onPostExecute的java.lang.NullPointerException？

我有这些类，我在向服务器发送SOAP请求 . 我有我的主类，AsyncTask类，解析器类，接口 . 我的问题是我总是得到这个NullpointerException . 我正在尝试做的是在我的主要活动中我将向AsyncTask发送一个字符串，然后在AsyncTask中发送onPostExecute的结果，我需要将它传递给Parser类，在这部分我遇到了问题 . 我使用上一个问题的界面，但它不起作用 .

AsyncTask类：

public class TestAsyncTask extends AsyncTask<String, Void, String> {

public TestInterface delegate = null;
String soapString = "http://-------------"; 
String serverString = "https:-----------";

@Override
protected String doInBackground(String... sString) {
String yourValue = sString[0];
String resString = null; //This will be the storage of the response.

try {

    //Uses URL and HttpURLConnection for server connection
    URL url = new URL(serverString); 
    HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); 
    urlConnection.setDoOutput(true); 
    urlConnection.setDoInput(true); 
    urlConnection.setUseCaches(false); 
    urlConnection.setChunkedStreamingMode(0); 
    urlConnection.addRequestProperty("SOAPAction", soapString); 
    urlConnection.addRequestProperty("Content-Type", "text/xml; charset=utf-8"); 
    urlConnection.addRequestProperty("Content-Length", "" + yourValue.length()); 
    urlConnection.setRequestMethod(HttpPost.METHOD_NAME); 

    // Using OutputStream and Writer to send a request to the server.
    OutputStream outputStream = urlConnection.getOutputStream(); 
    Writer writer = new OutputStreamWriter(outputStream); 
    writer.write(yourValue); 
    writer.flush(); 
    writer.close(); 

    //Using InputStream to get the response of the request from the server.
    InputStream inPutStream = urlConnection.getInputStream(); 
    BufferedReader buffReader = new BufferedReader(new InputStreamReader(inPutStream)); 
    ByteArrayBuffer byteBuffer = new ByteArrayBuffer(50);

    int resint = urlConnection.getResponseCode(); 

    while ((resint = buffReader.read()) != -1) {
        byteBuffer.append(resint); 
    }

    resString = new String(byteBuffer.toByteArray()); 

    } catch (Exception aException) {
    resString = aException.getMessage(); 
    }

    return resString; 
}


protected void onPostExecute(String aReturnValueString) {
    //I THINK HERE IS WHERE THE PROBLEM EXIST
            delegate.processFinish(aReturnValueString);
}
}

接口，我不确定：

public interface TestInterface {
  void processFinish(String output);
}

解析器类：

public class TestParser implements TestInterface {

TestAsyncTask a= new TestAsyncTask();
TextView oTextView[], aTextView[], pTextView[], dTextView[]; //Create a new TextView array to store the parsing results.
private LinearLayout linearLayout;
int pars;

Context contxt;

//Constructor
public TestParser(Context cContext){
    contxt = cContext; //Pass Context to constructor
}

//Getter for LinearLayout.
    public LinearLayout getLinearLayout(){
        return linearLayout;
    }
    //Setter for LinearLayout.
    public void setLinearLayout(LinearLayout aSetterLinearLayout){
        this.linearLayout = aSetterLinearLayout;
    }


    public void onCreate(Bundle savedInstanceState) {
     a.delegate = this;
    }

 public void processFinish(String output) {
    // TODO Auto-generated method stub
    linearLayout = new LinearLayout(this);

    //The try/catch statement encloses some code and is used to handle errors and exceptions that might occur in that code.
    try {

        //Use SAXParser(Simple API for XML) to handle the parsing of XML(Response). */

        SAXParserFactory saxParF = SAXParserFactory.newInstance(); 
        SAXParser sAXPar = saxParF.newSAXParser(); 
        XMLReader xMLReader = sAXPar.getXMLReader(); 

        // Create handler to handle XML Tags (GBXMLHandler extends DefaultHandler).         
        TestXMLHandler xMLHandler = new TestXMLHandler(); 
        xMLReader.setContentHandler(xMLHandler); 
        InputSource inputSource = new InputSource(new StringReader(output)); 
        xMLReader.parse(inputSource);

        TestData data = TestXMLHandler.aData; 

        int aone = data.getoName().size();
        int atwo = data.getDes().size();

        oTextView = new TextView[aone];  
        aTextView = new TextView[aone]; 
        dTextView = new TextView[atwo];
        pTextView = new TextView[atwo];

        //The for statement provides a compact way to iterate over a range of values.
        for (pars = 0; pars + 1 < atwo; pars++) {

        dTextView[pars] = new TextView(getApplicationContext()); 
        dTextView[pars].setText("Description = " + data.getDes().get(pars)); 
        linearLayout.addView(dTextView[pars]); 

        pTextView[pars] = new TextView(getApplicationContext()); 
        pTextView[pars].setText("RegularSellUnitPrice = " + data.getRegularSellUnitPrice().get(pars)); 
        linearLayout.addView(pTextView[pars]);
        }

        for (pars = 0; pars < aone; pars++){
        oTextView[pars] = new TextView(getApplicationContext()); 
        oTextView[pars].setText("OperatorName = " + data.getoName().get(pars)); 
        linearLayout.addView(oTextView[pars]);

        aTextView[pars] = new TextView(getApplicationContext()); 
        aTextView[pars].setText("type = " + data.getType().get(pars));
        linearLayout.addView(aTextView[pars]);      
        }
    } catch (Exception e) {
        System.out.println("XML Pasing Exception = " + e);
    }
}
}