android Wifi application craches

Question

I wrote an android application that scans for wifi connection.

i used the following code

package com.android.wifitester;

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.widget.TextView;

public class WifiTester extends Activity { TextView mainText; WifiManager mainWifi; WifiReceiver receiverWifi; List wifiList; StringBuilder sb = new StringBuilder();

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mainText = (TextView) findViewById(R.id.mainText);
    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) {
        sb = new StringBuilder();
        wifiList = mainWifi.getScanResults();
        for(int i = 0; i < wifiList.size(); i++){
            sb.append(new Integer(i+1).toString() + ".");
            sb.append((wifiList.get(i)).toString());
            sb.append("\n");
        }
        mainText.setText(sb);
    }
}

}

when I run the application on the emulator, it crashes

the manifest file is:

<?xml version="1.0" encoding="utf-8"?>

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

<uses-sdk android:minSdkVersion="8" />

my question is why it crashes although i added the permission line