Mobile app development means the development of applications for both Android and iOS using technologies like React Native, Ionic, PWA, Xamarin, and so on.
Mobile app developers are in high demand by companies as well as freelancers and they can earn around $171,500 per year.
Here are the most popular and frequently asked “Mobile App Developer Interview Questions and Answers” that help you ace the technical rounds easily in top companies.
1. What are the benefits of using React Native in building mobile apps?
Implementing React Native technology in mobile app development has the following benefits
- Optimal performance
- Code reusability
- Pre-developed components
- Large community
- Live and hot reloading
- Cost-effective
- Simple user interface
- Third-party plugins
- Modular architecture
- Handy solutions with libraries
2. List some of the advantages of hybrid apps
Hybrid app development has the following advantages over native apps
- Performs on multiple platforms
- Unified development
- Quicker development
- Low-cost development
- Easy to update
3. Define Ionic framework
Ionic framework is an open-source UI toolkit for developing high-quality mobile and desktop applications using some the web technologies like HTML, CSS, and JavaScript.
It is focused on the front-end user experience or UI interaction of an app with controls, interactions, animations, and gestures.
The ionic framework can be integrated easily with Angular, React, and Vue.
4. Explain Xamarin
Xamarin is the popular and cross-platform mobile app development technology developed by Microsoft for developing the native app using the same code for all platforms like iOS, UWP, and Android along with C# language support.
It uses two major approaches for mobile app development and they are Xamarin.Forms and Xamarin.Native. Xamarin.Forms are using MVVM and XAML and Xamarin.
Native is using Native UI technology and MVC or MVVM cross-architecture.
5. Explain Singleton pattern
Singleton pattern is the pattern used to create an object while ensuring that only a single object gets created.
It comes under the creational patterns category to introduce a class for creating an object.
It provides a way to access its only object that can be accessed directly without requiring instantiating the object of the class.
Singleton
– Singleton: Singleton
– Singleton()
+ getInstance(): Singleton
6. Define activity
An activity is a thing that offers a window that allows the app draws its user interface.
It fills the screen or may be smaller than the screen and floats on the top of other windows. One activity applies one screen in an app.
For example, one of an app’s activities can implement a preference screen and the other activity implements a Select Photo screen.
7. Explain the progressive web app
The progressive web app (PWA) is the approach introduced by Google in 2015 and it is a web app that have look and feels like other native apps.
The progressive web app allows websites to offer various functionalities like working offline, device hardware access, and push notifications.
8. Explain builder pattern
The builder pattern is the pattern that builds a complicated object using simple objects to be used in a step-by-step approach and it is independent of other objects.
The Director class is used to ensure whether the building steps are performed in the right order with the right data by the right builder. It is optional for validating and delegating.
Builder or Direct pattern’s steps invocations can be semantically offered by method chaining or Fluent Interface Syntax.
Apple apple = new Apple.Builder()
.color(true)
.taste(true)
.build();
9. Explain an intent in Android
An intent is a message that is transferred between components like Activities, Broadcast Receivers, Services, and Content Providers.
It is relevant to parameters passed to API calls. The basic differences between API calls and invoking components through intents are
- API calls are synchronous but intent-based invocations are asynchronous
- API calls are compile-time binding but intent-based calls are run-time binding
We should implement a broadcast receiver to listen for a broadcast intent that can be passed the intent.
We should declare an intent filter in our app’s manifest file for declaring to handle another app’s intent like “take a picture”.
An intent offers a facility to perform late runtime binding between the code in various applications.
10. List some of the limitations of PWA
The disadvantages of PWA (Progressive Web App) are
- Less access to system features as it is limited for accessing native system features than native apps. All browsers are not supporting the full features but it will be the new standard of development.
- More Android – Less Apple iOS as it is supported majorly by Android devices but partially supported by iOS for Apple devices
- No review standard as it doesn’t require any kind of review system that is applicable for native apps from the app store. It may be faster in making progress but lacks benefits for promotional features from the app store.
11. Differentiate Upcast and Downcast in Swift
The Upcast is the thing that goes from a derived class to a base class and it can be checked at compile time that never fails.
The Downcast can fail as we can’t ensure always about the specific class and if you have a UIView, It is possible for UITableView or a UIButton.
- It must be either optional with as? or
- “forced failable” with as! When sure about the type
12. Explain the security issues with Ionic apps
Security is a common issue in building hybrid apps that can be reversed engineered. Ionic CLI was not provided built-in code uglification since 4the version.
It is a common technique of using the code complicate to read by hackers but it is also required to know that if we are using Angular CLI or an older version of Ionic, there is no code uglification processing.
The developers will have uglified the code. There are many ways to compromise the process with a mobile app or PWA like a man-in-the-middle attack.
The major takeaway is that ionic interacts with the backend using usual HTTP calls.
