How To Write A Simple Android App

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To create a native Android app, one that can directly use all the features and functionality available on an Android phone or tablet, you need to use the Android platform's Java API framework. This is the API that allows you to perform common tasks such as drawing text, shapes, and colors on the screen, playing sounds or videos, and interacting with a device's hardware sensors. Over the years, the Android API framework has evolved to become more stable, intuitive, and concise. As a result, being an Android developer today is easier than ever—even more so if you use Android Studio, the official tool for working with the framework.

In this tutorial, I'll show you how to create your first Android app. While doing so, I'll also introduce you to important Android-specific concepts such as views, layouts, and activities.

We'll be starting from scratch to create a very simple app in this tutorial. If you prefer writing less code or need to develop your app as quickly as possible, however, consider using one of the native Android app templates available on CodeCanyon.

CodeCanyon mobile Android app template bestsellers

Using an app template, you can have a polished, ready-to-publish app in just a matter of hours. You can learn how to use an Android app template by referring to the following tutorial:

Prerequisites

To be able to follow along, you'll need:

the latest version of Android Studio
a device or emulator running Android Marshmallow or higher

If you don't have Android Studio, do refer to the following tutorial to learn how to install and configure it:

1. Create a New Project

You'll need an Android Studio project to design, develop, and build your app. So launch Android Studio and click on the Start a new Android Studio project button.

On the next screen, choose Add No Activity because we don't want to use any of the templates offered by Android Studio. Then press Next to proceed.

You'll now see a form where you can enter important details about your app, such as its name and package name. The name is, of course, the name your users will see on their phones when they install your app.

The package name, on the other hand, is a unique identifier for your app on Google Play. You must follow the Java package naming conventions while specifying it. For example, if your app's name is MyFirstApp and you work for an organization whose website address is example.com, the package name would ideally be "com.example.myfirstapp".

Next, you must decide the programming language you want to use while coding the app. For now, selectJava and press Finish.

Android Studio will now take a minute or two to generate and configure the project.

2. Create an Activity

An activity is one of the most important components of an Android app. It is what allows you to create and display a user interface to your users. An app can have one or more activities, each allowing the user to perform an action. For example, an email client app can have three activities: one for the user to sign up, one to sign in, and one to compose an email.

To keep this tutorial simple, we'll be creating an app with just one activity. To create the activity, in the Project panel of Android Studio, right-click on appand select New > Activity > Empty Activity.

In the dialog that pops up, type in MainActivity as the name of the activity, check the Launcher Activity option, and press Finish.

Checking theLauncher Activity option is important because it is what allows your users to open the activity using an Android launcher. As such, a launcher activity serves as an entry point to your app.

3. Create a Layout

Each activity usually has at least one layout associated with it. When you created your activity in the previous step, you also generated an empty layout for it. To take a look at it, open the activity_main.xml file.

An activity's layout primarily consists of views and view groups. A view, sometimes referred to as a widget, is an individual component of your user interface. Buttons, text fields, labels, and progress bars are common examples of views. A view group is a component that can serve as a container for views. Usually, view groups also help you position and set the dimensions of your views.

ConstraintLayout is one of the most powerful and flexible view groups available today. By default, it is the root node of your activity's layout XML file. It looks like this:

<?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout     xmlns:android="https://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">          <!-- More code here -->      </androidx.constraintlayout.widget.ConstraintLayout>

We'll be creating a simple clock app in this tutorial. In addition to the local time, it will be able to show the current time in two different countries: India and Germany.

To allow the user to choose the country they're interested in, our layout will have two Button views, one for Germany, and one for India. And to actually show the time, our layout will have a TextClock view.

Accordingly, add the following code inside the ConstraintLayout:

<TextClock     android:id="@+id/my_clock"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     app:layout_constraintBottom_toBottomOf="parent"     app:layout_constraintTop_toTopOf="parent"     app:layout_constraintLeft_toLeftOf="parent"     app:layout_constraintRight_toRightOf="parent"     android:format12Hour="h:mm:ss a"     android:textSize="32sp"/>  <Button     android:layout_width="match_parent"     android:layout_height="wrap_content"     app:layout_constraintBottom_toBottomOf="parent"     android:text="Time in Germany"     android:onClick="onClickGermany"     android:id="@+id/germany_button"/>  <Button     android:layout_width="match_parent"     android:layout_height="wrap_content"     app:layout_constraintBottom_toTopOf="@id/germany_button"     android:text="Time in India"     android:onClick="onClickIndia"     android:id="@+id/india_button"/>

Note that each view must have thelayout_width and layout_height properties. They decide how large the view is. Other properties such as layout_constraintBottom_toBottomOf and layout_constraintLeft_toLeftOf are necessary to position the view. With the above code, the TextClock view will be placed at the center of the screen, and both the Button views towards the bottom of the screen.

By default, the TextClock view only shows the hours and minutes. The format12Hour property, however, allows you to change that. In the above code, its value is set to h:mm:ss a. This tells the TextClock view that it should display the hours, minutes, seconds, and also an AM/PM suffix.

Also note that each Button view has an onClick property. This property is used to assign click event handlers to the buttons.

The handlers don't exist yet, but you can ask Android Studio to generate them for you. To do so, hover over the name of the handler until you see a red light bulb appear beside it. Then click on the light bulb and select the second option, the one with the yellow light bulb.

Create onClick handlers with Android Studio

At this point, you can try pressingShift-F10 to run the app. If there are no errors in your XML code, you should see something like this on your phone or emulator:

Although the buttons don't work yet, the TextClock view should show the local time, updating itself every second.

4. Implement Event Handlers

When you generated event handlers for the two buttons, Android Studio added two methods to your activity's Java file, MainActivity.java. If you open it, you should find the following code in it:

public void onClickGermany(View view) {      }  public void onClickIndia(View view) {      }

Inside the event handlers, all we need to do is change the time zone of the TextClock view. But how do you reference a view that's in your layout XML file from inside your Java file? Well, you just use the findViewById() method.

Once you have a reference to the TextClock view, you can call itssetTimeZone() method to change its time zone. So add the following code inside the onClickGermany() method:

TextClock clock = findViewById(R.id.my_clock); clock.setTimeZone("Europe/Berlin");

Similarly, add the following code inside the onClickIndia() method:

TextClock clock = findViewById(R.id.my_clock); clock.setTimeZone("Asia/Kolkata");

If you're wondering what R is, it's an auto-generated class that contains, among other things, the IDs of all the views you have in your layouts. The findViewById() method expects you to use this class while passing an ID to it.

At this point, you can press Shift-F10 again to re-run the app. You should now be able to click on the buttons to change the clock's time zone.

Conclusion

You just created your first fully functional, native app for Android! I encourage you to make a few changes to it. For instance, you could try using other time formats or time zones. You could also try changing the positions of the buttons and the clock view.

There are dozens of views and view groups you can use to create your apps. Do refer to the official documentation to learn about them.

Android App Templates and UI Kits From CodeCanyon

You may have noticed that our app looks very plain and simple. That's because we're using the default theme, without applying any styles to our views. CodeCanyon is full of Android UI kits that offer beautiful, hand-crafted styles you can apply to your views.

The kits generally also have several custom views and layouts. You can refer to the following articles to learn more about them:

Ashraff Hathibelagal

Hathibelagal is an independent Android app developer and blogger who loves tinkering with new frameworks, SDKs, and devices.