如果不起作用。即使我做 *ngIf= "true"它也没有显示，*ngIf= 也不会显示"false"

Question

如果某个变量是null，我想隐藏一个div，但即使我直接分配true，*ngIf也不起作用。

tree.component.ts

import { Component, OnInit } from '@angular/core';
import { Tree} from '../model/tree';
import { TreeService } from '../service/tree.service';
@Component({
selector: 'app-tree',
templateUrl: './tree.component.html',
styleUrls: ['./tree.component.css']
})
export class TreeComponent implements OnInit {
canShow: boolean = true;
tree!: Tree;
constructor(private treeService:TreeService) {
}
ngOnInit(): void {
this.tree= this.treeService.returnTree();
}
}

tree.component.html

...
<div *ngIf="canShow">
<h1 class="sm:text-2xl font-medium mb-2 text-gray-900">Significado dos nomes populares</h1>
<p class="pb-3 leading-relaxed text-gray-500">{{tree.nameMeaning}}</p>
</div>
...

tree.component.html

...
<div *ngIf="true">
<h1 class="sm:text-2xl font-medium mb-2 text-gray-900">Significado dos nomes populares</h1>
<p class="pb-3 leading-relaxed text-gray-500">{{tree.nameMeaning}}</p>
</div>
...

控制台错误：

NG0303: Can't bind to 'ngIf' since it isn't a known property of 'h2'.

psyklotz在链路上的解决方案

我已将TreeComponent导入app.module.ts的@NgModuledeclarations中。

Answer 1

ngIf需要Angular中的CommonModule

将CommonModule安装到组件的父模块中，因为它具有ngIf指令。我没有在你的例子中看到这一点。

import {CommonModule} from '@angular/common';
@NgModule({
imports: [CommonModule]
})