Was Galileo expecting to see so many stars? Error messages need to be short. Applications of super-mathematics to non-super mathematics. For more details, see our cookbook chapter for this only prints errors and does nothing else. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, class customException implements Exception { String _message = ""; customException([this._message]); String toString() => "LatLngException: message=${_message}"; }i solve this using this piece of code defined @AlexandreArdhuin is correct. https://github.com/dart-lang/language/issues/984. Every built-in exception in Dart comes under a pre-defined class named Exception. flutter web detect refresh page. To prevent the program from exception we make use of try/on/catch blocks in Dart. Even literals are objects, allowing you to write code like 5.isOdd, which will resolve to true. Until next time, keep Darting! This leaves many with the idea that inheritance has no place in software construction, Source: https://cdn-images-1.medium.com/max/1600/0*gD64Y8ECWBBuSZrx At Google I/O 2019 developer conference, Google launched version 1.5 of Flutter, it's open source mobile UI framework that helps developers build native interfaces for Android and iOS. By using this, the program did not stop its execution. The try block needs to follow a catch block that has an exception parameter of the type object. The user doesnt want to read a novel A short explanation is enough. A new Message instance must now be created with explicit parameter names, shown next formatted in the typical Flutter style using lots of newlines and a trailing comma: It takes up a few extra lines, but it's obvious at a glance that you're creating a Message with an ID and a bit of content, and it's easy to edit the parameter values quickly. (41)] Unhandled Exception: MissingPluginException(No implementation found for method StartSecondActivity on channel com.example) Only restarting the . The top-level kReleaseMode constant indicates By default, And how far should we rely on them or should we just build all the possible failures into our return value? Even How to catch and print the full exception traceback without halting/exiting the program? How can I safely create a directory (possibly including intermediate directories)? Example: Creating custom exceptions in the dart. Not the answer you're looking for? chicken of the woods ottawa; how tall was prophet idris; how much money did hercules in new york make A marker interface implemented by all core library exceptions. console, allowing you to inspect the Should I include the MIT licence of a library which I use from a CDN? Making statements based on opinion; back them up with references or personal experience. I'm not getting the desired output could someone explain to me how to handle it?? Not only can an exception cause an ugly error, but it can also break the users flow. CatchError doesn't catch the error when the status is not 200. If you use sum types or some other mechanism to plumb both success and failure values through the normal return mechanism of the function, then you get all of the nice static checkings you want from checked exceptions. We also wrap our code in a try/catch block to catch any SocketExceptions that might occur if there is a network connection error. To prevent the program from exception we make use of try/on/catch blocks in Dart. I am trying to get data from youtube API and using it in the UI part. whether the app was compiled in release mode. PTIJ Should we be afraid of Artificial Intelligence? How can I safely create a directory (possibly including intermediate directories)? Thanks for contributing an answer to Stack Overflow! In lib/features/post/data/repositories_impl/posts_repository_impl.dart we convert exceptions (impure states) to failure objects (pure states) and we either return a list of posts on the Rights side of the Either object or, as we said, a Failure on the Left side. typically by setting them to values in This handler can also be used to report errors to a logging service. the ErrorWidget.builder callback is To catch an error, we have to wrap the method that throws the error into a try-block. How to choose voltage value of capacitors. While doing error handling we have 2 main broad objectives: I hope that in this article I managed to show how functional programming dramatically helps us in achieving these goals as it forces us to think about the possible application states and to proactively manage them. 542), How Intuit democratizes AI development across teams through reusability, We've added a "Necessary cookies only" option to the cookie consent popup. Asking for help, clarification, or responding to other answers. Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? See also t: labels. Here is an example of a traditional object instantiation, using the new keyword: When an exception occurs inside a program the normal flow of the program is disrupted and it terminates abnormally, displaying the error and exception stack as output. REST API l g. Methods dont declare which exceptions they might throw, and you arent required to catch any exceptions. Flutter UI code is made much clearer through the use of named parameters, and it has become customary to prefer them in a Flutter code base: We indicate these parameters should be optional and named using the surrounding curly braces in the constructor's parameter list. Refresh the page, check Medium 's site status, or find something interesting to read. If the exception is of type BirdNotFoundException or BirdDoesNotExistException, it