एंड्रॉइड: स्कैनिंग वाईफ़ाई नेटवर्क + चयन करने योग्य सूची

Question

मैं एक ऐसा एप्लिकेशन बनाने की कोशिश कर रहा हूं जो आपको उपलब्ध वाईफाई नेटवर्क स्कैन करने दे, और फिर उन्हें एक चयन योग्य सूची में प्रदर्शित कर सके। कि मैं इस कोड के साथ की कोशिश की करने के लिए:

package android.nacho.WifiScan; 

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.WifiManager; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 
import android.widget.TextView; 
import android.widget.AdapterView.OnItemClickListener; 

public class WifiScan extends Activity { 
    TextView mainText; 
    WifiManager mainWifi; 
    WifiReceiver receiverWifi; 
    List<ScanResult> wifiList; 
    StringBuilder sb = new StringBuilder(); 
    ListView listView = new ListView(this); 
    ArrayAdapter<String> adapter; 
    Context context = this; 

    static String[] NETWORKS; 

    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_wifi_scan); 
     mainText = (TextView) findViewById(R.id.text); 
     mainWifi = (WifiManager) getSystemService(Context.WIFI_SERVICE); 
     receiverWifi = new WifiReceiver(); 
     registerReceiver(receiverWifi, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)); 
     mainWifi.startScan(); 
     mainText.setText("\\nStarting Scan...\\n"); 


    } 

    public boolean onCreateOptionsMenu(Menu menu) { 
     menu.add(0, 0, 0, "Refresh"); 
     return super.onCreateOptionsMenu(menu); 
    } 

    public boolean onMenuItemSelected(int featureId, MenuItem item) { 
     mainWifi.startScan(); 
     mainText.setText("Starting Scan"); 
     return super.onMenuItemSelected(featureId, item); 
    } 

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

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

    class WifiReceiver extends BroadcastReceiver { 
     public void onReceive(Context c, Intent intent) { 


      wifiList = mainWifi.getScanResults(); 
      NETWORKS = new String[wifiList.size()]; 
      for(int i = 0; i < wifiList.size(); i++){ 

       NETWORKS[i]=i+"-"+(wifiList.get(i)).toString(); 


      } 


      System.out.println("debería imprimir: "+NETWORKS[2]); 


      adapter = new ArrayAdapter<String>(context, android.R.layout.simple_list_item_multiple_choice, NETWORKS); 
      // adapter.setDropDownViewResource(android.R.layout.select_dialog_multichoice); 
      listView.setAdapter(adapter); 
      listView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE); 
      listView.setOnItemClickListener(new OnItemClickListener() { 

       public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,long arg3) { 


       } 

      }); 

      setContentView(listView); 

     } 
    } 
} 

लेकिन मैं इस त्रुटियों हो रही है:

06-18 12:36:32.670: W/dalvikvm(15499): threadid=1: thread exiting with 
uncaught exception (group=0x40dfb930) 

06-18 12:36:32.670: E/AndroidRuntime(15499): FATAL EXCEPTION: main 

06-18 12:36:32.670: E/AndroidRuntime(15499): 
java.lang.RuntimeException: Unable to instantiate activity 
ComponentInfo{android.nacho.WifiScan/android.nacho.WifiScan.WifiScan}: 
java.lang.NullPointerException 

06-18 12:36:32.670: E/AndroidRuntime(15499): at 
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106) 

06-18 12:36:32.670: E/AndroidRuntime(15499): at 
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 

