School, Intent example, 28.01.18

activity.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:id="@+id/llyBack">

    <Button
        android:id="@+id/btnClickMe"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/myColor"
        android:textSize="32sp"
        android:text="click me"/>

    <TextView
        android:id="@+id/tvMessgae"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="28sp"
        android:text="Hello"
        android:gravity="center"
        android:layout_marginTop="16dp"
        />
    <EditText
        android:id="@+id/etName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="28sp"
        android:hint="your name . . ."
        android:gravity="center"
        android:layout_marginTop="16dp"
        />
</LinearLayout>

MainActivity.java
------------------
package com.example.mohamadpc.myapplication140118;

import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.TextView;

import java.util.Random;

// step 3
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    // step 1
    Button btnClick;
    TextView tvMessage;
    LinearLayout llyBack;
    Random rnd = new Random();
    EditText etName;
    int myColor;

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

        // step 2
        btnClick = findViewById(R.id.btnClickMe);
        tvMessage = findViewById(R.id.tvMessgae);
        llyBack = findViewById(R.id.llyBack);
        etName = findViewById(R.id.etName);

        tvMessage.setText("Wellcome");
        // step 5
        btnClick.setOnClickListener(this);
        tvMessage.setOnClickListener(this);
        llyBack.setOnClickListener(this);
    }

    // step 4
    @Override
    public void onClick(View view) {
        // step 6
        if (view.getId() == R.id.btnClickMe) {
            // when button clicked
            setColor();
        } else if (view.getId() == R.id.tvMessgae) {
            // when text view is clicked
            tvMessage.setText("");
        } else {
            // click on background
            Intent i;
            i = new Intent(this, Main2Activity.class);

            String name = etName.getText().toString();

            i.putExtra("UserName", name);
            i.putExtra("Color", myColor);

            startActivity(i);
            //finish();
        }
    }

    private void setColor() {
        int red = rnd.nextInt(256);
        int green = rnd.nextInt(256);
        int blue = rnd.nextInt(256);

        myColor = Color.rgb(red, green, blue);

        llyBack.setBackgroundColor(myColor);
        tvMessage.setText(myColor + "");
    }
}

activity_main2.xml
-------------------
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/myColor"
    android:orientation="vertical">

    <Button
        android:id="@+id/btnBackToMain"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Back to Main Activity"
        android:textSize="24sp" />

    <TextView
        android:id="@+id/tvWellcome"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="dogma"
        android:textSize="32sp" />
</LinearLayout>

Main2Activity.java
-------------------
package com.example.mohamadpc.myapplication140118;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;

public class Main2Activity extends AppCompatActivity implements View.OnClickListener {
    TextView tvWellcome;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        findViewById(R.id.btnBackToMain).setOnClickListener(this);
        tvWellcome = findViewById(R.id.tvWellcome);

        // get data from previous screen
        Intent i;
        i = this.getIntent();

        String name = i.getStringExtra("UserName");
        int color = i.getIntExtra("Color", 255);

        tvWellcome.setText("Wellcome " + name);
        tvWellcome.setBackgroundColor(color);


    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btnBackToMain:
                /*
                // create a new activity
                Intent i;
                i = new Intent(this, MainActivity.class);
                startActivity(i);
                */

                finish();
                break;

        }
    }
}