will execute its corresponding block.If one of the typed exceptions were executed, the catch block will not be invoked. Additionally, it's no longer necessary to include data types in the parameter list, because Dart can infer the types from the types of the matching member variables. uri}) const Properties hashCode int The hash code for this object. Simply fire an exception like this: You can also create an abstract exception. Apphud is all-in-one infrastructure for your app growth. catchError is sometimes a bit tricky to get right. Now we have created a custom Class named GradeException and it implements the Exception interface. In Dart, it is possible to throw everything. These are issues you probably encounter almost every day! Maybe it is because you want to zip together other exceptions or desire to handle a state where your method cannot behave correctly anymore. To throw an exception, just use the throw keyword. Here's how we can convert our previous example to use it: Now our function signature tells us exactly what the function does: As a result, we can update our calling code like so: And if we want to handle the result, we can use pattern matching with the when method: This forces us to handle the error case explicitly, as omitting it would be a compiler error. Ackermann Function without Recursion or Stack. To catch such an error, use PlatformDispatcher.instance.onError. There is also an optional stack trace parameter in the catch-block. Although it is optional to include the finally block if you include it then it should be after try and catch block are over. How to Append or Concatenate Strings in Dart? Call flutter packages get to install the plugin or your editor may automatically do it. (Wiki) Flutter 2 Open in app. Proper way to Handle Exceptions in Flutter | by Vipin Vijayan | Medium Write Sign In 500 Apologies, but something went wrong on our end. It is thrown when a deferred library fails to load. Catch multiple exceptions in one line (except block), Retrieve the current price of a ERC20 token from uniswap v2 router using web3js, Ackermann Function without Recursion or Stack. Like most programming languages, Dart is also offering us a way to execute some code that is called whether an error occurred or not. Since named parameters are optional, this poses a problem. Manually raising (throwing) an exception in Python. type they can catch. The on block is used when the exception type needs to be specified. Get all the latest & greatest posts delivered straight to your inbox, Creating Objects and Classes in Dart and Flutter, Immutable Data Patterns in Dart and Flutter, Creational Design Patterns for Dart and Flutter: Factory Method. Trong bi vit ny, Bo Flutter s hng dn cc bn chi tit v cc k thut lm vic vi REST API trong lp trnh Flutter. https://jsonplaceholder.typicode.com/users'. I think if a functions failure values are so important to be handled that you want static checking for them, then they should be part of the functionsreturn typeand not an exception. Astute readers will have realized assertions could be used along with optional parameters to simulate required arguments, but assertions occur at runtime, whereas parameters marked with @required work with Dart's code analyzer to catch problems during development. We all make mistakes but it is important that we learn from them. The user may enter an incorrect input, a network request may fail, or we could have made a programmer mistake somewhere, and our app will crash. Unlike the more traditional positional parameters, named function parameters must be prefixed by their names in a function call and are optional by default. Could very old employee stock options still be accessible and viable? Exception is a runtime unwanted event that disrupts the flow of code execution. behavior so that errors can also be routed to the IDEs Easiest way to remove 3/16" drive rivets from a lower screen door hinge? The architecture of the sample app is inspired by the principles of Clean Architecture (+ Repository Pattern) and its certainly well over-engineered for the simplicity of the goal, but since this article wants to present an advanced way of handling errors in software, I have reckoned it made more sense to have a well-architected sample app (plus I intend to reuse part of it for future articles). Often, constructors take parameters to initialize member variables: The this keyword is necessary to disambiguate the parameters from the member variables. in debug mode this shows an error message in red, As a nice tip: You can enable the only_throw_errors lint rule in your analysis_options.yaml to enforce that only classes that implement Exception can be thrown. Should any error happen, the application will properly reflect them in the UI. your void main() function. From this layer to the repository implementation layer, exceptions (impure application status) are converted to Failures (pure status). this calls FlutterError.presentError, By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. george halas family tree; albany county family court law guardians; ardc recent suspensions; skull indentation in adults nhs; homes for rent in summerville, sc no . When will the moons and the planet all be on one straight line again? fixed with the return in the above reference. It is intended to be caught, and it should contain useful data fields. By using our site, you Sign up . @OlegSilkin Yes, always make things final unless mutations are a requirement. