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

作为 Android 编程的新手，我正在尝试使用 WifiManager 获取 SSID 列表getScanResults()方法，但它仍然是空的，即使我已经授予它ACCESS_COARSE_LOCATION许可以及CHANGE_WIFI_STATE（为了startScan()方法），无论是在清单中还是在运行时检查/请求它。

在广播接收器中SCAN_RESULTS_AVAILABLE_ACTION，我什至用 key 检查意图的额外字段EXTRA_RESULTS_UPDATED结果返回true。

然而，list.size()始终返回 0。

我在这里缺少什么？我正在 Android 7.0 API 24 设备上进行测试。

Edit:代码如下：

MainActivity.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();
        }
    }
}

在清单中：

<?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>

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。

您还可以触发意图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（接入点地址）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他们的位置信息在使用您的应用程序时正在被访问。