I been trying to migrate my Ionic 1 application to Ionic 2 and have been encountering alot of new terms and problems.
I do not really understand the need for get parameters() and when and what variables to return in that function.
For example(To Navigate):
static get parameters() {
return [[NavController]];
}
Previously in an older ionic build(I'm not sure which version I was developing upon), I can navigate to pages without this function. In the latest ionic 2 build(2.0.0-beta.25) , without this get parameters() function, it just wont navigate to the next targeted page , but there are no errors.
I'm aware of a existing post:
Angular/Ionic 2 - what is a provider and what does `static get parameters()` do?
Therefore, in what occasion I should return and what variables do I return?
In ES6 dependency injection gets the list of types it needs to resolve and pass instances for to the constructor of the class.
It has to be static, otherwise they could not be read before an instance is created.
In TypeScript it can aquire these types from the constructor parameters if they are applied (or #Inject() annotations).
Return the types for the constructor parameters of your class in the order they are listed in the constructor parameter list.
See https://stackoverflow.com/a/34546344/217408 for an example.
In fact, Angular2 tries to find out what to inject into the constructor of the class using the parameters method of the ReflectionCapabilities class:
https://github.com/angular/angular/blob/master/modules/angular2/src/core/reflection/reflection_capabilities.ts#L126
This method tries several things:
within the parameters of the type (i.e. a class property, i.e. static property)
#Component({
(...)
})
export class SomeComponent {
constructor(http) {
}
static get parameter() {
return [[Http]];
}
}
within the parameters metadata for the class if any. It's populated by #Inject decorator. Not that parameter decorators aren't supported in ES6
#Component({
(...)
})
export class SomeComponent {
constructor(#Inject(Http) http) { // == http:Http
}
}
within the design:paramtypes metadata that is internally created using the parameter types of the constructor. With ES6, this metadata isn't available since types for method parameters can't be used.
#Component({
(...)
})
export class SomeComponent {
constructor(http:Http) {
}
}
Based on these types, Angular2 looks for corresponding providers to get instances to inject.
Related
I'm new in CakepHP and I want to use a method (that returns a value) in an action in CakePHP 3. Sort of like this:
public function specify(){
if(isObject1){
// do something}
}
private isObject1($objname){
return true;
}
What is the right syntax?
CakePHP is PHP
The way to call a method from another method of the same class is the same as with any php project using objects - by using $this:
public function specify() {
$something = 'define this';
if($this->isObject1($something)) {
// do something
}
}
private function isObject1($objname) {
return true;
}
There's more info on how to use objects in The PHP manual.
The answer by #AD7six suggests adding a method within the controller which is not right if it is not going to be used as an action.
I think you should consider creating classes under vendor and including them in your controller and calling your class/method. The convention is vendor/$author/$package. You can either autoload them with composer or use a require call to include your file. If you don't want to create a class and just want to have functions, that can be done too.
Do take a look at cakephp's loading vendor files section.
Since upgrading to TypeScript 1.6, I've been getting what appears to be a spurious error with all my ng.Types:
Typescript 1.6 class 'derivedClass' cannot extend class 'baseClass':
types of property $timeout of types base class and derived class are
incompatible
Here's the code sample:
module app.Test {
class derivedClass extends baseClass {
// Notice there's nothing in the derived class
}
class baseClass {
constructor(timeout: ng.ITimeoutService, val1: string, otherVal: ng.ILogService) {
var vm = this;
vm.$timeout = timeout;
vm.someValue = val1;
vm.otherValue = otherVal;
}
$timeout: ng.ITimeoutService; // angular.ITimeoutService works
someValue: string;
otherValue: ng.ILogService;
}
}
angular.ITimeoutService works, or adding import ng= angular; in my modules also works. This didn't used to be an issue in the previous versions of Typescript.
Is it best practice to repeat the alias (eg: import ng = angular) in each module before using it, even though that's already done in the angular.d.ts?
Is it best practice to repeat the alias (eg: import ng = angular) in each module before using it, even though that's already done in the angular.d.ts
NO. The error is happening probably because you have done this.
