//sajed//27/10/2017

MainActivity
----------------
package com.example.asusproi5win10.myapplication;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    EditText etUserName, etPassword;
String c;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        connectToLayout();
    }

    private void connectToLayout() {
        etUserName = (EditText) findViewById(R.id.etUserName);
        etPassword = (EditText) findViewById(R.id.etPassword);


        findViewById(R.id.btnCancel).setOnClickListener(this);
        findViewById(R.id.btnLogin).setOnClickListener(this);
        findViewById(R.id.btnRegister).setOnClickListener(this);

    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btnLogin:
                String userName = etUserName.getText().toString();
                String password = etPassword.getText().toString();


                if (userName.length() == 0 || password.length() == 0) {
                    Toast.makeText(this, "Please fill user name and password!", Toast.LENGTH_LONG).show();
                    return;
                }


                if (isValid(userName, password)) {
                    if(isTeasher(password)) {
                        Intent i = new Intent(this, Teasher.class);
                        i.putExtra("CurrentUser", userName);
                        startActivity(i);
                    }
                    else{
                        Intent i = new Intent(this, WelcomeActivity.class);
                        i.putExtra("CurrentUser", userName);
                        startActivity(i);
                    }

                } else {
                    Toast.makeText(this, "Invalid username or password!", Toast.LENGTH_LONG).show();
                }
                break;
            case R.id.btnCancel:
                this.finish();
                break;

            case R.id.btnRegister:
                userName = etUserName.getText().toString();
                password = etPassword.getText().toString();

                if (!isUserExist(userName)) {
                    if (addNewUser(userName, password)) {

                        Toast.makeText(this, "User was added!", Toast.LENGTH_LONG).show();
                        etUserName.setText("");
                        etPassword.setText("");
                    } else {
                        Toast.makeText(this, "Error adding a user " + userName, Toast.LENGTH_LONG).show();
                    }
                }
            break;
            default:
                Toast.makeText(this, "Error on click", Toast.LENGTH_LONG).show();
                break;
        }
    }

   private boolean isTeasher(String password) {

        String s = password.substring(0,4);

        return (s.equals("0000"));
    }


    private boolean addNewUser(String userName, String password) {
        SharedPreferences prefs = this.getSharedPreferences("myUsers", Context.MODE_PRIVATE);

        SharedPreferences.Editor editor = prefs.edit();
        editor.putString(userName, password);
        return editor.commit();
    }


    private boolean isUserExist(String userName) {
        SharedPreferences prefs = this.getSharedPreferences("myUsers", Context.MODE_PRIVATE);

        String savedPassword = prefs.getString(userName, "");

        return (!savedPassword.equals(""));
    }


    private boolean isValid(String userName, String password) {

        SharedPreferences prefs = this.getSharedPreferences("myUsers", Context.MODE_PRIVATE);

        String savedPassword = prefs.getString(userName, "");

        return (savedPassword.equals(password));
    }
}

WelcomeActivity
----------------
package com.example.asusproi5win10.myapplication;

import android.content.Context;
import android.content.SharedPreferences;
import android.database.DataSetObserver;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

public class WelcomeActivity extends AppCompatActivity  implements View.OnClickListener{
    private TextView tvWelcome;
    private String userName;
    private ListView lsvGrades;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_welcome);

        userName = getIntent().getStringExtra("CurrentUser");

        tvWelcome = (TextView) findViewById(R.id.tvWellcome);
        lsvGrades = (ListView) findViewById(R.id.lsvGrades);
        findViewById(R.id.btnCancel).setOnClickListener(this);

        tvWelcome.setText(userName);

        //lsvGrades.setAdapter(new GradesAdapter(userName,this));


    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btnCancel:
                this.finish();
                break;
            default:
                Toast.makeText(this, "Error on click", Toast.LENGTH_LONG).show();
                break;
        }
    }


}




Teasher
--------
package com.example.asusproi5win10.myapplication;

import android.app.Dialog;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

import android.os.Bundle;
import android.app.AlertDialog;
import android.content.ClipData;
import android.content.Context;
import android.content.DialogInterface;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;

import static android.os.Build.VERSION_CODES.M;
import static com.example.asusproi5win10.myapplication.R.id.btnAdd;
import static com.example.asusproi5win10.myapplication.R.id.etGrade;
import static com.example.asusproi5win10.myapplication.R.id.etStudentName;
import static com.example.asusproi5win10.myapplication.R.id.tvItemSubject;
import static com.example.asusproi5win10.myapplication.R.id.tvSubject;

public class Teasher extends AppCompatActivity implements View.OnClickListener {
    private TextView tvTeasher;
    private static ListView lsvStudent;
    Context context;
    private static String userName;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_teasher);
        context = this;
        userName = getIntent().getStringExtra("CurrentUser");

        lsvStudent = (ListView) findViewById(R.id.lsvStudent);
        tvTeasher = (TextView) findViewById(R.id.tvTeasher);
        findViewById(R.id.btnCancel).setOnClickListener(this);
        findViewById(R.id.btnAdd).setOnClickListener(this);
        tvTeasher.setText(userName);

        lsvStudent.setAdapter(new GradeAdapter(userName,this));


