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Andrei Matveev

Freelance Mobile App Developer

SingaporeToptal Member Since July 28, 2016

Andrei is an experienced full-stack web developer with almost a decade of experience working with a large variety of technologies—over half of that working remotely. He is equally comfortable collaborating with a team of developers or flying solo. He has worked with satisfied clients from the US, Australia, Kuwait, and Russia.

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Niels Vanspauwen

Freelance Mobile App Developer

BelgiumToptal Member Since November 11, 2016

Niels is a seasoned software architect and entrepreneur with over fifteen years of experience. He's a generalist with strong communication and business skills who speaks the language of customers as well as techies. He has extensive experience as a product architect in B2B hi-tech software as well as B2C web and mobile software. Niels enjoys designing and implementing simple solutions to complex problems.

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João Dias Barbosa

Freelance Mobile App Developer

PortugalToptal Member Since February 4, 2014

João is a passionate iOS and Android developer with a strong attention to detail that has yielded great apps. He has delivered many projects for millions of users, for both startups and big companies, and he's worked extensively on back-end and API integrations. He has a very positive attitude and works well both alone and on teams.

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Adel Tahir

Freelance Mobile App Developer

MalaysiaToptal Member Since March 24, 2014

Adel is a senior full-stack web developer with solid experience in Node.js, React, and AngularJS as well as PHP and Python/Django. He also has solid experience in iOS and Android mobile app development and he has worked in teams of all sizes.

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Luís Martinho

Freelance Mobile App Developer

PortugalToptal Member Since October 30, 2011

As an entrepreneur, Luís understands the importance of proactivity and results, and has learned the meaning of responsibility and accountability. He is more of a generalist than a specialist, though he loves the detail and deep understanding that comes from intense focus and work on development projects.

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Lorand Csatlos

Freelance Mobile App Developer

RomaniaToptal Member Since May 29, 2017

With over a decade of programming experience and 6+ years as a business owner, Lorand knows the importance of great communication and understanding with a client. He's obsessed with high quality and attention to detail, and he strives to find the best solutions possible. He currently focuses on using Magento or TYPO3 in his projects.

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Chetan Surpur

Freelance Mobile App Developer

United StatesToptal Member Since August 9, 2019

Chetan is an entrepreneur with nearly a decade of professional experience in software engineering. He has founded a mobile gaming company and released two games, one of which has over 6 million downloads on iOS and Android. Chetan was previously an engineer and researcher at a cutting-edge AI company, and the first engineering hire at a social mobile startup. He can fit easily into any project, delivering products that surprise and delight.

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Hugh Ediet

Freelance Mobile App Developer

United StatesToptal Member Since December 8, 2018

In a nutshell, Hugh delivers positive outcomes. When he encounters a problem, he identifies the essential dynamics, hypothesizes a remedy, monitors, and iterates. When the issues extend, impact, or involve others, he acts quickly, focusing on communication and the roadmap. Hugh has over 25 years of experience developing applications and solving problems across a breadth of technical and business domains.

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Andrew Giangrant

Freelance Mobile App Developer

United StatesToptal Member Since June 24, 2018

Andrew is a remote senior full-stack web and Android developer, who is always ready to devise a new solution to the next problem. He enjoys designing and planning strategies ahead of a project, and the implementation that follows, ensuring your project requirements are met, giving feedback and ideas where appropriate. Given the task at hand, Andrew adjusts well to a variety of programming languages and technologies.

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Eric Peterson

Freelance Mobile App Developer

United StatesToptal Member Since December 18, 2013

Eric is a full-stack developer who specializes in creating ambitious UIs. For the past five years, he's been developing in software, with the most recent two, building full-stack apps in JavaScript and React. He relishes projects requiring complex security or creative visualizations and with tech ranging from SQL to Android to OAuth 2.0. He communicates exceptionally well and has delivered in both small agile teams and corporate enterprises.

