这是Android 8+上的预期行为。如果需要连续扫描，则在这种情况下需要一种周期性的机制。有关在不同的Android版本和不同方式上进行扫描的更多信息。在此处

This is the expected behavior on Android 8+. if you need to scan continuously a periodic mechanism is needed in this case. For more information about scanning on different Android versions and different ways. Have a look here