使用屏幕管理器时不显示相机图像

Question

我需要在单独的屏幕中实现相机预览。应使用按钮启动和停止相机。我已经实现了下面的代码。当我按下开始相机按钮时，相机正在闪烁并且正在工作。但是来自相机的图像没有显示在我的屏幕上（在 UploadScreen 中。）请帮助。

ma​​in.py

from kivymd.app import MDApp
from kivy.lang.builder import Builder
from kivy.uix.screenmanager import Screen
from screen_nav import screen_helper
from kivy.uix.image import Image
from kivy.graphics.texture import Texture
from kivy.clock import Clock
import cv2
from kivy.properties import BooleanProperty


class MenuScreen(Screen):
    pass


class ProfileScreen(Screen):
    pass


class UploadScreen(Screen):
    cameraActive = BooleanProperty(False)
    capture = cv2.VideoCapture()

    def start_camera(self):

        if not self.cameraActive:
            self.ids.camera_button.text = 'Stop Camera'
            self.image = Image()
            self.capture = cv2.VideoCapture(0)
            if self.capture.isOpened():
                self.cameraActive = True
                Clock.schedule_interval(self.update, 1.0 / 10.0)
            else:
                print('Cannot Open the Camera at index 0')
        else:
            self.cameraActive = False
            self.ids.camera_button.text = 'Start Camera'
            if self.capture.isOpened():
                self.capture.release()

        return self.capture

    def on_upload_back(self):
        self.cameraActive = False
        self.ids.camera_button.text = 'Start Camera'
        if self.capture.isOpened():
            self.capture.release()
        self.manager.current = 'menu'

    def update(self, dt):
        ret, frame = self.capture.read()
        if ret:
            # convert it to texture
            buf1 = cv2.flip(frame, 0)
            buf = buf1.tobytes()
            image_texture = Texture.create(size=(frame.shape[1], frame.shape[0]), colorfmt='bgr')
            image_texture.blit_buffer(buf, colorfmt='bgr', bufferfmt='ubyte')
            # display image from the texture
            self.image.texture = image_texture
            self.ids.my_image = self.image


class DemoApp(MDApp):

    def build(self):
        screen = Builder.load_string(screen_helper)
        return screen


DemoApp().run()

screen_nav.py

screen_helper = """

ScreenManager:
    MenuScreen:
    ProfileScreen:
    UploadScreen:

<MenuScreen>:
    name: 'menu'
    MDRectangleFlatButton:
        text: 'Profile'
        pos_hint: {'center_x':0.5,'center_y':0.5}
        on_press: root.manager.current = 'profile'
    MDRectangleFlatButton:
        text: 'Upload'
        pos_hint: {'center_x':0.5,'center_y':0.4}
        on_press: root.manager.current = 'upload'

<ProfileScreen>:
    name: 'profile'
    MDLabel:
        text: 'Profile'
        halign: 'center'
    MDRectangleFlatButton:
        text: 'Back'
        pos_hint: {'center_x':0.5,'center_y':0.1}
        on_press: root.manager.current = 'menu'    

<UploadScreen>:
    name: 'upload'
    Image:
        id: my_image
    MDRectangleFlatButton:
        text: 'Back'
        pos_hint: {'center_x':0.5,'center_y':0.1}
        # on_press: root.manager.current = 'menu'
        on_press: root.on_upload_back()
    MDRectangleFlatButton:
        id: camera_button
        text: 'Start Camera'
        pos_hint: {'center_x':0.7,'center_y':0.1}
        on_press: root.start_camera()
        # on_press: camera.play = not camera.play

"""

Answer 1

一个小问题，一行：

self.image = Image()

正在创建一个新的Image 对象，该对象将使用来自相机的图像进行更新。但是那个Image 实例不是您在kv 中定义的实例，也不在您的GUI 中。只需将该行替换为：

self.image = self.ids.my_image

访问 GUI 中的 Image。