Skip to main content

​
MainActivity

The MainActivity class is the primary entry point for the TechSales Android application, extending AppCompatActivity and implementing modern Android UI patterns.

​
Full Source Code

Location: ~/workspace/source/TechSales/app/src/main/java/com/teamtech/techsales/MainActivity.java 
package com.teamtech.techsales;

import android.os.Bundle;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_main);
        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
            Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
            return insets;
        });
    }
}

​
Class Structure

​
Package and Imports

package com.teamtech.techsales;

import android.os.Bundle;
import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
  • android.os.Bundle: State management for activity lifecycle
  • androidx.activity.EdgeToEdge: Modern immersive display API
  • androidx.appcompat.app.AppCompatActivity: Base activity class with backwards compatibility
  • androidx.core.graphics.Insets: Represents window inset dimensions
  • androidx.core.view.ViewCompat: View compatibility utilities
  • androidx.core.view.WindowInsetsCompat: Backwards-compatible window insets

​
onCreate() Method

The onCreate() method initializes the activity and sets up the UI. Let’s break down each component:

​
1. Super Call

super.onCreate(savedInstanceState);
Calls the parent class implementation to ensure proper activity initialization. The savedInstanceState parameter allows restoration of previous state if the activity is being recreated.

​
2. EdgeToEdge Enable

EdgeToEdge.enable(this);
This is called before setContentView() to ensure the window configuration is set up correctly before inflating the layout.

​
What EdgeToEdge.enable() Does

Enables the app to draw content behind the system bars (status bar and navigation bar), creating an immersive, full-screen experience.Before EdgeToEdge:
[Status Bar - System Controlled]
[App Content]
[Navigation Bar - System Controlled]
After EdgeToEdge:
[App Content + Transparent Status Bar]
[App Content]
[App Content + Transparent Navigation Bar]

​
3. Content View Inflation

setContentView(R.layout.activity_main);
Inflates the XML layout file activity_main.xml and sets it as the activity’s content view. This establishes the UI hierarchy for the activity. Location reference: MainActivity.java:17

​
4. Window Insets Handling

ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
    Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
    v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
    return insets;
});
This critical code ensures content doesn’t get obscured by system UI elements.
Step 1: Find the root view
findViewById(R.id.main)
Retrieves the root ConstraintLayout from the inflated layout.Step 2: Set the listener
ViewCompat.setOnApplyWindowInsetsListener(..., (v, insets) -> { ... })
Registers a callback that executes whenever window insets change (e.g., keyboard appears, system bars change).Step 3: Extract system bar insets
Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
Gets the dimensions of system UI elements (status bar, navigation bar).Step 4: Apply padding
v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
Adds padding to prevent content from being drawn under system bars.Step 5: Return insets
return insets;
Passes insets to child views for further processing.

​
Insets Visualization

┌─────────────────────────┐
│   systemBars.top        │ ← Status Bar Height
├─────────────────────────┤
│                         │
│   Content Area          │
│   (Padded)              │
│                         │
├─────────────────────────┤
│   systemBars.bottom     │ ← Navigation Bar Height
└─────────────────────────┘
  ↑                   ↑
  left              right

​
Lifecycle Methods

Currently, MainActivity only overrides onCreate(). The activity lifecycle follows the standard Android pattern: 
Activity Started
       ↓
   onCreate()     ← Implemented
       ↓
   onStart()
       ↓
   onResume()
       ↓
[Activity Running]
Additional lifecycle methods like onPause(), onStop(), and onDestroy() can be added as needed for resource management, state saving, or cleanup operations.

​
Key Concepts

​
AppCompatActivity

public class MainActivity extends AppCompatActivity
Extends AppCompatActivity instead of Activity to provide:
  • Backwards compatibility with older Android versions
  • Material Design component support
  • ActionBar/Toolbar support (even though we use NoActionBar)
  • Fragment management utilities

​
Lambda Expression

The insets listener uses a lambda expression for concise code: 
(v, insets) -> {
    // Implementation
    return insets;
}
This is equivalent to implementing the OnApplyWindowInsetsListener interface.

​
Common Modifications

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    EdgeToEdge.enable(this);
    setContentView(R.layout.activity_main);
    
    // Add toolbar
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    
    ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
        Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
        v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
        return insets;
    });
}

ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
    Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
    // Only apply top and bottom padding, allow content to extend to edges
    v.setPadding(0, systemBars.top, 0, systemBars.bottom);
    return insets;
});

ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
    Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
    Insets ime = insets.getInsets(WindowInsetsCompat.Type.ime());
    
    // Apply system bars and keyboard insets
    v.setPadding(
        systemBars.left,
        systemBars.top,
        systemBars.right,
        Math.max(systemBars.bottom, ime.bottom)
    );
    return insets;
});

​
Best Practices

  1. Always call EdgeToEdge.enable() before setContentView()
    • Ensures proper window configuration
  2. Handle window insets for all root views
    • Prevents content from being obscured by system UI
  3. Return insets from the listener
    • Allows child views to also process insets
  4. Use ViewCompat for backwards compatibility
    • Ensures code works on older Android versions
  5. Test on devices with different screen configurations
    • Different notch sizes, navigation bar styles, etc.

Layouts

View the activity_main.xml layout

Overview

Components architecture overview

Build docs developers (and LLMs) love

Get started for freeTalk to us