Registration screen return

I have a registration screen, which compares the edittext text with the bank field, and this comparison is working normally.

What I would like to do is that if there was already the email field in the bank, the activity does not proceed.

Code:

 mEmail = email.getText().toString();

        new getUser().execute();




        btnfincad.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                if (("".equals(email.getText().toString().trim()))) {
                    Toast.makeText(PostCadastro.this, "Nenhum campo pode ser nulo !", Toast.LENGTH_LONG).show();
                    return;
                } else if (("".equals(password.getText().toString().trim()))) {
                    Toast.makeText(PostCadastro.this, "Nenhum campo pode ser nulo !", Toast.LENGTH_LONG).show();
                    return;
                } else if (("".equals(nick.getText().toString().trim()))) {
                    Toast.makeText(PostCadastro.this, "Nenhum campo pode ser nulo !", Toast.LENGTH_LONG).show();
                    return;
                } else if (("".equals(number.getText().toString().trim()))) {
                    Toast.makeText(PostCadastro.this, "Nenhum campo pode ser nulo !", Toast.LENGTH_LONG).show();
                    return;
                } else if (("".equals(sexo.getText().toString().trim()))) {
                    Toast.makeText(PostCadastro.this, "Nenhum campo pode ser nulo !", Toast.LENGTH_LONG).show();
                    return;
                } else if (("".equals(data.getText().toString().trim()))) {
                    Toast.makeText(PostCadastro.this, "Nenhum campo pode ser nulo !", Toast.LENGTH_LONG).show();
                    return;
                } else if (("".equals(number.getText().toString().trim()))) {
                    Toast.makeText(PostCadastro.this, "Nenhum campo pode ser nulo !", Toast.LENGTH_LONG).show();
                    return;
                }






                mName = name.getText().toString();
                mNick = nick.getText().toString();
                mPassword = password.getText().toString();
                mNumber = number.getText().toString();
                mSexo = sexo.getText().toString();
                mData = data.getText().toString();
                mEmail = email.getText().toString();

My return that does not work correctly is this:

  protected void onPostExecute(final String result) {

           super.onPostExecute(result);


           try {

               JSONObject json = new JSONObject(result);

               JSONArray array = new JSONArray(json.getString("resource"));
               for (int i = 0; i < array.length(); i++) {

                   JSONObject jsonObj = array.getJSONObject(i);

                   String email = jsonObj.getString("tx_email");
                   System.out.println(email);


                   if (mEmail.equals(email)) {
                       Toast.makeText(PostCadastro.this, "Email já existe", Toast.LENGTH_LONG).show();
                        return ;


                   }
               }


           } catch (JSONException e) {
               e.printStackTrace();
           }

       }