Angular 4 事件绑定
Angular 4 事件绑定
在本节,我们将讨论如何在Angular 4中进行事件绑定。当用户以键盘操作、鼠标点击或鼠标悬停的形式与应用程序交互时,它会生成一个事件,需要有对应的事件处理器来响应操作,这就是所谓的事件绑定。
让我们通过例子来更好地理解事件绑定。
app.component.html
<!--The content below is only a placeholder and can be replaced.--> <div style = "text-align:center"> <h1> Welcome to {{title}}. </h1> </div> <div> Months : <select> <option *ngFor = "let i of months">{{i}}</option> </select> </div> <br/> <div> <span *ngIf = "isavailable; then condition1 else condition2"> Condition is valid. </span> <ng-template #condition1>Condition is valid</ng-template> <ng-template #condition2>Condition is invalid</ng-template> </div> <button (click)="myClickFunction($event)"> Click Me </button>
在app.component.html文件中,我们定义了一个按钮,并给click事件绑定了一个函数。
下面是定义按钮并向其添加函数的语法。
(click)="myClickFunction($event)"
函数在app.component.ts文件中定义。
import { Component } from '@angular/core'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { title = 'Angular 4 Project!'; //array of months. months = ["January", "Feburary", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]; isavailable = true; myClickFunction(event) { //just added console.log which will display the event details in browser on click of the button. alert("Button is clicked"); console.log(event); } }
点击按钮后,控件将执行MyClickFunction,并出现一个对话框,显示点击按钮,如下图所示:
现在让我们将事件绑定给下拉列表中。
以下代码行将帮助您将更改事件添加到下拉列表中:
<!--The content below is only a placeholder and can be replaced.--> <div style = "text-align:center"> <h1> Welcome to {{title}}. </h1> </div> <div> Months : <select (change) = "changemonths($event)"> <option *ngFor = "let i of months">{{i}}</option> </select> </div> <br/> <div> <span *ngIf = "isavailable; then condition1 else condition2"> Condition is valid. </span> <ng-template #condition1>Condition is valid</ng-template> <ng-template #condition2>Condition is invalid</ng-template> </div> <button (click) = "myClickFunction($event)">Click Me</button>
该函数在app.component.ts中声明
import { Component } from '@angular/core'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { title = 'Angular 4 Project!'; //array of months. months = ["January", "Feburary", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]; isavailable = true; myClickFunction(event) { alert("Button is clicked"); console.log(event); } changemonths(event) { console.log("Changed month from the Dropdown"); console.log(event); } }
控制台消息“Changed month from the Dropdown”与事件一起显示在控制台中。
当下拉列表中的值发生变化时,让我们在app.component.ts添加一条警告消息,如下所示:
import { Component } from '@angular/core'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { title = 'Angular 4 Project!'; //array of months. months = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]; isavailable = true; myClickFunction(event) { //just added console.log which will display the event details in browser on click of the button. alert("Button is clicked"); console.log(event); } changemonths(event) { alert("Changed month from the Dropdown"); } }
当下拉列表中的值发生变化时,将出现一个对话框,并显示以下消息:“Changed month from the Dropdown”。