Angular의 지시문, 파이프 및 서비스에 대한 심층 분석

<div *ngIf="data.length == 0">没有更多数据</div>

<div *ngIf="data.length > 0; then dataList else noData"></div>
<ng-template #dataList>课程列表</ng-template>
<ng-template #noData>没有更多数据</ng-template>

<div [hidden]="data.length === 0">没有更多数据</div>

interface List {
  id: number
  name: string
  age: number
}

list: List[] = [
  { id: 1, name: "张三", age: 20 },
  { id: 2, name: "李四", age: 30 }
]

<!--  
    i: 索引
    isEven: 是否为偶数行
    isOdd: 是否为奇数行
    isFirst: 是否是第一项
    isLast: 是否是最后一项
-->
<li
    *ngFor="
      let item of list; 
      let i = index;
      let isEven = even;
      let isOdd = odd;
      let isFirst = first;
      let isLast = last;
    "
></li>

<li *ngFor="let item of list; trackBy: identify"></li>

identify(index, item){
  return item.id; 
}

<div [appHover]="{ bgColor: &#39;skyblue&#39; }">Hello Angular</div>

$ ng g d appHover
# 全称 ng generate directive

import { AfterViewInit, Directive, ElementRef, HostListener, Input } from "@angular/core"

// 接收参的数类型
interface Options {
  bgColor?: string
}

@Directive({
  selector: "[appHover]"
})
export class HoverDirective implements AfterViewInit {
  // 接收参数
  @Input("appHover") appHover: Options = {}
  // 要操作的 DOM 节点
  element: HTMLElement
  // 获取要操作的 DOM 节点
  constructor(private elementRef: ElementRef) {
    this.element = this.elementRef.nativeElement
  }
  // 组件模板初始完成后设置元素的背景颜色
  ngAfterViewInit() {
    this.element.style.backgroundColor = this.appHover.bgColor || "skyblue"
  }
  // 为元素添加鼠标移入事件
  @HostListener("mouseenter") enter() {
    this.element.style.backgroundColor = "pink"
  }
  // 为元素添加鼠标移出事件
  @HostListener("mouseleave") leave() {
    this.element.style.backgroundColor = "skyblue"
  }
}

<p>{{ date | date: "yyyy-MM-dd" }}</p>

// summary.pipe.ts
import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
   name: 'summary' 
});
export class SummaryPipe implements PipeTransform {
    transform (value: string, limit?: number) {
        if (!value) return null;
        let actualLimit = (limit) ? limit : 10;
        return value.substr(0, actualLimit) + '...';
    }
}

// app.module.ts
import { SummaryPipe } from './summary.pipe'
@NgModule({
    declarations: [SummaryPipe] 
});

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

@Injectable({
  providedIn: 'root'
})

export class CarListService {
}

import { Injectable } from '@angular/core';
import { CarModule } from './car.module';

@Injectable({
  providedIn: CarModule,
})

export class CarListService {
}

import { CarListService } from './car-list.service';

@NgModule({
  providers: [CarListService],
})
export class CarModule {
}

import { Component } from '@angular/core';
import { CarListService } from '../car-list.service.ts'

@Component({
  selector:    'app-car-list',
  templateUrl: './car-list.component.html',
  providers:  [ CarListService ]
})