    }




    public static void getGrade(final Context context) {

        AlertDialog.Builder bldr = new AlertDialog.Builder(context);
        final View v = LayoutInflater.from(context).inflate(R.layout.dialog_add_grade, null);

        bldr.setView(v);
        bldr.setTitle("Add New Student");

        bldr.setPositiveButton("Save", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                String studentName = ((EditText) v.findViewById(R.id.etStudentName)).getText().toString();
                int grade = Integer.parseInt(((EditText) v.findViewById(R.id.etGrade)).getText().toString());
                if (!studentName.isEmpty()) {
                    saveGrade(context, studentName, grade);
                }

            }

        });

        bldr.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
            }
        });

        bldr.show();

    }

   private static void saveGrade(Context context, String studentName, int grade) {

       SharedPreferences sharedPrefs = context.getSharedPreferences(userName, Context.MODE_PRIVATE);

        sharedPrefs.edit().putInt( studentName,grade).commit();
       lsvStudent.setAdapter(new GradeAdapter(userName,context));

    }
    private List<Grade> loadFromFile() {
        SharedPreferences sharedPrefs = context.getSharedPreferences(userName, Context.MODE_PRIVATE);
        Object[] keys = sharedPrefs.getAll().keySet().toArray();

        List<Grade> lst = new ArrayList<>();
        for (int i = 0; i < keys.length; i += 1) {
            String name = (String) keys[i];
            lst.add(new Grade(name, sharedPrefs.getInt(name, 0)));
        }
        return lst;
    }



    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btnAdd:
                getGrade(context);
                break;
            case R.id.btnCancel:
                this.finish();
                break;
            default:
                Toast.makeText(this, "Error on click", Toast.LENGTH_LONG).show();
                break;
        }

    }



}
GradesAdapter
-------------
package com.example.asusproi5win10.myapplication;

import android.content.Context;
import android.content.SharedPreferences;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

import static android.icu.lang.UCharacter.GraphemeClusterBreak.T;
public class GradesAdapter extends BaseAdapter {
    private Context context;
    private String userName;
    private ListView lsvGrades;
    private List<GradeItem> gradesList;
    private static String studentName;
    public GradesAdapter(String userName, Context context) {
        this.userName = userName;
        this.context = context;
        this.gradesList = LoadStudentGrades( userName, context);

    }


    @Override
    public int getCount() {
        return gradesList.size();
    }

    @Override
    public Object getItem(int i) {
        return gradesList
                .get(i);
    }

    @Override
    public long getItemId(int i) {
        return 0;
    }

    @Override
    public View getView(final int i, View view, ViewGroup viewGroup) {

        View rowView = LayoutInflater.from(context).inflate(R.layout.grade_item_layout, null);
        TextView tvSubjectName = (TextView) rowView.findViewById(R.id.tvItemSubject);
        final EditText etGrade = (EditText) rowView.findViewById(R.id.etItemGrade);
        tvSubjectName.setText(gradesList.get(i).getSubjectName());
        etGrade.setText(gradesList.get(i).getGrade() + "");
        LoadStudentGrades( userName, context);


        return rowView;
    }

        private List<GradeItem> LoadStudentGrades (String userName, Context context){
        SharedPreferences gradePrefs = context.getSharedPreferences(userName, Context.MODE_PRIVATE);
        List<GradeItem> res = new ArrayList<>();

        Object[] subjects = gradePrefs.getAll().keySet().toArray();

        for (int i = 0;  i < subjects.length; i += 1) {
            String subjectName = (String) subjects[i];
            int grade = gradePrefs.getInt(subjectName, 0);
            res.add(new GradeItem(subjectName, grade));
        }
        return  res;
    }


}

GradeAdapter
------------
package com.example.asusproi5win10.myapplication;

import android.content.Context;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

public class GradeAdapter extends BaseAdapter {
    private Context context;
    private String studentName;
    private String userName;

    private List<Grade> lst;

    public GradeAdapter(String userName, Context context) {
        this.userName = userName;
        this.context = context;
        this.lst = LoadStudentGrades(userName, context);

    }
    @Override
    public int getCount() {
        return lst.size();
    }
    @Override
    public Object getItem(int i) {
        return lst.get(i);
    }
    @Override
    public long getItemId(int i) {
        return 0;
    }
    @Override
    public View getView(final int i, View view, ViewGroup viewGroup) {
        View rowView = LayoutInflater.from(context).inflate(R.layout.activity_grade_adapter, null);
        TextView etStudentName = (TextView) rowView.findViewById(R.id.tvItemStudentName);
        final EditText etGrade = (EditText) rowView.findViewById(R.id.etItemGrade);
        etStudentName.setText(lst.get(i).getStudentName());
        etGrade.setText( lst.get(i).getGrade() + "" );
        LoadStudentGrades( userName, context);

        return rowView;
    }
    public static List<Grade> LoadStudentGrades(String userName, Context context) {
        SharedPreferences sharedPrefs = context.getSharedPreferences(userName, Context.MODE_PRIVATE);
        List<Grade> res = new ArrayList<>();

        Object[] studentsNames = sharedPrefs.getAll().keySet().toArray();

        for (int i = 0; i < studentsNames.length; i += 1) {
            String SName = (String) studentsNames[i];
            int grade = sharedPrefs.getInt(SName, 0);
            res.add(new Grade(SName, grade));

        }
        return res;
    }
}


Grade
-------
package com.example.asusproi5win10.myapplication;

public class Grade {
        private String StudentName;
        private int grade;
      public Grade(String StudentName, int grade) {
            this.StudentName = StudentName;
            this.grade = grade;
        }

        public String getStudentName() {
            return StudentName;
        }

        public void setStudentName(String StudentName) {
            this.StudentName = StudentName;
        }

        public int getGrade() {
            return grade;
        }

        public void setGrade(int grade) {
            this.grade = grade;
        }



}

GradeItem
-----------
package com.example.asusproi5win10.myapplication;
public class GradeItem {
    private String subjectName;
    private int grade;

    public GradeItem(String subjectName, int grade) {
        this.subjectName = subjectName;
        this.grade = grade;
    }

    public String getSubjectName() {
        return subjectName;
    }

    public void setSubjectName(String subjectName) {
        this.subjectName = subjectName;
    }

    public int getGrade() {
        return grade;
    }

    public void setGrade(int grade) {
        this.grade = grade;
    }

}
activity_teasher
-----------------
<?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_teasher"
    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="com.example.asusproi5win10.myapplication.Teasher">

    <TextView
        android:id="@+id/tvTeasher"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="12dp" />


    <Button
        android:id="@+id/btnCancel"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1.5"
        android:text="Cancel"
        android:textSize="20sp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true" />

    <Button
        android:id="@+id/btnAdd"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1.5"
        android:text="Add"
        android:textSize="20sp"
        android:layout_below="@+id/tvTeasher"
        android:layout_alignParentStart="true"
        android:layout_marginTop="19dp" />

    <ListView
        android:id="@+id/lsvStudent"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/btnAdd"
        android:layout_alignParentEnd="true">

    </ListView>


</RelativeLayout>

activity_main
---------------
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:weightSum="1">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="15dp"
        android:gravity="center"
        android:text="@string/app_name"
        android:textColor="#000ff0"
        android:textSize="32sp" />

    <EditText
        android:id="@+id/etUserName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="15dp"
        android:hint="UserName"
        android:textSize="24sp" />

    <EditText
        android:id="@+id/etPassword"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Password"
        android:inputType="textPassword"
        android:textSize="24sp" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_weight="0.14">

        <Button
            android:id="@+id/btnLogin"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:layout_weight="1"
            android:text="Login"
            android:textSize="18sp" />


        <Button
            android:id="@+id/btnRegister"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:layout_weight="1"
            android:text="Register"
            android:textSize="18sp" />

        <Button
            android:id="@+id/btnCancel"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:layout_weight="2.02"
            android:text="Cancel"
            android:textSize="18sp" />


</LinearLayout>


</LinearLayout>

activity_welcome
-----------------
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:weightSum="1">

    <TextView
        android:id="@+id/tvWellcome"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp" />

    <ListView
        android:id="@+id/lsvGrades"
        android:layout_width="match_parent"
        android:layout_height="284dp"
        android:layout_weight="0.97">

    </ListView>

    <Button
        android:id="@+id/btnCancel"
        android:layout_width="match_parent"
        android:layout_height="63dp"
        android:layout_margin="10dp"
        android:text="Cancel"
        android:textSize="18sp" />
</LinearLayout>

grade_item_layout
-------------------
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#00fff0"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/tvItemSubject"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="Subject Name"
        android:textSize="20sp" />

    <EditText
        android:id="@+id/etItemGrade"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:inputType="number"
        android:maxLength="3"
        android:text="Grade"
        android:textSize="20sp" />

</LinearLayout>
dialog_add_grade
------------------
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/etStudentName"
        android:hint="Enter Student..." />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/etGrade"
        android:hint="Enter Grade..." />
</LinearLayout>
activity_grade_adapter
-----------------------
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#00fff0"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/tvItemStudentName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="Student Name"
        android:textSize="20sp" />

    <EditText
        android:id="@+id/etItemGrade"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:inputType="number"
        android:maxLength="3"
        android:text="Grade"
        android:textSize="20sp" />

</LinearLayout>