why when opening opencv the second time the camera doesn't open a window and only the webcam turns on

[bobwatcherx]

i'm making an application. if you scan the QR Code from your cellphone to your laptop's webcam. then it will automatically be filled into the table. And the first attempt was successful. but second try. flet won't open the camera window. and just turn on the webcam light . what are bugs?

my code

from flet import *
import cv2
import pyzbar.pyzbar as pyzbar

def main(page:Page):

	mytable = DataTable(
		columns=[
			DataColumn(Text("name")),
			DataColumn(Text("total_items")),
			DataColumn(Text("price"))
		],
		rows=[]

		)
	def decode_qr(frame):
	    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
	    qr_codes = pyzbar.decode(gray)
	    if len(qr_codes) > 0:
	        qr_data = qr_codes[0].data.decode('utf-8')
	        name, total_items, item_price = qr_data.split('|')
	        price = int(total_items) * int(item_price)
	        

	        cv2.putText(frame, 'found text Qr Guys', (10, 30), cv2.FONT_HERSHEY_SIMPLEX, 0.8, (0, 255, 0), 2, cv2.LINE_AA)
	        print(f"nama:{name} - item_price:{total_items} - price:{price}")
	        
	        mytable.rows.append(
	        	DataRow(
	        		cells=[
	        			DataCell(Text(name)),
	        			DataCell(Text(total_items)),
	        			DataCell(Text(price))

	        		]

	        		)

	        	)
	        page.snack_bar = SnackBar(
	        	Text("Found Qr Code",size=25,
	        		color="white",weight="bold"
	        		),
	        	bgcolor="green"
	        	)
	        page.snack_bar.open = True
	        page.update()


	    cv2.imshow("QR Code Scanner", frame)
	def opencamera(e):
	    cap = cv2.VideoCapture(0)
	    qr_found = False  # inisialisasi variable qr_found
	    while not qr_found:  # loop hanya berjalan jika QR code belum ditemukan
	        ret, frame = cap.read()
	        if ret:
	            decode_qr(frame)
	            if len(mytable.rows) > 0:
	                qr_found = True  # QR code sudah ditemukan, loop berhenti
	        if cv2.waitKey(1) & 0xFF == ord('q'):
	            break
	    cap.release()
	    cv2.destroyAllWindows()


	page.add(
		AppBar(
		title=Text("Datatable camera",size=30,color="white"),
		bgcolor="blue"

		),
	Column([
		Column([
		mytable
		],scroll="always"),


		ElevatedButton("open camera",
		bgcolor="blue",color="white",
		on_click=opencamera
		)
		])

	)
flet.app(target=main)

[iron3oxide]

Do you get any error messages on the second try?

[bobwatcherx]

Do you get any error messages on the second try?

no error. but the webcam window won't open. and just turn on the webcam light only.

[iron3oxide]

Then we'll need to debug.

from flet import *
import cv2
import pyzbar.pyzbar as pyzbar

def main(page:Page):

	mytable = DataTable(
		columns=[
			DataColumn(Text("name")),
			DataColumn(Text("total_items")),
			DataColumn(Text("price"))
		],
		rows=[]

		)
	def decode_qr(frame):
	    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
	    qr_codes = pyzbar.decode(gray)
	    if len(qr_codes) > 0:
	        qr_data = qr_codes[0].data.decode('utf-8')
	        name, total_items, item_price = qr_data.split('|')
	        price = int(total_items) * int(item_price)
	        

	        cv2.putText(frame, 'found text Qr Guys', (10, 30), cv2.FONT_HERSHEY_SIMPLEX, 0.8, (0, 255, 0), 2, cv2.LINE_AA)
	        print(f"nama:{name} - item_price:{total_items} - price:{price}")
	        
	        mytable.rows.append(
	        	DataRow(
	        		cells=[
	        			DataCell(Text(name)),
	        			DataCell(Text(total_items)),
	        			DataCell(Text(price))

	        		]

	        		)