The code you have posted works fine by default:
Both Java and Javascript allow for a different way of executing static code. Java allows you to have static code in the body of a class while JS allows you to execute static code outside class definitions. Examples:
Java:
public class MyClass {
private static Map<String,String> someMap = new HashMap<String,String();
static {
someMap.put("key1","value");
someMap.put("key2","value");
SomeOtherClass.someOtherStaticMethod();
System.out.println(someMap);
}
}
JS (basically any JS code outside a class):
var myint = 5;
callSomeMethod();
$(document).ready(function () {
$("#hiddenelement").hide();
});
However, it seems like Dart supports either of both ways. Declaring global variables and methods is supported, but calling methods and executing code like in JS is not. This can only be done in a main() method. Also, static code inside a class is not allowed either.
I know Dart has other ways to statically fill a Map like my first example, but there is another case that I can think of for which this is required.
Let's consider the following CarRegistry implementation that allows you to map strings of the car model to an instance of the corresponding class. F.e. when you get the car models from JSON data:
class CarRegistry {
static Map<String, Function> _factoryMethods = new HashMap<String, Function>();
static void registerFactory(String key, Car factory()) {
_factoryMethods[key] = factory;
}
static Car createInstance(String key) {
Function factory = _factoryMethods[key];
if(factory != null) {
return factory();
}
throw new Exception("Key not found: $key");
}
}
class TeslaModelS extends Car {
}
class TeslaModelX extends Car {
}
In order to be able to call CarRegistry.createInstance("teslamodelx");, the class must first be registered. In Java this could be done by adding the following line to each Car class: static { CarRegistry.registerFactory("teslamodelx" , () => new TeslaModelX()); }. What you don't want is to hard-code all cars into the registry, because it will lose it's function as a registry, and it increases coupling. You want to be able to add a new car by only adding one new file. In JS you could call the CarRegistry.registerFactory("teslamodelx" , () => new TeslaModelX()); line outside the class construct.
How could a similar thing be done in Dart?
Even if you would allow to edit multiple files to add a new car, it would not be possible if you are writing a library without a main() method. The only option then is to fill the map on the first call of the Registry.createInstance() method, but it's no longer a registry then, just a class containing a hard-coded list of cars.
EDIT: A small addition to the last statement I made here: filling this kind of registry in the createInstance() method is only an option if the registry resided in my own library. If, f.e. I want to register my own classes to a registry provided by a different library that I imported, that's no longer an option.
Why all the fuss about static?
You can create a getter that checks if the initialization was already done (_factoryMethods != null) if not do it and return the map.
As far a I understand it, this is all about at what time this code should be executed.
The approach I showed above is lazy initialization.
I think this is usually the preferred way I guess.
If you want to do initialization when the library is loaded
I don't know another way as calling an init() method of the library from main() and add initialization code this libraries init() method.
Here is a discussion about this topic executing code at library initialization time
I encountered the same issue when trying to drive a similarly themed library.
My initial attempt explored using dart:mirrors to iterate over classes in a library and determine if they were tagged by an annotation like this (using your own code as part of the example):
#car('telsamodelx')
class TelsaModelX extends Car {
}
If so, they got automatically populated into the registry. Performance wasn't great, though, and I wasn't sure if how it was going to scale.
I ended up taking a more cumbersome approach:
// Inside of CarRegistry.dart
class CarRegister {
static bool _registeredAll = false;
static Car create() {
if (!_registeredAll) { _registerAll()); }
/* ... */
}
}
// Inside of the same library, telsa_model_x.dart
class TelsaModelX extends Car {}
// Inside of the same library, global namespace:
// This method registers all "default" vehicles in the vehicle registery.
_registerAll() {
register('telsamodelx', () => new TelsaModelX());
}
// Inside of the same library, global namespace:
register(carName, carFxn) { /* ... */ }
Outside of the library, consumers had to call register(); somewhere to register their vehicle.
It is unnecessary duplication, and unfortunately separates the registration from the class in a way that makes it hard to track, but it's either cumbersome code or a performance hit by using dart:mirrors.
YMMV, but as the number of register-able items grow, I'm starting to look towards the dart:mirrors approach again.
First the Model class:
class Xxxx_model extends Model
{
function XxxxModel()
{
parent::Model();
$this->load->database();
}
function isInDatabase()
{
// Please ignore the sql query, it's just to show some random sql code with results
11. $result = $this->db->query('SELECT * FROM someTable WHERE ...');
$numberOfRows = $result->num_rows();
...
return $test;
}
}
Now the controller:
function someLogic()
{
$this->load->model('xxxx_Model', 'xxxxModel'); // not necessary to specify
$this->xxxxModel->isInDatabase();
}
When I run this I get the error:
Severity: Notice --> Undefined property: Xxxx_model::$db .../xxxx_model.php line 11
I have no idea why this is. If I put the db code in the controller it seems to work, it's only with this setup in the model that it fails. I can't for the life of me figure out where the code is astray...