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Joshua Ballanco

Freelance Mobile App Developer

United StatesToptal Member Since November 22, 2013

Joshua is an architect, engineer, and scientist with experience building large-scale systems dealing with everything from massive amounts of video data to heavy web traffic. He also has experience breaking monoliths into scalable microservice architectures, and going the other way 'round. He's worked for Apple and AOL, and has also led a group of 50+ consultants as their chief scientist.

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A Hiring Guide

Guide to Hiring a Great Mobile App Developer

In a bipolar smartphone world where Android dominates devices and iOS dominates application revenue, it is impossible to ignore one platform and develop on another. Here is a guide to help you find those rare masters of both Android and iOS platforms.

Mobile App Hiring Resources

More Resources to Hire Mobile App Developers

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We needed a expert engineer who could start on our project immediately. Simanas exceeded our expectations with his work. Not having to interview and chase down an expert developer was an excellent time-saver and made everyone feel more comfortable with our choice to switch platforms to utilize a more robust language. Toptal made the process easy and convenient. Toptal is now the first place we look for expert-level help.

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Working with Toptal has been a great experience. Prior to using them, I had spent quite some time interviewing other freelancers and wasn't finding what I needed. After engaging with Toptal, they matched me up with the perfect developer in a matter of days. The developer I'm working with not only delivers quality code, but he also makes suggestions on things that I hadn't thought of. It's clear to me that Amaury knows what he is doing. Highly recommended!

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A Toptal director of engineering will work you to understand your goals, technical needs, and team dynamics.
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Within days, we'll introduce you to the right mobile app developer for your project. Average time to match is under 24 hours.
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Work with your new mobile app developer for a trial period (pay only if satisfied), ensuring they're the right fit before starting the engagement.

FAQs

  • How are Toptal Mobile App Developers different?

    At Toptal, we thoroughly screen our Mobile App Developers to ensure we only match you with talent of the highest caliber. Of the more than 100,000 people who apply to join the Toptal network each year, fewer than 3% make the cut. You'll work with engineering experts (never generalized recruiters or HR reps) to understand your goals, technical needs, and team dynamics. The end result: expert vetted talent from our network, custom matched to fit your business needs.

  • How fast can I hire Mobile App Developers through Toptal?

    Depending on availability and how fast you can progress, you could start working with a Mobile App Developer within 48 hours of signing up.

  • What is the no-risk trial period for Mobile App Developers?

    We make sure that each engagement between you and your mobile app developer begins with a trial period of up to two weeks. This means that you have time to confirm the engagement will be successful. If you're completely satisfied with the results, we'll bill you for the time and continue the engagement for as long as you'd like. If you're not completely satisfied, you won't be billed. From there, we can either part ways, or we can provide you with another expert who may be a better fit and with whom we will begin a second, no-risk trial.

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Mobile App

How to Hire a Great Mobile App Developer

In a bipolar smartphone world where Android dominates devices and iOS dominates application revenue, it is impossible to ignore one platform and develop on another. To build and release an application on both dominant platforms, you need special breed of developers. Rare developers that are familiar with both iOS optimized border shadowing and flattened Android UI hierarchies using merge layout tags.

Here is a guide to help you find those rare masters of both Android and iOS platforms.

We also suggest that you read our Android Hiring Guide and iOS Hiring Guide for more advanced and in-depth information that will help you find the right developers.

Preface

As smartphones gained popularity, many developers jumped on the trend and started creating iOS or Android applications.

Most of them had previous experience with web or desktop applications, and tried to copy old concepts onto new platforms, but they failed. Smartphone platforms differ from all other types of platforms in many aspects, most of them related to small screen size and how the user interacts with device.

After realizing that new platforms bring new concepts, good developers embraced them and started creating applications aligned with the platform they ran on.

Next, developers who created applications on one platform started working on the other one. Again, many didn’t realize how different Android and iOS are despite some similarities, and continued working with mindsets aligned to the platform they started with. Some recognized this difference and embraced another platform as completely new.

You want to find one of those rare gems - developers who natively understand both Android and iOS and can work on the same application created for both platforms, similar in functionality but differing in user experience and adapted to their platforms.

