I have a service that has a public property declared as follows:
public indiceUsuarios: IndiceUsuario[] = [];
After changing data and doing operations I reload that property with the following method in the same class:
private reloadIndiceLocal(indiceUsuarios: IndiceUsuario[]): void {
let self = this;
self.indiceUsuarios.length = 0;
self.indiceUsuarios.push(...indiceUsuarios);
}
I'm injecting this service into another component and referencing that property on the ngOnInit() using the following line this.indiceUsuarios = this.sesionService.indiceUsuarios; (this local property is not initialized before this). I'm then using this local property on this component's view. It shows perfectly fine and is changing when I add elements to the array.
The issue is that if I remove elements from the array they will keep showing (the view is not updating to reflect these changes).
Any ideas?
Well, In my case it turned out to be that I was relying on a singleton that was poorly written and wasn't acting as a singleton (effectively linking my view to an object with a different instance to the one I was changing). My bad.
Related
I have a variable that stores the available cars at any moment. Is there a way to automatically re-evaluate this function on every change?
Just using this.carFactory.available in this case is not a solution, because this example I'm showing is simplified - the real calculation in my project is alot more complex.
calculateAvailableCars(){
this.carFactory.available.forEach(function(item){
this.availableCars.push(car.id);
}.bind(this));
}
How could I do this in Angular 2? In Angular JS there was the possibility to $watch a function.
I could of course manually call this function everytime something changes, but it would be nice not to have to call this function in every part of the application that can change the data.
Using template function reference with auto change detection
You can use this function output on template:
carOutput(): cars[] {
this.calculateAvailableCars()
return this.availableCars;
}
and use output on template:
<p>My car ratio is {{ carOutput() }} </p>
However this will trigger very aggressive change detection strategy on this variable. This solution is the simpliest one, but from engineering perspective rather worst: consumes tons of unnecessary function calls. One note, that hosting element must not be set to detect changes onPush.
Separate data model to parent component and pass as property to child
You can store car list display in separate component, and pass new car array as input property to this component:
<car-display [cars]="availableCars"></car-display>
Then you can set changeDetetcion policy in this component to onPush, and each time input property bind to availableCars will change, <car-display> will re-render.
If update relays on some host binding
If some external host action is triggering new cars calculation, then hostBinding may help:
#hostListener(`hover`) recalculateCars() {
this.calculateAvailableCars()
}
And finally, (because you describe your use case quite cryptically, without many details, thus I'm scratching all possible scenarios) if some external component action shall trigger re-calculation, you can hook to ngLifecycle ngOnChanges() if for example external input property change shall re-trigger cars calculation.
In other words and summing all that up, it depends who and from where triggers changes, that shall re-trigger available cars recalculation.
And very important, see an answer from #chiril.sarajiu, because what we are trying to work around here can be handled automatically by single observable. This requires additional setup (service, provide observable to components, e.c.t.) but it's worth.
--- EDIT ---
If each variable change shall retrigger data
As OP clarified, that changes are related with model bound to component. So another option with mentioned by #marvstar is using set, where each model variable change will retrigger fetching function:
modelSchangeSubject: Subject<Model> = new Subject<Model>();
ngOnInitt() {
this.modelSchangeSubject
.subscribe((v: Model) => {
this.calculateAvailableCars()
})
}
/* Rest of controller code */
set modelBounded(v: Model) {
this.modelSchangeSubject.next(v);
}
You need RxJS. What you do is you create a data service, which will store an Observable (in my case a BehaviorSubject, which is mostly the same, but in my case I start with a value).
export class DataService {
private dataStorage$ = new BehaviorSubject(null); //here is the data you start with
get getDataStorage() {
return this.dataStorage$.asObservable(); // so you won't be able to change it outside the service
}
set setDataStorage(data: any) {
this.dataStorage$.next(data);
}
}
Then you subscribe to this data changes everywhere you need to:
constructor(private dataService: DataService){}
ngOnInit() {
this.dataService.getDataStorage.subscribe((data) => this.calculateAvailableCars(data));
}
calculateAvailableCars(){
this.carFactory.available.forEach(function(item){
this.availableCars.push(car.id);
}.bind(this));
}
Read more about best practices of using RxJS in Angular, as there can be quite a bit of pitfalls and problems.
