咨询：启动时仅初始化的视频源设备列表能否在运行时更新？

Hey there! Great question—yes, you absolutely can update your video source device list at runtime, even if it’s currently only initialized once on startup. The core issue here is that your current setup only scans for devices once during app launch, but we can adjust this to react to device changes as they happen.

Here’s a breakdown of actionable steps to make this work:

• Listen for device plug/unplug events
  Most operating systems offer native APIs to detect when hardware (like USB cameras) is added or removed. For example:

  • Windows: Use RegisterDeviceNotification to monitor events for the video device class
  • Linux: Leverage udev to track changes to /dev/video* devices
  • macOS: Use IOKit to listen for USB or video hardware notifications
    These events will trigger a refresh of your device list whenever a new video source connects or an existing one disconnects.

• Refactor your device enumeration logic
  Take the code that currently runs once at startup to build the device list, and wrap it in a reusable function (e.g., refreshVideoSources()). This lets you call the function both during initialization and whenever a device change event fires.

• Sync updates with your UI and dependencies
  If your device list is tied to a UI component (like a dropdown menu), make sure to refresh the UI after updating the list to reflect the latest state. Also, clean up any references to removed devices (e.g., stop active streams from a disconnected camera) to avoid runtime errors.

Here’s a simplified pseudocode example to illustrate the flow:

# Example in Python (concept applies to all languages)
def enumerate_video_devices():
    # Original startup-time device scanning logic
    devices = []
    # Call system APIs to fetch active video sources
    # ...
    return devices

def on_device_change(event):
    # Callback triggered when a device is added/removed
    global video_source_list
    video_source_list = enumerate_video_devices()
    # Refresh UI to show updated list
    update_video_source_dropdown(video_source_list)

# App initialization
video_source_list = enumerate_video_devices()
# Register listener for device changes
register_device_change_listener(on_device_change)

A few extra tips to smooth things out:

• Permissions: Ensure your app has the necessary permissions to access device events (e.g., udev access on Linux, accessibility permissions on macOS).
• Thread safety: If device change callbacks run on a background thread, synchronize access to your device list to avoid race conditions.
• Device validation: When re-enumerating, double-check that each device is actually accessible (some devices might appear in system listings but be in use or unavailable).

内容的提问来源于stack exchange，提问作者chfisch