Example of an explicit Android Intent, calling another Intent

Android Intent
Explicit Intent example
Appendix: Design main_activity.xml
Appendix: Design greeting_activity.xml

1. Android Intent

Android Intent

2. Explicit Intent example

Example preview:

This is the model of the example:

Create "Empty Activity" project named ExplicitIntentExample:

Name: ExplicitIntentExample
Package name: org.o7planning.explicitintentexample

main_activity.xml

If you are interested in the steps to design the interface of this application, please see the appendix at the end of the article.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="27dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="26dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:text="Full Name:"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/editText_fullName"
        android:layout_width="0dp"
        android:layout_height="46dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="15dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <Button
        android:id="@+id/button_sendMessage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="28dp"
        android:text="Send message to GreetingActivity"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText_fullName" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="0dp"
        android:layout_height="34dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="34dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:text="Feedback from GreetingActivity:"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button_sendMessage" />

    <TextView
        android:id="@+id/textView_feedback"
        android:layout_width="0dp"
        android:layout_height="46dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="23dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:text="((Feedback))"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2" />
</androidx.constraintlayout.widget.ConstraintLayout>

When users click the button, the program will call a other Activity to displays a greeting. You need to create an Activity with name GreetingActivity.

File > New > Activity > Empty Activity

activity_greeting.xml

activity_greeting.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".GreetingActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="29dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="27dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:text="Message sent from MainActivity:"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView_message"
        android:layout_width="0dp"
        android:layout_height="42dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="23dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:text="((Message))"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <Button
        android:id="@+id/button_back"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="63dp"
        android:text="Back"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView_message" />
</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package org.o7planning.explicitintentexample;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private EditText editTextFullName;
    private TextView textFeedback;

    private Button buttonSendMessage;

    public static final int MY_REQUEST_CODE = 100;

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

        this.editTextFullName = (EditText)this.findViewById(R.id.editText_fullName);
        this.textFeedback = (TextView)this.findViewById(R.id.textView_feedback);

        this.buttonSendMessage = (Button)this.findViewById(R.id.button_sendMessage);

        this.buttonSendMessage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sendMessage();
            }
        });
    }

    // When 'Greeting Activity' completed, it sends back a feedback.
    // (If you have started it by startActivityForResult())
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (resultCode == Activity.RESULT_OK && requestCode == MY_REQUEST_CODE) {
            String feedback = data.getStringExtra("feedback");
            this.textFeedback.setText(feedback);
        } else {
            this.textFeedback.setText("!?");
        }
    }

    // The method is called when the user clicks on "Send Message to GreetingActivity" button.
    public void sendMessage( )  {
        String fullName= this.editTextFullName.getText().toString();
        String message = "Hello, Please say hello me!";

        Intent intent = new Intent(this,GreetingActivity.class);
        intent.putExtra("fullName", fullName);
        intent.putExtra("message", message);

        // Start Activity and no need feedback.
        // this.startActivity(intent);

        // Start Activity and get feedback.
        this.startActivityForResult(intent, MY_REQUEST_CODE);
    }

}

GreetingActivity.java

package org.o7planning.explicitintentexample;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class GreetingActivity extends AppCompatActivity {

    private TextView textViewMessage;
    private Button buttonBack;

    private String fullName;
    private String message;

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

        this.textViewMessage =(TextView) this.findViewById(R.id.textView_message);
        this.buttonBack = (Button) this.findViewById(R.id.button_back);

        this.buttonBack.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                goBack();
            }
        });

        // Intent is passed into
        Intent intent = this.getIntent();

        this.fullName = intent.getStringExtra("fullName");
        this.message = intent.getStringExtra("message");

        this.textViewMessage.setText(this.message );
    }

    // When completed this Activity, send feedback to the caller.
    @Override
    public void finish() {
        // Prepare data intent
        Intent data = new Intent();
        String feedback = "OK, Hello " + this.fullName + ". How are you?";
        data.putExtra("feedback", feedback);

        // Activity finished ok, return the data
        this.setResult(Activity.RESULT_OK, data);
        super.finish();
    }


    // The method is called when the user clicks the "Back" button.
    public void goBack()  {
        // Calling onBackPressed() method to back to the previous Activity.
        this.onBackPressed();
    }


}

Running application: