How to throw an exception in Dart :
We can throw an exception manually in Dart. Dart has a couple of predefined Exceptions and these are thrown automatically on any unexpected result. You can raise predefined exceptions, custom exceptions or arbitrary objects. In this post, I will quickly show you how to throw an exception in dart with examples.
Throw predefined exceptions :
main() {
throw FormatException("Please enter a valid format.");
}
This will throw one FormatException like below :
Unhandled exception:
FormatException: Please enter a valid format.
#0 main (file:///Users/cvc/Documents/sample-programs/dart/example.dart:2:3)
#1 _startIsolate.< anonymous closure=""> (dart:isolate-patch/isolate_patch.dart:305:19)
#2 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:172:12)
You can wrap this code inside a try-catch block.
Throw arbitrary object :
main() {
throw "Not implemented exception";
}
This is another way to throw an exception. Output :
Unhandled exception:
Not implemented exception
#0 main (file:///Users/cvc/Documents/sample-programs/dart/example.dart:2:3)
#1 _startIsolate.< anonymous closure=""> (dart:isolate-patch/isolate_patch.dart:305:19)
#2 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:172:12)
rethrow :
If you handle an exception with a catch block, it doesn’t throw the exception, but you can throw it using rethrow even with a catch block.
main() {
try {
throw "Not implemented exception";
} catch (e) {
print("Exception...");
}
}
This program will result :
Exception...
But if you add one rethrow after the print statement,
main() {
try {
throw "Not implemented exception";
} catch (e) {
print("Exception...");
rethrow;
}
}
It will throw the exception :
Exception...
Unhandled exception:
Not implemented exception
#0 main (file:///Users/cvc/Documents/sample-programs/dart/example.dart:3:5)
#1 _startIsolate.< anonymous closure=""> (dart:isolate-patch/isolate_patch.dart:305:19)
#2 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:172:12)
