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PONullPointerException at ListView
 

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  1. PONullPointerException at ListView
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    <p>I get an NPE at Line 29 (<code>private ListView lv = (ListView) findViewById(R.id.ScanList);</code>), but I guess this is because of the following line:</p> <pre><code>this.adapter = new SimpleAdapter(ScannerActivity.this, arraylist, R.layout.row, new String[] { ITEM_KEY }, new int[] { R.id.list_value }); </code></pre> <p>What belongs into "R.id.list_value" and "R.layout.row" is it a row.xml? I dont get what I have to write in there!</p> <p>To know how the code works I paste a the relvant parts:</p> <pre><code>public class ScannerActivity extends Activity implements OnClickListener { private WifiManager wifi; private ListView lv = (ListView) findViewById(R.id.ScanList); private Button buttonScan = (Button) findViewById(R.id.scannow_button); private Switch enable; private int size = 0; private List&lt;ScanResult&gt; results; private final String ITEM_KEY = "key"; private final ArrayList&lt;HashMap&lt;String, String&gt;&gt; arraylist = new ArrayList&lt;HashMap&lt;String, String&gt;&gt;(); private SimpleAdapter adapter; /* Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_scan); buttonScan.setOnClickListener(this); wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE); enable.setChecked(wifi.isWifiEnabled()); enable.setOnCheckedChangeListener(new OnCheckedChangeListener() { @Override public void onCheckedChanged(CompoundButton compoundbutton, boolean flag) { wifi.setWifiEnabled(flag); if (flag) { arraylist.clear(); lv.setVisibility(View.VISIBLE); buttonScan.setEnabled(true); wifi.startScan(); } else { lv.setVisibility(View.INVISIBLE); buttonScan.setEnabled(false); } } }); this.adapter = new SimpleAdapter(ScannerActivity.this, arraylist, R.layout.activity_scan, new String[]{ITEM_KEY}, new int[]{R.id.ScanList}); lv.setAdapter(this.adapter); lv.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView&lt;?&gt; arg0, View arg1, int position, long id) { lv.getSelectedItemPosition(); Intent myIntent = new Intent(ScannerActivity.this, MyActivity.class); String mac = results.get(size).BSSID; myIntent.putExtra("mac", mac); ScannerActivity.this.startActivity(myIntent); } }); </code></pre> <p>This is my first ListView, so please help me :)</p>
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    1. USuser2521471
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      1. PONullPointerException at ListView
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A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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