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.
Related
This question already has answers here:
The difference between the use of constructor " className() and className._()
(2 answers)
Closed 1 year ago.
I'm still getting used to Dart and I've searched for an answer to this, but I haven't found one. What does the second line, 'ClassA._();', of the class definition do? The list declaration is only shown to give the class a reason for being.
class ClassA {
ClassA._();
static final List<String> someList = ["A", "B", "C"];
}
If it's a constructor, how would it be invoked?
After doing some more sleuthing I see it creates a singleton. But when is the singleton created? Is there a way to get in front of the instantiation and make some mods?
Thanks in advance for any help given.
ClassA._();
Is a named constructor with the name _. In dart, identifiers that start with underscore (_) are only visible inside the library it is contained in.
The reason you would define a class this way, is that you want to prevent people from creating instances of this class.
This question already has an answer here:
Migration error handling to Struts2
(1 answer)
Closed 2 years ago.
I am trying to update my code from Struts1 to Struts 2 but facing difficulty to update the below code can any one please suggest the replacement for below code.
final ActionMessages errors=new ActionMessages();
errors.add("Error Global", new ActionMessage("some_string_in_properties_file"));
sorterrormessage(errors);
Extending ActionSupport provides the addActionMessage method. It also provides getActionMessages and setActionMessages (Collection<String>) which would allow sorting them. 1
The tag library provides <s:actionmessage />, when combined with hasActionMessages allows checking for, and displaying, the action messages.
To use a property file use an appropriate getText() implementation in the action.
It would be good to know what difficulties you're actually facing as this is searchable on the web and it's in the S2 docs. A cursory examination of the functionality in ActionSupport would probably be a good idea.
1 Sorting messages is only rarely the right thing to do except under very particular circumstances, or if it's explicitly not an alphabetical sort.
This question already has answers here:
What is the difference between Class and Klass in ruby?
(4 answers)
Closed 4 years ago.
I saw klass in one of the existing rails project. Why is it used? and how come it's different from class in rails?
One is the name of a class and the other is just an undefined constant by default. And for the pair you're more likely to see, class and klass,
the former is a keyword for defining classes while the latter is just an identifier (like any other string of characters). It's used when you would like to write the word "class" but can't because it's a reserved keyword.
link hope it will help you.
This question already has answers here:
How to initialize properties that depend on each other
(4 answers)
Instance member cannot be used on type of custom class
(3 answers)
Closed 6 years ago.
I'm currently working on learning Swift 3 and I'm trying to implement an XML parser that parses data from a URL. I've created a separate file to handle the XML parsing and have setup it as follows.
let xmlDoc = NSURL(string: "http://labs.bible.org/api/?passage=random&type=xml")
var parser1 = XMLParser(contentsOf: xmlDoc)
I'm currently having issues with syntax however. Swift is highlighting the line where I initialize the XML Parser and giving the error "Cannot use instance member 'xmlDoc' within property initializer, property initializers run before 'self' is available.
This is probably something really simple but I wasn't able to find a solution in my google searches.
Any feedback is appreciated!
-Alex
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.