In java, we can write default methods in interfaces with implementations. And further use this in classes where this interface has been implemented. Also, it is not compulsory to implement this default method.
I was trying to find something similar in Flutter. In flutter, it asks me to implement all methods. Else I get an error 'Missing concrete implementations of '.
So, is there something I can do to get the same overall output?
Apologies if I sound vague here. Do let me know in the comments if more information is needed. Thanks!
Seems like you are searching for abstract class. Its the same concept in dart as well.
abstract class Animal{
void breathe(){
print("Breathing");
}
void move();
}
class FlyingAnimal extends Animal{
#override
void move() {
print("fly");
}
}
class WalkingAnimal extends Animal{
#override
void move() {
print("walk");
}
}
void main(){
FlyingAnimal flyingAnimal=FlyingAnimal();
flyingAnimal.move();
flyingAnimal.breathe();
}
Flyinganimal can breathe and move, where breath is inherited from parent class Animal.
I hope this makes sense to you and helps you.
You do not need to provide implementation fir already implemented methods (it'd have no sense), but you must implement all abstract methods.
Related
we have abstract classes in clean architecture where we just define functions and then write the whole code in an implementation class that implements those functions.
why not use only the second function?
abstraction
abstract class PriceTrackerDataSource {
Stream<dynamic> getActiveSymbols();
}
implementation
class PriceTrackerDataSourceImpl implements PriceTrackerDataSource {
#override
Stream<dynamic> getActiveSymbols() async* {
if (_ws != null) {
await _ws!.sink.close();
}
_connect();
yield* _ws!.stream;
}
Abstract classes are used to make each layers more independent (data, domain, presentation). And also to define main methods for the own classes
Abstract classes help us to define a template / common definition for our multiple derived classes also reducing code duplication.
Making the class abstract ensures that it cannot be used on its own, but the details must be defined in the derived class implementation.
For more explanation you can have a look at Dart Docs.
As you see in example,
I have Core class for distribute the shared variables/methods etc. into the mixins.
Abstract class for defining necessary methods, providing summary about api.
Main class for importing everything like a provider.
There isn't any runtime error of course.
Problem with this approach, mixin methods does not recognize #override annotation.
I want to create granular, clean structure for my packages. What is the best approach for this situation or what is the mistake I'm doing?
abstract class AbstractCore {
void foo();
void bar();
}
class Core {
var shared;
}
mixin Feature1 on Core {
#override // not recognized by syntax of course
void foo() {
// something with [shared]
}
}
mixin Feature2 on Core {
#override // not recognized
void bar() {
// yet another thing with [shared]
}
}
class Main with Core, Feature1, Feature2 implements AbstractCore {}
You can accept like:
Core: ApiBase(For sharing Client object, constants, keeping dispose method...)
Feature1: let's say Authentication related Api calls
Feature2: let's say Content related Api calls
Main: Api provider.
Annotations don't have any impact on what the code do. They are just used for readability and tooling.
In your care, it is the analyzer that is complaining about #override, because you're not overriding anything.
Simply remove the #override decorator — it wasn't needed to begin with.
I was given a class with pure virtual function like the following:
class IRecordingHour{
public:
virtual int getData() const = 0;
}
Now, I have another class that uses the IRecordingHour class:
class ProcessRecordingHours {
public:
ProcessRecordingHours (IRecordingHour &);
proteted:
IRecordingHour & recordingHour;
}
I was told that I am not allowed to implement the IRecordingHour class (the one with the pure virtual function).
My question is: without implementing the IRecordingHour clas, how do I use it in the ProcessingRecordingHours? That is, how do I create an instance of the IRecordingHour and pass it to the constructor of the ProcessRecordingHours?
You should create a subclass of IRecordingHour and implement the method getData, like
class ARecordingHour : public IRecordingHour
{
public:
int getData() const override //override is valid from C++11
{
return 42;
}
}
And then you can do:
ARecordingHour arh{};
ProcessRecordingHours prh{arh}; //{}- Modern C++ initialization
You can find similar examples in a good C++ programming book, such as The C++ Programming Language
Though you equate them, your two questions are in fact quite different.
how do I use it in the ProcessingRecordingHours?
