to tackle this?

putExtra doesn't seem to be working at all. Using ListView to get a string and using listView to display a string

I am programming a messaging app and I want to add users in a group. However, when a list of users pops up and I select one from the list, it doesn't pass the string (the username) to the other activity. All I get is an empty list.
Here is my code:
First Activity = Sending data (usernames from list) through putExtra()
public class ListUsersActivity extends Activity {
private String currentUserId;
private ArrayAdapter<String> namesArrayAdapter;
private ArrayList<String> names;
private ListView usersListView;
private Button logoutButton;
private ProgressDialog progressDialog;
private BroadcastReceiver receiver = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list_users);
Parse.initialize(this, "embpZ0spRUv5XwDgI23innll1sgHg0KZNiKzg6kl", "LPsU4UffPeqFXkQB1GfLCIJ4kvg20llPgbOnLise");
currentUserId = ParseUser.getCurrentUser().getObjectId();
names = new ArrayList<>();
ParseQuery<ParseUser> query = ParseUser.getQuery();
query.whereNotEqualTo("objectId", currentUserId);
query.findInBackground(new FindCallback<ParseUser>() {
public void done(List<ParseUser> userList, com.parse.ParseException e) {
if (e == null) {
for (int i=0; i<userList.size(); i++) {
names.add(userList.get(i).getUsername().toString());
}
usersListView = (ListView)findViewById(R.id.usersListView);
namesArrayAdapter =
new ArrayAdapter<String>(getApplicationContext(),
R.layout.user_list_item, names);
usersListView.setAdapter(namesArrayAdapter);
usersListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> a, View v, int i, long l) {
Intent goBackToAddPoolIntent = new Intent(ListUsersActivity.this, addNewPoolActivity.class);
addNewPoolActivity checker = new addNewPoolActivity();
checker.checkIfUserIsSelected(usersListView.getItemAtPosition(i).toString());
goBackToAddPoolIntent.putExtra("username", usersListView.getItemAtPosition(i).toString());
startActivity(goBackToAddPoolIntent);
}
});
} else {
Toast.makeText(getApplicationContext(),
"Error loading user list",
Toast.LENGTH_LONG).show();
}
}
});
}
Second Activity = Receiving data from putExtra()
public class addNewPoolActivity extends Activity {
private static ArrayList<String> addedUsers;
private ArrayAdapter <String> addedUserAdapter;
private boolean userIsSelected;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_new_pool);
Button addMembers = (Button) findViewById(R.id.bAddMembers);
addedUsers = new ArrayList<>();
//addedUsers.add("Group Members");
addMembers.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent showUsersToSelect = new Intent(addNewPoolActivity.this, ListUsersActivity.class);
startActivity(showUsersToSelect);
}
});
ListView addedUsersList = (ListView) findViewById(R.id.addedUsersListView);
addedUserAdapter = new ArrayAdapter<>(this, R.layout.user_list_item, addedUsers);
addedUsersList.setAdapter(addedUserAdapter);
if(userIsSelected){
Bundle extras = getIntent().getExtras();
addedUsers.add(extras.getString("username"));
}
}
public void checkIfUserIsSelected(String user){
if (user!=null){
userIsSelected = true;
}else{
userIsSelected = false;
}
}

Since the default value for a boolean is false, the code is never called because
if(userIsSelected){
will always evaluate to false since you have declared the varaible as
private boolean userIsSelected;
and the first snippet here is in onCreate() so it will only run the first time the Activity is created.
Maybe you are wanting to call checkIfUserIsSelected(someUser) before that code but without more context of what you hope to accomplish, it's hard to say.
Possibly, you want to use startActivityForResult() in some way?

In addition to #codeMagic 's answer (Since your boolean value is false, it won't call the statement that you are adding the new data). It's also because of you parse the Data "username" after you setAdapter of your ListView. So basically you are setting the data, and then trying to add the new data you parsed to the list. Either you need to do it before setting your data set to your adapter, or call addedUsersAdapter.notifyDataSetChanged() to refresh your listView's data set.
addedUserAdapter = new ArrayAdapter<>(this, R.layout.user_list_item, addedUsers);
addedUsersList.setAdapter(addedUserAdapter);
Bundle extras = getIntent().getExtras();
// Check if the username has been sent to this Activity.
if(extras != null && extras.containsKey("username")){
addedUsers.add(extras.getString("username"));
// Refresh Your Data Set
addedUserAdapter.notifyDataSetChanged();
}

Passing Object with multiple parts from one activity to another

Hi I have a Requirement like Person Details for that i have multiple details like personal,educational,job like In first activity am enter personal details and then educational and then job like that one after another for that how can i maintain all details in single object and pass through app please help me.

