问题描述
限时送ChatGPT账号..我想在我的构造函数中的一个组件上设置一个字符串属性,但是当我尝试这样的事情时
I'm wanting to setup a string property on a component in my constructor, but when I try something like this
@Component({
selector: 'wg-app',
templateUrl: 'templates/html/wg-app.html'
})
export class AppComponent {
constructor(private state:string = 'joining'){
}
}
我收到 DI 异常
EXCEPTION: No provider for String! (AppComponent -> String)
显然,注入器正试图找到一个字符串"提供者,但找不到任何.
Clearly, the injector is trying to find a 'string' provider, and can't find any.
我应该使用什么样的模式来处理这种类型的事情?例如.将初始参数传递给组件.
What sort of pattern should I be using for this type of thing? Eg. passing initial parameters to a component.
应该避免吗?我应该注入初始字符串吗?
Should it be avoided? Should I be Injecting the initial string?
推荐答案
您可以使用 @Input()
属性.
<my-component [state]="'joining'"></my-component>
export class AppComponent {
@Input() state: string;
constructor() {
console.log(this.state) // => undefined
}
ngOnInit() {
console.log(this.state) // => 'joining'
}
}
构造函数通常只用于 DI...
Constructor should generally be used just for DI...
但如果你真的,真的需要它,你可以创建可注射变量(plunker):
But if you really, really need it you can create injectable variable (plunker):
let REALLY_IMPORTANT_STRING = new OpaqueToken('REALLY_IMPORTANT_STRING');
bootstrap(AppComponent, [provide(REALLY_IMPORTANT_STRING, { useValue: '!' })])
export class AppComponent {
constructor(@Inject(REALLY_IMPORTANT_STRING) public state: REALLY_IMPORTANT_STRING) {
console.log(this.state) // => !
}
}
最简单的选择是设置类属性:
Simplest option is to just set class property:
export class AppComponent {
private state:string = 'joining';
constructor() {
console.log(this.state) // => joining
}
}
正如@Mark 指出的,另一种选择是使用服务:
As @Mark pointed out, another option is to use a service:
export class AppService {
public state:string = 'joining';
}
export class AppComponent {
constructor(private service: AppService) {
console.log(this.service.state) // => joining
}
}
这篇关于Angular 2 向构造函数传递参数会引发 DI 异常的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
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