Written on: October 2023
1. Introduction
One of the most exciting projects when starting Android app development is creating the keypad screen of a phone app. In this tutorial, you will learn how to implement the keypad, a core feature of the phone, using the Java language. The keypad provides an interface for users to enter phone numbers and includes the ability to make calls through a simple layout and button click events.
This tutorial covers defining the XML layout, handling button click events with Java code, and how to input and visually display phone numbers. Finally, we will integrate these components to implement a keypad screen with full phone functionality.
2. Setting Up the Development Environment
Let’s explain how to set up the necessary development environment for Android app development.
2.1. Installing Android Studio
First, you need to install Android Studio. Android Studio is the official IDE for Android development. Download the installation file from Google’s official website and follow the installation process.
2.2. Creating a Project
After starting Android Studio, create a new project using the following settings:
- Application name: DialerApp
- Package name: com.example.dialerapp
- Save location: Appropriate location
- Language: Java
- Minimum API level: API 21: Android 5.0 (Lollipop)
This configuration will create a basic Android project.
3. Structuring the UI Layout
The next step is to structure the UI layout of the keypad using an XML file. Open the activity_main.xml file and modify it as follows:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/phoneNumberTextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="30sp"
android:padding="16dp"
android:gravity="end" />
<GridLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@id/phoneNumberTextView"
android:columnCount="3"
android:rowCount="4">
<Button
android:id="@+id/button1"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="1"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button2"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="2"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button3"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="3"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button4"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="4"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button5"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="5"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button6"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="6"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button7"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="7"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button8"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="8"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button9"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="9"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/buttonStar"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="*"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/button0"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="0"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
<Button
android:id="@+id/buttonPound"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="#"
android:layout_columnWeight="1"
android:layout_rowWeight="1" />
</GridLayout>
</RelativeLayout>
The above XML layout structures the UI for the phone keypad. The TextView displays the entered phone number, and the GridLayout contains the number buttons.
4. Implementing Java Code
Now we will write the Java code for the main activity to handle button click events and update the phone number in the text view. Open the MainActivity.java file and add the following code:
package com.example.dialerapp;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
private TextView phoneNumberTextView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
phoneNumberTextView = findViewById(R.id.phoneNumberTextView);
setButtonListeners();
}
private void setButtonListeners() {
for (int i = 0; i <= 9; i++) {
final int number = i;
String buttonID = "button" + number;
int resID = getResources().getIdentifier(buttonID, "id", getPackageName());
Button button = findViewById(resID);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
appendNumber(String.valueOf(number));
}
});
}
findViewById(R.id.buttonStar).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
appendNumber("*");
}
});
findViewById(R.id.buttonPound).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
appendNumber("#");
}
});
}
private void appendNumber(String number) {
String currentText = phoneNumberTextView.getText().toString();
phoneNumberTextView.setText(currentText + number);
}
}
The above code adds click listeners to each button, allowing the user to input phone numbers and update the TextView whenever a button is pressed. The setButtonListeners method sets listeners for the number buttons from 0 to 9, as well as the ‘*’ and ‘#’ buttons.
5. Adding Call Functionality
Now, let’s add the feature that allows users to initiate a call after inputting a phone number. We will add a call button in the appendNumber method. To create a call menu and enable calling, please add the following code:
// Additional code for the call button
findViewById(R.id.callButton).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String phoneNumber = phoneNumberTextView.getText().toString();
if (!phoneNumber.isEmpty()) {
Intent callIntent = new Intent(Intent.ACTION_DIAL);
callIntent.setData(Uri.parse("tel:" + phoneNumber));
startActivity(callIntent);
}
}
});
This code retrieves the current text view content when the call button is clicked and starts an intent to dial the phone number using a phone URI.
6. Testing and Debugging
Now, you need to build and run the app to ensure that all features work correctly. Click the “Run” button in Android Studio, and the app will launch on the AVD (Android Virtual Device). Enter a phone number and press the call button to verify that the dialing function works properly.
Additionally, you may need an account to check if the click events for the buttons are functioning correctly and if the text view is being updated. If you find any issues, use Android Studio’s Logcat to find error messages and debug.
7. Conclusion
In this tutorial, we created the keypad screen of a basic phone app using Java. We structured the UI layout with XML and handled button click events using Java classes to input phone numbers. We also implemented the functionality to actually input phone numbers and make calls.
Now, you understand the basic components of an Android app utilizing a keypad, which you can build upon to develop more complex applications. Try adding various UI features or additional effects to create a unique application of your own!
Future advanced features could include recent call history, adding favorite contacts, and searching through the phonebook. Good luck on your app development journey!