13. Differentiate “Self” and “self”
There is a difference between Self (capital S) and self (small s) when we are writing protocols and protocol extensions.
It is used a capital S in Self to refer to the type that is common to the protocol. For example, String or Int.
The self with lowercase s refers to the value inside the type as “hello” or 536.
Example of BinaryInteger
extension BinaryInteger
{ func squared() à Self
{
Return self * self
}
}
Self with capital S means whatever type is conforming to the protocol as in the example, Int to BinaryInteger. Int is the method that returns an Int.
The self with lowercase refers to whatever value the type holds. Int in the above example is storing the value 5 as it would effectively be 5 * 5.
14. Define IndexDB and explain how it is used in PWA
is a large-scale and NoSQL storage system that allows developers to store anything in the user’s browser and it also supports transactions.
It is a low-level API for client-side storage of important amounts of structured data that includes files or blobs.
This API utilizes indexes to allow high-performance searches of the data. DOM storage is useful for storing smaller amounts of data.
It is useful for storing large amounts of structured data. IndexDB offers a solution with the context of PWA in the recommendation for storing data offline
- Use the Cache API as a part of service workers for the network resource needed to load your app offline
- Use IndexDB with a promise’s wrapper for all other data.
15. Define Android Data Binding
The Data Binding Library is a support library that enables developers to bind UI components in the layouts to data sources in the app using a declarative format instead of programmatically.
The Layouts are defined in activities with code that calls UI framework methods. Following is the code calls findViewById() to discover a TextView widget and bind it to the username property of the viewModel variable
TextView textview = findViewById (R.id.sample_text);
textView.setText(viewModel.getUserName());
We can use Data Binding Library to assign text to the widget directly in the layout file for removing the need for the Java code above with the following example
<textView
android.text = “@{viewmodel.username}” />
16. What are the advantages of Android Data Binding?
The advantages of Android Data Binding are as follows
- Reduced boilerplate code that turns brings
- Less coupling and stronger readability
- Powerful and easy to implement custom view and custom attribute
- Faster than findViewById for binding a single pass on the view hierarchy that extracts the Views with IDs. This mechanism will be faster than calling findViewById for various views.
17. Define Explicit Intent
Explicit Intents are used to call a specific component and when you understand which component you want to deploy and you do not want to give the user free control on which component to be used.
If you have an application that contains two activities like Activity A and Activity B that want to launch, you have to define them as an explicit intent that targets activity B and then call directly.
18. What is the mutating keyword in swift?
Mutating is the keyword that requires changing the values of self-variables inside the structure’s function. Following is the example to explain mutating keyword implementation
struct MyStruct
{
var abc: String = “Initial Value”
func changeValue()
{
abc = “some other value”.
}
}
If we are trying to change the value of the variable abc inside the function declared in the struct itself, we will get the compile-time error.
Hence, here is the code that makes function mutate to make change value inside the structure.
struct MyStruct
{
var abc: String = “Initial Value”
mutating func changeValue()
{
abc = “some other value”
}
}
19. Differentiate PhoneGap, Cordova, and Ionic
PhoneGap is a library that shows native phone functionalities as JavaScript API. Its open-source core was defined by the Apache Software Foundation with the name Cordova when Adobe purchased PhoneGap.
Initially, there was no difference between Cordova and PhoneGap. Later, Adobe started including properties with the set of services to PhoneGap.
Now, it is safe to say PhoneGap is Cordova plus added Adobe Services.
Ionic framework is using Cordova for its core tools as native mobile phone functionalities.
It gives structure and code scalability to JavaScript apps by using AngularJS (Angular, Vue, and React for Ionic4).
Ionic also offers a set of Angular directives and components to fasten up application development.
20. Differentiate let and var in Swift
The let is the keyword defines the constant for fundamental types
let theAnswer = 42
The value of a constant is not needed to be known at compile time but we must assign the value
The var defines an ordinary variable
The var and let are known as pointers or references and let is a constant reference or pointers. The difference comes when using them with class instances.
class CTest
{
var str : String = “”
}
let letTest = CTest()
letTest.str = “test” // OK
letTest.str = “another test” // Still OK
//letTest = CTest() // Error
var varTest1 = CTest()
var varTest2 = CTest()
var varTest3 = CTest()
varTest1.str = “var 1”
varTest2.str = “var 2”
varTest3 = varTest1
varTest1.str = “var 3”
varTest3.str
Conclusion
The learning of mobile app development helps gain skills like a programming language, computer proficiency, back-end computing, user interface design, cross-platform development, cybersecurity, product management, and the internet of things.
There are many things to be learned to become a successful mobile app developer.
Learn how to develop and deploy mobile apps from scratch in our Mobile App Development Training in Chennai at Softlogic Systems.
