How to stop the reader and turn off the camera

[DarrenWainwright]

Using: "@zxing/browser": "0.0.5"
Codebase: TypeScript project using lit-element

Hello,

I'm trying to implement this browser version of the library in a small UI to scan PDF417 barcodes.

I am having a hard time understanding how to stop listening/scanning/reading and turning the camera off.

In the /library version I see I can call stop() on the reader, though it doesn't appear to be available in this browser version for both types of VideoDevice decodes.

These pieces of code are lifted from the overall solution I'm trying to build.

In this first snippet I'm trying to decode once.

In this case, how can I stop the stream and turn off the camera - like a reset

  async decodeOnce(codeReader: BrowserPDF417Reader, selectedDeviceId: string){
    const videoElem = this.shadowRoot?.getElementById('video');    
    codeReader.decodeOnceFromVideoDevice(selectedDeviceId, videoElem).then((result) =>{
      console.log(result); 
    }).catch( (reason) => {
          console.log(reason);
    });
  }

In the DecodeContinously I can grab controls to stop the stream. I can now call this.controls.stop()

async decodeContinuously(codeReader: BrowserPDF417Reader, selectedDeviceId: string) {
   const videoElem = this.shadowRoot?.getElementById('video');
   this.controls =  await codeReader.decodeFromVideoDevice(selectedDeviceId, videoElem, (result, error, controls)=>{
     if (result){
       console.log(result);
     }
     // TODO - handle exceptions
   });
}

How to we properly turn off the camera and stop listening in the decodeOnce version?

[odahcam]

BRUH

There isn't a way for doing that!

Why?

Because I designed it for being stopable by Prosime cancellation, but then I discovered that in JS there isn't such API. (...)

Here's how it's written by now:

browser/src/readers/BrowserCodeReader.ts

Lines 965 to 999 in 90929d6

	public scanOneResult(
	element: HTMLVisualMediaElement,
	retryIfNotFound = true,
	retryIfChecksumError = true,
	retryIfFormatError = true,
	): Promise<Result> {
	return new Promise((resolve, reject) => {
	// reuses the scan API, but returns at the first successful result
	this.scan(element, (result, error, controls) => {
	if (result) {
	// good result, returning
	resolve(result);
	controls.stop();
	return;
	}
	if (error) {
	// checks if it should retry
	if (error instanceof NotFoundException && retryIfNotFound) { return; }
	if (error instanceof ChecksumException && retryIfChecksumError) { return; }
	if (error instanceof FormatException && retryIfFormatError) { return; }
	// not re-trying
	controls.stop(); // stops scan loop
	reject(error); // returns the error
	}
	});
	});
	}

So... I would say you should use the continuously decoding APIs for having full control over tha scanning proccess.

[odahcam]

Related to #17

[DarrenWainwright]

@odahcam - Thanks. I've since removed all async/await items.

Stopped the camera dying, but now being killed by the TypeError.

I've also since moved over to the BrowserMultiFormatReader to read PDF417 and it seems less brittle - no idea why..

[odahcam]

Yeah, that is a PDF417 Reader error, I think we should move this conversation to #23 then.

[thisconnect]

Because I designed it for being stopable by Prosime cancellation, but then I discovered that in JS there isn't such API. (...)

Now there is the AbortController, but might not work everywhere

• https://developer.mozilla.org/en-US/docs/Web/API/AbortController
• https://caniuse.com/abortcontroller
• https://www.npmjs.com/package/abort-controller

[odahcam]

Nice, I think we can do similar implementation in here.

[thisconnect]

Althoug I never liked the AbortController, just codeReader.reset() would be nice if it is possible.

[odahcam]

It was a bad design, hard to maintain and father of many bugs, it won't come back. Instead we will create a simpler and elegant solution for this. When I have some free time, of course, or some kind soul sends a PR.

[piechoo]

Could we reopen this issue ? It's still a problem and I assume it can be implemented via abortController :)