Try using setter and getter.
private _YourVariable:any;
public set YourVariable(value:any){
this._YourVariable = value;
//do your logik stuff here like. calculateAvailableCars
}
public get YourVariable():any{
return this._YourVariable ;
}
I am in doubt if the following design pattern would cause a memory leak.
I have been using it for some time with success, but I haven't seen this pattern used by others, so I'd like some confirmation if you see something wrong with it.
As from next month I have to start working on a large project, and I want to know for sure that I can use this without problems, or if I should use another strategy.
controller.js:
var Controller = function(options){
};
Controller.prototype.makeView = function(options){
options.controller = this;
options.otheroption = options.otheroption;
var view = new View(options);
};
Controller.prototype.getModel = function(options){
//--- Get model ---
var model = new Model();
var promise = model.fetch();
return promise;
});
view.js:
var View = Backbone.View.extend({
initialize: function(options){
this.controller = options.controller;
this.otheroption = options.otheroption;
},
getModel: function(){
var promise = this.controller.getModel();
promise.done(_.bind(function(model){
//Do something with the returned model instance
}, this));
};
});
Instantiate controller, eg. from the router, or another controller:
//--- Instantiate the controller and build the view ---//
var controller = new Controller();
controller.makeView(options)
To me, this doesn't look like a circular reference, because both the controller and view are declared as a local variable.
Yet the instantiated view can access the controller functions, which allows me to isolate the RESTful server interactions via models / collections that the view uses.
For me it would seem as if the only reference remaining would be the view that keeps a reference to the controller object.
What I do afterwards is clean up the view (I destroy the instance and its references when I don't need it anymore.
Your opinion on this pattern is highly appreciated.
My purpose is to isolate creation of views / server interactions in separate controller files: if you see holes in my method and have a better way of doing it, please share.
Thanks.
Short answer: There is no memory leak problem in the code you have posted. The view holds a reference to the controller, but not vice versa. So as long as the controller lives longer than the view, that reference does not keep your objects from being garbage-collected. I don't see a circular reference anywhere in your code.
Longer answer: The pitfalls would be in the code you haven't posted. In particular, any event handlers in your view must be cleaned up properly, otherwise your views never fade into oblivion. But you have said in your question that you clean up your view, so I guess you are aware of that sort of problem.
What controller doing is here looks like a utility to me. Could have been easily managed by a global level singleton. I see some issues in first glance.
Code repetition, assuming you would creating separate Controller for different types of Models and Views, makeView and getModel code needs to be repeated for each controller. If you extending from a BaseController, then you need to pass View and Model Class to getModel and makeView functions.
How do you handle a use-case where you have to use same model in different Views?
makeView and getModel is designed assuming for each makeView there would be a getModel call, in assumed order
I would rather write a utility function which can create and deploy views for me.
var deployView = function(view, config){
//do the view rendering
view.render();
view.$el.appendTo(config.el);
}
var createView = function(config) {
var view;
var viewType = 'model';
if (config.collection || config.Collection) {
viewType = 'collection';
}
if (viewType === 'model') {
if (config.Model) {
config.model = new config.Model(config.modelAttributes);
//fetch if needed
}
} else {
if (config.Collection) {
config.collection = new config.Collection(config.items);
//fetch if needed
}
}
var filteredConfig = _.omit(config, 'Collection', 'Model', 'View');
view = new config.View(filteredConfig);
deployView(view, filteredConfig)
}
JavaScript implementations haven't had a problem with circular references for a long time. (IE6 did have a memory leak from circular references if I recall correctly, which wasn't shared by any other major browser from that period.)
Modern JavaScript implementations perform garbage collection through a "mark and sweep" algorithm. First they scan through your web app's entire memory structure starting from the global object, and mark everything they find. Then they sweep through every object stored in memory and garbage collect anything that wasn't marked. As long as there isn't a reference to your object from the global object or any stored function, it can be garbage collected.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Memory_Management#Mark-and-sweep_algorithm
You're probably thinking of a reference counting-based implementation, which does have issues with memory leaks from circular references. In that implementation as long as one object contained a reference to another, that second object can't be garbage collected. That method was once used in web browsers but not anymore.
