Common bugs in React Native

React Native is a great framework to implement your app for both Android and iOS platforms. But while it’s widely supported by the React community and Facebook, it’s still far from version 1.0.

Some of the errors you may encounter could be misleading or very hard to find. Recently, the React Native team asked developers to help them determine which of these annoying errors lead to the most frustration. While they did address some of the worst errors, there is still a handful remaining that could go under the radar.

Let’s look at a few of these issues and discuss how to address them if they pop up while you’re developing your next React Native app.

Import error

Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it’s defined in, or you might have mixed up default and named imports.

Check the render method of ‘App’.

This error is located at:

in RCTScrollContentView (at ScrollView.js:1038)
in RCTScrollView (at ScrollView.js:1178)
in ScrollView (at App.js:25)
in RCTSafeAreaView (at SafeAreaView.js:55)
in SafeAreaView (at App.js:24)
in App (at renderApplication.js:40)
in RCTView (at AppContainer.js:101)
in RCTView (at AppContainer.js:119)
in AppContainer (at renderApplication.js:39)

The React Native team has made this error more descriptive since the last version. Usually, mixed-up default and named imports are the culprits.

It’s still tricky because, as you can see, the error is caused by a component that is imported into the app, but we can’t tell which one is imported improperly. The prompt does not identify the component or even the line on which the error appears.

To avoid this error when creating and exporting components, remember not to mix default and named imports. What’s the difference?

Let’s say your component has the following.

export const componentName

You’d have to import it like this:

import { componentName } from './file'

But what if you use default export?

export default componentName

In that case, you’d have to import it without curly braces, but the naming is not important. You could do it like this:

import componentName from './file' //ok
import someOtherName from './file' //ok
import { componentName } from './file' //wrong!

Animated.View error

Invariant Violation: [453,”RCTView”,1,
{“width”:250,”height”:50,”backgroundColor”:4289781990,”opacity”:1}] is not usable as a native method argument

This error is located at:

in RCTView (at file.js:27)
in FadeInView (at file.js:42)
in RCTView (at file.js:41)
in _default (at App.js:29)
in RCTScrollContentView (at ScrollView.js:1038)
in RCTScrollView (at ScrollView.js:1178)
in SafeAreaView (at App.js:24)
in App (at renderApplication.js:40)
in RCTView (at AppContainer.js:101)
in RCTView (at AppContainer.js:119)
in AppContainer (at renderApplication.js:39)

Developers often encounter this error when using animated elements from React Native. It’s one of the trickiest errors you’ll come across, and the prompt might look slightly different depending on the use case.

Although the message is confusing, the error is caused by a simple mistake: when creating an animated component, you have to create an element (e.g., View), like this:

<Animated.View>

If you use a normal view, the above error will pop up.

It can be difficult to identify this error, and understanding it can save you a lot of time. There’s an issue for this listed in the React Native repository among other annoying errors to fix, and the team is expected to improve on it in an upcoming release.

Autolinking error

error React Native CLI uses autolinking for native dependencies, but the following modules are linked manually:

…

This is likely happening when upgrading React Native from below 0.60 to 0.60 or above. Going forward, you can unlink this dependency via “react-native unlink ” and it will be included in your app automatically. If a library isn’t compatible with autolinking, disregard this message and notify the library maintainers.

As of React Native version 0.60, we no longer need to use the react-native link command, which makes the process of setting up an app much easier. However, it can also trigger new errors, especially if you’re using an old library that doesn’t support the autolinking feature.

If you used react-native link in your 0.60+ project, run react-native unlink and then try running your app. If you didn’t use the command but received the error anyway, it’s likely that one of your dependencies is not suitable for autolinking. If that’s the cause, you can try using [patch-package](https://www.npmjs.com/package/patch-package) to fix it on your own.

Be sure to create a pull request with your solution to the library repository — you may be able to help others save a lot of time.

Null in the image element

JSON value ‘’ of type NSNull cannot be converted to NSString

This error occurs when an image element has a URI set as null.

<Image source={{ uri: null }} />

It can be especially hard to tackle this error if the URI you want to open is fetched from the backend and you’re not sure whether it’s a proper link or null.

