Angular 角度7视图儿童投掷错误，无法识别模态

我试图使用@viewchild，但我一直收到一个错误：

import {Component, ElementRef, Input, ViewChild} from '@angular/core';
import {ActivatedRoute, Router} from '@angular/router';
import {ApiService} from '../../../api.service';
import { Category } from '../../../category';

@Component({
  selector: 'app-add-category',
  templateUrl: './add-category.component.html',
  styleUrls: ['./add-category.component.scss']
})
export class AddCategoryComponent {
  @Input() category = new Category();
  public id: string;

  constructor(private route: ActivatedRoute, private router: Router, private data: ApiService) {}
  onSubmit() {
    @ViewChild('submitModal') modal;
    this.id = this.route.snapshot.paramMap.get('id');
    this.category.company = '5c5392a3bc107f4452ee222f';
    this.data.postCategory(this.category).subscribe(data => {
      console.log(data);
    }, (err) => {
      console.log(err);
    });
  }
}

错误：

错误TS1146:需要声明

我试图使用@viewChild获取Dom元素，然后在提交时关闭一个模态

@viewChild'submitModal'模态；是您在方法中声明的属性，它不会以这种方式工作。您应该在方法外部和类内部声明一个属性

export class AddCategoryComponent {
  @Input() category = new Category();
  public id: string;
  @ViewChild('submitModal') modal; //declare properties inside class, outside methods

  constructor(private route: ActivatedRoute, private router: Router, private data: ApiService) {}
  onSubmit() {

    this.id = this.route.snapshot.paramMap.get('id');
    this.category.company = '5c5392a3bc107f4452ee222f';
    this.data.postCategory(this.category).subscribe(data => {
      console.log(data);
    }, (err) => {
      console.log(err);
    });
  }
}

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显示完整的ts代码相关@PrashantPimpaledone@Input类别=新类别@ViewChild'submitModal'模态；