I am creating an app and when I click login in the android simulator it says unfortunately the app has stopped but I checked my code multiple times and I don't see any errors with the code . I am following a tutorial so it should all be correct because it works for the guy doing the tutorial .
MainActivity.java :
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity {
EditText UsernameEt, PasswordEt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
UsernameEt = (EditText)findViewById(R.id.etUserName);
PasswordEt = (EditText)findViewById(R.id.etPassword);
}
public void OnLogIn(View view) {
String username = UsernameEt.getText().toString();
String password = PasswordEt.getText().toString();
String type = "login";
BackgroundWorker backgroundWorker = new BackgroundWorker(this);
backgroundWorker.execute(type, username, password);
}
}
Backgroundworker.java :
import android.app.AlertDialog;
import android.content.Context;
import android.os.AsyncTask;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
public class BackgroundWorker extends AsyncTask<String,Void,String> {
Context context;
AlertDialog alertDialog;
BackgroundWorker (Context ctx) {
context = ctx;
}
@Override
protected String doInBackground(String... params) {
String type = params[0];
String login_url = "http://192.168.1.7/login.php";
if (type.equals("login")){
try {
String user_name = params[1];
String password = params[2];
URL url = new URL(login_url);
HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
OutputStream outputStream = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
String post_data = URLEncoder.encode("user_name" , "UTF-8")+"="+URLEncoder.encode(user_name , "UTF-8")+"&"
+URLEncoder.encode("user_pass" , "UTF-8")+"="+URLEncoder.encode(password , "UTF-8");
bufferedWriter.write(post_data);
bufferedWriter.flush();
bufferedWriter.close();
outputStream.close();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, "iso-8859-1"));
String result="";
String line;
while((line = bufferedReader.readLine())!= null ){
result += line;
}
bufferedReader.close();
inputStream.close();
httpURLConnection.disconnect();
return result;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPreExecute() {
alertDialog = new AlertDialog.Builder(context).create();
alertDialog.setTitle("Login Status");
}
@Override
protected void onPostExecute(String result) {
alertDialog.setMessage(result);
alertDialog.show();
}
@Override
protected void onProgressUpdate(Void... values) {
super.onProgressUpdate(values);
}
}
Login button in content_main.xml :
<Button
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="LogIn"
android:id="@+id/login"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:onClick="OnLogIn"
/>
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:hint="Username"
android:ems="10"
android:id="@+id/etUserName"
android:layout_below="@+id/textView"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPassword"
android:ems="10"
android:hint="Password"
android:id="@+id/etPassword"
android:layout_below="@+id/etUserName"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
login.php :
<?php
require"db.php";
$user_name = "user";
$password = "pass";
$mysql_qry = "select * from users where username = '$user_name' and password = '$password';";
$result = mysqli_query($conn, $mysql_qry);
if(mysqli_num_rows($result) > 0) {
echo"login success";
}
else {
echo"not success";
}
?>
Error :
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference at com.example.User.App.MainActivity.OnLogIn(MainActivity.java:22)
(line 22 mainactivity: String username = UsernameEt.getText().toString();)