URI versus URL in the image element

When displaying a remote image in the image element, you should name the source object as a URI, like this:

<Image source={{ uri: 'https://facebook.github.io/react-native/img/homepage/phones.png' }} />

If you mistakenly name it “URL” instead of the “URI,” the image will be displayed on the iOS device, but it will fail silently on the Android device. Being aware of this error could save you a lot of time and energy debugging.

String outside text

Invariant Violation: Text strings must be rendered within

This error is located at:

in a (at App.js:29)
in RCTScrollContentView (at ScrollView.js:1038)
in RCTScrollView (at ScrollView.js:1178)
in ScrollView (at App.js:25)
in RCTSafeAreaView (at SafeAreaView.js:55)
in SafeAreaView (at App.js:24)
in App (at renderApplication.js:40)
in RCTView (at AppContainer.js:101)
in RCTView (at AppContainer.js:119)
in AppContainer (at renderApplication.js:39)

This error message is fairly straightforward, and you can see that it’s located in the app.js file on line 29, but it’s still worth mentioning the possible causes.

If you encounter this error, you may have forgotten to wrap your string with a Text component or introduced a typo that rendered your component unrecognizable. The latter is the most common cause — an additional bracket here, a superfluous comma there. These typos can be hard to spot, even if we know where to look.

It would be nice if, in future versions, the error message could include more useful information, such as the specific string that caused the issue.

Dependencies error

Error: undefined Unable to resolve module @babel/runtime/helpers/interopRequireDefault from App.js: @babel/runtime/helpers/interopRequireDefault could not be found within the project.

If you are sure the module exists, try these steps:
1. Clear watchman watches: watchman watch-del-all
2. Delete node_modules: rm -rf node_modules and run yarn install
3. Reset Metro’s cache: yarn start ––reset-cache
4. Remove the cache: rm -rf /tmp/metro-*

If an error like this appears seemingly out of nowhere, the first suspects should be NPM or Yarn and dependencies in the node_modules folder.

First, you can try reinstalling the whole dependencies directory. If a major dependency is somehow changed in your repository, it could cause issues. Run the command in the main project directory where you see the node_modules folder to remove and install them again.

rm -rf node_modules && yarn

If this doesn’t work, you can try following the steps outlined in the error message. Here is a slightly modified command ready to copy to your terminal:

watchman watch-del-all && rm -rf /tmp/haste-map-react-native-packager-* && rm -rf /tmp/metro-bundler-cache-* && rm -rf node_modules/ && yarn cache clean && yarn

This will clear watchman watches, reset the metro bundler cache, remove the haste cache, reinstall the whole node_modules directory, and clear the yarn cache.

Additional troubleshooting for Android and iOS

If you still have errors, you could try cleaning your project. The steps will vary depending on the platform you are developing on.

Android

Try clearing the Gradle cache by typing the following command from the main project directory.

cd android && ./gradlew clean

iOS

Try cleaning your project if you’re opening it from the XCode. Click “Product” and “Clean” from the upper menu bar.

You may also want to try running pod deintegrate in the ios directory to remove pods completely, then running pod install again.

Finally, removing derived data can be very helpful:

rm -rf ~/Library/Developer/Xcode/DerivedData/*

Summary

Now you should be able to address seven of the most common bugs you’re likely to encounter while developing a React Native app. Some of them are being fixed as you read this article, and error messages will evolve to be more descriptive and informative as new versions are released. But for now, we need to work with what we’ve got. Knowing the context behind these errors can save you a lot of painful time spent debugging. After all, while most of these errors are difficult to spot, they’re usually easy to fix if you know what you’re looking for.

#react-native #ios #android #mobile-app

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How native is React Native? | React Native vs Native App Development

If you are undertaking a mobile app development for your start-up or enterprise, you are likely wondering whether to use React Native. As a popular development framework, React Native helps you to develop near-native mobile apps. However, you are probably also wondering how close you can get to a native app by using React Native. How native is React Native?

In the article, we discuss the similarities between native mobile development and development using React Native. We also touch upon where they differ and how to bridge the gaps. Read on.