Be aware that you need to bundle an object in an Intent, that object must implement the Parcelable interface. Here's a common implementation taken from the Parcelable documentation...
public class MyParcelable implements Parcelable {
private int mData;
public int describeContents() {
return 0;
}
public void writeToParcel(Parcel out, int flags) {
out.writeInt(mData);
}
public static final Parcelable.Creator<MyParcelable> CREATOR
= new Parcelable.Creator<MyParcelable>() {
public MyParcelable createFromParcel(Parcel in) {
return new MyParcelable(in);
}
public MyParcelable[] newArray(int size) {
return new MyParcelable[size];
}
};
private MyParcelable(Parcel in) {
mData = in.readInt();
}
}
Once you've done that, simply pass the object around in an Intent...
Intent i = new Intent(getApplicationContext(), ACTIVITY_TO_START.class);
i.putExtra("extra_key", new MyParcelable());
startActivity(i);
to retrieve the object for the starting activity...
Bundle extras = getIntent().getExtras();
if(extras != null && extras.containsKey("extra_key"))
{
MyParcelable p = (MyParecelable)extras.getParcelable("extra_key");
}

Simple solution: Use intents for this
Personal.class
public class Personal extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.personal);
Intent i = new Intent(getApplicationContext(), Educational.class);
i.putExtra("personal_details",<-get data from object->);
startActivity(i);
}
}
Educational.class
public class Personal extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.personal);
String personal_details;
Bundle extras = getIntent().getExtras();
if (extras != null) {
personal_details= extras.getString("personal_details");
}
Intent i = new Intent(getApplicationContext(), educational.class);
i.putExtra("personal_details",personal_details);
i.putExtra("educational_details",<-get data from object->);
startActivity(i);
}
}
Job.class
public class Personal extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.personal);
String personal_details,educational_details;
Bundle extras = getIntent().getExtras();
if (extras != null) {
personal_details= extras.getString("personal_details");
educational_details= extras.getString("educational_details");
}
Intent i = new Intent(getApplicationContext(), FinalResult.class);
i.putExtra("personal_details",personal_details);
i.putExtra("educational_details",educational_details);
i.putExtra("job_details",<-get data from object->);
startActivity(i);
}
}
FinalResult.class
public class Personal extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.personal);
String personal_details,educational_details,job_details;
Bundle extras = getIntent().getExtras();
if (extras != null) {
personal_details= extras.getString("personal_details");
educational_details= extras.getString("educational_details");
job_details= extras.getString("job_details");
}
}
}
{EDIT-1}
have a look at one of my answers in different storage options in
android - Click Here
You can achieve it using application variable or shared
preferences but i would not recommend it. !
Try storing it in POJO(Plain old Java class)
{EDIT-2}
Hmm if i understand correctly your question:: You are connected to internet(Wifi,Wired,... etc) basically you are trying to show a dialog when there is no network connectivity ! .... You can take the help of Broadcast receivers ...
Try this:: Set the broadcast receiver to fire the intent when there is no net connectivity ....
Write the code to catch that intent and pop the dialog .... In this dialog give the user option to reconnect the connectivity !

NullPointerException on calling a public method from another activity

I have an Activity SaveData.class with a public method addEvent() use to add some information in a DataBase table as follows:
public class SaveData extends Activity implements OnClickListener {
public SoftCopyDatabase dB ;
public static String FILE_NAME;
String _subject, _topic,_lecturenumber,_date;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.save);
View add = findViewById(R.id.saveSave);
add.setOnClickListener(this);
View home = findViewById(R.id.saveBack);
home.setOnClickListener(this);
}public void onStart() {
super.onStart();
dB = new SoftCopyDatabase(this);
}
public void onStop() {
super.onStop();
if (dB.getReadableDatabase().isOpen()) {
//dB.close();
}
}
public void onDestroy() {
super.onDestroy();
if (dB.getReadableDatabase().isOpen()) {
dB.close();
}
}
public void onClick(View v) {
switch (v.getId()) {
case R.id.saveBack:
Intent i = new Intent(this, OpenScreen.class);
startActivity(i);
break;
case R.id.saveSave:
EditText subject = (EditText) findViewById(R.id.subjectid);
EditText topic = (EditText) findViewById(R.id.topicid);
EditText lecturenumber = (EditText) findViewById(R.id.lecturenumberid);
EditText date = (EditText) findViewById(R.id.dateid);
_subject = ((TextView) subject).getText().toString();
_topic = ((TextView) topic).getText().toString();
_lecturenumber = ((TextView) lecturenumber).getText()
.toString();
_date = ((TextView) date).getText().toString();
FILE_NAME = _subject + _topic + _lecturenumber;
//addEvent();
Intent j = new Intent(this, LectureNoting.class);
startActivity(j);
break;
}
}
public void addEvent() {
ContentValues values = new ContentValues();
values.put(SUBJECT, _subject);
values.put(TOPIC, _topic);
values.put(LECTURENUMBER, _lecturenumber);
values.put(DATE, _date);
values.put(_DATA, FILE_NAME + ".png");
dB.getWritableDatabase().insertOrThrow(TABLE_NAME, null, values);
}
}
Another activity LectureNoting.class is used to save Drawings on the disk and updates the entry in Database Table as follows:
public class LectureNoting extends Activity implements View.OnTouchListener{
private SaveData sD=new SaveData();
private File directory = new File("/sdcard/SoftCopy");
//...remaining code
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.drawing_activity);
}
//...remaining code
public void onClick(View view){
switch (view.getId()){
case R.id.saveBtn:
addEvent();
final Activity currentActivity = this;
Handler saveHandler = new Handler(){
#Override
public void handleMessage(Message msg) {
Toast.makeText(currentActivity, "Lecture Saved", Toast.LENGTH_SHORT).show();
}
} ;
new ExportBitmapToFile(this,saveHandler, softCopyInterface.getBitmap()).execute();
break;
//...remaining code
}
private class ExportBitmapToFile extends AsyncTask<Intent,Void,Boolean> {
private Context mContext;
private Handler mHandler;
private Bitmap nBitmap;
public ExportBitmapToFile(Context context,Handler handler,Bitmap bitmap) {
mContext = context;
nBitmap = bitmap;
mHandler = handler;
}
#Override
protected Boolean doInBackground(Intent... arg0) {
try {
if (!directory.exists()) {
directory.mkdirs();
}
final FileOutputStream out = new FileOutputStream(new File(directory + "/"+SaveData.FILE_NAME+".png"));
nBitmap.compress(Bitmap.CompressFormat.PNG, 90, out);
out.flush();
out.close();
return true;
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
return false;
}
#Override
protected void onPostExecute(Boolean bool) {
super.onPostExecute(bool);
if ( bool ){
mHandler.sendEmptyMessage(1);
}
}
}
}
And I am receiving following error:
Unable to start activity componentInfo(com.ned.LectureNoting):NullPointerException
At the addEvent(), used in the onClick method of LectureNoting.
Kindly tell me where I am going wrong. One point I would like to mention is if addEvent() is called from the same activity in which it was defined, this error does not appear.

Couple of things:
Logcat should be giving more information about the error. You may have to scroll down a bit to see the source of the problem in your code, but there should be more info.
you shouldnt be defining public methods inside of classes that extend Activity to be used by other classes. If you want to expose some database method to multiple activities, then create a separate class for that and then call that method inside of your activity. You said LectureNoting extends Activity. You sure about this? You must have it extending SaveData if you are just calling addEvent() like that.
Either way, DON'T CALL METHODS FROM ONE ACTIVITY INSIDE OF ANOTHER. If you want to expose a method to multiple activities, create it in it's own class with a sensible name related to the group of functions that you expose.

