"Expression has changed after it was checked" 的控制台错误

Question

我的父组件中有一个 div，它根据使用 [ngClass] 的某些条件应用不同的 css 类，并根据来自的输出装饰器检查该条件的值子组件和我面临以下控制台错误：

我的父组件html div:-

 <div [ngClass]="{'alerton1': isAlertClass1 ,'alerton2': isAlertClass2,'alerton3': isAlertClass3,'alerton4': isAlertClass4,
        'alerton5': isAlertClass5,'alerton6': isAlertClass6 ,'alerton7': isAlertClass7, 'alertoff': isAlertClass}">

 <!-- top navbar-->
 <app-header class="topnavbar-wrapper"(activityData)="GetActivityDetail($event)"></app-header>

我的父组件Ts代码：-

GetActivityDetail(classname) {
        switch (classname) {
            case '1': {
                this.isAlertClass1 = true;
                this.isAlertClass2 = false;
                this.isAlertClass3 = false;
                this.isAlertClass4 = false;
                this.isAlertClass5 = false;
                this.isAlertClass6 = false;
                this.isAlertClass7 = false;
                this.isAlertClass = false;
                break;
            }
            case '2': {
                this.isAlertClass1 = false;
                this.isAlertClass2 = true;
                this.isAlertClass3 = false;
                this.isAlertClass4 = false;
                this.isAlertClass5 = false;
                this.isAlertClass6 = false;
                this.isAlertClass7 = false;
                this.isAlertClass = false;
                break;
            }
           default: {
                this.isAlertClass = true;
                this.isAlertClass1 = false;
                this.isAlertClass2 = false;
                this.isAlertClass3 = false;
                this.isAlertClass4 = false;
                this.isAlertClass5 = false;
                this.isAlertClass6 = false;
                this.isAlertClass7 = false;
                break;
            }
}

我的子组件条件代码：-

switch (i) {
            case 1: {
                this.activityData.emit('1');
                break;
            }
            case 2: {
                this.activityData.emit('2');
                break;
            }
     default: {
                this.activityData.emit('0');
                break;
            }
}

Answer 1

您可以使用 ChangeDetectorRef Base class

它提供变化检测功能。变更检测树收集要检查变更的所有视图。使用这些方法在树中添加和删除视图，启动更改检测，并将视图显式标记为脏视图，这意味着它们已更改并需要重新呈现。

import { ChangeDetectorRef } from '@angular/core';

constructor(protected cdr: ChangeDetectorRef) {}

ngOnInit() {
   this.cdr.detectChanges();
}

"Expression has changed after it was checked" 的控制台错误

console error for "Expression has changed after it was checked"

javascript

angular7