Injection in Angular 2. How does it work? -


i'm learning angular 2, , i've been learning few days. when read injectable() concept in angular 2 , try applying tuturial's example code follow link : angular 2 - dependency injection, have got problem.

they said need putting annotation @injectable() in top of class other class can inject, :

import {     injectable  } '@angular/core';   @injectable()  export class appservice {      getapp(): string {        return "hello world";     }  }

the problem when drop injectable(), app still running well? what's wrong me? incidentally, can me figure out " how injection in angular 2 work?"

as stated in documentation:

as happens, have omitted @injectable() first version of heroservice because had no injected parameters. must have service has injected dependency. need because angular requires constructor parameter metadata in order inject logger.

https://angular.io/guide/dependency-injection#why-injectable

so in short, if injectables have injectors, @injectable decorator resolves cyclic-dependency.

" how injection in angular 2 work?"

this broad question sum angular injection system creates instance of provider object/function , uses instance in component when inject in constructor.

if haven't provided in component using go it's parent component, module it's been used until finds instance. each level has own map of provider instances , component use first instance finds when traverses injection tree upwards.

so provider singleton instance point defined.


Comments

Post a Comment

Popular posts from this blog

PHP and MySQL WP -

i trying accomplish 2 things here code. writing php directly wp page using insert php plugin. 1) query mysql database , return results 1 column 4 columns. 2) make each result own hyperlink directs user new wp page runs new query on page. i able query show results , turn results dynamic hyperlink, cannot formatting down. right returns result 1 column. here have: [insert_php] $servername = "localhost"; $username = "login"; //edited privacy $password = "password"; //edited privacy $database = "database"; //edited privacy // create connection $conn = new mysqli($servername, $username, $password, $database); // check connection if ($conn->connect_error) { die("connection failed: " . $conn->connect_error); } echo "connected successfully"; //get results database $result = mysqli_query($conn,"select mine mines order mine"); $all_property = array(); //declare array saving property //showing proper...
Read more

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m...
Read more

go - golang pprof for c library code -

i have been trying profile golang application pprof, seems details of c code(linked static library) missed in output result. flame graph from frame graph can see c code time consuming reported within "runtime._externalcode", no details @ all. , sure static library compiled debug enable. so there way make pprof details(like stack trace) of 3rd party c code? or there other golang profiling tool this?
Read more