Errors vs Exceptions in Flutter¶

What’s the difference between errors and exceptions in Flutter?

→ Errors are programmer mistakes. They are fatal and we should not try to recover from them
→ Exceptions are failure conditions that are our of our control. We should handle them and recover gracefully

Thread 🧵

Errors are fatal and when they happen the program cannot recover normally.

→ we want to discover (and fix) them as early as possible in the development process
→ we should track them in production using a crash reporting solution, so that we can measure impact and severity

The most common errors we may encounter are:

• AssertionError
• TypeError
• ArgumentError
• RangeError
• UnimplementedError
• StateError

and many others.

They all extend the base Error class, and the full list of errors can be found here:

• Error class | Flutter docs

Exceptions are not fatal and we should always handle them gracefully.

We can choose to map them to our own exception type inside a try/catch block.

Or we can let them propagate on the call stack (until something else catches them).

How to recover when an exception happens?

Eventually, we want to catch them somewhere and show a user-friendly error message.

One common way to do this is to emit an error state that the widget can listen to.

I’ve covered this before:

• How to handle loading and error states with StateNotifier & AsyncValue in Flutter

Some common exceptions you may encounter are:

• FormatException
• IOException
• PlatformException
• TimeoutException

They all implement the base Exception class (you may create your own if you want), and the full list can be found here:

• Exception class | Flutter docs

Source code¶