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. This message is extremely important and defines a critical point in your app because your user has to take the extra mile to perform their task. class GradeException implements Exception {. Its worth mentioning that there exists, in the flutter ecosystem, also another FP library, called fpdart with 143 Likes, at the moment of writing this article. While Functional Programming (FP) is a programming paradigm known to bring many advantages in specific software domains (compilers, programs that involve parallelism, concurrency, distributed computing, and more), Ill argue that some elements of FP can be very beneficial in state-intense applications too. The user needs to know what to do next. When using try/catch there is a difference when using await or not in front of your async function. How did Dominion legally obtain text messages from Fox News hosts? Not the answer you're looking for? following handler: Note: try { return api.getBird (); } catch (exception) { log ('Not type exception was executed'); } For Futures we can also use this shorter way: return api.getBird ().catchError ( (e) => log (Exception was thrown $e)); Now we ended up in a catch block What should we do next? Do EMC test houses typically accept copper foil in EUT? jQuery Ajax error handling, show custom exception messages. While and do-while Break and continue Switch and case Assert Exceptions Throw Catch Finally Classes Using class members Using constructors Getting an object's type Instance variables Constructors Methods Abstract classes Implicit interfaces Extending a class Extension methods Enumerated types Adding features to a class: mixins Does With(NoLock) help with query performance? Mobile Software Engineer (Flutter) at Quandoo, // We connect with the API trying to get some value, // If we managed to retrieve the data from the API, the bloc will emit a success state, https://jsonplaceholder.typicode.com/posts. The try block found the error the control transferred to the block that has the code to handle the error. Or we can make our life easy and use the multiple_result package, which gives us a Result type that we can use to specify Success and Error types. An Exception is intended to convey information to the user about a failure, I have a Flutter app with a native android component for scanning barcodes, on first run this native component runs fine and does what it needs to then returns to the Flutter section of app. And that will be the topic of my next article, which will cover functional error handling in more detail. For example:- when we try to access the elements from the empty list. Finally we unpack the Either object inside the bloc at lib/features/post/presentation/bloc/posts_list.dart and we emit different states based on what is needed. By using our site, you Here's the same object instantiation without using new: The advantage of this less verbose habit is emphasized when we look at typical Flutter code, where you commonly need to instantiate whole trees of objects. To handle such events at runtime is called Exception Handling. So you must always be prepared! Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Suppose, you are making a GET request using BLoC as your state management library.For implementing BLoC state management, we generally have bloc, state and event files.. Now in our case, In the . commentededited by danagbemava-nc. They will only execute in debug mode. If the second parameter is omitted, isComplete will automatically initialize to false: Using named parameters for boolean values is always a good habit, even when there are positional parameters, since it's difficult to intuit the effect of a boolean parameter from its passed value. your errors handling on next code snippet: Except as otherwise noted, For Message, it's best to make use of the @required metatag, which is available in package:flutter/foundation.dart or in the meta package on Pub: Now both parameters are required instead of optional. This allows you share properties and methods between classes that are similar, but not exactly the same. And in the next articles, we'll tackle more complex use cases where we need to run multiple asynchronous calls sequentially. Languages such as Kotlin and Swift define their own Result type using language features known as sealed classes (Kotlin) or enums with associated values (Swift). If you want to catch an exception but still want to propagate it to the caller, use rethrow because it preserves the stack trace. The named parameters allow for more readable code than the traditional approach using positional parameters. Instead, its forwarded to the PlatformDispatcher. Final block:The final block in dart is used to include specific code that must be executed irrespective of error in the code. You can pass an optional second parameter if you want to customize the exception message: For Dart and Flutter projects, assertions are not evaluated in production code. Even though you've made all of the Message class's constructor parameters required, it's still possible to explicitly pass null arguments to thwart this effort: Use assert() to prevent invalid arguments at runtime: This version of the class will throw an exception of type AssertionError if either property of an instance is initialized to null at runtime. Dart Exceptions are the run-time error. The finally block of code This way exceptions are logged and the program does not crash and exit. class in tests or during development. void main() { print (str2Num ( "a" )); //FormatException: a } num str2Num (String str) { return num.parse (str); }Copy the code 5.2: Exception capture This is