CODEWITHSUNDEEP
androidnullpointerexceptionandroid-wifiwifimanager
Roy Hinkley
Roy Hinkley

Reputation: 10641

Determine Wi-Fi availability in Android

When attempting to determine if Wi-fi is even available, my app crashes.

I have a try/catch block surrounding 

WifiManager wifi = (WifiManager) activity.getSystemService(Context.WIFI_SERVICE);

but it's mere presence crashes the app with a null pointer exception.

Manifest permissions:

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />

How does one determine if wi-fi is even available otherwise?

EDIT

Stack Trace:

10-08 20:10:21.820: E/AndroidRuntime(14331): FATAL EXCEPTION: main
10-08 20:10:21.820: E/AndroidRuntime(14331): java.lang.NullPointerException
10-08 20:10:21.820: E/AndroidRuntime(14331):    at com.myapp.ui.FragmentSettingsDetailWireless.loadControls(FragmentSettingsDetailWireless.jav   a:121)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at com.myapp.ui.FragmentSettingsDetailWireless.onActivityCreated(FragmentSettingsDetailWireles    s.java:110)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:814)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:998)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.app.BackStackRecord.run(BackStackRecord.java:622)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1330)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.app.FragmentManagerImpl$1.run(FragmentManager.java:417)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.os.Handler.handleCallback(Handler.java:605)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.os.Handler.dispatchMessage(Handler.java:92)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.os.Looper.loop(Looper.java:137)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at android.app.ActivityThread.main(ActivityThread.java:4340)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at java.lang.reflect.Method.invokeNative(Native Method)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at java.lang.reflect.Method.invoke(Method.java:511)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
10-08 20:10:21.820: E/AndroidRuntime(14331):    at dalvik.system.NativeStart.main(Native Method)

The activity variable was NULL. Mea Culpa!

Upvotes: 1

Views: 1053

Answers (2)

louielouie
louielouie

Reputation: 14941

I would take a look at the Android Advanced Training: Managing Network Usage, Check a Device's Network Connection. It is a good tutorial on how to properly check the network state of an Android device.

Inside, you'll find a way to more generally query the network state and then in particular, you can check if the user is on WiFi or not.

The relevant code:

ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI); 
boolean isWifiConn = networkInfo.isConnected();
Log.d(DEBUG_TAG, "Wifi connected: " + isWifiConn);

The relevant permissions:

android.permission.INTERNET - Allows applications to open network sockets.
android.permission.ACCESS_NETWORK_STATE - Allows applications to access information about networks.

Upvotes: 1

Luis
Luis

Reputation: 12058

Repalce activity in your code above by your activity name, or just remove it if you are within the activity.

Upvotes: 0

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