	        	)
	        page.snack_bar = SnackBar(
	        	Text("Found Qr Code",size=25,
	        		color="white",weight="bold"
	        		),
	        	bgcolor="green"
	        	)
	        page.snack_bar.open = True
	        page.update()


	    cv2.imshow("QR Code Scanner", frame)
	def opencamera(e):
	    cap = cv2.VideoCapture(0)
	    if not cap.isOpened():
                print("Failed to open capture.")
	    qr_found = False  # inisialisasi variable qr_found
	    while not qr_found:  # loop hanya berjalan jika QR code belum ditemukan
	        ret, frame = cap.read()
                print(ret)
	        if ret:
	            decode_qr(frame)
	            if len(mytable.rows) > 0:
	                qr_found = True  # QR code sudah ditemukan, loop berhenti
	        if cv2.waitKey(1) & 0xFF == ord('q'):
	            break
	    cap.release()
	    cv2.destroyAllWindows()


	page.add(
		AppBar(
		title=Text("Datatable camera",size=30,color="white"),
		bgcolor="blue"

		),
	Column([
		Column([
		mytable
		],scroll="always"),


		ElevatedButton("open camera",
		bgcolor="blue",color="white",
		on_click=opencamera
		)
		])

	)
flet.app(target=main)

As you can see, I added two print statements that will hopefully give us a bit more information.

[thetrotfreak]

@bobwatcherx , did you get it to work?

Here's what I noticed:

• On my end, the camera opens up fine (any number of times) without any errors.
• But, it starts exhibiting the behavior you described after it fails to unpack the decoded qr_data.
• Since it's a ValueError, I'm assuming that you wrote your code for a specific type of QR, and that decode_qr() works for that type of QR only.
• The QR I tested this on was a QR code generated by Chrome for a webpage.

[thetrotfreak]

This works.

import cv2
import pyzbar.pyzbar as pyzbar

from flet import (
    AppBar,
    Column,
    DataCell,
    DataColumn,
    DataRow,
    DataTable,
    FloatingActionButton,
    FontWeight,
    Page,
    Ref,
    ScrollMode,
    SnackBar,
    Text,
    app,
    colors,
    icons,
)


def main(page: Page):
    snack_bar_text = Ref[Text]()
    mytable = DataTable(
        columns=[
            DataColumn(Text("name")),
            DataColumn(Text("total_items")),
            DataColumn(Text("price")),
        ],
        rows=[],
    )

    def decode_qr(frame):
        cv2.imshow("QR code scanner", frame)

        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        qr_codes = pyzbar.decode(gray)

        if qr_codes:
            qr_data = qr_codes[0].data.decode("utf-8")
            try:
                name, total_items, items_price = qr_data.split("|")
            except ValueError:
                if not page.snack_bar.open:
                    snack_bar_text.current.value = "Invlaid QR Code"
                    page.snack_bar.bgcolor = colors.RED
                    page.snack_bar.open = True
                    page.update()
            else:
                price = int(total_items) * int(items_price)

                # cv2.putText(
                #     frame,
                #     "Found text QR",
                #     (10, 30),
                #     cv2.FONT_HERSHEY_SIMPLEX,
                #     0.8,
                #     (0, 255, 0),
                #     2,
                #     cv2.LINE_AA,
                # )

                mytable.rows.append(
                    DataRow(
                        cells=[
                            DataCell(Text(name)),
                            DataCell(Text(total_items)),
                            DataCell(Text(price)),
                        ]
                    )
                )

                page.snack_bar.open = True
                page.update()
                return True
        return False

    def opencamera(e):
        cap = cv2.VideoCapture(0)

        if cap.isOpened():
            qr_found = False
            while not qr_found:
                ret, frame = cap.read()

                if ret and decode_qr(frame):
                    qr_found = True

                if cv2.waitKey(1) & 0xFF == ord("q"):
                    break

        # release cv2 resources
        cap.release()
        cv2.destroyAllWindows()

    page.add(
        AppBar(
            title=Text(value="Datatable camera", size=32, color=colors.WHITE),
            bgcolor=colors.BLUE,
        ),
        Column(
            controls=[mytable],
            scroll=ScrollMode.ALWAYS,
        ),
    )

    page.snack_bar = SnackBar(
        content=Text(
            ref=snack_bar_text,
            value="QR code found",
            size=24,
            color=colors.WHITE,
            weight=FontWeight.BOLD,
        ),
        bgcolor=colors.GREEN,
    )

    page.floating_action_button = FloatingActionButton(
        icon=icons.CAMERA_ALT, text="Open camera", on_click=opencamera
    )

    page.update()


if __name__ == "__main__":
    app(target=main)

[thetrotfreak]

• In your original code at line 58 and 59:

if len(mytable.rows) > 0:
    qr_found = True

• This renders the while loop useless because after the first successful QR scan, it appends the data to the table making that if condition evaluate to True every time thereafter.
• This has the effect that camera indicator lights up, sees that there's already a row in mytable and exits the while loop.