similar to Java, where try. Every built-in exception in Dart comes under a pre-defined class named Exception. are out of the scope of this article and I will not focus on them now, but I do welcome questions regarding any aspect of the software presented. Flutter Forms: Multiple widgets used the same GlobalKey, Flutter FCM is not working when app is closed, Flutter/Dart get_It singleton locator method failure, type 'MappedListIterable . The output of flutter doctor -v. Your pubspec.yaml. Here is an example of a method that calls several other async methods internally: If any of the methods above throws an exception, we can catch it in one place and handle it as needed. Errors that don't occur within Flutter's callbacks can't be caught by the framework, but you can handle them by setting up an error handler on the PlatformDispatcher. Did the residents of Aneyoshi survive the 2011 tsunami thanks to the warnings of a stone marker? For Futures we can also use this shorter way: Throwing exceptions yourself is also straightforward. As an example, here's a simple Dart function that we can use to fetch a location from an IP address: In the code above, we're using the http package to make a GET request to an external API. Unfortunately, it is still possible to explicitly pass null values to a required parameter, but there are measures we can take. Get the subscription state of any user through powerful SDKs. Whenever possible, you should define sensible default values for your named parameters. At the bottom rev2023.3.1.43269. To fix this, we need to wrap it in a try/catch block: Now our code is more robust. There is also an official async package from the Dart team. Like most of the programming languages, Dart has you covered and implements a way to handle those arising errors. Building cool Flutter apps for other businesses is what we do at QuickBird Studios , Do you search for a job as a Flutter Developer?Do you want to work with people that care about good software engineering?Join our team in Munich. For example, to make your application quit immediately any time an PlatformDispatcher. In our opinion, it only makes sense to only throw classes that are implementing the Exception interface. Exceptions must be handled to prevent the application from terminating abruptly. Do a mistake once, ok, do it twice, ok, do it thrice: youre an idiot!. How did Dominion legally obtain text messages from Fox News hosts? But thats no longer, Stay up to date! Also, it allows different subtypes to share a common runtime type so that static analysis doesn't fail. One problem you may have noticed with using named parameters is that they're optional, and sometimes that is undesirable. I was trying to find this answer when got to this page, hope it helps: https://stackoverflow.com/a/57736915/12647239, Basicly i was just trying to catch an error message from a method, but i was calling. This is a decision that was made on purpose by the Dart team. But it was too easy to forget to add the try/catch block in the first place. Example 1: Using a try-on block in the dart. within Flutters callbacks cant be caught by the framework, Functional Error Handling with Either and fpdart in Flutter: An Introduction, return a success value with the resulting. I launched a brand new course that covers error handling in great depth, along with other important topics like state management with Riverpod, app architecture, testing, and much more: Learn about State Management, App Architecture, Navigation, Testing, and much more by building a full-stack Flutter eCommerce app on iOS, Android, and web. No, dont do that. In the above example, we created a custom exception, Age. The library Ill use in this post is dartz, the most popular FP package on pub.dev with 579 Likes. The code raised the exception if the entered amount is not within the excepted range, and we enclosed the function invocation in the trycatch block. This article will review the basics of exception handling in Dart and Flutter (using try and catch) and explore how the Result type can help us leverage the type system to handle errors more explicitly. Please i need some help for i have being trying to resolve this for quite some time.Thank you. The user may enter an incorrect input, a network request may fail, or we could have made a programmer mistake somewhere, and our app will crash. acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Data Structure & Algorithm-Self Paced(C++/JAVA), Android App Development with Kotlin(Live), Full Stack Development with React & Node JS(Live), GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam. A common approach when dealing with a database from an Object-Oriented Programming language (or OOP for short) is to deal with objects that mirror the structure of the tables in a database: this makes the code more reliable, easier to read, and helps prevent data inconsistencies. instead of the one that failed. Creating objects succinctly Like most OOP languages, Dart supports the keyword new for creating instances of classes. Connect and share knowledge within a single location that is structured and easy to search. rev2023.3.1.43269. I'm trying to learn on how to create a Flutter app and connect it to Firebase and one of the steps in the course that I'm learning from, the instructor wrote this line in the terminal: PS C:\Users\Rashed\Desktop\workspace\firebase_practice\android> ./gradlew signingreport. A direct action e.g a button that solves the situation is always superior to just an info text that instructs the user on what to do. And that's because the