OnPostExecute结果为null

问题描述

我正在将一些数据从我的应用程序发送到外部服务器。

public class PostKey extends AsyncTask<String, String, String> {
    public AsyncResponse delegate = null;

    @Override
    protected String doInBackground(String... params) {
        postData(params[0]);
        return null;
    }

    @Override
    protected void onPostExecute(String result){
        Log.d(String.valueOf(result), " Result?");
        delegate.processFinish(result); // Returns NullPointerException
    }

    public void postData(String valueIWantToSend) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost     = new HttpPost("http://domain.com/post.php");

        try {
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
            nameValuePairs.add(new BasicNameValuePair("hoi", "test"));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

            HttpResponse response = httpclient.execute(httppost);
            String responseStr = EntityUtils.toString(response.getEntity());

            Log.d(responseStr, "");
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
        } catch (IOException e) {
            // TODO Auto-generated catch block
        }
    }

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

Log.d(responseStr, ""); 确实会根据发送的数据返回true或false并将其记录下来。

delegate.processFinish(result); 返回NullPointerException public class PostKey extends AsyncTask<String, String, String>即使所有参数都声明为Strings public class PostKey extends AsyncTask<String, String, String>也提到public class PostKey extends AsyncTask<String, String, String> 。

我也尝试过用responseStr替换result ，但这也不起作用。

将您的代码更改为

public class PostKey extends AsyncTask<String, String, String> {
    public AsyncResponse delegate = null;

    public PostKey(AsyncResponse asyncResponse) {
        delegate = asyncResponse;
    }   

    @Override 
    protected String doInBackground(String... params) {
        return postData(params[0]);
    } 

    @Override 
    protected void onPostExecute(String result){
        Log.d(String.valueOf(result), " Result?");
        delegate.processFinish(result);
    } 

    public String postData(String valueIWantToSend) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost     = new HttpPost("http://domain.com/post.php");

        try { 
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
            nameValuePairs.add(new BasicNameValuePair("hoi", "test"));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

            HttpResponse response = httpclient.execute(httppost);
            String responseStr = EntityUtils.toString(response.getEntity());

            Log.d(responseStr, "");
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block 
        } catch (IOException e) {
            // TODO Auto-generated catch block 
        } 
        return responseStr;
    } 

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

如果您想要postData（）的结果，则将postData（）的返回类型从void更改为String，然后将结果返回到onPostExecute，如下所示：

public class PostKey extends AsyncTask<String, String, String> {
    public AsyncResponse delegate = null;

    @Override
    protected String doInBackground(String... params) {
        return postData(params[0]);
    }

    @Override
    protected void onPostExecute(String result){
        Log.d(String.valueOf(result), " Result?");
        delegate.processFinish(result); // Returns NullPointerException
    }

    public String postData(String valueIWantToSend) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost     = new HttpPost("http://domain.com/post.php");

        try {
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
            nameValuePairs.add(new BasicNameValuePair("hoi", "test"));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

            HttpResponse response = httpclient.execute(httppost);
            String responseStr = EntityUtils.toString(response.getEntity());
            return responseStr;
            Log.d(responseStr, "");
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
        } catch (IOException e) {
            // TODO Auto-generated catch block
        }
       return null;
    }

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