Differences

Although Android and iOS have the same main concepts, they also have many differences. Devices for both platforms are handheld and user input is touch based. But if we dig deeper, we will find more and more differences. They start with design of UI controls, continue with how they interact with the user, how new views are opened, or how users can navigate around the application and platform itself. Background differences are even bigger.

App developers versed in both platforms should know how each of them works, and on top of that understand the differences between them. Developer should know where to use platform specific concepts and also recognize similar concepts called with different names.

Questions and Answers

Q: Describe what classes are and how they used in Objective-C and Java. What about methods and functions? How are nil/null object pointers handled?

This is a simple question as every developer should know what classes are and how they are used. You can use this question to check how good a developer is at explaining concepts and how she/he can explain similarities and differences of two implementations of the same concept. Here is a shortened definition of class from the iOS Developer Library:

A class describes the behavior and properties common to any particular type of object. For any object, the class offers various ways to examine and convert the internal data that it represents. In the same way that multiple buildings constructed from the same blueprint are identical in structure, every instance of a class shares the same properties and behavior as all other instances of that class.

For a class to be useful, it needs a way to receive a message saying it should do something. The terms “method” and “function” refer to the same thing in Objective-C and Java. A method (function) is a section of code that can be called from elsewhere in our code, and the method (function) will perform some action and return some result that can be used by a caller. Method (functions) are used to organize class code into meaningful and understandable sections.

Variables that keep reference to one object, one instance of class, actually hold memory address where that object is located. Special address nil in Objective-C, null in Java signifies that there is no actual object. (This can mean that object was not yet created or that it has been removed from memory.) If you call method of such non-existing object in Objective-C nothing will happen, but if you do the same thing in Java, it will result with a runtime exception completely stopping your application. This is an interesting difference in otherwise very similar behavior of classes and objects in Objective-C and Java.

Q: What are the similarities and differences between protocols and interfaces? How and when are they used?

In Objective-C, a protocol is used to declare methods and properties that are independent of any specific class. On one side, one class can use protocol as definition of requirements that one of method parameters need to satisfy, and on another side, other class can choose to implement the same protocol. In this example, protocol is a list of requirements that method parameter needs to satisfy to be used as such.

Interface is protocol in the Java world.

Q: Describe the relationship between selector message and method in Objective-C. Is there a similar concept in Java?

In objective-C, Selector, message, and method are very connected concepts that build on top of another. A Selector is the name of a method. It does not imply class to which method could belong. A message is a selector and the arguments you are sending with it. A method is a combination of a selector and an implementation (actual code that can be executed).

In Java, there is a method reference that references defined method of defined classes and can be used for dynamic method invocation.

Q: What is category in Objective-C? When is it used?

Categories provide the ability to add functionality to an object without subclassing or changing the actual object. They are often used to add methods to existing classes created by other developers. The biggest problem with categories is the possibility that two categories define methods with the same name. In that case, it is not defined which method will be used.

Java does not have a similar concept.

This question was taken from Stackoverflow.

Q: What is runtime object type checking, and when is it useful?

During application run time, method or function can check type of passed parameter and decide how to treat it depending on its type. For example, a method expecting object of type Contact can inspect the received object to see whether it is PersonalContact or BusinessContact (in this example PersonalContact and BusinessContact are both subclasses of the Contact class).

Q: Explain differences in error handling between Android and iOS.

In Java (and Android), all problems that arise during the execution of a program are communicated through the concept of throwing and catching exceptions. Throwing an exception stops execution of the current function and continues in catch and finally blocks of try-catch-finally construct somewhere up in the function calling hierarchy.

Although the same try-catch-finally construct exists in Objective-C, it is not so widely used. Instead, Apple’s Cocoa handles problems by using objects of type NSError. The two most common approaches are:

  • Pass a blank NSError object into a method and when the method completes, check to see if that object is still blank or contains an error.
  • Pass an NSError object to some failure delegate method or callback method.

NSError objects contain information about the occurred error that error handling code can use to decide further actions.

