在Angular 7中渲染组件之前加载数据 [英] Load data before rendering component in Angular 7

问题描述

在渲染组件之前，我试图从服务中恢复数据，但出现此错误:TypeError:无法读取未定义的属性'dataEntries'

I tried to recuperate data from service before rendering my component but i have this error: TypeError: Cannot read property 'dataEntries' of undefined

这是我的代码:

ngOnInit() {
 this.route.params.subscribe((params:Params)=>{
  this.ActivityId=params['id']
 })
 this.activityInstanceIdentifier= {
  "class":"eu.w4.engine.client.bpmn.w4.runtime.ActivityInstanceIdentifier",
  "id":this.ActivityId
 }
 this.activityInstanceAttachement= {
  "class":"eu.w4.engine.client.bpmn.w4.runtime.ActivityInstanceAttachment",
  "dataEntriesAttached":true
 }
this.activityService.getActivityInstance(this.sessionService.getPrincipal(),
                                         this.activityInstanceIdentifier,
                                         this.activityInstanceAttachement)
                                        .subscribe((ActivityInstance)=>{
                                          this.dataInstance=ActivityInstance                                 
                                        });
 }

forms = [
 {
  dataEditionMode:DataEditionMode.DISPLAY,
  name:"demande",
  editedInstance:this.dataInstance["dataEntries"]["demande"]["value"],
  component:DemandeFormComponent,
  multiple:false
 }
]

我也尝试使用'resolve'，但是它不起作用，有帮助吗?

I tried to use 'resolve' also but it doesn't work , any help ?

推荐答案

JS是异步的.这意味着它不会等待任何I/O请求完成后，将继续执行下一行代码.

JS is Asynchronous. Which means it won't wait for any I/O request to get complete and will keep executing next lines of code.

在您的情况下， getActivityInstance 方法是异步的，因此JS不会等待它完成，它将执行下一行.因此

In you case getActivityInstance method is asynchronous hence JS won't wait for it to get complete and it will execute the next line . Hence

editedInstance:this.dataInstance ["dataEntries"] ["demande"] ["value"] 在服务返回数据之前执行(此时 dataInstance 将是 undefined (如果尚未初始化).

editedInstance : this.dataInstance["dataEntries"]["demande"]["value"] gets executed before service returns the data (that time dataInstance will be undefined if you haven't initialized it) .

像这样修改您的代码:

this.activityService.getActivityInstance(this.sessionService.getPrincipal(),
                                         this.activityInstanceIdentifier,
                                         this.activityInstanceAttachement)
                                        .subscribe((ActivityInstance)=>{
                                          this.dataInstance=ActivityInstance;

 forms = [
 {
  dataEditionMode:DataEditionMode.DISPLAY,
  name:"demande",
  editedInstance:this.dataInstance["dataEntries"]["demande"]["value"],
  component:DemandeFormComponent,
  multiple:false
 }
]
  });

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