什么是angular2中的多提供者 [英] What is multi provider in angular2

问题描述

我知道提供程序是用于从另一个类获取服务，但是什么是多提供程序和令牌呢?

I understand that provider is for getting service from another class but what is multi-provider and token thing?

还有当我们做multi=true吗?

provide(NG_VALIDATORS, { useExisting: class),    multi: true })

推荐答案

multi: true表示一个提供者令牌提供了一组元素.例如，路由器支持routerLink，router-outlet的所有指令均由ROUTER_DIRECTIVES提供.
如果使用令牌ROUTER_DIRECTIVES注册了新的提供程序，则它将覆盖以前注册的指令.如果设置了multi: true(在第一个注册的和新提供程序上)，则将新指令添加到先前注册的指令中，而不是覆盖它们.

multi: true means that one provider token provides an array of elements. For example all directives for router support routerLink, router-outlet are provided by ROUTER_DIRECTIVES.
If a new provider is registered with the token ROUTER_DIRECTIVES, then it overrides the previously registered directives. If multi: true (on the first registered and the new provider) is set, the new directives are added to the previously registered directives instead of overriding.

当注入ROUTER_DIRECTIVES时(constructor(@Inject(ROUTER_DIRECTIVES) directives) {})，将注入指令实例数组.注入ROUTER_DIRECTIVES通常没有任何意义.我将其用作示例，因为它是multi: true.

When ROUTER_DIRECTIVES is injected (constructor(@Inject(ROUTER_DIRECTIVES) directives) {}) an array of directive instances is injected. It usually doesn't make sense to inject ROUTER_DIRECTIVES. I used it just as an example because it is multi: true.

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