You have to load the db library first. In autoload.php add below code,
$autoload[‘libraries’] = array(‘database’);
add library 'datatabase' to autoload.
/application/config/autoload.php
$autoload['libraries'] = array(
'database'
);
Propably you're started new project, like me ;-)
To add to atno's answer:
class Xxxx_model extends Model
{
function XxxxModel() //<--- does not match model name Xxxx_model
{
parent::Model();
$this->load->database();
}
Basically, you are not constructing the class or the parent class Model. If you are on PHP5, you may use __construct(), otherwise you must match the class name exactly, regardless of what alias you load it with in your controller. Example:
class Xxxx_model extends Model
{
function __construct()
{
parent::__construct(); // construct the Model class
}
}
I may be mistaken (haven't used 1.x in a while), but if you construct the Model class, there's no need to load the database if you are using the default connection settings in config/database.php, it should already be loaded for you.
If function XxxxModel() isn't your constructor, you're not loading the database by calling $this->xxxxModel->isInDatabase();
Try autoloading the database library from within autoload.php, or create a proper constructor in your model.
I've got a CustomersModule.cs with the following Initialize() method:
public void Initialize()
{
container.RegisterType<ICustomersRepository, CustomersRepository>(new ContainerControlledLifetimeManager());
CustomersPresenter customersPresenter = this.container.Resolve<CustomersPresenter>();
}
The class I resolve from the container looks like this:
class CustomersPresenter
{
private CustomersView view;
private ICustomersRepository customersRespository;
public CustomersPresenter(CustomersView view,
ICustomersRepository customersRepository,
TestWhatever testWhatever)
{
this.view = view;
this.customersRespository = customersRepository;
}
}
The TestWhatever class is just a dummy class I created:
public class TestWhatever
{
public string Title { get; set; }
public TestWhatever()
{
Title = "this is the title";
}
}
Yet the container happily resolves CustomersPresenter even though I never registered it, and also the container somehow finds TestWhatever, instantiates it, and injects it into CustomersPresenter.
I was quite surprised to realize this since I couldn't find anywhere in the Prism documentation which explicitly stated that the container was so automatic.
So this is great, but it what else is the container doing that I don't know about i.e. what else can it do that I don't know about? For example, can I inject classes from other modules and if the modules happen to be loaded the container will inject them, and if not, it will inject a null?
There is nothing magical going on. You are specifying concrete types, so naturally they are resolvable, because if we have the Type object, we can call a constructor on it.
class Fred { };
Fred f1 = new Fred();
Type t = typeof(Fred);
Fred f2 = (Fred)t.GetConstructor(Type.EmptyTypes).Invoke(null);
The last line above is effectively what happens, the type t having been found by using typeof on the type parameter you give to Resolve.
If the type cannot be constructed by new (because it's in some unknown separate codebase) then you wouldn't be able to give it as a type parameter to Resolve.
In the second case, it is constructor injection, but it's still a known concrete constructable type. Via reflection, the Unity framework can get an array of all the Types of the parameters to the constructor. The type TestWhatever is constructable, so there is no ambiguity or difficulty over what to construct.
As to your concern about separate modules (assemblies), if you move TestWhatever to another assembly, that will not change the lines of code you've written; it will just mean that you have to add a reference to the other assembly to get this one to build. And then TestWhatever is still an unambiguously refeferenced constructable type, so it can be constructed by Unity.
In other words, if you can refer to the type in code, you can get a Type object, and so at runtime it will be directly constructable.
Response to comment:
If you delete the class TestWhatever, you will get a compile-time error, because you refer to that type in your code. So it won't be possible to get a runtime by doing that.
The decoupling is still in effect in this arrangement, because you could register a specific instance of TestWhatever, so every call to Resolve<TestWhatever>() will get the same instance, rather than constructing a new one.
The reason this works is because Unity is designed for it. When you Resolve with a concrete type, Unity looks to see if it can resolve from the container. If it cannot, then it just goes and instantiates the type resolving it's dependencies. It's really quite simple.