未在Android應用程序中顯示的Wi-Fi網絡

Question

我試圖顯示附近所有Wi-Fi網絡的列表。我編寫的代碼給出了一個錯誤，一旦Wi-Fi在應用程序中打開，並且如果Wi-Fi已經打開，應用程序甚至不會啓動。 logcat低於附加的代碼。

編輯 - 我寫了新的代碼，如下所示： CODE：

package com.example.wifiapplication; 

import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.Iterator; 
import java.util.List; 

import android.app.Activity; 
import android.content.BroadcastReceiver; 
import android.content.Context; 
import android.content.Intent; 
import android.content.IntentFilter; 
import android.net.wifi.ScanResult; 
import android.net.wifi.WifiConfiguration; 
import android.net.wifi.WifiConfiguration.AuthAlgorithm; 
import android.net.wifi.WifiConfiguration.GroupCipher; 
import android.net.wifi.WifiConfiguration.KeyMgmt; 
import android.net.wifi.WifiConfiguration.PairwiseCipher; 
import android.net.wifi.WifiConfiguration.Protocol; 
import android.net.wifi.WifiManager; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.CompoundButton; 
import android.widget.CompoundButton.OnCheckedChangeListener; 
import android.widget.ListView; 
import android.widget.SimpleAdapter; 
import android.widget.Switch; 
import android.widget.TextView; 
import android.widget.Toast; 

public class MainActivity extends Activity implements OnClickListener, OnCheckedChangeListener{ 

    Button search; 
    Switch change; 
    ListView list; 
    int size=0; 
    List <ScanResult> results; 
    ArrayList <HashMap<String, String>> arraylist = new ArrayList<HashMap<String, String>>(); 
    SimpleAdapter adapter; 
    WifiManager manage; 
    String ITEM_KEY = "key"; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     // TODO Auto-generated method stub 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.fragment_main); 
     search = (Button) findViewById(R.id.bSearch); 
     change = (Switch) findViewById(R.id.wifi); 
     list = (ListView) findViewById(R.id.lv); 
     change.setOnCheckedChangeListener(this); 
     search.setOnClickListener(this); 
     manage = (WifiManager) getSystemService(Context.WIFI_SERVICE); 
      change.setChecked(manage.isWifiEnabled()); 
    } 


    @Override 
    public void onClick(View arg0) { 
     // TODO Auto-generated method stub 
     WifiConfiguration config = new WifiConfiguration(); 
     arraylist.clear();   
     if(manage.startScan()){ 

      Toast.makeText(this, "Scanning...." + size, Toast.LENGTH_SHORT).show(); 
      try 
      { 
       size = size - 1; 
       while (size >= 0) 
       { 
        HashMap<String, String> item = new HashMap<String, String>();      
        item.put(ITEM_KEY, results.get(size).SSID + " " + results.get(size).capabilities); 

        arraylist.add(item); 
        size--; 
        adapter.notifyDataSetChanged();     
       } 
      } 
      catch (Exception e) 
      { }   
     } 
     }  


    @Override 
    public void onCheckedChanged(CompoundButton arg0, boolean arg1) { 
     if(arg1==true) 
     { 
     manage.setWifiEnabled(true); 
     //search.setText("Start Searching"); 
     this.adapter = new SimpleAdapter(MainActivity.this, arraylist, R.layout.row, new String[] { ITEM_KEY }, new int[] { R.id.list_value }); 
     list.setAdapter(adapter); 

     registerReceiver(new BroadcastReceiver(){ 

      @Override 
      public void onReceive(Context arg0, Intent arg1) { 
       // TODO Auto-generated method stub 
       results = manage.getScanResults(); 
       size = results.size(); 
      } 

     }, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)); 

     //Search for available Wi-Fi networks; 
      } 
     else{ 
      Toast.makeText(getApplicationContext(), "Wi-Fi is disabled", Toast.LENGTH_LONG).show();; 
      manage.setWifiEnabled(false); 
      search.setText("Turn on Wi-Fi"); 

      } 
     } 

     // TODO Auto-generated method stub 

} 

的logcat：

06-23 10:04:18.200: E/AndroidRuntime(1173): FATAL EXCEPTION: main 
06-23 10:04:18.200: E/AndroidRuntime(1173): Process: com.example.wifiapplication, PID: 1173 
06-23 10:04:18.200: E/AndroidRuntime(1173): java.lang.NullPointerException 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at com.example.wifiapplication.MainActivity.onCheckedChanged(MainActivity.java:94) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.widget.CompoundButton.setChecked(CompoundButton.java:127) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.widget.Switch.setChecked(Switch.java:666) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.widget.CompoundButton.toggle(CompoundButton.java:87) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.widget.CompoundButton.performClick(CompoundButton.java:99) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.view.View$PerformClick.run(View.java:18422) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.os.Handler.handleCallback(Handler.java:733) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.os.Handler.dispatchMessage(Handler.java:95) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.os.Looper.loop(Looper.java:136) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at android.app.ActivityThread.main(ActivityThread.java:5017) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at java.lang.reflect.Method.invokeNative(Native Method) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at java.lang.reflect.Method.invoke(Method.java:515) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
06-23 10:04:18.200: E/AndroidRuntime(1173):  at dalvik.system.NativeStart.main(Native Method) 

是否有人可以幫助我，我在哪裏犯錯，可以做些什麼來解決這個問題呢？

Answer 1

掃描結果不同步。你必須註冊一個BroadcastReceiver監聽Intent用行動WifiManager.SCAN_RESULTS_AVAILABLE_ACTION，然後，以顯示效果，使用方法：

List <ScanResult> results = manage.getScanResults();