This question already has answers here:
Null aware function invocation operator
(2 answers)
Closed 3 months ago.
Does the Dart language have anything better to handle the potential of the callback being null than I have done here:
if(widget.onChanged!=null){
widget.onChanged!(value);
}
In case onChanged is of type Function, you can use
onChanged?.call(value);
This will only call the function if it is not undefined/null.
Related
This question already has answers here:
How to get current method's name in Delphi 7?
(3 answers)
How To Get the Name of the Current Procedure/Function in Delphi (As a String)
(6 answers)
Closed last year.
I'm creating an error report generator as part of a global exception handler. Right now I'm relying on the user to tell us what exactly they were doing when the exception happened.
I'm already adding the "exception.message" string to the report, but is there any way to grab the name of the procedure or the call stack "log" so I can add it to the report as well?
This question already has answers here:
Properties vs Methods
(16 answers)
Closed 3 years ago.
When is it preferable to use getters instead of functions in Dart?
In other words, when would you use getters to get something, which at the same time could be also got with a function?
You can read from the effective dart guide:
DO use getters for operations that conceptually access properties.
The operation does not take any arguments and returns a result.
The caller cares mostly about the result.
The operation does not have user-visible side effects.
The operation is idempotent.
The resulting object doesn’t expose all of the original object’s state.
This question already has an answer here:
What are the semantics of _internal?
(1 answer)
Closed 4 years ago.
I have the following code in a flutter tutorial that discusses global state:
static GlobalState instance = new GlobalState._();
GlobalState._();
What exactly is the ._ doing? Is this technically just a blank method?
It's a private constructor. This pattern is used to prevent clients from instantiating or subclassing GlobalState, so the only available instance of GlobalState in the program is instance.
This question already has answers here:
What are function typedefs / function-type aliases in Dart?
(7 answers)
Closed 4 years ago.
This seems like a very obvious question to me, but I cannot seem to find the answer.
How do I write a function type in Dart.
I can use some canned forms like ValueChanged<T> or ValueSetter<T>, but how are they defined? How can I write general function types like T -> U -> V
If I understood your question correctly, I think you are referring to Generic Types. These types are used by functions when you are not sure which type your function is going to use in order to avoid code duplication. For example, let's say you have a class with a method that stores numbers in a List:
class StoreInt {
storeInList(int value);
}
But later, you decide you now want it to store Strings, so you create another class:
class StoreString {
storeInList(String value);
}
Generics allow you to write this class once and use it to store any kind of object you want:
class Store<T> {
storeInList(T value);
}
As far as I know, you don't create generics in dart, you just specify a single letter in between diamond operators as shown in the previous example.
You can find more information on generics here: https://www.dartlang.org/guides/language/language-tour#generics
This question already has an answer here:
How do I lookup a string constant at runtime in Objective-C?
(1 answer)
Closed 8 years ago.
Is it possible to dynamically reference a constant in objective c:
e.g. NSForegroundColorAttributeName is declared in UIKit/NSAttributedString.h as a const NSString. Its value is #"NSColor". In compiled code, I just specify the constant to use it, but what if I need to refer to it dynamically at run time (say a user might type it out)?
I could just use #"NSColor", but that may change as the SDK changes.
Is there a function like NSClassFromString, say ConstFromString:
ConstFromString(#"NSForegroundColorAttributeName") --> #"NSColor"
If the symbol is a public, exported symbol, then you might be able to look it up at runtime using dlsym and friends, but I agree with the commenter that this sounds like a bad idea.