How to Recreate a Fitness Tracker App from Video to React Native with Replay (2026)

TL;DR: Recreate a fully functional React Native fitness tracker app from a simple screen recording using Replay's behavior-driven reconstruction, complete with Supabase integration and style injection.

The year is 2026. The age of pixel-perfect screen-to-code conversion is dead. We're now building applications based on intent, not just appearance. Welcome to the era of Behavior-Driven Reconstruction.

This article walks you through the process of recreating a fitness tracker app from a video recording using Replay. We'll leverage Replay's unique ability to understand user behavior from video, generate React Native code, integrate with Supabase for data persistence, and inject custom styles to match the original design.

Understanding Behavior-Driven Reconstruction#

Traditional screenshot-to-code tools are limited. They analyze static images, missing crucial contextual information about user interactions, animations, and application flow. Replay changes the game by analyzing video – the closest thing we have to a true record of user intent.

Replay's engine, powered by advanced AI (including Gemini), understands:

• •User actions: Taps, swipes, scrolls, and input field interactions.
• •Application flow: Navigation between screens, data updates, and state changes.
• •UI elements: Identifying components, text, images, and interactive elements.

This understanding allows Replay to generate code that not only looks like the original app but also behaves like it.

Setting the Stage: The Fitness Tracker App#

Our goal is to recreate a simplified fitness tracker app that allows users to:

• •Track daily steps.
• •View historical data.
• •Set goals.

We have a short video recording demonstrating the app's functionality. This video showcases the user navigating between screens, inputting data, and interacting with the UI. This is all Replay needs to get started.

Step-by-Step Reconstruction with Replay#

Step 1: Uploading the Video to Replay#

First, upload your video recording to the Replay platform. Replay supports various video formats, including MP4, MOV, and WebM.

💡 Pro Tip: Ensure your video is clear and captures all relevant user interactions. A stable recording environment will improve accuracy.

Step 2: Replay Analyzes the Video#

Once uploaded, Replay's engine begins analyzing the video. This process involves:

1. •Frame-by-frame analysis: Identifying UI elements and their properties.
2. •Behavioral pattern recognition: Understanding user actions and their context.
3. •State management inference: Determining how the application's state changes based on user interactions.

This analysis takes a few minutes, depending on the video's length and complexity.

Step 3: Generating React Native Code#

After analysis, Replay generates the React Native code. This includes:

• •Component structure: Recreating the UI hierarchy using React Native components (e.g.,
  text

  View
  ,
  text

  Text
  ,
  text

  TouchableOpacity
  ).
• •Navigation logic: Implementing screen transitions using React Navigation.
• •State management: Handling application state using React's
  text

  useState
  hook or a more advanced solution like Redux or Zustand (configurable in Replay settings).
• •Event handling: Implementing event listeners for user interactions (e.g.,
  text

  onPress
  ,
  text

  onChangeText
  ).

Here's a snippet of the generated React Native code for the main screen:

typescript
// Generated by Replay
import React, { useState, useEffect } from 'react';
import { View, Text, StyleSheet, TouchableOpacity } from 'react-native';
import { useNavigation } from '@react-navigation/native';
import { supabase } from './supabase'; // Assuming Supabase is configured

interface StepData {
  date: string;
  steps: number;
}

const MainScreen = () => {
  const [steps, setSteps] = useState<number>(0);
  const [goal, setGoal] = useState<number>(10000);
  const [stepData, setStepData] = useState<StepData[]>([]);
  const navigation = useNavigation();

  useEffect(() => {
    fetchSteps();
  }, []);

  const fetchSteps = async () => {
    const { data, error } = await supabase
      .from('steps')
      .select('*')
      .order('date', { ascending: false });

    if (error) {
      console.error('Error fetching steps:', error);
      return;
    }

    setStepData(data as StepData[]);
  };

  const incrementSteps = () => {
    setSteps(steps + 100);
  };

  return (
    <View style={styles.container}>
      <Text style={styles.title}>Daily Steps</Text>
      <Text style={styles.stepCount}>{steps}</Text>
      <Text style={styles.goal}>Goal: {goal}</Text>
      <TouchableOpacity style={styles.button} onPress={incrementSteps}>
        <Text style={styles.buttonText}>Add Steps</Text>
      </TouchableOpacity>
      <TouchableOpacity style={styles.button} onPress={() => navigation.navigate('History')}>
        <Text style={styles.buttonText}>View History</Text>
      </TouchableOpacity>
    </View>
  );
};

