Multiple cameras: first Camera crashes when requesting permission for the second

[saki4510t]

Multiple cameras: first Camera crashes when requesting permission for the second

[saki4510t]

Hi,
If you want to use two camera at the same time on this sample, it is better to give permanent permission to app for each camera at least before starting second camera. Because, as you can see sample project, if the activity lost focus (ex. by displaying permission request dialog of USB), app try to stop/release all camera and unregister/release USBMonitor on onPause/onDestroy method.
It is possible to keep camera and USBMonitor working while background but just removing those code is not a good idea and it needs additional code.
I assume at least following modification will need.

1. pass Application context instead of Activity when creating USBMonitor on onCreate
2. check whether mUSBMonitor is null or not when creation.
3. register USBMonitor after creating instead of onResume.
4. unregister USBMonitor on onDestroy instead of onPause.
5. add intent filter for USB attaching event so that app can keep permission permanently.
6. check whether Activity is active or not on all code related to USBMonitor and View and their life cycle(Note:all View and Activity context will become invalid if the Activity lost focus).
   ...
   This is just sample and the main target is showing each concept by easy way/simple code. Those modifications will make app complex and difficult to understand what it do.

saki

[btut]

Hi,
I don't mind if the preview is destroyed if the application looses focus.
How can I keep the permission permanently as you write?
And sorry, you are right. This is not an issue of the library but of the sample project, but I just can't figure out a way how to get it to work. I worked on this for quite a while.
Thanks for your help!
On Oct 14, 2015 9:55 PM, saki [email protected] wrote:Hi,
If you want to use two camera at the same time on this sample, it is better to give permanent permission to app for each camera at least before starting second camera. Because, as you can see sample project, if the activity lost focus (ex. by displaying permission request dialog of USB), app try to stop/release all camera and unregister/release USBMonitor on onPause/onDestroy method.
It is possible to keep camera and USBMonitor working while background but just removing those code is not a good idea and it needs additional code.
I assume at least following modification will need.

1. pass Application context instead of Activity when creating USBMonitor on onCreate
2. check whether mUSBMonitor is null or not when creation.
3. register USBMonitor after creating instead of onResume.
4. unregister USBMonitor on onDestroy instead of onPause.
5. add intent filter for USB attaching event so that app can keep permission permanently.
6. check whether Activity is active or not on all code related to USBMonitor and View and their life cycle(Note:all View and Activity context will become invalid if the Activity lost focus).
   ...
   This is just sample and the main target is showing each concept by easy way/simple code. Those modifications will make app complex and difficult to understand what it do.

saki

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[saki4510t]

Hi,

To Holding a permanent permission for USB, you need to add intent filter to activity section onAndroidManifest.xml. Additionally, it is better to add launchMode in activity section as singleTask orsingleInstance(I usually use singleTask).
(Regarding details about launchMode and why it is better to set as this, please check Android Developer site.)

<activity
    android:launchMode="singleTask"
    ...
    <intent-filter>
        <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
        <meta-data
            android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"
            android:resource="@xml/device_filter" />
    </intent-filter>
    ...

You can see this on AndroidManifest.xml of UsbCameraTest4 sample project.
If there is above intent filter in AndroidManifest.xml and once user choose the app as default app(always use the app for the device), Android system automatically give a permission to the Activity every time connecting the USB device (and you can not select other similar app). You can clear this setting on Apps setting.
You can also add USB_DEVICE_DETACHED intent filter to your AndroidManifest.xml, but some Android devices with some Android version can not handle this intent filter correctly.
Please mind that adding above intent filter let app accept all connecting event of UVC camera. This means when connect UVC camera to your device and the app does not have permission for the device, Android system always ask you permission. If you only need specific UVC camera, please add the vendor id and product id to device_filter.xml

saki

[btut]

Thanks for your help. Now, when I plug in the hub the app opens and the preview for both cameras starts fine, just as I wanted!