Digital Signature Implementation Using Angular 2 Signature pad
Create A New Angular Project
Use the Angular CLI tool to create an Angular project. Execute the following command to create the project.
– ng new signaturePadProject
– Would you like to add Angular routing? Yes
– Which stylesheet format would you like to use? CSS
What is a SignaturePad?
SignaturePad is used to sign a document digitally using a stylus or mouse cursor pointer. At the end of the document, there will be a box that allows the user to sign the document on a web application. After saving the document the signature gets stored in a base64 type image.
What’s Different Here In Our Blog?
In this blog, we will use angular2-signature pad dependency for the signature pad but the signature pad returns the base64 URL for the image if we wanted the actual image of the signature then what should we do?
Install Signature pad
To install the angular2-signature pad use this command
~ npm I angular2-signature pad
Your package.json will look like this
Now, add go to AppModule.ts file and add SignaturePadModule in imports
Now, in the app.component.ts file add this
@ViewChild(SignaturePad) signaturePad: SignaturePad;
signaturePadOptions = {
minWidth: 2, // used for pen width after writing
canvasWidth: 400, // for canvas width
canvasHeight: 100, // for canvas height
}
Add this in-app component HTML file
n the CSS file add this
Create A Service Image-Conversion
Now we’ll create a new service for Image compression to keep the code of image conversion in one place so that we won’t have to write the code again and again. To generate the image conversion service in the service folder, execute the following command
– ng generate service services/image conversion
This will create an ImageConversionService inside the services folder.
“Also Read — Angular CLI Project Setup”
Update the ImageConversionService
Now, open the image-conversion-service.ts file inside the services folder and make the following changes:
Import {Observable} from ‘rxjs’
We will create a separate method in the image-conversion.service.ts file called convertToImage() that will take base64 as a parameter and this will return an observable of File type. The function will look like
As you can see, it’s showing an error because we are not returning the Observable, so let’s add the functionality to convert the base64 to an image
Here, we are getting an image using the function createImage function in which we have passed the base64 string and that function is returning an image.
CreateImage() function will look like this.
After getting the image from the createImage() function, we are creating a canvas element using the document.createElement(‘canvas’). Using the canvas element we will create a 2D rendering context using the function getContext(‘2d’) as CanvasRenderingContext2D that will return into a new variable ctx.
Using the ctx variable we will create the image and then using the toBlob function we will return the observable of the image.
Your Final Code Will Look Like This
app.module.ts
import { SignaturePadModule } from ‘angular2-signaturepad’;
Imports: [ SignaturePadModule ]
image-conversion.service.ts
import { Observable } from ‘rxjs’;
convertToImage(base64): Observable<File> {
return Observable.create(observer => {
const img = this.createImage(base64);
setTimeout(() => {
const elem = document.createElement(‘canvas’);
const ctx = elem.getContext(‘2d’) as CanvasRenderingContext2D;
ctx.drawImage(img, 0, 0, 400, 100);
ctx.canvas.toBlob(
blob => {
observer.next(
new File([blob], ‘Digital Signature.png’, {
type: ‘image/png’,
lastModified: Date.now(),
}),
);
},
‘image/png’,
);
});
});
}
createImage(ev) {
const imageContent = ev;
const img = new Image();
img.src = imageContent;
return img;
}
app.component.ts
import { Component, ViewChild } from ‘@angular/core’;
import { SignaturePad } from ‘angular2-signaturepad’;
import { ImageConversionService } from ‘./services/image-conversion.service’;
@ViewChild(SignaturePad) signaturePad: SignaturePad;
signaturePadOptions = {
minWidth: 2,
canvasWidth: 400,
canvasHeight: 100,
};
constructor(private imageConversionService: ImageConversionService) { }
drawComplete(): void {
}
clearSignature(): void {
this.signaturePad.clear();
}
drawStart(): void {
// will be notified of szimek/signature_pad’s onBegin event
}
save(): void {
const base64 = this.signaturePad.toDataURL();
this.imageConversionService.convertToImage(base64).subscribe(image => {
const img = image;
console.log(img);
});
}
“Also Read — Angular 11 + Firebase Cloud Messaging Push Notifications“app.component.html
<div>
<signature-pad [options]=”signaturePadOptions” (onBeginEvent)=”drawStart()” (onEndEvent)=”drawComplete()”>
</signature-pad>
</div>
<div>
<button class=”btn clear” (click)=”clearSignature()”>Clear</button> <button class=”btn save”
(click)=”save()”>Save</button>
</div>
app.component.css
.btn {color: white;
height: 30px;
width: 70px;
border-radius: 4px;
cursor: pointer;
}
.save {
background-color: deepskyblue;
border: 1px solid deepskyblue;
}
.clear {
background-color: red;
border: 1px solid red;
margin-right: 20px;
margin-left: 14px;
}
:host ::ng-deep canvas {
border-style: dashed;
border-width: 1px;
margin-bottom: 20px;
margin-left: 15px;
}
Originally published at https://www.devstringx.com on June 06, 2022