signature of our function doesn't make it explicit that it can throw an exception: In fact, the only way to find out if the function throws is to read its documentation and implementation. Sealed classes are extremely powerful and have many applications that I intend to detail more in future articles. This is my exception class. So always prefer direct actions if possible. To learn more, see our tips on writing great answers. For the sake of this article, I have created a simple application (here is the link for GitHub). Dart also provides a safety net where we can easily catch exceptions that went through. To help users of your constructors and methods write less code and produce fewer errors, you can provide default values for parameters. In the above code, we declared two-variable geek and geek2 in the main () function. Here, we'll explore a few for class design and object instantiation. How do you assert that a certain exception is thrown in JUnit tests? Asking for help, clarification, or responding to other answers. Creative Extending classes (inheritance) on Saturday, 18th of July, 2020. It is just extremely important that we are aware of any unexpected errors in our Flutter app because our users might encounter them but instead of reporting them to us, they just uninstall the app.Thats why it is important to log unexpected errors and export them in a way so that we can access them. It can be occurred because of a programmer's mistake or by wrong user input. Exception class has been implemented by the abstract exception class of flutter. It is thrown when a scheduled timeout happens while waiting for an async result. A way flutter exception class handle those arising errors throw keyword runtime unwanted event that disrupts the flow code! Plugin or your editor may automatically do it twice, ok, do it thrice: youre an idiot.... Which will cover functional error handling, show custom exception messages contain useful data fields library fails to.! Yourself is also straightforward be executed irrespective of error in the main ( ) function thats No,! Wrap our code is more robust empty list any error happen, program! The named parameters in Dart is used to include specific code that be! Are issues you probably encounter almost every day moons and the planet all be on one straight line again class... Main ( ) function read a novel a short explanation is enough to. ( impure application status ) are converted to Failures ( pure status are! At lib/features/post/presentation/bloc/posts_list.dart and we emit different states based on opinion ; back them up with or. Print the full exception traceback without halting/exiting the program of try/on/catch blocks in is! The on block is used to include specific code that must be irrespective... Fewer errors, you should define sensible default values for parameters subtypes to share a runtime. To make your application quit immediately any time an PlatformDispatcher unwanted event that disrupts flow. And catch block that has an exception like this: you can provide default values for your named parameters optional. Less code and produce fewer errors, you should define sensible default values for your named is. Here, we created a simple application ( here is the link GitHub! Like this: you can also be used to report errors to a logging.! Break the users flow allowing you to write code like 5.isOdd, which will cover functional error handling show. The named parameters allow for more details, see our cookbook chapter for this object one line. Stone marker ( throwing ) an exception cause an ugly error, we need to wrap it the! On one straight line again when the exception type needs to be specified planet be... Found for method StartSecondActivity on channel com.example ) only restarting the: MissingPluginException ( No implementation found for StartSecondActivity... Have noticed with using named parameters allow for more details, see our tips on writing great answers for! The desired output could someone explain to me how to handle it? immediately time. Encounter almost every day null values to a logging service empty list help, clarification or. Idiot! the hash code for this only prints errors and does nothing else state of any user powerful! From this layer to the block that has the code is needed, it only makes to. The member variables: the this keyword is necessary to disambiguate the parameters from the flutter exception class.! Time.Thank you allow for more details, see our tips on writing great answers ugly error, but are. Resolve this for quite some time.Thank you code than the traditional approach using positional.. 1: using a try-on block in the UI part and geek2 in the above example, to your! Program from exception we make use of try/on/catch blocks in Dart, it is still possible to an! Similar, but there are measures we can easily catch exceptions that went through: - when try! Your RSS reader to prevent the application from terminating abruptly declared two-variable geek and geek2 in above! More complex use cases where we can also break the users flow also wrap our is... Include specific code that must be handled to prevent the program from exception we use... More robust above code, we need to run multiple asynchronous calls sequentially is optional to include code! And the program from exception we make use of try/on/catch blocks in Dart is used when status... User needs to know what to do next survive the 2011 tsunami thanks to warnings! And does nothing else / logo 2023 stack Exchange Inc ; user contributions under... Sometimes that is undesirable this URL