如何过滤wifi扫描结果？

Question

我正在尝试在android中编写一个代码，它将显示以MYNET开头的可用wifi网络列表。我能够显示所有可用网络的列表，但是当我过滤列表时，我的应用程序崩溃了。请帮我解决一下这个。 我的代码如下。

package com.mynet.wifilist;


import android.annotation.SuppressLint;
import android.app.Dialog;
import android.app.ListActivity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.gesture.Prediction;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.wifi.ScanResult;
import android.net.wifi.WifiConfiguration;
import android.net.wifi.WifiManager;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.CompoundButton;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Switch;
import android.widget.TextView;
import android.widget.Toast;

import java.util.Collection;
import java.util.Collections;
import java.util.List;

public class MainActivity extends ListActivity {
    WifiManager wfmanager;
    WifiScanReceiver wifiReciever;
    ListView list;
    String all_wifi[];
    String wifilist[];
    Switch wfswitch;

    EditText pass;

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

        wfswitch = (Switch)findViewById(R.id.switch1);
        list=getListView();
        wfmanager = (WifiManager) 
          getApplicationContext().getSystemService(Context.WIFI_SERVICE);
        wifiReciever = new WifiScanReceiver();


        ConnectivityManager connectivityManager = (ConnectivityManager) 
          getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = 
          connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);

        if(networkInfo.isConnected()){
            wfswitch.setChecked(true);
        }
        else{
            wfswitch.setChecked(false);
        }


        wfswitch.setOnCheckedChangeListener(new 
             CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean 
             isChecked) {
                if(isChecked && !wfmanager.isWifiEnabled()){
                    Toast.makeText(getApplicationContext(),"Turning  WiFi 
                  On.......",Toast.LENGTH_LONG).show();
                    wfmanager.setWifiEnabled(true);
                    wfmanager.startScan();
                }

                else if(!isChecked && wfmanager.isWifiEnabled()){
                    Toast.makeText(getApplicationContext(),"Turning  WiFi 
                       Off...",Toast.LENGTH_LONG).show();
                    //unregisterReceiver(wifiReciever);
                    //list.setAdapter(null);
                    wfmanager.setWifiEnabled(false);


                }
            }
        });


        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view, int 
          position, long id) {

                // selected item
                String ssid = ((TextView) view).getText().toString();
                connectToWifi(ssid);
                Toast.makeText(MainActivity.this,"Wifi SSID : 
                "+ssid,Toast.LENGTH_SHORT).show();

            }
        });
    }

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

    protected void onResume() {
        registerReceiver(wifiReciever, new 
        IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
        super.onResume();
    }
    class WifiScanReceiver extends BroadcastReceiver {
        @SuppressLint("UseValueOf")
        public void onReceive(Context c, Intent intent) {
            List<ScanResult> wifiScanList = wfmanager.getScanResults();
            all_wifi = new String[wifiScanList.size()];

            wifilist = new String[wifiScanList.size()];
            for(int i = 0; i < wifiScanList.size(); i++){
                all_wifi[i] = (wifiScanList.get(i)).toString();
                /*if(all_wifi[i].startsWith("MYNET")){
                    wifilist[i] = wifiScanList.get(i).toString();

                }*/
            }
            String wf_filter_list[] = new String[wifiScanList.size()];
            int counter = 0;


            for (String eachWifi : wifilist) {

                  String[] temp = eachWifi.split(",");

                  wf_filter_list[counter] = temp[0].substring(5).trim();

                  counter++;

            }
            list.setAdapter(new ArrayAdapter<String> 
            (getApplicationContext(),R.layout.list_item,R.id.label, 
             wf_filter_list));

        }
    }

    private void finallyConnect(String networkPass, String networkSSID) {
        WifiConfiguration wifiConfig = new WifiConfiguration();
        wifiConfig.SSID = String.format("\"%s\"", networkSSID);
        wifiConfig.preSharedKey = String.format("\"%s\"", networkPass);

        int netId = wfmanager.addNetwork(wifiConfig);
        wfmanager.disconnect();
        wfmanager.enableNetwork(netId, true);
        wfmanager.reconnect();

        WifiConfiguration conf = new WifiConfiguration();
        conf.SSID = "\"\"" + networkSSID + "\"\"";
        conf.preSharedKey = "\"" + networkPass + "\"";
        wfmanager.addNetwork(conf);
    }

    private void connectToWifi(final String wifiSSID) {
        final Dialog dialog = new Dialog(this);
        dialog.setContentView(R.layout.connect);
        dialog.setTitle("Connect to Network");
        TextView textSSID = (TextView) dialog.findViewById(R.id.textSSID1);

        Button dialogButton = (Button) dialog.findViewById(R.id.okButton);
        pass = (EditText) dialog.findViewById(R.id.textPassword);
        textSSID.setText(wifiSSID);


        dialogButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String checkPassword = pass.getText().toString();
                finallyConnect(checkPassword, wifiSSID);
                dialog.dismiss();
            }
        });
        dialog.show();

    }
}

我的过滤列表逻辑如下，在代码中有注释。取消注释并运行应用程序将导致应用程序崩溃。

if(all_wifi[i].startsWith("MYNET")) {
    wifilist[i] = wifiScanList.get(i).toString();
}

提前致谢。