Application closes when I try to log in without filling in the fields

Question

I’m developing an application, and I’m not getting the login screen to check if the fields are being filled in or if they have the wrong username and password. Follow the login code.

It logs normal, the same problem is when I click on login without filling the fields or with wrong user or password.

package com.rafaeljacinto.newtest4;

import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class Telalogin extends AppCompatActivity {



    EditText name, password;
    Button login;
    String Name, Password;
    Context ctx=this;
    String codAlu =null, nomeAlu = null,  emailAlu = null, foneAlu = null;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_telalogin);

        name = (EditText) findViewById(R.id.name);
        password = (EditText) findViewById(R.id.password);
        login = (Button)findViewById(R.id.login);
        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Name = name.getText().toString();
                Password = password.getText().toString();
                BackGround b = new BackGround();
                b.execute(Name, Password);

            }
        });
    }

    class BackGround extends AsyncTask<String, String, String> {

        @Override
        protected String doInBackground(String... params) {
            String name = params[0];
            String password = params[1];
            String data="";
            int tmp;

            try {
                URL url = new URL("http://192.168.0.12/ProjetoNewWebService/Login.php");
                String urlParams = "name="+name+"&password="+password;

                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                httpURLConnection.setDoOutput(true);
                OutputStream os = httpURLConnection.getOutputStream();
                os.write(urlParams.getBytes());
                os.flush();
                os.close();

                InputStream is = httpURLConnection.getInputStream();
                while((tmp=is.read())!=-1){
                    data+= (char)tmp;
                }

                is.close();
                httpURLConnection.disconnect();

                return data;
            } catch (MalformedURLException e) {
                e.printStackTrace();
                return "Exception: "+e.getMessage();
            } catch (IOException e) {
                e.printStackTrace();
                return "Exception: "+e.getMessage();
            }
        }
        @Override
        protected void onPostExecute(String s) {
            String err=null;


            try {
                JSONObject jo = new JSONObject(s);
                JSONObject dados = jo.getJSONObject("usuario");
                codAlu    = dados.getString("codAlu");
                nomeAlu   = dados.getString("nomeAlu");
                emailAlu  = dados.getString("emailAlu");
                foneAlu   = dados.getString("foneAlu");

            } catch (JSONException e) {
                e.printStackTrace();
                err = "Exception: "+e.getMessage();

            }

            //Toast.makeText(TelaLogin.this, s,Toast.LENGTH_SHORT).show();
            Intent in = new Intent(Telalogin.this,Teladisciplinas.class);
            in.putExtra("codAlu",codAlu);
            in.putExtra("nomeAlu",nomeAlu);
            in.putExtra("emailAlu",emailAlu);
            in.putExtra("foneAlu",foneAlu);
            startActivity(in);

        }
    }
}

Answer 1

At first just do a validation to check if it has characters typed in the fields name and password. Example:

Name = name.getText().toString();
Password = password.getText().toString();

if(Name.length()>0  && Password.length()>0){              

    BackGround b = new BackGround();
    b.execute(Name, Password);

 } else {

    Toast.makeText(this, "Preencha todos os campos", Toast.LENGTH_SHORT).show();
}

See other ideas:

• How to test if an Edittext is empty?
• Check if Edittext is empty.
• Validating Edittext in Elegant Way on Android
• Android: How can I validate Edittext input?

For the second situation, in which you are entering an incorrect validation, you should check the return within the onPostExecute. Your Intent must be within a condition of success or error when logging in. See below for an example. If your String s is not a JSONObject, this will give you a JSONException.

Example:

 @Override
 protected void onPostExecute(String s) {
    String err=null;

     try {
            JSONObject jo = new JSONObject(s);
            JSONObject dados = jo.getJSONObject("usuario");
            codAlu    = dados.getString("codAlu");
            nomeAlu   = dados.getString("nomeAlu");
            emailAlu  = dados.getString("emailAlu");
            foneAlu   = dados.getString("foneAlu");

            //Toast.makeText(TelaLogin.this, s,Toast.LENGTH_SHORT).show();
            Intent in = new Intent(Telalogin.this,Teladisciplinas.class);
            in.putExtra("codAlu",codAlu);
            in.putExtra("nomeAlu",nomeAlu);
            in.putExtra("emailAlu",emailAlu);
            in.putExtra("foneAlu",foneAlu);
            startActivity(in);

        } catch (JSONException e) {
            e.printStackTrace();
            err = "Exception: "+e.getMessage();

        }
 }