A brief introduction to React Native

Let’s briefly set the context first. We will briefly touch upon what React Native is and how it differs from earlier hybrid frameworks.

React Native is a popular JavaScript framework that Facebook has created. You can use this open-source framework to code natively rendering Android and iOS mobile apps. You can use it to develop web apps too.

Facebook has developed React Native based on React, its JavaScript library. The first release of React Native came in March 2015. At the time of writing this article, the latest stable release of React Native is 0.62.0, and it was released in March 2020.

Although relatively new, React Native has acquired a high degree of popularity. The “Stack Overflow Developer Survey 2019” report identifies it as the 8th most loved framework. Facebook, Walmart, and Bloomberg are some of the top companies that use React Native.

The popularity of React Native comes from its advantages. Some of its advantages are as follows:

• Performance: It delivers optimal performance.
• Cross-platform development: You can develop both Android and iOS apps with it. The reuse of code expedites development and reduces costs.
• UI design: React Native enables you to design simple and responsive UI for your mobile app.
• 3rd party plugins: This framework supports 3rd party plugins.
• Developer community: A vibrant community of developers support React Native.

Why React Native is fundamentally different from earlier hybrid frameworks

Are you wondering whether React Native is just another of those hybrid frameworks like Ionic or Cordova? It’s not! React Native is fundamentally different from these earlier hybrid frameworks.

React Native is very close to native. Consider the following aspects as described on the React Native website:

• Access to many native platforms features: The primitives of React Native render to native platform UI. This means that your React Native app will use many native platform APIs as native apps would do.
• Near-native user experience: React Native provides several native components, and these are platform agnostic.
• The ease of accessing native APIs: React Native uses a declarative UI paradigm. This enables React Native to interact easily with native platform APIs since React Native wraps existing native code.

Due to these factors, React Native offers many more advantages compared to those earlier hybrid frameworks. We now review them.

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Being one of the emerging frameworks for app development the need to develop react native apps has increased over the years.

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Want to develop app using React Native? Here are the tips that will help to reduce the cost of react native app development for you.
Cost is a major factor in helping entrepreneurs take decisions about investing in developing an app and the decision to hire react native app developers in USA can prove to be fruitful in the long run. Using react native for app development ensures a wide range of benefits to your business. Understanding your business and working on the aspects to strengthen business processes through a cost-efficient mobile app will be the key to success.

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How much does it cost to develop a React Native mobile app?

React Native allows developers to develop mobile apps that have compatibility with Android, iOS & other operating systems. Due to the features like Native-like functionality and single code reusability and the access of various frameworks in the market, React Native has excelled as the most suitable framework for cross-platform mobile app development.

Why Do Businesses Prefer React Native App Development?

React Native is integrated with JS library that works as the fundamental for developing the app UI. Most businesses choose for developing React Native apps just due to their cross-platform & open-source features. A few further reasons why entrepreneurs & developers choose React Native app development include:

• Lowered Expedition Time

• Simple UI

• Cross-Platform and Code Sharing

• Lesser Workforce and Resources

• Community Assistance

• In-Built Elements and Reusable Codes

• Hot Reload

• JavaScript as Programming Language

• Easy to Execute Updates

Factors That Decide Cost of React Native App Development

If you are an entrepreneur or start-up and looking for cost-effective app development, React Native is one of the ideal options available out there.

• App’s UI/UX Design

• User Authorization

• App Complexity and Functionality

• App Development Team

• App Maintenance

• App Add-ons

• App Distribution

• Location of Development Company

• App Category

React Native cost depends widely on the complexity of a project or the app requirements. The price may also vary based on business requirements. React Native app development per hour can cost from $20 and $30 per hour in India. It can vary as per different locations.

Is React Native a good choice for mobile apps development?

Yes, React Native is the best choice for mobile app development as React apps are faster to develop and it offers better quality than hybrid apps. Additionally, React Native is a mature cross-platform framework.

Best React Native App Development Agency

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If you have any mobile app development project in mind get in touch with AppClues Infotech and get the best solution for your business.

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