ChangeDetectionStrategy 无法正常工作

Question

我正在使用离子 2

这是我的代码：

<div class="messagesholder" 
      *ngFor="let chat of chatval | orderby:'[date]'; let i = index;let first=first;let last = last;">
           {{last ? callFunction() : ''}} 

       <div *ngIf="chat.sender == currentuser || chat.receiver == currentuser" >
       {{checkdate(chat.date)}} 
       <p class="chat-date"  id="abc" #abc>{{msgdate | amDateFormat:'LL'}}</p>

     </div> 

这是我的checkdate 函数：

checkdate(date)
  {
    var res = date.split(" ");
    var A=res[0];
    var local=localStorage.getItem('chatdate');
    this.msgdate="";
    if(local === undefined || local === null)
    {
      this.msgdate=A;
      localStorage.setItem('chatdate',this.msgdate);

    }
    else if(local !== undefined)
    {
      console.log(local != A);
      if(local != A)
      {

        this.msgdate = A;
         localStorage.setItem('chatdate',this.msgdate);
      }
    }

   }

    callFunction(){
    this.content.scrollToBottom(0)
  }

这是工作。但是我收到了这个错误。

FIREBASE WARNING: Exception was thrown by user callback. Error: Expression has changed after it was checked. Previous value: 'April 10, 2017'. Current value: ''.

因为我通过在我的代码中包含这些行来完成这项工作：

import {  Component, ChangeDetectionStrategy } from '@angular/core';
@Component({
  changeDetection: ChangeDetectionStrategy.OnPush,
  selector: 'page-chat',
  templateUrl: 'chat.html',
  
})

现在。我没有收到错误消息。但内容不显示。

我安慰了chatval。它很好。但它没有显示任何价值。

在我去后退按钮的同时，内容显示一秒。

如果我删除ChangeDetectionStrategy，

我再次收到此错误消息

FIREBASE WARNING: Exception was thrown by user callback. Error: Expression has changed after it was checked. Previous value: 'April 10, 2017'. Current value: ''.

为什么使用ChangeDetectionStrategy？ UI 值不显示。

Answer 1

说真的，您正在修改模型经过检查后的状态。如果没有绑定到变量，您不应该这样做。删除

this.msgdate="";