javascript - 无法使用自定义过滤器管道读取未定义的属性 '0'

Question

因为我已经为数组创建并添加了自定义过滤器管道，所以在加载 View 时出现此异常:

TesttypesListComponent - inline template:35:14 caused by: Cannot read property '0' of undefined

这一定与我加载数据的方式有关。

在我添加之前，管道数据加载成功了!

我可以在管道中放置一个断点，但它永远不会因为错误而在内部命中。

有人知道我的第一个 pipe 哪里做错了吗？

管道

从 '@angular/core' 导入 { Pipe, PipeTransform };

@Pipe({
    name: 'TestTypePipe'
})
export class TestTypePipe implements PipeTransform {
    transform(testTypes, args?) {
        let [currentSubject, currentSchoolclass] = args;
        if (!currentSubject || !currentSchoolclass) {
            return [];
        }
        else {
            return testTypes.filter(s => {
                return s.subjectId == currentSubject.subjectId && s.schoolclassId == currentSchoolclass.schoolclassId;
            });
        }
    }
}

HTML

  <tbody>
          <tr *ngFor="let t of testTypes | TestTypePipe:currentSubject:currentSchoolclass; let i = index">
            <template [ngTemplateOutlet]="getTemplate(t)" [ngOutletContext]="{ $implicit: t, index: i }"></template>
          </tr>
        </tbody>

组件

  currentSubject: Subject;
  currentSchoolclass: Schoolclass;

      ngOnInit() {
this.route.params.subscribe(params => { this.schoolyearId = parseInt(params['id']); });

        this.testService.getTestTypes(this.schoolyearId).subscribe(data => {
          this.schoolclasses = data.schoolclasses.map(m => new Schoolclass(m));
          this.subjects = data.subjects.map(m => new Subject(m));

          for (let t of data.testTypes) {
            t.viewMode = ViewMode.Displaying;
            let testType = new AssignedTestType(t);
            this.testTypes.push(testType)
          }
        }

);

Answer 1

Pipe#transform 采用可选的顶级参数，而不是单个 args: []。

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
    name: 'TestTypePipe'
})
export class TestTypePipe implements PipeTransform {
    transform(testTypes, ...args) {
        let [currentSubject, currentSchoolclass] = args;
        if (!currentSubject || !currentSchoolclass) {
            return [];
        }
        else {
            return testTypes.filter(s => {
                return s.subjectId == currentSubject.subjectId && s.schoolclassId == currentSchoolclass.schoolclassId;
            });
        }
    }
}