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Angular7 Templates

Angular7 Templates

Now let's use the prototype together with the condition if else, and see the efficiency.

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)" name = "month">
      <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 from template</ng-template>
   <ng-template #condition2>Condition is invalid from template</ng-template>
</div>
<button (click) = "myClickFunction($event)">Click Me</button>

We've inserted the if statement with the other condition for the Span tag, and will call condition1 example, otherwise condition2.

The templates are to be numbered accordingly –


<ng-template #condition1>Condition is valid from template</ng-template> 
<ng-template #condition2>Condition is invalid from template</ng-template>

If the condition is true, then the template of condition1 is called, otherwise of condition2.

app.component.ts


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 = false; // 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"); 
   } 
}

Isavailable variable is false so the template condition2 is printed. When you press the button it will call the respective template.

app.component.ts


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 = false; //variable is set to true  
   myClickFunction(event) { 
      this.isavailable = !this.isavailable; 
      // variable is toggled onclick of the button 
   } 
   changemonths(event) {
      alert("Changed month from the Dropdown"); 
   }
}

The isavailable variable is toggled on click of the button as shown below −


myClickFunction(event) { 
   this.isavailable = !this.isavailable; 
}

While we have added the span tag and the <ng-template> for the condition in app.component.html as shown below


<span *ngIf = "isavailable;then condition1 else condition2">
   Condition is valid.
</span> 
<ng-template #condition1>Condition is valid from template</ng-template>
<ng-template #condition2>Condition is invalid from template</ng-template>

As we inspect the same in browser, we don't see the span tag and even the <ng-template> in the dom structure.

The following line of html code will help us to get the span tag in the dom –


<!--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)" name = "month"> 
      <option *ngFor = "let i of months">{{i}}</option>
   </select> 
</div> 
<br/>

<div> 
   <span *ngIf = "isavailable; else condition2">
      Condition is valid.
   </span>
   <ng-template #condition1>Condition is valid from template </ng-template> 
   <ng-template #condition2>Condition is invalid from template</ng-template> 
</div>
<button (click) = "myClickFunction($event)">Click Me</button>

If we delete the condition then we get the message "Condition is valid" in the browser and the span tag is also available in the dom. For example we have made the isavailable variable true in app.component.ts.