🚀 Company-Wise iOS Technical Interview Questions

Prepared By: Shobhakar Tiwari

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Walmart Mock Interview Question

• Walmart Interview Question
  • Problem Statement
  • Technical Requirements
  • Implementation Guide
  • Code Solution
  • Technical Deep Dive

Problem Statement

Real-time ETA Tracking in Ride-Sharing Application

Design and implement a feature for a ride-sharing application that displays real-time ETA (Estimated Time of Arrival) updates for drivers. The system must efficiently handle periodic network requests while maintaining optimal resource usage and user experience.

Technical Requirements

1. Implement periodic ETA fetching (10-second intervals)
2. Handle view lifecycle management
3. Implement proper network request management
4. Ensure thread-safe UI updates
5. Implement memory leak prevention
6. Handle error cases and network failures

Implementation Guide

Architecture Components

• Timer System: Manages periodic network requests
• Network Layer: Handles API communication
• UI Layer: Updates and manages view state
• Error Handling: Implements retry mechanism with exponential backoff

Key Considerations

• Resource optimization during screen transitions
• Thread safety in UI updates
• Memory management
• Network failure resilience

Code Solution

import UIKit

class ETAViewController: UIViewController {
    // MARK: - Properties
    private var timer: Timer?
    private let etaURL = URL(string: "https://api.example.com/driver/eta")!
    
    // MARK: - Lifecycle Methods
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        startFetchingETA()
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        stopFetchingETA()
    }
    
    // MARK: - Private Methods
    private func startFetchingETA() {
        timer = Timer.scheduledTimer(
            timeInterval: 10.0,
            target: self,
            selector: #selector(fetchETA),
            userInfo: nil,
            repeats: true
        )
        timer?.fire()
    }
    
    private func stopFetchingETA() {
        timer?.invalidate()
        timer = nil
    }
    
    @objc private func fetchETA() {
        let task = URLSession.shared.dataTask(with: etaURL) { [weak self] data, response, error in
            guard let self = self else { return }
            
            if let error = error {
                print("Failed to fetch ETA: \(error)")
                return
            }
            
            guard let data = data else { return }
            if let eta = self.parseETA(from: data) {
                DispatchQueue.main.async {
                    self.updateUI(with: eta)
                }
            }
        }
        task.resume()
    }
    
    private func parseETA(from data: Data) -> String? {
        return String(data: data, encoding: .utf8)
    }
    
    private func updateUI(with eta: String) {
        print("ETA Updated: \(eta)")
    }
}

Technical Deep Dive

1. Network Failure Handling

Implement an exponential backoff strategy for handling network failures:

private func retryRequest(after delay: TimeInterval) {
    DispatchQueue.main.asyncAfter(deadline: .now() + delay) { [weak self] in
        self?.fetchETA()
    }
}

2. Thread Safety Implementation

Ensure UI updates occur on the main thread:

DispatchQueue.main.async {
    self.updateUI(with: eta)
}

3. Request Cancellation

Implement proper request cancellation to prevent resource leaks:

private var currentTask: URLSessionDataTask?

@objc private func fetchETA() {
    currentTask?.cancel()
    currentTask = URLSession.shared.dataTask(with: etaURL) { [weak self] data, response, error in
        // Handle response
    }
    currentTask?.resume()
}

Contributing

We welcome contributions! Please feel free to submit a Pull Request. For major changes, please open an issue first to discuss what you would like to change.

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