How to Create an Activity in Android: Step-by-Step Guide

To create an activity in Android, define a new class that extends AppCompatActivity and override the onCreate() method to set the UI layout with setContentView(). Then, register this activity in the AndroidManifest.xml file to make it part of your app.

Syntax

An Android activity is a single screen in your app. To create one, you write a class that extends AppCompatActivity. Inside, override the onCreate() method to set the layout using setContentView(R.layout.your_layout). Finally, declare the activity in AndroidManifest.xml so the system knows about it.

• class YourActivity extends AppCompatActivity: Defines the activity class.
• onCreate(Bundle savedInstanceState): Called when activity starts.
• setContentView(): Sets the UI layout.
• AndroidManifest.xml: Registers the activity.

java

public class YourActivity extends AppCompatActivity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_your);
  }
}

<!-- In AndroidManifest.xml -->
<activity android:name=".YourActivity" />

Example

This example shows a simple activity named MainActivity that displays a layout called activity_main.xml. It also shows how to register it in the manifest file.

java

package com.example.myapp;

import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
  }
}

<!-- AndroidManifest.xml -->
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapp">

  <application
      android:allowBackup="true"
      android:label="MyApp"
      android:supportsRtl="true">

    <activity android:name=".MainActivity">
      <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
      </intent-filter>
    </activity>

  </application>
</manifest>

Output

App launches showing the UI defined in activity_main.xml layout.

Common Pitfalls

Common mistakes when creating activities include:

• Forgetting to register the activity in AndroidManifest.xml, causing the app to crash when starting it.
• Not calling super.onCreate(savedInstanceState) inside onCreate(), which can break the activity lifecycle.
• Using the wrong layout resource ID in setContentView(), leading to blank screens or errors.

java

/* Wrong: Missing super call */
@Override
protected void onCreate(Bundle savedInstanceState) {
  setContentView(R.layout.activity_main);
}

/* Right: Include super call */
@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
}

Quick Reference

Remember these key steps to create an activity:

• Create a class extending AppCompatActivity.
• Override onCreate() and call super.onCreate().
• Set the UI with setContentView().
• Register the activity in AndroidManifest.xml.
• Use correct layout resource IDs.

Key Takeaways

Create an activity by extending AppCompatActivity and overriding onCreate().

Always call super.onCreate() before setting the content view.

Register your activity in AndroidManifest.xml to avoid runtime errors.

Use setContentView() with the correct layout resource to display UI.

Check for common mistakes like missing manifest entries or super calls.