networkInfo.isConnected（）错误

Question

我在执行此代码时收到错误。

连接到wifi时，该功能应显示MAC地址，否则＆＃34; ---＆＃34;

private void DisplayWifiStatus() {

    ConnectivityManager conMgr = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = conMgr.getActiveNetworkInfo();
    wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
    WifiInfo info = wifi.getConnectionInfo();

    if (networkInfo.isConnected()) {
        textMac.setText(info.getMacAddress());

    }else {
        textMac.setText("-----");
    }
}

logcat的/堆栈跟踪：

03-11 21:32:07.532    3348-3348/com.light87sakurahimegmail.wifiscanner E/dalvikvm﹕ >>>>> Normal User
03-11 21:32:07.532    3348-3348/com.light87sakurahimegmail.wifiscanner E/dalvikvm﹕ >>>>> com.light87sakurahimegmail.wifiscanner [ userId:0 | appId:10337 ]
03-11 21:32:07.782    3348-3348/com.light87sakurahimegmail.wifiscanner E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.light87sakurahimegmail.wifiscanner, PID: 3348
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.light87sakurahimegmail.wifiscanner/com.light87sakurahimegmail.wifiscanner.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2292)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2350)
            at android.app.ActivityThread.access$800(ActivityThread.java:163)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1257)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5335)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.light87sakurahimegmail.wifiscanner.MainActivity.DisplayWifiStatus(MainActivity.java:79)
            at com.light87sakurahimegmail.wifiscanner.MainActivity.onCreate(MainActivity.java:43)
            at android.app.Activity.performCreate(Activity.java:5389)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2256)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2350)
            at android.app.ActivityThread.access$800(ActivityThread.java:163)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1257)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5335)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
            at dalvik.system.NativeStart.main(Native Method)