java - wifiManager.getScanResult() 返回空值

Question

我正在搜索可用的 wifi 网络扫描，但 getScanResults() 方法返回空列表。

我包含了所需的所有权限:

android.permission.ACCESS_COARSE_LOCATION
android.permission.CHANGE_WIFI_STATE
android.permission.ACCESS_FINE_LOCATION
android.permission.ACCESS_WIFI_STATE

主要 Activity 类是:

public class Home extends Activity {`

    Context context;
    WifiManager wifiManager = null;
    WiFiReceiver wifiReceiver = null;

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

        context = this;
        wifiManager = (WifiManager) 
        context.getSystemService(Context.WIFI_SERVICE);
        wifiReceiver = new WiFiReceiver(wifiManager);

        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
        registerReceiver(wifiReceiver, intentFilter);

        wifiManager.startScan();
        List<ScanResult> results = wifiReceiver.results;
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

        unregisterReceiver(wifiReceiver);
    }
}

广播接收器是:

public class WiFiReceiver extends BroadcastReceiver {`

    public List<ScanResult> results;
    private WifiManager wifiManager;

    public WiFiReceiver(WifiManager wifiManager) {
        this.wifiManager = wifiManager;
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        boolean success = intent.getBooleanExtra(WifiManager.EXTRA_RESULTS_UPDATED, false);
        if (success) {
            results = wifiManager.getScanResults();
            Log.e("wiFi Manager", "Done");

        } else {
            Log.e("wiFi Manager", "Scan failure");
        }
    }
}

Answer 1

问题是您假设 startScan() 将立即产生结果，但它实际上只执行所说的操作，开始扫描。您正在触发 WiFiReceiver 中的 onReceive 之前访问 then results 变量，这就是为什么它始终为空(您的日志记录应该确认这一点) .

您需要的是在结果准备好时使用回调来获取结果，如代码here做。请注意 onReceive 方法如何调用 scanSuccess()，并且结果仅在 scanSuccess() 中访问，而不是在调用 startScan( )。另请注意他们如何通过检查 boolean startScan() 返回来检查启动扫描是否确实成功