如何限制 ngFor 重复 Angular 中的某些项目?

问题描述 投票:0回答:9

我的代码:

<li *ngFor="let item of list; let i=index" class="dropdown-item" (click)="onClick(item)">
  <template [ngIf]="i<11">{{item.text}}</template>
</li>

我试图在任何时候只显示 10 个列表元素。正如 answer here 中所建议的,我使用了

*ngIf
但这会导致页面上显示空列表项(超过 10 个)。

angular
9个回答
437
投票

这对我来说似乎更简单:

<li *ngFor="let item of list | slice:0:10; let i=index" class="dropdown-item" (click)="onClick(item)">{{item.text}}</li>

更接近你的方法:

<ng-container *ngFor="let item of list; i as index">
  <li class="dropdown-item" (click)="onClick(item)" *ngIf="i<11">{{item.text}}</li>
</ng-container>

替代方案:

<ng-template ngFor let-item [ngForOf]="list" let-i="index">
  <li class="dropdown-item" (click)="onClick(item)" *ngIf="i<11">{{item.text}}</li>
</ng-template>

38
投票

您可以直接将

slice()
应用于变量。 StackBlitz 演示

<li *ngFor="let item of list.slice(0, 10);">
   {{item.text}}
</li>

35
投票

例如,假设我们只想显示数组的前 10 项,我们可以使用 SlicePipe 来完成此操作,如下所示:

<ul>
     <li *ngFor="let item of items | slice:0:10">
      {{ item }}
     </li>
</ul>

12
投票

您可以通过应用三元运算符动态限制

*ngFor

示例 1 -

<div *ngFor="let item of (showAllFlag ? list : list.slice(0,2))" >
</div>

10
投票

这个效果非常好:

<template *ngFor="let item of items; let i=index" >
 <ion-slide *ngIf="i<5" >
  <img [src]="item.ItemPic">
 </ion-slide>
</template>

4
投票

除了@Gunter的答案之外,您还可以使用trackBy来提高性能。 trackBy 接受一个有两个参数的函数:index 和 item。您可以从函数返回对象中的唯一值。它将停止重新渲染 ngFor 中已显示的项目。在您的 html 中添加 trackBy 如下。

<li *ngFor="let item of list; trackBy: trackByFn;let i=index" class="dropdown-item" (click)="onClick(item)">
  <template [ngIf]="i<11">{{item.text}}</template>
</li>

并在 .ts 文件中编写这样的函数。

trackByfn(index, item) { 
  return item.uniqueValue;
}

0
投票

html

<table class="table border">
    <thead>
        <tr>
            <ng-container *ngFor="let column of columns; let i = index">
                <th>{{ column }}</th>
            </ng-container>
        </tr>
    </thead>
    <tbody>
        <tr *ngFor="let row of groups;let i = index">
            <td>{{row.name}}</td>
            <td>{{row.items}}</td>
            <td >
                <span class="status" *ngFor="let item of row.Status | slice:0:2;let j = index">
                    {{item.name}}
                   </span><span *ngIf = "i < 2" class="dots" (mouseenter) ="onHover(i)" (mouseleave) ="onHover(-1)">.....</span> <span [hidden] ="test" *ngIf = "i == hoverIndex" class="hover-details"><span  *ngFor="let item of row.Status;let j = index">
                    {{item.name}}
                   </span></span>
           </td>

        </tr>
  </tbody>
</table>

<p *ngFor="let group of usersg"><input type="checkbox" [checked]="isChecked(group.id)" value="{{group.id}}" />{{group.name}}</p>

<p><select [(ngModel)]="usersr_selected.id">
   <option *ngFor="let role of usersr" value="{{role.id}}">{{role.name}}</option> 
</select></p>

打字稿

import { Component, OnInit } from '@angular/core';
import { CommonserviceService } from './../utilities/services/commonservice.service';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';
@Component({
  selector: 'app-home',
  templateUrl: './home.component.html',
  styleUrls: ['./home.component.css']
})
export class HomeComponent implements OnInit {
  getListData: any;
 dataGroup: FormGroup;
 selectedGroups: string[];
    submitted = false;
    usersg_checked:any;
    usersr_selected:any;
    dotsh:any;
    hoverIndex:number = -1;
    groups:any;
    test:any;
 constructor(private formBuilder: FormBuilder) {


     }
     onHover(i:number){
 this.hoverIndex = i;
}
     columns = ["name", "Items","status"];

public usersr = [{
    "id": 1,
    "name": "test1"

}, {
    "id": 2,
    "name": "test2",

}];


  ngOnInit() {
      this.test = false;
      this.groups=[{
        "id": 1,
        "name": "pencils",
        "items": "red pencil",
        "Status": [{
            "id": 1,
            "name": "green"
        }, {
            "id": 2,
            "name": "red"
        }, {
            "id": 3,
            "name": "yellow"
        }],
        "loc": [{
            "id": 1,
            "name": "loc 1"
        }, {
            "id": 2,
            "name": "loc 2"
        }, {
            "id": 3,
            "name": "loc 3"
        }]
    },
    {
        "id": 2,
        "name": "rubbers",
        "items": "big rubber",
        "Status": [{
            "id": 1,
            "name": "green"
        }, {
            "id": 2,
            "name": "red"
        }],
        "loc": [{
            "id": 1,
            "name": "loc 2"
        }, {
            "id": 2,
            "name": "loc 3"
        }]
    },
    {
        "id": 3,
        "name": "rubbers1",
        "items": "big rubber1",
        "Status": [{
            "id": 1,
            "name": "green"
        }],
        "loc": [{
            "id": 1,
            "name": "loc 2"
        }, {
            "id": 2,
            "name": "loc 3"
        }]
    }

];

      this.dotsh = false;

      console.log(this.groups.length);

this.usersg_checked = [{
    "id": 1,
    "name": "test1"

}, {
    "id": 2,
    "name": "test2",

}];

 this.usersr_selected = {"id":1,"name":"test2"};;

this.selectedGroups = [];
this.dataGroup = this.formBuilder.group({
            email: ['', Validators.required]
});
  }

  isChecked(id) {
   console.log(this.usersg_checked);
  return this.usersg_checked.some(item => item.id === id);
}
 get f() { return this.dataGroup.controls; }
onCheckChange(event) {
  if (event.target.checked) {
 this.selectedGroups.push(event.target.value);
} else {
 const index = this.selectedGroups.findIndex(item => item === event.target.value);
 if (index !== -1) {
  this.selectedGroups.splice(index, 1);
}
}
}

   getFormData(value){
      this.submitted = true;

        // stop here if form is invalid
        if (this.dataGroup.invalid) {
            return;
        }
      value['groups'] = this.selectedGroups;
      console.log(value);
  }


}

CSS

.status{
    border: 1px solid;
    border-radius: 4px;
    padding: 0px 10px;
    margin-right: 10px;
}
.hover-details{
    position: absolute;


    border: 1px solid;
    padding: 10px;
    width: 164px;
    text-align: left;
    border-radius: 4px;
}
.dots{
    position:relative;
}

0
投票
 <div *ngFor="let item of list;trackBy: trackByFunc" >
   {{item.value}}
 </div>

在你的 ts 文件中

 trackByFunc(index, item){
    return item ? item.id : undefined;
  }

0
投票

我发现下面是很好的方法

<ul class="list-group col-auto" *ngFor="let result of searchResults.slice(0,10)">
                    <li class="list-group-item">
                        <b>{{result.name}}</b>
                        <p>{{result.email}}</p>
                        <p>{{result.body | slice:0:64}}</p>
                    </li>
                </ul>
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