When I Click The Button The Loaded Listview Will Disappear

When i click the get data button . listview loaded .when i click second time listview display below the first loaded datas...now i want the 1st loaded datas should be cleared. then display the data in main page when i click second time.. below is my code..where i want to insert clear listview coding?

public void onClick(View view) {

new JSONParse().execute();

}
});

}

private class JSONParse extends AsyncTask<string, string,="" jsonobject=""> {
private ProgressDialog pDialog;
@Override
protected void onPreExecute() {
super.onPreExecute();

Status = (TextView)findViewById(R.id.textView2);
Id= (TextView)findViewById(R.id.textView1);
DateTime = (TextView)findViewById(R.id.textView3);
JobNo =(EditText)findViewById(R.id.editText1);
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Getting Data ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();

}

@Override
protected JSONObject doInBackground(String... args) {

JSONParser jParser = new JSONParser();

ArrayList<basicnamevaluepair> params = new ArrayList<basicnamevaluepair>();
params.clear();

params.add(new BasicNameValuePair("JobNo",JobNo.getText().toString()));

// Getting JSON from URL
JSONObject json = jParser.getJSONFromUrl(url,params);
return json;

}

@Override
protected void onPostExecute(JSONObject json) {
pDialog.dismiss();
try {
if (JobNo.getText().toString().equals(""))
{
Toast.makeText(MainActivity.this, " Enter Your JobNo", Toast.LENGTH_SHORT).show();
}
else
{

// Getting JSON Array from URL
Cargo = json.getJSONArray(TAG_CargoTrack);

for(int i = 0; i < Cargo.length(); i++){
JSONObject c = Cargo.getJSONObject(i);

// Storing JSON item in a Variable
String Status = c.getString(TAG_Status);
String Id = c.getString(TAG_Id);
String DateTime = c.getString(TAG_DateTime);

// Adding value HashMap key => value
//list.clearFocus();
HashMap<string, string=""> map = new HashMap<string, string="">();

map.put(TAG_Status, Status);
map.put(TAG_Id, Id);
map.put(TAG_DateTime, DateTime);

CargoTracklist.add(map);
list=(ListView)findViewById(R.id.listView1);

SpecialAdapter adapter = new SpecialAdapter(MainActivity.this, CargoTracklist,
//ListAdapter adapter = new SimpleAdapter(MainActivity.this, CargoTracklist,
R.layout.listview,
new String[] { TAG_Status,TAG_Id, TAG_DateTime }, new int[] {
R.id.textView2,R.id.textView1, R.id.textView3});