This sample using jni to fork a detached process to monitor/detect the app uninstall by user. By checking the app data root directory's existence, to know the app is uninstall by user. After that, it will sent an intent with a specified URL(usually a feedback web page of your app) to open in the browser.
Note: This solution didn't test on all Android platfrom and device, it might not work on your device.
This solution won't work after Android 5.0 (Lollipop), the forked native process will be killed after main process stopped or killed.