There is no particular problem in implementing ProcessingRecordingHours without implementing a subclass of IRecordingHour. You don't need to do anything special. You simply avoid relying on anything not declared by IRecordingHour, which is no different than you ought to do anyway.
how do I create an instance of the IRecordingHour and pass it to the constructor of the ProcessRecordingHours?
You cannot. A class with a pure virtual method cannot be directly instantiated. Your ProcessRecordingHours can be used in conjunction with classes that extend IRecordingHour, but if you are not permitted to create such a class then you cannot exercise those parts of your ProcessRecordingHours class that depend on an IRecordingHour.
Perhaps, however, you have misunderstood the problem. You may be forbidden from implementing IRecordingHour::getData(), but not from implementing a subclass that overrides that method with a concrete one. Such a subclass could be instantiable, and would be usable in conjunction with ProcessRecordingHours.
I think your teacher plan to inject an implementation of IRecordingHour into ProcessRecordingHours.
Also, you can't use that class unless you generate a stub for IRecordingHour or you implement one yourself with some dummy return values.
/// <summary>
/// in C# and interface can only contain virtual methods. so no need to say virtual.
/// </summary>
interface IRecordingHour
{
int getData();
}
class MockRecordingHour : IRecordingHour
{
public int getData()
{
//just return something. This will be enough to get ProcessRecordingHours to work
return 100;
}
}
/// <summary>
/// this class expects a IRecordingHour.
///
/// how we get a IRecordingHour depends on who's implementing it. You, some 3rd party vendor or another developer who's using this class that you've written.
///
/// Oh wait. Since you're building ProcessRecordingHours, you need a IRecordingHour to get against. You can use a mocking tool or create one yourself that returns some dummy data
/// </summary>
class ProcessRecordingHours
{
private IRecordingHour _recording;
public ProcessRecordingHours(IRecordingHour recording)
{
this._recording = recording;
}
public void DoSomething() {
Console.WriteLine("Recording Data: {0}", this._recording.getData());
}
}
I'm writing a program using TypeScript. The problem is I implemented HTMLElement interface.
export class IEElement implements HTMLElement {
// something here
}
The compiler shows many errors that I have some properties missing (IEElement declares an interface but does not implement it). I have implemented about 5 properties that I need to. The rest is redundant. How to avoid errors? Do I need to implement all the interface members?
Yes, you need to implement all non-optional interface members.
The interface is a contract, if you have a class that implements that contract you are promising to implement everything in that contract.
The HTMLElement interface has a lot to implement - but if you just want to add a bit of behaviour, perhaps you could start with an existing implementation...
interface SpecialElement extends HTMLElement {
myCustomFunction: () => void;
}
var element = <SpecialElement>document.getElementById('example');
element.myCustomFunction = function () { };
I've skimmed through the language documentation and it seems that the Google Dart does not support mixins (no method bodies in interfaces, no multiple inheritance, no Ruby-like modules). Am I right about this, or is there another way to have mixin-like functionality in Dart?
I'm happy to report that the answer is now Yes!
A mixin is really just the delta between a subclass and a superclass. You can then "mix in" that delta to another class.
For example, consider this abstract class:
abstract class Persistence {
void save(String filename) {
print('saving the object as ${toJson()}');
}
void load(String filename) {
print('loading from $filename');
}
Object toJson();
}
You can then mix this into other classes, thus avoiding the pollution of the inheritance tree.
abstract class Warrior extends Object with Persistence {
fight(Warrior other) {
// ...
}
}
class Ninja extends Warrior {
Map toJson() {
return {'throwing_stars': true};
}
}
class Zombie extends Warrior {
Map toJson() {
return {'eats_brains': true};
}
}
Restrictions on mixin definitions include:
Must not declare a constructor
Superclass is Object
Contains no calls to super
Some additional reading:
http://www.dartlang.org/articles/mixins/
http://blog.sethladd.com/2013/03/first-look-at-dart-mixins.html
Edit:
The Dart team have now released their proposal for Mixins, the original issue for Mixins was here.
It's not implemented yet, but in the meantime I've released an extensible Mixins library for Dart which includes a port of the popular Underscore.js functional utility library: https://github.com/mythz/DartMixins