Question

作为Android编程的新手，我正在尝试使用WifiManager的getScanResults()方法获取SSID列表，但它仍然为空，即使我已授予它ACCESS_COARSE_LOCATION权限以及CHANGE_WIFI_STATE（对于startScan()方法），在清单中以及在运行时检查/请求它。

在SCAN_RESULTS_AVAILABLE_ACTION的广播接收器中，我甚至用键EXTRA_RESULTS_UPDATED检查意图的额外字段，结果返回true。

然而，list.size()总是返回0.

我在这里缺少什么？我正在使用Android 7.0 API 24设备进行测试。

编辑：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>

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。授予权限只是完成的一半工作。

您还可以触发将用户重定向到此设置的意图：

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（接入点的地址）等信息。此信息还可用于检测设备的位置。通过要求定位服务，操作系统可确保用户在使用您的应用时了解他们的位置信息。

Android WifiManager :: getScanResults（）仍返回空列表

1 个答案: