myTask

activity_main.xml
======================
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:layout_margin="16dp">

    <!-- place for logo -->
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:orientation="vertical"
        android:gravity="center">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="MY TASK"
            android:textSize="64sp"/>
    </LinearLayout>

    <!-- place for user input -->
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:orientation="vertical"
        android:gravity="center">
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="@string/userName"
            android:id="@+id/txtUser"/>
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="@string/userPass"
            android:inputType="textPassword"
            android:layout_marginTop="20dp"
            android:id="@+id/txtPass"/>
    </LinearLayout>

    <!-- place for buttons-->
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:orientation="horizontal"
        android:gravity="top">
        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/register"
            android:textColor="#ffffff"
            android:background="#009fff"
            android:textSize="22sp"
            android:layout_weight="1"
            android:layout_margin="20dp"
            android:id="@+id/btnRegister"/>
        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/login"
            android:textColor="#ffffff"
            android:background="#009fff"
            android:textSize="22sp"
            android:layout_weight="1"
            android:layout_margin="20dp"
            android:id="@+id/btnLogin"/>
    </LinearLayout>

</LinearLayout>


activity_register.xml
=======================
<?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="match_parent"
    android:layout_margin="16dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="2"
        android:orientation="vertical"
       >
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:text="LOGO"
            android:textSize="62sp"
            android:layout_gravity="center"
            />
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:orientation="vertical"
        android:layout_margin="30dp">
        <EditText
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/regUserName"
            android:hint="Enter a user name..."
            android:layout_weight="1"
            android:gravity="bottom"/>
        <EditText
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/regPass1"
            android:hint="Enter your password...."
            android:layout_weight="1"
            android:gravity="bottom"
            android:inputType="textPassword"/>
        <EditText
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/regPass2"
            android:hint="Re-Enter your password..."
            android:layout_weight="1"
            android:gravity="bottom"
            android:inputType="textPassword"
            />
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="2"
        android:orientation="horizontal">
        <Button
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="@string/register"
            android:textColor="#ffffff"
            android:background="#009fff"
            android:textSize="32sp"
            android:layout_weight="1"
            android:layout_margin="10dp"
            android:id="@+id/btnRegRegister"/>
        <Button
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="cancel"
            android:textColor="#ffffff"
            android:background="#009fff"
            android:textSize="32sp"
            android:layout_weight="1"
            android:layout_margin="10dp"
            android:id="@+id/btnRegCancel"/>
    </LinearLayout>
</LinearLayout>

android manifest (example only)
======================================
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.teacher.mytasks">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".RegisterActivity"/>
    </application>

</manifest>


RegisterActivity.java
=========================

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

/**
 * Created by teacher on 12/21/2017.
 */

public class RegisterActivity extends AppCompatActivity {
    Context context;
    EditText regUser,regPass1,regPass2;
    Button btnRegister,btnCancel;
    UtlUserSP userUtil=new UtlUserSP();

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

    private void setPointer() {
        this.context=this;
        userUtil.setContext(context);
        regUser=findViewById(R.id.regUserName);
        regPass1=findViewById(R.id.regPass1);
        regPass2=findViewById(R.id.regPass2);
        btnCancel=findViewById(R.id.btnRegCancel);
        btnCancel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });
        btnRegister =findViewById(R.id.btnRegRegister);
        btnRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //check if password o.k.
                if (!regPass1.getText().toString().equals(regPass2.getText().toString()))
                {
                    Toast.makeText(context, "Password not match", Toast.LENGTH_SHORT).show();
                    return;
                }
                if (regPass1.getText().toString().length()<3)
                {
                    Toast.makeText(context, "Password must be 3 letter minimum", Toast.LENGTH_SHORT).show();
                    return;
                }
                if(!userUtil.registerUser(regUser.getText().toString(),regPass1.getText().toString()))
                {
                    Toast.makeText(context, "Error in user registration....", Toast.LENGTH_SHORT).show();
                    return;
                }
                Toast.makeText(context, "new user is add...", Toast.LENGTH_SHORT).show();
                finish();
            }
        });

    }
}



MainActivity.java
======================
import android.content.Context;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {
    EditText txtUser, txtPass;
    Button btnLogin, btnRegister;
    Context context;

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

    private void setPointer() {
        this.context = this;
        txtUser = findViewById(R.id.txtUser);
        txtPass = findViewById(R.id.txtPass);
        btnLogin = findViewById(R.id.btnLogin);
        btnRegister = findViewById(R.id.btnRegister);

        btnRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent myIntent=new Intent(context,RegisterActivity.class);
                startActivity(myIntent);
            }
        });
    }
}




UtlUserSp.java
=====================
package com.example.teacher.mytasks;

import android.content.Context;
import android.content.SharedPreferences;
import android.widget.Toast;

/**
 * Created by teacher on 12/21/2017.
 */

public class UtlUserSP implements UserAble {
    Context context;

    public UtlUserSP() { }

    @Override
    public void setContext(Context context) {
        this.context=context;
    }

    @Override
    public boolean registerUser(String userName, String userPass) {
        //User Exists
        if (userExists(userName)) {
            Toast.makeText(context, "user already exists...", Toast.LENGTH_SHORT).show();
            return false;
        }
        //save user and password

        //declaration of shared preference
        SharedPreferences prefs = context.getSharedPreferences("myPrefs", Context.MODE_PRIVATE);

        //declaration of shared preference editor
        SharedPreferences.Editor editor = prefs.edit();

        //put data inside, we use hash map, so we need KEY,VALUE (k,v)
        editor.putString(userName, userPass);

        //sending data to my shared preferences file.
        editor.commit();
        return true;
    }

    @Override
    public boolean userExists( String userName) {
        //declaration of shared prefernces
        SharedPreferences prefs=context.getSharedPreferences("myPrefs",Context.MODE_PRIVATE);

        //get user pass
        String spPass=prefs.getString(userName,"na");

        //return if users exists, if not (na) return false
        return !spPass.equals("na");
    }

    @Override
    public boolean checkUser( String userName, String userPass) {
        return false;
    }
}