确定Android中的Wi-Fi可用性

Question

在尝试确定Wi-Fi是否可用时，我的应用程序崩溃了。

我有一个围绕

的try / catch块

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

但它只是存在使用空指针异常崩溃应用程序。

清单权限：

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

如何确定wi-fi是否可以使用？

修改

堆栈追踪：

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)

活动变量为NULL。 Mea Culpa！

Answer 1

我会看一下Android Advanced Training: Managing Network Usage, Check a Device's Network Connection。这是一个关于如何正确检查Android设备的网络状态的好教程。

在里面，你会找到一种更一般地查询网络状态的方法，然后特别是你可以检查用户是否在WiFi上。

相关代码：

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);

相关权限：

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

Answer 2

通过您的活动名称在上面的代码中重新activity，或者如果您在活动中，则将其删除。