我看过一个例子,我想要重现它.
名称和年龄在类中声明,服务(Injectable)在构造
函数中
添加.
我想知道在这里使用class和constructor声明变量之间的区别.任何人都可以帮助我了解不同之处.
而不是声明名称和年龄不能我在建筑本身内声明？
这是我的代码：
import {Component} from 'angular2/core';
import {CommonService} from './commonService';
import {commonServiceIndipendent} from './commonSerivceIndipendent';
@Component({
selector : 'component1',template : `
<h1>Component 1</h1>
<input type="text" #message />
<button (click)="onLog(message.value)" >Component1 - Message </button>
`,providers:[commonServiceIndipendent]
})
export class Component1 {
name:string; //why here?
age:number; //why here?
//can't i add to constructor? if so how?
constructor (
private _commonService : CommonService,private _commonServiceIndipendent:commonServiceIndipendent) {}
//sending to same service. it has other instance in history
onLog(message:string) {
this._commonService.log( message );
this.name = "Arif",this.age = 20;
this.onData();
}
onData() {
this._commonServiceIndipendent.myData(this.name,this.age);
}
}
@H_
404_10@
在这种情况下
export class Component1 {
constructor (
private _commonService : CommonService,private _commonServiceIndipendent:commonServiceIndipendent) {
}
与此类似
export class Component1 {
private _commonService : CommonService;
private _commonServiceIndipendent:commonServiceIndipendent;
constructor (
_commonService : CommonService,_commonServiceIndipendent:commonServiceIndipendent) {
this._commonService = _commonService;
this._commonServiceIndipendent = _commonServiceIndipendent;
}
如果您不在构造函数protected,private或public中使用,例如DI,则变量_commonService的范围是您无法从另一个函数使用的构造函数{}的范围.
例如：
export class Component1 {
constructor (
_commonService : CommonService,_commonServiceIndipendent:commonServiceIndipendent) {
_commonService .... Work
}
foo(){
_commonService ..... Cannot find name '_commonService'.
this._commonService ..... Property '_commonService' does not exist on type 'yourClass'.
}
如果您没有将它分配给具有该类范围的另一个变量,那么您不能使用此关键字引用此变量.
export class Component1 {
name:string; //why here?
age:number; //why here?
//can't i add to constructor? if so how?
在没有Angular2的打字稿中,你可以做到这一点：
constructor (name:string,age:number) {}
但是在使用Angular2的打字稿中,Angular2负责在大多数情况下使用DI来实现：
constructor (private _commonServiceIndipendent:commonServiceIndipendent){}
你用于那些提供者：[commonServiceIndipendent].
Angular2: Inject a non @Injectable class
How to use Dependency Injection (DI) correctly in Angular2?
