Question

我尝试使用apache commons库从我的Android应用程序发送帖子请求，但遇到了一些问题，可能是由于我对ASyncTasks缺乏了解

这是我写的相关代码

private class MyAsyncTask extends AsyncTask<String, Integer, Double>{
    @Override
    protected Double doInBackground(String... params) {
        postData(params[0]);
        return null;
    }

};

    public void postData(String name) {

        //showMessage("Transaction timed out");

        HttpClient httpClient = new DefaultHttpClient();
        // replace with your url
        HttpPost httpPost = new HttpPost("http://posttestserver.com/post.php");


        //Post Data
        List<NameValuePair> nameValuePair = new ArrayList<NameValuePair>(2);
        nameValuePair.add(new BasicNameValuePair("username", name));
        nameValuePair.add(new BasicNameValuePair("password", "123456789"));


        //Encoding POST data
        try {
            httpPost.setEntity(new UrlEncodedFormEntity(nameValuePair));
        } catch (UnsupportedEncodingException e) {
            // log exception
            e.printStackTrace();
        }

        //making POST request.
        try {
            HttpResponse response = httpClient.execute(httpPost);
            // write response to log
            Log.d("Http Post Response:", response.toString());
        } catch (ClientProtocolException e) {
            // Log exception
            e.printStackTrace();
        } catch (IOException e) {
            // Log exception
            e.printStackTrace();
        }
}

   public void postClick(View v)
{
    new MyAsyncTask().doInBackground("JACK");
}

如果有必要，

可以发布堆栈跟踪，但我可能只是做了一些愚蠢的错误，但我无法弄清楚为什么

Answer 1

直接来自：docs

AsyncTask的泛型类型：

异步任务使用的三种类型如下：

参数，执行时发送给任务的参数类型。
进度，后台计算期间发布的进度单位的类型。
结果，后台计算结果的类型。

并非所有类型都始终由异步任务使用。要将类型标记为未使用，只需使用类型Void：

private class MyTask extends AsyncTask<Void, Void, Void> { ... }

用法示例：

    imageView = (ImageView) findViewById(R.id.image_view);

//This task is going to execute "downloadFile(imageHttpAddress)"
// and so it defines String as its param type - this will be sent to doInBackground(),
// it will not post any progress and so Void for progress and finally, Bitmap as its answer
            new AsyncTask<String, Void, Bitmap>(){
                @Override
                protected void onPreExecute() {
                    super.onPreExecute();

                }

                @Override
                protected Bitmap doInBackground(String... url) {
                    return downloadFile(url[0]);
                }

                @Override
                protected void onPostExecute(Bitmap bitmap) {
                    super.onPostExecute(bitmap);
                    imageView.setImageBitmap(bitmap);
                }
            }.execute(imageHttpAddress);
    //This method takes a string (url to some image) and returns a bitmap
            private Bitmap downloadFile(String imageHttpAddress) {
                URL imageUrl = null;
                try {
                    imageUrl = new URL(imageHttpAddress);
                    HttpURLConnection conn =(HttpURLConnection)imageUrl.openConnection(); 
                    conn.connect();
                    loadedImage = BitmapFactory.decodeStream(conn.getInputStream());
                    return loadedImage; 
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

希望这有帮助。

Answer 2

来自文件： AsyncTask 是Android提供的一个抽象类，它可以帮助我们正确使用UI线程。该类允许我们执行长/后台操作并在UI线程上显示其结果，而无需操纵线程。 AsyncTask有四个步骤：

doInBackground ：此方法执行长时间运行的代码。当单击按钮执行onClick方法时，它调用execute方法接受参数并自动调用doInBackground方法并传递参数。

onPostExecute ：在doInBackground方法完成处理后调用此方法。来自doInBackground的结果将传递给此方法。

onPreExecute ：在调用doInBackground方法之前调用此方法。

onProgressUpdate ：通过从doInBackground调用此方法随时调用publish-progress来调用此方法。

 public class Restcaliing extends AsyncTask<Void, Void, Void> {
    @Override
    protected Void doInBackground(Void... params) {
        try {
            ServiceHandler serviceHandler = new ServiceHandler();
            reststring = serviceHandler.makeServiceCall(prepaerdurl, ServiceHandler.POST);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        Toast.makeText(getApplicationContext(), "" + reststring, Toast.LENGTH_SHORT).show();
    }

}

这是我的ServiceHandler类。

public class ServiceHandler {

static String response = null;
public final static int GET = 1;
public final static int POST = 2;

public ServiceHandler() {

}

/**
 * Making service call
 *
 * @url - url to make request
 * @method - http request method
 */
public String makeServiceCall(String url, int method) {
    return this.makeServiceCall(url, method, null);
}

/**
 * Making service call
 *
 * @url - url to make request
 * @method - http request method
 * @params - http request params
 */
public String makeServiceCall(String url, int method, List<NameValuePair> params) {
    try {
        // http client
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpEntity httpEntity = null;
        HttpResponse httpResponse = null;

        // Checking http request method type
        if (method == POST) {
            HttpPost httpPost = new HttpPost(url);
            // adding post params
            if (params != null) {
                httpPost.setEntity(new UrlEncodedFormEntity(params));
            }

            httpResponse = httpClient.execute(httpPost);

        } else if (method == GET) {
            // appending params to url
            if (params != null) {
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
            }
            HttpGet httpGet = new HttpGet(url);

            httpResponse = httpClient.execute(httpGet);

        }
        httpEntity = httpResponse.getEntity();
        response = EntityUtils.toString(httpEntity);
        Log.d("serv handler response"," "+response);

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    return response;

}

}

  new Restcaliing().execute();

这就是我如何调用AsyncTask。

希望你能理解并帮助你。

Android执行发布请求

2 个答案: