没有错误，但没有显示警告对话框

Question

I have non-activity class MenuHandler to handle menu-related events, I am trying to display developers message in alert dialog box, this message fetch from firebase real time database.

Everything is fine but alert dialog not displaying, I try debugger to check there any error in database but I got value properly from database. No Error to get value from database.

when I select menu from MainActivity , developerMessage toast shows then nothing happened.

I pass context to MenuHandler class properly. Can I Show Alerdialog in using context? or I need to write code only in MainActivity only(ie only activity class).

Code:

 public void developersMessage()
    {

        if (isInternetOn()) {

            Toast.makeText(mContext,"Loading message please wait",Toast.LENGTH_SHORT).show();

            DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();

            mDatabase.child("version_1_0").child("dev").addListenerForSingleValueEvent(new ValueEventListener() {

                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {

                        try {

                            final AlertDialog.Builder builder = new AlertDialog.Builder(mContext, R.style.AppCompatAlertDialogStyle);
                            builder.setTitle(mContext.getString(R.string.welcome_msg));
                            builder.setMessage(dataSnapshot.child("dev_msg").getValue(String.class));
                            builder.setPositiveButton("ok",null);

                            builder.create().show();
                        }
                        catch (Exception e)
                        {
                            e.printStackTrace();
                        }
                    }


                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

        }
        else
        {
            Toast.makeText(mContext,"please turn on internet ",Toast.LENGTH_SHORT).show();
        }
    }

Answer 1

Build your AlertDialog out of

mDatabase.child("version_1_0").child("dev").addListenerForSingleValueEvent(...);

The addListenerForSingleValueEvent(...) method runs on a different background thread, so the UI can't be updated inside off UI thread. Thus building your AlertDailog out of the addListenerForSingleValueEvent(...) method should solve your problem.

Answer 2

You should use activity context to create AlertDialog.

And please debug to make sure onDataChange() is called

Also try with runOnUiThread: https://developer.android.com/reference/android/app/Activity.html#runOnUiThread(java.lang.Runnable)

yourActivity.runOnUiThread(new Runnable() { public void run() {... code to create & show dialog ...} })

Answer 3

I got the answer, There nothing wrong in the code but bug lies in how I send context from mainactivity

here I wrongly init Menuhandler class

public boolean onOptionsItemSelected(MenuItem item) {

 final MenuHandler mMenuHandler = new MenuHandler(this.getApplicationContext());//bug lies here

if we are showing alertdialog then we need this way to pass context so our alertdialog display properly

public boolean onOptionsItemSelected(MenuItem item) {
        final MenuHandler mMenuHandler = new MenuHandler(MainActivity.this);//this is right way to pass context

hope this is helpful to someone in future.