Q: What is the source of exc_bad_access error in iOS?

exc_bad_access errors are a common source of frustration for iOS developers due to the lack of useful debugging information that they provide. They often occur when trying to access an object that was never initialized or has already been released. These errors can also result from passing a parameter to a message that the message is not intended to receive (such as passing a NSInteger when an NSString is expected).

To find the source of the problem, a developer can enable NSZombies in Xcode and keep objects that would normally be released alive as “zombies”. After enabling NSZombies, you can then follow what is happening in your code and receive a message when the application tries to access an object that has been released, thereby identifying the problem in your code.

Q: What can cause ANR error on Android?

We can find a perfect explanation on the Android Developer website.

The system displays an ANR if an application cannot respond to user input. For example, if an application blocks some I/O operation (frequently a network access) on the UI thread so the system can’t process incoming user input events. Or perhaps the app spends too much time building an elaborate in-memory structure, or computing the next move in a game on the UI thread. It’s always important to make sure these computations are efficient, but even the most efficient code still takes time to run.

Q: What are the advantages of Swift over Objective-C?

This is an open ended question, so you can use it to test how a developer handles conflicting situations by taking the opposite viewpoint of their claims. Almost any difference between Objective-C and Swift can be seen from both sides, either as a step in good direction or step in bad direction. You can find more information about Swift on our blog From Objective-C to Learning Swift

Q: Compare UITableView/UITableViewDelegate on iOS with ListViews/ListAdapter on Android.

On iOS, UITableView (table view) is a part of UIKit, used for displaying and editing hierarchical lists of information. A table view displays a list of items in a single column allowing users to scroll through the table. UITableViewDelegate is a protocol that delegates of UITableView must adopt. Methods of protocol allow delegate to manage data and presentation of data in the table view. We could say that object implementing UITableViewDelegate protocol adapts data so it can be used inside table view.

On Android, ListView is used for displaying data in a scrollable table, and ListAdapter is an interface that needs to be implemented by class adapting data for ListView that displays it.

In short, UITableView/UITableViewDelegate and ListViews/ListAdapter are the same concept named differently.

Q: How are animations created on Android and iOS?

Android documentation gives a nice description of animation options on Android.

Android provides two mechanisms that you can use to create simple animations: tweened animation, in which you tell Android to perform a series of simple transformations (position, size, rotation, and so on) to the content of a View; and frame-by-frame animation, which loads a series of Drawable resources one after the other. Both animation types can be used in any View object to provide simple rotating timers, activity icons, and other useful UI elements.

Tweened animation is the preferred option, as it allows more granular programmatic control over what happens and is easier to adjust for specific requirements.

On iOS, the most preferred animation option is creating animations using UIView class methods (animateWithDuration:animations:, animateWithDuration:animations:completion:, and animateWithDuration:delay:options:animations:completion:) All three methods are block based, and as they are UIView class methods, animations are not tied to any particular view so one animation can animate multiple properties of multiple views.

Q: How do Memory Management and Garbage Collection Function?

Objective-C keeps track of what objects are in use by keeping a retain count for each object. When an object is referenced, retain count is increased. When dereferenced, retain count is decreased. When count goes to zero, the object is removed from memory. Retain count can be managed manually (Manual Retain-Release - MRR) or automatically (Automatic Reference Count - ARC).

With MRR, developers had to worry about retaining and releasing an object. In contrast, ARC automatically takes care of updating retain count. As result of that, most iOS applications and developers are using ARC.

On Android, memory management is completely different. Dalvik virtual machine performs routine garbage collection and removes memory from all objects not referenced by other objects. This usually works as it should, but common sources of problems are Bitmaps. You can find more about Bitmap memory management here.

Conclusion

We just scratched the tip of the iceberg of knowledge needed to be a top Android and iOS app developer, although we highlighted some important core concepts and differences.

Taking into account the complexity of each of platform, it becomes clear that it can take years for developers to master all necessary knowledge. We hope that questions and answers presented in this post will help you find the right app developer for your project.

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