Simple Overlap

Use FlxG.overlap() to check if the bounding box of a FlxObject (or any objects in a group) overlaps the bounding box of another FlxObject (or any objects in the same or another group).

FlxG.overlap() will return true if it detects an overlap, and false. if it does not.

// overlaps will be true if the two objects are overlapping each other
overlaps = FlxG.overlap(objectA, objectB);

Demonstration

Source

View Source on GitHub 

package;

import flixel.FlxG;
import flixel.FlxSprite;
import flixel.FlxState;

class PlayState extends FlxState
{
	var sprite:FlxSprite;
	var box:FlxSprite;
	
	override function create()
	{
		super.create();
		
		box = new FlxSprite("assets/bigbox.png");
		box.screenCenter();
		add(box);
		
		sprite = new FlxSprite("assets/sprite.png");
		sprite.y = FlxG.height / 2 - sprite.height / 2;
		sprite.velocity.x = 100;
		add(sprite);
	}
	
	override function update(elapsed:Float)
	{
		super.update(elapsed);
		// if touching the right side of the screen
		if (sprite.velocity.x > 0 && sprite.x >= FlxG.width - sprite.width)
		{
			sprite.velocity.x *= -1;
		}
		// if touching the left side of the screen
		else if (sprite.velocity.x < 0 && sprite.x <= 0)
		{
			sprite.velocity.x *= -1;
		}
		
		box.alpha = FlxG.overlap(sprite, box) ? 0.5 : 1;
	}
}