activity__main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="please.help.myapplication.MainActivity">

    <EditText
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:inputType="textPersonName"
    android:ems="10"
    android:layout_below="@+id/textView"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_marginLeft="11dp"
    android:layout_marginStart="11dp"
    android:layout_marginTop="40dp"
    android:id="@+id/textUser"
    android:hint="Username" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPassword"
        android:ems="10"
        android:layout_marginTop="16dp"
        android:id="@+id/textPass"
        android:hint="Password"
        android:layout_below="@+id/textUser"
        android:layout_alignLeft="@+id/textUser"
        android:layout_alignStart="@+id/textUser" />

    <Button
        android:text="Login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textPass"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="53dp"
        android:id="@+id/buttonLogin"
        android:onClick="onLogin (MainActivity)" /> //THE PROBLEM IS HERE, If I change line to android:onClick="onLogin" it works fine

</RelativeLayout>

MainActivity.java

package please.help.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

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



    public void onLogin(View v){
        EditText user = (EditText) findViewById(R.id.textUser);
        EditText pass = (EditText) findViewById(R.id.textPass);

        Log.i("Login Info", (user.getText().toString()) + ":" + (pass.getText().toString()));
    }

}