Ionic cordova-plugin-qrscanner has no camera preview

There is a div, with class=“nav-decor”, which has a black background, this needs to be changed to transparent.

I changed 3 things to transparent for the camera to show: ion-app, ion-content and .nav-decor

My solution was to have a “cameraView” class, which would set the ion-app, ion-content and .nav-decor to have a transparent background.

I used this CSS

ion-app.cameraView, ion-app.cameraView ion-content, ion-app.cameraView .nav-decor {
  background: transparent none !important; 
}

And then these functions to show the camera after qrScanner.show() and hide it after I’m finished scanning

showCamera() {    
  (window.document.querySelector('ion-app') as HTMLElement).classList.add('cameraView');
}
hideCamera() {    
  (window.document.querySelector('ion-app') as HTMLElement).classList.remove('cameraView');
}

In top level index.html:

<ion-app style="background: none transparent;"></ion-app>

In camera display page html file:

<ion-content style="background: none transparent;">

After some research even i found the answer and surely this works fantastic for all ,but @nokeieng answer helped me too..

1) First, make a new component for qrscanner. In ionic there is a lifecycle in ionic so go according to that after entering the component this event trigger ionViewDidEnter().In this event the camera opens and let you scan.

 ionViewDidEnter(){
     this.qrScanner.prepare()
    .then((status: QRScannerStatus) => {
      if (status.authorized) {
        // camera permission was granted

        var camtoast = this.toastCtrl.create({
          message: 'camera permission granted',
          duration: 1000
        });
        camtoast.present();
        // start scanning

        this.qrScanner.show()
        window.document.querySelector('ion-app').classList.add('cameraView');

        let scanSub = this.qrScanner.scan().subscribe((text: string) => {

          console.log('Scanned something', text);

          window.document.querySelector('ion-app').classList.remove('cameraView');
          this.qrScanner.hide(); // hide camera preview

          const toast = this.toastCtrl.create({
            message: 'You scanned text is this :'+text,
            duration: 6000
          });
          toast.present();
          scanSub.unsubscribe(); // stop scanning
        });


      } else if (status.denied) {
        const toast = this.toastCtrl.create({
          message: 'camera permission was denied',
          duration: 3000
        });
        toast.present();
        // camera permission was permanently denied
        // you must use QRScanner.openSettings() method to guide the user to the settings page
        // then they can grant the permission from there
      } else {
        const toast = this.toastCtrl.create({
          message: 'You can ask for permission again at a later time.',
          duration: 3000
        });
        toast.present();
        // permission was denied, but not permanently. You can ask for permission again at a later time.
      }
    })
    .catch((e: any) => console.log('Error is', e));

}

2) After this remove the camera class when back button is pressed for that add this code. ionViewWillLeave() will triggers when component is destroyed or left.

ionViewWillLeave(){

  window.document.querySelector('ion-app').classList.remove('cameraView');

}

3) We are done with .ts file. Now we have to make the component and the main element i.e ion-app transparent so that we can see the camera for that we add this css inside theme/variables.scss

ion-app.cameraView ion-nav{opacity:0}

and

ion-app.cameraView,ion-app.cameraView ion-content,ion-app.cameraView .nav-decor,{
background: transparent url("../../assets/imgs/camera_overlay.png") !important;
background-size: 100% 100% !important;}

4) As you can see I have given a background image so that we get a camera overlay preview

and you are done with the code just run this command in terminal to see live changes in ionic

ionic cordova run android --livereload

You just need to toggle the ion-app display between "none" and "block" if the status is authorized.

const ionApp = <HTMLElement>document.getElementsByTagName("ion-app")[0];
                // start scanning
                const scanSub = this.qrScanner.scan().subscribe((link: string) => {
                    ionApp.style.display = "block";

                    this.qrScanner.hide(); // hide camera preview
                    scanSub.unsubscribe(); // stop scanning
                });
                ionApp.style.display = "none";
                this.qrScanner.show();