Angular7 - 事件绑定

在本章中，无涯教程将讨论事件绑定在Angular 7中的工作方式，当用户以键盘移动，鼠标单击或鼠标悬停的形式与应用程序交互时，它将生成一个事件。需要处理这些事件以执行某种操作，让无涯教程考虑一个示例以更好地理解这一点。

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，无涯教程定义了一个按钮，并使用click事件为其添加了一个函数。

以下是定义按钮并为其添加函数的语法。

(click)="myClickFunction($event)"

该函数在: app.component.ts 中定义

无涯教程网

import { Component } from '@angular/core';
@Component({
   selector: 'app-root',
   templateUrl: './app.component.html',
   styleUrls: ['./app.component.css']
})
export class AppComponent {
   title='Angular 7';
   
   //declared array of months.
   months=["January", "February", "March", "April", "May","June", "July", 
      "August", "September", "October", "November", "December"];
   
   isavailable=true; //variable is set to 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);
   }
}

单击按钮后，控件将转到函数 myClickFunction ，然后将出现一个对话框，其中显示已单击按钮，如以下屏幕截图所示-

按钮的样式添加在add.component.css中-

button {
   background-color: #2B3BCF;
   border: none;
   color: white;
   padding: 10px 10px;
   text-align: center;
   text-decoration: none;
   display: inline-block;
   font-size: 20px;
}

现在让无涯教程将onchange事件添加到下拉列表中，以下代码行将帮助您将change事件添加到下拉列表中-

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 (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>
<br/>

<button (click)="myClickFunction($event)">
   Click Me
</button>

该函数在 app.component.ts 文件中声明-

import { Component } from '@angular/core';
@Component({
   selector: 'app-root',
   templateUrl: './app.component.html',
   styleUrls: ['./app.component.css']
})
export class AppComponent {
   title='Angular 7';
   
   //declared array of months.
   months=["January", "Feburary", "March", "April", "May", "June", "July", 
      "August", "September", "October", "November", "December"];
   
   isavailable=true; //variable is set to 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) {
      console.log("Changed month from the Dropdown");
      console.log(event);
   }
}

从下拉列表中选择月份，您会在控制台中看到控制台消息" Changed month from the Dropdown"以及事件。

当下拉列表中的值更改时，让无涯教程在 app.component.ts 中添加警报消息，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 7'; 
   
   //declared array of months. 
   months=["January", "February", "March", "April", "May", "June", "July", 
      "August", "September", "October", "November", "December"]; 
   
   isavailable=true; //variable is set to 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");
   } 
}

更改下拉列表中的值时，将出现一个对话框，并显示以下消息:

"Changed month from the Dropdown"。