How to implement text to speech in non-activity class

I want to implement text to speech in non-activity class, I want when user click on custom ListView to listen the word who is written.
The code is next:
public class BankAdapter extends BaseAdapter {
List<BankItem> items;
LayoutInflater inflater;
//class who implements TextToSpeech
**TextToSpeach ttl1;**
OnClickListener l;
static class BankItemHolder {
TextView wordView;
TextView descriptionView;
}
Activity myMainActivity;
public BankAdapter(Activity mainActivity) {
// TODO Auto-generated constructor stub
super();
this.myMainActivity=mainActivity;
}
public BankAdapter(Context ctx, List<BankItem> items) {
this.items = items;
inflater =(LayoutInflater)ctx.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
.
.
.
.
.
public View getView(final int position, View convertView, ViewGroup parent) {
final BankItemHolder bih;
if (convertView == null) {
RelativeLayout rl = (RelativeLayout) inflater.inflate(R.layout.v_bank_item, null);
convertView = rl;
bih = new BankItemHolder();
bih.wordView = (TextView) rl.findViewById(R.id.txtWord);
bih.descriptionView = (TextView) rl.findViewById(R.id.txtDescription);
convertView.setTag(bih);
} else {
bih = (BankItemHolder) convertView.getTag();
}
bih.wordView.setText(items.get(position).getWord());
bih.descriptionView.setText(items.get(position).getDescriprion());
l=new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
String w1 = items.get(position).getWord();
int i1 = w1.indexOf(" ");
String w2=w1.substring(0, i1);
**ttl1.speakWords(w2);**
}
};;;
convertView.setOnClickListener(l);
return convertView;
.
.
.
.
}
}
Now the class who implements TextToSpeech
public class TextToSpeach extends Activity implements OnInitListener {
private int MY_DATA_CHECK_CODE = 0;
private TextToSpeech tts;
/**
* Called when the activity is first created.
*/
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
// setContentView(R.layout.main);
// Fire off an intent to check if a TTS engine is installed
Intent checkIntent = new Intent();
checkIntent.setAction(TextToSpeech.Engine.ACTION_CHECK_TTS_DATA);
startActivityForResult(checkIntent, MY_DATA_CHECK_CODE);
}
public void speakWords(String word) {
tts.speak(word, TextToSpeech.QUEUE_ADD, null);
}
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == MY_DATA_CHECK_CODE) {
if (resultCode == TextToSpeech.Engine.CHECK_VOICE_DATA_PASS) {
// success, create the TTS instance
tts = new TextToSpeech(this, this);
}
else {
// missing data, install it
Intent installIntent = new Intent();
installIntent.setAction(TextToSpeech.Engine.ACTION_INSTALL_TTS_DATA);
startActivity(installIntent);
}
}
}
public void onInit(int status) {
if (status == TextToSpeech.SUCCESS) {
Toast.makeText(TextToSpeach.this, "Text-To-Speech engine is initialized", Toast.LENGTH_LONG).show();
}
else if (status == TextToSpeech.ERROR) {
Toast.makeText(TextToSpeach.this, "Error occurred while initializing Text-To-Speech engine",
Toast.LENGTH_LONG).show();
}
}
/**
* Be kind, once you've finished with the TTS engine, shut it down so other
* applications can use it without us interfering with it :)
*/
#Override
public void onDestroy()
{
// Don't forget to shutdown!
if (tts != null)
{
tts.stop();
tts.shutdown();
}
super.onDestroy();
}
}

This question is symptomatic when you want to use Android framework outside of a android context..
From my little experience and lecture,
Here my own best practice in this question context.
FIRST:
Custom Service, Activity, Broadcastreceiver, ContentProvider are android context and/or are provided with android context.
This context is very important to get access to android services.
TTS is not in exception : it needs to be intantiated with a context and a listener to notify when it is ready (not ready at contruction time)
So you may do TextToSpeech actions in non-GUI component like a service for instance.
SECOND:
Avoid to design your code with a mix of App Logic and GUI in same code
THIRD:
if logic need to act on android framework it's a good way to provide context only when needed at runtime (as a parameter for instance)
as example : context can be a service or activity instance.
FOURTH:
Avoid as much as possible to keep reference to a context.
because android framework,for memory allocation strategy, may destroy /reconstruct context at it's own discretion.
hope that help