Nowadays, most memory leaks are from globally-accessible objects you forget to clean up and accidentally retaining data in function closures (a function that creates another function and passes/saves it somewhere). Since the closure's local variables can be accessed by the function created inside of them, they have to be retained as long as that function exists.
So go ahead and add all the circular references you want. Unless you need to target IE6, your code's fine.
I have an object in an array
var
sidelist = [
{
name:"MURICA",
types:[...]
}
];
I have a box that displays the object's name. Then I have a text field and a button. On button press the object's name gets set to text field value. But I don't know how to make the name in the box change accordingly.
As I understand putting the object in a session variable is not an option since I will not be able to modify properties of objects inside of it without resetting the whole session var. I tried it and failed.
html
<template name="asdf">
{{#with object}}
<div>{{name}}</div>
{{/with}}
</template>
js
Template.asdf.object = function() {
return Objects.findOne(...);
};
EDIT
I think I've got your question wrong, sorry. If you have a value in memory that you'd like to change and have the DOM updated, use dependencies:
html
<template name="asdf">
{{property}}
</template>
js
var property;
// Create new dependency object that will manage refreshing property value:
var _dep = new Deps.Dependency;
updateProperty = function(value) {
property = value;
// Whenever you change value of the property, call changed() function:
_dep.changed();
};
Template.asdf.value = function() {
// Within reactive function, call depend() to rerun the function
// each time the value is changed:
_dep.depend();
return value;
};
How about a different and in my opinion simpler solution - using a local collection for your data.
I am not sure exactly why do you keep that sort of data into an array, but if it is because you only need it on the client then you can instead create a local collection and have all the reactivity benefits without writing all that code for making the array reactive. The data stored in a local collection is never sent to the server, so no communication or storage overhead.
You'd do it like that:
Sidelist = new Meteor.Collection(null);
[EDIT] Put the above line in your client-side-only part of the code.
Notice the null parameter. This will give you a collection that is only stored on the client and is a regular Meteor reactive source. Then you go about using it in your code and html just as you would a normal collection.
Hope that helps.
I have a constructor for a model (similar to Backbone model) which uses an instance of a store (e.g. MongoDB / Redis) which is passed to the model factory. Now inside the constructor for the model, I do
this.store = options.store;
Store is now available as this.store once I construct an instance with var model = new Model().
Then I faced a situation when I my Model has "public" methods, e.g. Model.find() which will work without instantiating the model. But now because it's not been instantiated, functions inside Model can not access store by this.store.
What I did, is I started also adding store to the constructor itself Model.store = options.store which fixes the problem. But now store is exposed to anything that uses Model constructor and this is not desirable.
I am guessing I am doing something wrong. So I would appreciate some help.
If I get what you're saying correctly, then I think what you want is to allow for a "static" find() method on Model without exposing the store variable. Javascript doesn't really have a formal private scope for classes, but you can get what you want using closures. Here's a fiddle:
http://jsfiddle.net/52FPy/
EDIT:
An updated fiddle to demonstrate various ways to expose/hide info using closures:
http://jsfiddle.net/52FPy/2/
Briefly:
var Model = function(){
var store = 'this is a store';
var Model = function(){
}
Model.find = function(){
return store;
}
return Model;
}()
This will "hide" the store variable in the way you want.
In Typescript, how would I use a getter/setter for all the properties of an object? For example, I can have the following code:
class Div {
private _container: HTMLDivElement;
public get container() {
return this._container;
}
public set container(value) {
alert("Updated!");
this._container = value;
}
testDiv() {
this.container = <HTMLDivElement>document.createElement('div');
this.container.style.width = "100px";
}
}
var newDiv: Div = new Div();
newDiv.testDiv();
"Updated!" is alerted only once - when the div is first set (which, I guess, is really what it should be), but I want it to alert "Updated!" even when I'm setting a property on that object. Is there a way to do this, or should I come up with some kind of workaround?
Create an event system that triggers when your objects state changes. Do not allow direct access to properties. Funnel all activity through a controller that triggers state change as necessary.
Or look into using a framework that already does this. Backbone, Knockout, Angularjs etc.