为什么 queryParams 为空 [英] Why queryParams are empty

问题描述

我目前正在尝试了解如何在 Angular 组件中收集 queryParameters.由于我只想在 init 期间收集它们一次，因此我首先尝试了快照模式:

I'm currently trying to understand how to collect the queryParameters in an Angular component. As I want to only collect them once during the init, I firstly tried the snapshot pattern:

ngOnInit() {
    console.log(this.route.snapshot.queryParamMap);
    console.log('param test = ' + this.route.snapshot.queryParamMap.get('test'));
}   

查看 Stackblitz 上的演示:https://stackblitz.com/edit/angular-2tuafn可通过以下网址进行测试:https://angular-2tuafn.stackblitz.io?test=123

See the demo on Stackblitz: https://stackblitz.com/edit/angular-2tuafn Testable through the folowwing URL: https://angular-2tuafn.stackblitz.io?test=123

但结果，queryParam "test" 为空，queryParamMap 为空，见控制台输出:

But as a result, the queryParam "test" is null and the queryParamMap is empty, see console output:

ParamsAsMap {params: {…}}
    keys: Array(0)
    params: {}
    __proto__: Object
param test = null

=> 为什么queryParamMap 为空???

=> Why does the queryParamMap is empty ???

然后，我尝试使用 Observable 模式:

Then, I tried with the Observable pattern:

ngOnInit() {
    this.route.queryParamMap.subscribe(
      (params: ParamMap) => {
        console.log(params);
        console.log('param test = ' + params.get('test'));
      }
    );
}

在 Stackblitz 上查看演示:https://stackblitz.com/edit/angular-hfqx8a可通过以下网址进行测试:https://angular-hfqx8a.stackblitz.io?test=123

See the demo on Stackblitz: https://stackblitz.com/edit/angular-hfqx8a Testable through the folowwing URL: https://angular-hfqx8a.stackblitz.io?test=123

但结果，queryParam "test" 首先为空，然后取正确的值 (123)，请参阅控制台输出:

But as a result, the queryParam "test" is firstly null and then it take the correct value (123), see console output:

ParamsAsMap {params: {…}}
    keys: Array(0)
    params: {}
    __proto__: Object
param test = null
Angular is running in the development mode. Call enableProdMode() to enable the production mode.
ParamsAsMap {params: {…}}
    keys: Array(1)
    params: {test: "123"}
    __proto__: Object
param test = 123

=> 为什么第一个控制台输出为空，然后控制台输出具有正确的 queryParam 值?

=> Why there is a first console output empty and then the console output with the correct queryParam value ?

经过几次研究后，我不明白发生了什么:-(

After several researsh I don't reach to understand what's going on :-(

=> 预先感谢您的帮助

=> Thanks in advance for your help

问候

感谢 Dimanoid 和 Pravin Pokharkar，我明白了我的问题.=> 因为组件是在应用实际路由之前加载的！！！

Thanks to Dimanoid and Pravin Pokharkar, I understood my issue. => Because component is loaded before the actual routing applied!!!

因此我更新了我的代码，现在我正确地收集了查询参数:

Thus I have update my code an now I properly collect the queryparams:

this.router.events.subscribe(
  (event: RouterEvent) => {
    if (event instanceof NavigationEnd) {
        this.test = parseInt(
              this.activatedRoute.snapshot.queryParamMap.get('test')
        );
    }
  }
);

推荐答案

因为在应用实际路由之前加载组件.将 { enableTracing: true } 添加到 RouterModule 以查看幕后发生的事情.

Because component is loaded before the actual routing applied. Add { enableTracing: true } to the RouterModule to see what is happening behind the scene.

RouterModule.forRoot([], { enableTracing: true })

https://stackblitz.com/edit/angular-boghpy?file=src/app/app.module.ts

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