Android Wifi Scan - 无法调用SCAN_RESULTS_AVAILABLE_ACTION的BroadcastReceiver

Question

这是我的代码:

public class FloatWifiManager implements IWifiManager {

    private WifiManager wifiManager;

    private BroadcastReceiver wifiScanReceiver;

    public FloatWifiManager(Context context) {
        ...
        wifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);

        // Registering Wifi Receiver
        wifiScanReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context c, Intent intent) {
                if (intent.getAction().equals(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)) {
                    // not getting called, only after running app and manually going to the wifi settings in android
                }
            }
        };

        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
        context.registerReceiver(wifiScanReceiver, intentFilter);
        wifiManager.startScan();
    }

我注册的BroadcastReceiver就像我在所有的例子中看到的那样,并且做到了startScan.

会发生什么,wifi列表正在改变(当然,我测试过),但onReceive如果我只是留在应用程序中则不会被调用.

是什么让onReceive终于到了被称为-是启动应用程序,使其保持运行状态,并在Android手机上要设置 - > 无线上网设置.去那里时,List突然更新并被onReceive调用.

这有什么问题？

1. 是否 wifiManager.startScan();只运行一次扫描？或者它是一个持续收听传入"扫描结果"的功能？

2. 显然,为什么接收器不被调用？

Answer 1

是的,startScan()只请求一次扫描.

你可以摆脱这种if (intent.getAction().equals(..))状况.其他任何事情似乎都没问题.

只是为了说清楚 - 我的目标是每当Wifi网络列表发生变化时都会调用一个接收器,而不必点击"开始扫描"按钮.

AFAIK无法在任何wifi网络发生变化时收到通知.您只能请求扫描startScan- 当然您可以startScan使用线程或处理程序重复调用.

文档说,SCAN_RESULTS_AVAILABLE_ACTION当"接入点扫描已完成,结果可从请求者处获得"时,会调用该文档.如何以及何时进行扫描取决于请求者的实施.Elenkov写道,"Android设备很少包含原始的wpa_supplicant代码;所包含的实现经常被修改以更好地与底层SoC兼容".

扫描接入点

此示例扫描可用的接入点和ad hoc网络.btnScan激活WifiManager.startScan()方法启动的扫描.扫描后,WifiManager调用SCAN_RESULTS_AVAILABLE_ACTIONintent,WifiScanReceiver类处理扫描结果.结果显示在a TextView.

public class MainActivity extends AppCompatActivity {

    private final static String TAG = "MainActivity";

    TextView txtWifiInfo;
    WifiManager wifi;
    WifiScanReceiver wifiReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        wifi=(WifiManager)getSystemService(Context.WIFI_SERVICE);
        wifiReceiver = new WifiScanReceiver();

        txtWifiInfo = (TextView)findViewById(R.id.txtWifiInfo);
        Button btnScan = (Button)findViewById(R.id.btnScan);
        btnScan.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.i(TAG, "Start scan...");
                wifi.startScan();
            }
        });
    }

    protected void onPause() {
        unregisterReceiver(wifiReceiver);
        super.onPause();
    }

    protected void onResume() {
        registerReceiver(
            wifiReceiver, 
            new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)
        );
        super.onResume();
    }

    private class WifiScanReceiver extends BroadcastReceiver {
        public void onReceive(Context c, Intent intent) {
            List<ScanResult> wifiScanList = wifi.getScanResults();
            txtWifiInfo.setText("");
            for(int i = 0; i < wifiScanList.size(); i++){
                String info = ((wifiScanList.get(i)).toString());
                txtWifiInfo.append(info+"\n\n");
            }
        }
    }
}

权限

需要在AndroidManifest.xml中定义以下权限:

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />

android.permission.ACCESS_WIFI_STATE打电话是必要的WifiManager.getScanResults().没有android.permission.CHANGE_WIFI_STATE你无法启动扫描WifiManager.startScan().

当编译为API级别23或更高的项目(在Android 6.0及以上),无论是android.permission.ACCESS_FINE_LOCATION或android.permission.ACCESS_COARSE_LOCATION必须插入.此外,需要申请许可,例如在onCreate主要活动的方法中:

@Override
protected void onCreate(Bundle savedInstanceState) {
    ...
    String[] PERMS_INITIAL={
            Manifest.permission.ACCESS_FINE_LOCATION,
    };
    ActivityCompat.requestPermissions(this, PERMS_INITIAL, 127);
}