06-18 12:36:32.670: E/AndroidRuntime(15499): at 
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
06-18 12:36:32.670: D/AndroidRuntime(15499): Shutting down VM 06-18 
12:36:32.670: E/AndroidRuntime(15499):  at 
android.os.Looper.loop(Looper.java:137) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at 
android.app.ActivityThread.main(ActivityThread.java:5039) 06-18 
12:36:32.670: E/AndroidRuntime(15499):  at 
java.lang.reflect.Method.invokeNative(Native Method) 06-18 
12:36:32.670: E/AndroidRuntime(15499):  at 
java.lang.reflect.Method.invoke(Method.java:511) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at 
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
06-18 12:36:32.670: E/AndroidRuntime(15499): at 
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 06-18 
12:36:32.670: E/AndroidRuntime(15499):  at 
dalvik.system.NativeStart.main(Native Method) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): Caused by: java.lang.NullPointerException 
06-18 12:36:32.670: E/AndroidRuntime(15499): at 
android.content.ContextWrapper.getResources(ContextWrapper.java:89) 
06-18 12:36:32.670: E/AndroidRuntime(15499): at 
android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:78) 
06-18 12:36:32.670: E/AndroidRuntime(15499): at 
android.view.View.<init>(View.java:3224) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at android.view.View.<init>(View.java:3279) 
06-18 12:36:32.670: E/AndroidRuntime(15499): at 
android.view.ViewGroup.<init>(ViewGroup.java:431) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at 
android.widget.AdapterView.<init>(AdapterView.java:235) 06-18 
12:36:32.670: E/AndroidRuntime(15499):  at 
android.widget.AbsListView.<init>(AbsListView.java:766) 06-18 
12:36:32.670: E/AndroidRuntime(15499):  at 
android.widget.ListView.<init>(ListView.java:143) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at 
android.widget.ListView.<init>(ListView.java:139) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at 
android.widget.ListView.<init>(ListView.java:135) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at 
android.nacho.WifiScan.WifiScan.<init>(WifiScan.java:27) 06-18 
12:36:32.670: E/AndroidRuntime(15499):  at 
java.lang.Class.newInstanceImpl(Native Method) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at 
java.lang.Class.newInstance(Class.java:1319) 06-18 12:36:32.670: 
E/AndroidRuntime(15499): at 
android.app.Instrumentation.newActivity(Instrumentation.java:1054) 
06-18 12:36:32.670: E/AndroidRuntime(15499): at 
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097) 
06-18 12:36:32.670: E/AndroidRuntime(15499): ... 11 more 

क्या मैं गलत कर रहा हूँ ??

Answer 1

इस एक यह मेरे लिए काम किया

public class MainActivity extends Activity { 


    WifiManager mainWifi; 
    WifiReceiver receiverWifi; 

    StringBuilder sb = new StringBuilder(); 

    private final Handler handler = new Handler(); 


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


     mainWifi = (WifiManager) getSystemService(Context.WIFI_SERVICE); 

     receiverWifi = new WifiReceiver(); 
     registerReceiver(receiverWifi, new IntentFilter(
       WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)); 
     if(mainWifi.isWifiEnabled()==false) 
     { 
      mainWifi.setWifiEnabled(true); 
     } 


     doInback(); 
    } 

    public void doInback() 
    { 
     handler.postDelayed(new Runnable() { 

      @Override 
      public void run() 
      { 
       // TODO Auto-generated method stub 
       mainWifi = (WifiManager) getSystemService(Context.WIFI_SERVICE); 

       receiverWifi = new WifiReceiver(); 
       registerReceiver(receiverWifi, new IntentFilter(
         WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)); 
       mainWifi.startScan(); 
       doInback(); 
      } 
     }, 1000); 

    } 

    public boolean onCreateOptionsMenu(Menu menu) { 
     menu.add(0, 0, 0, "Refresh"); 
     return super.onCreateOptionsMenu(menu);} 
    public boolean onMenuItemSelected(int featureId, MenuItem item) { 
     mainWifi.startScan(); 

     return super.onMenuItemSelected(featureId, item);} 


    @Override 
    protected void onPause() 
    { 
     unregisterReceiver(receiverWifi); 
     super.onPause(); 
    } 

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

    class WifiReceiver extends BroadcastReceiver 
    { 
     public void onReceive(Context c, Intent intent) 
     { 

      ArrayList<String> connections=new ArrayList<String>(); 
      ArrayList<Float> Signal_Strenth= new ArrayList<Float>(); 

      sb = new StringBuilder(); 
      List<ScanResult> wifiList; 
      wifiList = mainWifi.getScanResults(); 
      for(int i = 0; i < wifiList.size(); i++) 
      { 

       connections.add(wifiList.get(i).SSID); 
      } 


     } 
    } 



} 

Answer 2

कई WifiReceivers जो तब के रूप में वे सभी अपंजीकृत नहीं मिल सकता है एक अपवाद में खत्म हो जाएगा नहीं बना doInback() करता है की कोशिश करो ?!

शायद एस। जैसे कि यह ठीक हो सकता है:

if (receiveWifi==null) { 
    receiveWifi = new WifiReceiver(); 
}