Broadcast receiver with wifi scan not working

问题

I have the following code in a service which is called with an AlarmManager (this works well) but when when I start the wifi scan (which returns true) I never receive the results in the BroadcastReceiver I created:

public class WifiCheckerService extends IntentService {

    WifiManager wifiManager;
    List<Wifi> savedWifis;
    List<Wifi> wifisInRange;
    List<ScanResult> wifisInRangeResults;
    BroadcastReceiver broadcastReceiver;

    public WifiCheckerService() {
        super("WifiCheckerService");
    }

    @Override
    public void onCreate() {
        super.onCreate();

        setScanAlwaysAvailable();
        if(broadcastReceiver == null)
            broadcastReceiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context context, Intent intent) {
                    check();
                }
            };
        if (wifiManager == null)
            wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);
        registerReceiver(broadcastReceiver,
                new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));

    }

    @Override
    protected void onHandleIntent(Intent intent) {
        if (intent != null) {
            wifiManager.startScan();

        }
    }

    private void check() {
        // irrelevant stuff

            Intent intent = new Intent(Constants.BROADCAST_UPDATE_WIFI);
            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            sendBroadcast(intent);
        }
    }

    public List<Wifi> getSavedWifisInRange(List<Wifi> savedWifis,
                                           List<ScanResult> wifisInRangeResults) {

        List<Wifi> wifisInRange = new ArrayList<Wifi>();

        for (Wifi wifi : savedWifis) {
            for (int i = 0; i < wifisInRangeResults.size(); i++) {
                if (wifi.getSsid().equals(wifisInRangeResults.get(i).SSID)) {
                    wifi.setRssi(String.valueOf(wifisInRangeResults.get(i).level));
                    wifisInRange.add(wifi);
                }

            }
        }

        return wifisInRange;
    }

    public void setScanAlwaysAvailable() {
        /* Set scan always available if it is turned off*/
        WifiManager wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);
        if (Build.VERSION.SDK_INT > Build.VERSION_CODES.JELLY_BEAN_MR2) {
            if (!wifiManager.isScanAlwaysAvailable()) {
                startActivity(new Intent(WifiManager.ACTION_REQUEST_SCAN_ALWAYS_AVAILABLE));
            }
        }
    }

    public boolean isTetheringActive() {
        //irrelevant stuff

        return false;
    }

    private boolean isAnySavedWifiInRange() {
        //irrelevant stuff
        return true;

    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        unregisterReceiver(wifiScanReceiver);
    }

}

I have used BroadcastReceiver's with wifi scans before, but I don't know why this is not working.

What's wrong?

EDIT: AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.VIBRATE" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="com.android.vending.BILLING" />

<application
    android:name=".WifiSentinelApp"
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity
        android:name=".activities.MainActivity"
        android:label="@string/app_name"
        android:screenOrientation="portrait"
        android:theme="@style/AppTheme.NoActionBar">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".activities.DonateActivity"
        android:label="@string/donate"
        android:screenOrientation="portrait"
        android:theme="@style/AppTheme.NoActionBar" />
    <activity
        android:name=".activities.SettingsActivity"
        android:label="@string/settings"
        android:screenOrientation="portrait" />

    <receiver android:name=".receivers.AlarmReceiver" />

    <receiver android:name=".receivers.BootReceiver"
        android:enabled="false">
        <intent-filter>
            <action android:name="android.intent.action.BOOT_COMPLETED" />
        </intent-filter>
    </receiver>
    <service android:name=".services.WifiCheckerService" />
</application>

回答1:

My understanding of the IntentService is that it will only be active for the time needed to handle the request (ie, the time needed to run onHandleIntent()). I haven't tested your code, but my guess is that your broadcast receiver is being unregistered right away when onDestroy() runs, before the scan results are delivered. Probably an IntentService is not right for this. You might need to create a "regular" (long living background) service. Or, maybe it just makes more sense to have your BroadcastReceiver in the activity where you will show the scan results and get rid of this IntentService altogether. WifiManager::startScan() is asynchronous so it shouldn't be necessary to call that on a background service anyway.

来源：https://stackoverflow.com/questions/34497948/broadcast-receiver-with-wifi-scan-not-working