I'm using a Dart package and need to extend or otherwise change some of the state in a singleton class called Constants, i.e. a class with a private constructor. It appears I have to change the singleton to extend/subclass it. Having poured over their code, I admire their work and want to avoid changing their code. Is their another way to add some constants and change some of the values of the static const's in their Constants._() class? I'm new enough to Dart to be missing something obvious, so don't be shy about giving me obvious advise. I know I can change the class to have a public const constructor and then I'm able subclass it. Is a mixin the way to tackle this?
Thanks in advance for any help.
Related
I couldn't understand the difference between these two keywords.
By using extends we can get features from parent class. I think implements does that too.
First I thought the difference is overriding methods but with extends I can do that.(I might be wrong)
Is the difference of these two keywords about overriding methods or what? Thank you
extends means we get the implementation of a given class and we can then override members if we want our own implementation for certain variables or methods. You can also add new variables and methods.
implements means you get nothing from the class you implement from. But you promise that your class will be compatible with the interface of the class you are implementing. So no, you are not getting any implementation from the super class and you need to implement everything or declare your class abstract.
I am trying to learn Dart language. Following code seems very straight forward but does not work. I know it may be a foolish question for an expert but for me hard to understand why not ?
class Car{
carFun(){
print("Test");
}
}
main(){
Car.carFun();
}
Already answered but I'll give more context.
You need to mark your method as static:
static carFun(){ ...
This makes the method available as a 'Class Method'; right now, as you have defined it, it is an 'Object Method'. This means that you need to make an object out of the class Car to be able to use it, which would be something like this:
var myCar = new Car();
myCar.carFun();
This way you instantiated an object and used a defined method for it. Marking it as static would make this approach not work. This is one of the many differences between a Class and an Object.
Mark your method as static. Read more: https://dart.dev/guides/language/language-tour#class-variables-and-methods
I have a class written in Objective-C and I want to have another similar one. Except for few details. Is there any smart way of copying class implementation and making another class? I'd like to change few things, but ctrl+c + ctrl+v sounds so unintuitive.
Regards
PS. edit: I have multiple classes to implement, also I'd like to have neat solution for future.
Use class inheritance.
Implement class A with the common functionality
Derive classes B and C from A to add functional differences.
Take a look at Classes Inherit from Other Classes.
If you like to simply add a method without subclassing, see Categories Add Methods to Existing Classes. But be aware what you shouldn't do with categories!
If you like to change values, add appropriate properties to the interface declaration.
I need to do some custom data binding and I tried to use the #BindUsing annotation on a class (http://grails.org/doc/latest/api/org/grails/databinding/BindUsing.html), however, it's being ignored. I am under the assumption that since the annotation is used on the class that would mean that every time a data binding happens and that class is involved, the BindingHelper class would be used, but it's never actually called. Is there something that I'm missing or doing wrong?
Here's the class definition where UserBinding is a class that implements the BindingHelper interface:
#BindUsing(UserBinding)
class User extends SomeOtherClass
{
...
Also am I correct in understanding that basically creating a ValueConverter and using #BindUsing on a class accomplish the same thing?
BindUsing on a class is not used often and there seems to be a bug reported around that already. [From the link] The problem could be that there are multiple request parameters with the same name it might be using the helper only for the first one.
Using a property level #BindUsing annotation should be simpler to implement and is less likely to fail (even when there are multiple entries in the params map with the same name).
I just want to know if there's a way to access the properties from a utility class used by an Action class. To access the properties from an Action class we extend the ActionSupport and use the getText("property.key.name") method.
So, my question is -should every other class extend the ActionSupport to access properties, even though its not an Action class? or is there any other way?
Thanks
I wouldn't extend ActionSupport unless you're actually defining an action.
The S2/XW2 ActionSupport class uses com.opensymphony.xwork2.DefaultTextProvider; you might be able to use it in your own classes. I'm a little wary of this since I'm not convinced non-action classes should be accessing the web-app's resources, but I haven't given it much thought, so it could be valid. I also haven't tried to do it.
ActionSuport is kind of helper class being developed by S2 developers to supplement the Development as it provides many features OOTB.
getText() is one of the use-case where S2 provides a way to read the property files.This method is specific to S2 as it know how to transverse the hierarchy to read the property files and in what order.
There are many ways to read the property files in a application and few of them are
ResourceBundle
if you are using Spring, it has a very handy mechanism to read property files
- how-to-read-properties-file-in-spring
Apache Common also provides a way to read the file
Apache-Common
In short to read properties file there are many ways, S2 getText() is a way developed by the S2 to read the property file with respect to your actions.
//I wanna make you understand how struts doing it.
public class ActionSupport implements Action, Validateable, ValidationAware, TextProvider, LocaleProvider, Serializable {
//Action support implementation.
//Here TextProvider takes care about resource bundle thing.
}