const styles = StyleSheet.create({
  container: {
    flex: 1,
    alignItems: 'center',
    justifyContent: 'center',
    backgroundColor: '#f0f0f0',
  },
  title: {
    fontSize: 24,
    fontWeight: 'bold',
    marginBottom: 20,
  },
  stepCount: {
    fontSize: 48,
    marginBottom: 10,
  },
  goal: {
    fontSize: 18,
    marginBottom: 20,
  },
  button: {
    backgroundColor: '#4CAF50',
    padding: 15,
    borderRadius: 5,
    marginBottom: 10,
  },
  buttonText: {
    color: 'white',
    fontSize: 16,
    fontWeight: 'bold',
  },
});

export default MainScreen;

Step 4: Supabase Integration#

Replay automatically detects the need for data persistence and offers seamless integration with Supabase. It generates the necessary code to:

• •Create database tables.
• •Implement data fetching and storage logic.
• •Handle user authentication (if required).

📝 Note: You'll need to configure your Supabase credentials in the Replay settings.

Replay generates the

file (or similar, depending on your project setup) to interact with your Supabase database. Here's an example:

typescript
// supabase.ts
import { createClient } from '@supabase/supabase-js';
import { SUPABASE_URL, SUPABASE_ANON_KEY } from '@env'; // Assuming you're using environment variables

const supabaseUrl = SUPABASE_URL || process.env.SUPABASE_URL;
const supabaseAnonKey = SUPABASE_ANON_KEY || process.env.SUPABASE_ANON_KEY;

if (!supabaseUrl || !supabaseAnonKey) {
  throw new Error('Supabase URL and Anon Key are required.');
}

export const supabase = createClient(supabaseUrl, supabaseAnonKey);

Step 5: Style Injection#

Replay attempts to replicate the original app's styling using React Native's StyleSheet API. It extracts style attributes from the video and generates corresponding style rules.

⚠️ Warning: Style injection is not always perfect. You might need to manually adjust the generated styles to achieve pixel-perfect fidelity.

The styles are usually located within the React Native component files, as seen in the

example above.

Step 6: Product Flow Map#

One of Replay's standout features is its ability to generate a product flow map. This map visualizes the user's journey through the app, highlighting key screens and interactions. This map can be exported as a Mermaid diagram or a similar format for documentation and collaboration.

Step 7: Manual Refinement#

While Replay automates a significant portion of the development process, manual refinement is often necessary. This might involve:

• •Adjusting styles for pixel-perfect accuracy.
• •Adding custom logic or features.
• •Optimizing performance.
• •Fixing any minor bugs.

Replay vs. Traditional Methods#

Let's compare Replay with traditional development methods and screenshot-to-code tools:

Advantages of Using Replay#

• •Speed: Drastically reduces development time by automating code generation.
• •Accuracy: Captures user behavior and application flow for more accurate code.
• •Integration: Seamlessly integrates with Supabase for data persistence.
• •Accessibility: Lowers the barrier to entry for app development.
• •Understanding Intent: Replay understands what the user is trying to do, not just what they see.

Common Concerns and How Replay Addresses Them#

Concern: "The generated code might be messy or inefficient."

Replay's Solution: Replay prioritizes clean, readable code. However, developers can further optimize the code as needed.

Concern: "Style injection might not be perfect."

Replay's Solution: Style injection provides a solid foundation. Manual adjustments can be made to achieve pixel-perfect fidelity.

Concern: "Will Replay replace developers?"

Replay's Solution: Replay is a tool to augment developers, not replace them. It automates repetitive tasks, freeing up developers to focus on more complex and creative aspects of app development.

Frequently Asked Questions#

Is Replay free to use?#

Replay offers a free tier with limited features. Paid plans are available for more advanced features and higher usage limits.

How is Replay different from v0.dev or other AI code generation tools?#

While other tools might generate code from prompts or design files, Replay uniquely analyzes video to understand user behavior and application flow. This behavior-driven reconstruction sets Replay apart. It's not just about generating UI; it's about recreating the experience.

What if the video quality is poor?#

Replay works best with clear, stable video recordings. Poor video quality can impact the accuracy of the analysis.

Can Replay handle complex animations and transitions?#

Replay can handle many common animations and transitions. However, extremely complex animations might require manual implementation.

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Ready to try behavior-driven code generation? Get started with Replay - transform any video into working code in seconds.