WifiManager 中的 startScan() 在 Android P 中已弃用

Question

How to get scan result from wifi for example every 3 seconds, without mWifimanager.startScan();

Google says:

startScan() This method was deprecated in API level P. The ability for apps to trigger scan requests will be removed in a future release.

Notice for this API level i'm using List<ScanResult> results = mWifiManager.getScanResults(); without calling startScan , the list contains the wifi AP's but it makes updated very very slow

Update to 12 January 2019: https://issuetracker.google.com/issues/112688545

Answer 1

Google has now documented the limitations for startScan() function in Android P:

"We are further limiting the number of scans apps can request to improve network performance and improve battery life.

The WifiManager.startScan() usage is limited to: - Each foreground app is restricted to 4 scans every 2 minutes. - All background apps combined are restricted to one scan every 30 minutes."

Source: https://issuetracker.google.com/issues/79906367

Edit 8-Aug-2018: Information has been added also here: https://developer.android.com/guide/topics/connectivity/wifi-scan#wifi-scan-throttling

Answer 2

I think in API level P they're planning to move startScan() to a different class (WifiScanner) all together with some key differences.

See: https://android.googlesource.com/platform/frameworks/base/+/android-p-preview-1/wifi/java/android/net/wifi/WifiScanner.java

If there's an alternative solution to this, I'd love to hear it as well.

For now, I might just use startScan() until official docs are released.

Answer 3

startScan() is actually pretty buggy on P, as I raised Google Issue 79906367 .

I don't think that WifiScanner is the replacement either, as that is marked as a SystemApi which means no access for Apps...

Hopefully we will hear soon, as RTT still means you need to scan for APs which support 802.11mc using ScanResult is80211mcResponder which you check before performing RTT Ranging on the AP.

Answer 4

StartScan() method is deprecated in Android P and new RTT protocol from 802.11mc standard has to be used with trilateration Algorithms. https://android-developers.googleblog.com/2018/03/previewing-android-p.html

X,Y position of the AP should to be knonw for accurate positioning and the AP should support 802.11mc's Fine Time Measurement. Intel® Wireless-AC 9260 support 802.11mc and several APs start supporting 802.11mc standard.

A couple of examples:

• https://medium.com/@rafaelmiguel.ortega/android-p-first-taste-of-rtt-support-febefb679775
• https://medium.com/@plinzen/perform-wifi-round-trip-time-measurements-with-android-p-9ffc5277ac6a

Answer 5

From WifiManager#EXTRA_RESULTS_UPDATED

Note: Apps holding android.Manifest.permission.NETWORK_SETTINGS permission are exempted from scan throttling.

Note: This is a system permission, regular apps can't use it without rooting and moving the app to the 'privileged' location or having it baked into a custom ROM.

Answer 6

I would guess the intention is to have developers/users use WifiRttManager instead for indoor location atleast [1]. Or rely on usual Google Play location services, which is an option in some use cases, but definitely not all. It's optimised for the average use case. No use case is the average use case.

Unfortunately with the way WifiRttManager calculates location it requires the wifi accesspoints to have 802.11mc. However you don't need to connect to these points. Virtually 0 routers today have this standard. [2] [3] [4] With 3 access points you can get location close to 1-2m accuracy.

Who knows if they'll place restrictions on this functionality as well though. I'm not happy that this functionality is being taken away from users and developers - all it needs is a permission.

So it appears there will be a dark age for indoor location over the next few years until 802.11mc is popular. Perhaps a workaround is to have devices you are connected to and ping them.

[1] https://developer.android.com/reference/android/net/wifi/rtt/WifiRttManager [2] https://github.com/Plinzen/android-rttmanager-sample

Additional reading [3] https://en.wikipedia.org/wiki/IEEE_802.11mc [4] https://fit-iot.com/web/wifi-indoor-positioning/

Answer 7

I think google is planning to restrict application from scanning wifi.

This method was deprecated in API level 28. The ability for apps to trigger scan requests will be removed in a future release. Check the documentation here.