into your RSS reader disrupts the flow of code execution that. Error when the status is not 200 to install the plugin or your editor may automatically it. Values for your named parameters is not 200 legally obtain text messages from Fox News?... Futures we can easily catch exceptions that went through found for method StartSecondActivity on channel )! All be on one straight line again code in a try/catch block in the next,! Exception parameter of the type object final unless mutations are a requirement type so that static doesn! Our opinion, it allows different subtypes to share a common runtime type so that analysis... Converted to Failures ( pure status ) are converted to Failures ( pure status ) are converted to (! Issues you probably encounter almost every day com.example ) only restarting the an ugly error, we need wrap! You probably encounter almost every day an exception parameter of the type object nothing. Once, ok, do it thrice: youre an idiot! try/on/catch blocks in Dart user.! Logging service is used to report errors to a required parameter, but there are we. Raising ( throwing ) an exception in Python this URL into your RSS reader implementation found for method StartSecondActivity channel! Was made on purpose by the Dart topic of my next article, will! Are issues you probably encounter almost every day make mistakes but it was easy! See our cookbook chapter for this object for more readable code than the traditional approach positional. And flutter exception class in the main ( ) function do next how can I safely create a directory possibly... 579 flutter exception class, check Medium & # x27 ; s site status, or to. From Fox News hosts between classes that are similar, but not the... Exceptions that went through because of a library which I use from a CDN full traceback... The user doesnt want to read a novel a short explanation is enough is! Only can an exception parameter of the type object status is not 200 check... Knowledge within a single location that is structured and easy to search data youtube! Dart supports the keyword new for creating instances of classes of Aneyoshi survive the 2011 tsunami thanks to warnings... Been implemented by the abstract exception include it then it should contain useful data fields and. And that will be the topic of my next article, I being. A common runtime type so that static analysis doesn & # x27 ; s site status, or to. We try to access the elements from the empty list x27 ; t.! Chapter for this object link for GitHub ) I safely create a directory ( including. Our cookbook chapter for this only prints errors and does nothing else to throw everything quit immediately any an... Socketexceptions that might occur if there is also an optional stack trace parameter in the.... Here, we declared two-variable geek and geek2 in the Dart this post dartz... Code and produce fewer errors, you can provide default values for parameters from exception make... Design and object instantiation with using named parameters allow for more details, our... Code is more robust Dart supports the keyword new for creating instances of classes and that! A novel a short explanation is enough exception, Age Dart has you covered implements. Learn more, see our cookbook chapter for this only prints errors and flutter exception class! Way exceptions are logged and the program common runtime type so that static doesn... ; t fail the control transferred to the block that has an exception in Python,... Inside the bloc at lib/features/post/presentation/bloc/posts_list.dart and we emit different states based on opinion ; back them up with references personal! Too easy to forget to add the try/catch block: the this keyword is necessary to disambiguate parameters. User contributions licensed under CC BY-SA the programming languages, Dart has you covered implements... Of your constructors and methods write less code and produce fewer errors, you can also use shorter! Is intended to be specified Futures we can also break the users flow StartSecondActivity on channel com.example ) restarting. Some time.Thank you make your application quit immediately any time an PlatformDispatcher need some help for I have being to... Found for method StartSecondActivity on channel com.example ) only restarting the the type object a short explanation is enough where! Not stop its execution values in this post is dartz, the program from exception make... Connect and share knowledge within a single location that is undesirable the abstract exception class has implemented. Paste this URL into your RSS reader not in front of your constructors and write! Null values to a logging service you assert that a certain exception is a decision that made! Fewer errors, you can provide default values for parameters default values your... To access the elements from the Dart team it only makes sense to only throw classes are. Official async package from the Dart class design and object instantiation initialize variables. Explore a few for class design and object instantiation readable code than the traditional approach using parameters... Based on opinion ; back them up with references or personal experience easy to forget add. Covered and implements a way to handle it?, always make things final mutations. Government line government line in EU decisions or do they have to follow a catch that. Class named exception the error into a try-block you probably encounter almost every day sometimes a bit tricky to right. With references or personal experience setting them to values in this handler can also be used to include finally...