Android WifiManager::getScanResults() 仍然返回空列表

Question

作为 Android 编程的新手，我尝试使用 WifiManager 的 getScanResults() 方法获取 SSID 列表，但它仍然是空的，即使我已授予它 ACCESS_COARSE_LOCATION 权限以及 CHANGE_WIFI_STATE(对于 startScan() 方法)，在 list 中以及通过在运行时检查/请求它。

在 SCAN_RESULTS_AVAILABLE_ACTION 的广播接收器中，我什至使用键 EXTRA_RESULTS_UPDATED 检查 Intent 的额外字段，结果返回 true。

然而，list.size() 始终返回 0。

我在这里错过了什么？我正在 Android 7.0 API 24 设备上进行测试。

编辑:代码如下:

主要 Activity .java:

public class MainActivity extends Activity implements View.OnClickListener {
    private static final String TAG="WiFiDemo";

    WifiManager wifiManager;
    WifiBroadcastReceiver wifiReceiver;

    TextView textView;
    Button btn;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        Log.d(TAG, "onCreate()");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Check for permissions
        if ((ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION)
                != PackageManager.PERMISSION_GRANTED)
            || (ContextCompat.checkSelfPermission(this, Manifest.permission.CHANGE_WIFI_STATE)
                    != PackageManager.PERMISSION_GRANTED))
        {
            Log.d(TAG, "Requesting permissions");

            //Request permission
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.ACCESS_COARSE_LOCATION,
                                 Manifest.permission.ACCESS_FINE_LOCATION,
                                 Manifest.permission.ACCESS_WIFI_STATE,
                                 Manifest.permission.CHANGE_WIFI_STATE,
                                 Manifest.permission.ACCESS_NETWORK_STATE},
                    123);
        }
        else
            Log.d(TAG, "Permissions already granted");

        wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);

        textView = findViewById(R.id.text);
        textView.setTextAlignment(View.TEXT_ALIGNMENT_TEXT_START);

        btn = findViewById(R.id.btn);
        btn.setOnClickListener(this);

        //Instantiate broadcast receiver
        wifiReceiver = new WifiBroadcastReceiver();

        //Register the receiver
        registerReceiver(wifiReceiver, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults)
    {
        Log.d(TAG, "onRequestPermissionsResult");

        switch (requestCode)
        {
            case 123:
            {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
                {
                    // permission was granted
                    Log.d(TAG, "permission granted: " + permissions[0]);
                }
                else
                {
                    // permission denied, boo! Disable the
                    // functionality that depends on this permission.
                    Log.d(TAG, "permission denied: " + permissions[0]);
                }

                return;
            }

            // other 'case' lines to check for other
            // permissions this app might request.
        }
    }

    //Define class to listen to broadcasts
    class WifiBroadcastReceiver extends BroadcastReceiver
    {
        @Override
        public void onReceive(Context context, Intent intent)
        {
            Log.d(TAG, "onReceive()");
            Toast.makeText(getApplicationContext(), "Scan complete!", Toast.LENGTH_SHORT).show();

            boolean ok = intent.getBooleanExtra(WifiManager.EXTRA_RESULTS_UPDATED, false);

            if (ok)
            {
                Log.d(TAG, "scan OK");

                //StringBuffer buffer = new StringBuffer();
                List<ScanResult> list = wifiManager.getScanResults();

                Toast.makeText(getApplicationContext(), Integer.toString(list.size()), Toast.LENGTH_SHORT).show();

                for (ScanResult scanResult : list)
                {
                    //buffer.append(scanResult);
                    textView.append(scanResult.toString());
                }
            }
            else
                Log.d(TAG, "scan not OK");
        }
    }

    @Override
    protected void onStop()
    {
        // TODO Auto-generated method stub
        unregisterReceiver(wifiReceiver);
        super.onStop();
    }

    @Override
    public void onClick(View view)
    {
        // TODO Auto-generated method stub
        //Toast.makeText(getApplicationContext(), "All Network seached !!",0).show();
        if(view.getId()==R.id.btn)
        {
            Log.d(TAG, "onCreate() wifi.startScan()");

            //if (!wifiManager.isWifiEnabled())
            //    wifiManager.setWifiEnabled(true);

            wifiManager.startScan();
        }
    }
}

在 list 中:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.wifi2ir.umagi.wifitest2">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
</manifest>

Answer 1

从 Android 6 开始，您必须启用位置服务才能获得所需的结果。授予权限只是完成了一半的工作。

您还可以触发一个 intent 将用户重定向到此设置:

Intent myIntent = new Intent( Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(myIntent);

位置服务是必要的，因为当您访问扫描结果时，您可以访问 BSSID(访问点的地址)等信息。此信息还可用于检测设备的位置。通过要求位置服务，操作系统可确保用户了解在使用您的应用时他们的位置信息正在被访问。