我不知道如何解决的Android AsyncTask方法

Question

我调试了我的程序，我注意到我无法在同一个线程上运行网络（我搜索了这个错误，比如 2 天，因为在虚拟设备中应用程序正常工作 -.- ）。所以现在我知道我必须如何修复它，但我不知道如何将一些不全是字符串的参数提供给 doinBackground 方法。

我的方法需要一个 url 方法，我可以在 doInBackground 方法中使用 params[0] 和 params[1] 访问 afaik。但是 NameValuePairs 列表是怎么回事，如何在 doInBackground 方法中访问它？

非常感谢您的帮助:)

这是我的课：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.params.ClientPNames;
import org.apache.http.client.params.CookiePolicy;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import android.os.AsyncTask;
import android.util.Log;

public class JSONParser extends AsyncTask<String, Void, JSONObject>{

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }

    // Funktion um JSON aus einer URL zu holen
    // Es wird ein POST oder ein GET Request gesendet
    public JSONObject makeHttpRequest(String url, String method,
            List<NameValuePair> params) {

        // HTTP Request erstellen
        try {

            // Überprüfen welche Request Methode benutzt werden soll
            if(method == "POST"){
                DefaultHttpClient httpClient = new DefaultHttpClient();
                httpClient.getParams().setParameter(ClientPNames.COOKIE_POLICY,
                        CookiePolicy.BROWSER_COMPATIBILITY);
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();

            }else if(method == "GET"){
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
            }          

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

        //Stream in ein String umwandeln
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Fehler!", "Fehler mein umwandeln von Stream in String: " + e.toString());
        }

        // JSON Object parsen
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // Das JSONObject zurückgeben
        return jObj;

    }

    @Override
    protected JSONObject doInBackground(String... params) {
        // TODO Auto-generated method stub
        return null;
    }
}

Answer 1

我认为您并不完全理解 AsyncTasks 的完整概念。当您想在后台线程中运行操作时使用这些，这是完成此任务的一种非常好/灵活的方式。对我来说真正好的是onPostExecute() 在主线程上执行，所以一旦你的工作在doInBackground() 中完成，它确实可以做一些强大的事情。您应该记住，因为onPostExecute() 确实在主线程上执行，所以您不想在此处执行任何网络操作。

这是一个简单的 AsyncTask 示例：

private class myAsyncTask extends AsyncTask<String, Void, Boolean> {

    @Override
    protected void onPreExecute() {
        // before we start working
    }   

    @Override
    protected Boolean doInBackground(String... args) {
        //do work in the background
        return true;
    }

    @Override
    protected void onPostExecute(Boolean success) {
        // the work is done.. now what?
    }       
}

doInBackground() 是您完成大部分工作的地方，因此我将尝试帮助您完成所需的基本结构。我只是将您的代码复制并粘贴到我认为应该去的地方，所以这不是 100% 保证的，但希望它会帮助您开始您想做的事情：

private class JSONParser extends AsyncTask<String, Void, JSONObject> {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // variables passed in:
    String url;
    String method;
    List<NameValuePair> params;

    // constructor
    public JSONParser(String url, String method, 
        List<NameValuePair> params) {
        this.url = url;
        this.method = method;
        this.params = params;
    }


    @Override
    protected JSONObject doInBackground(String... args) {
        try {
            if(method == "POST"){
                DefaultHttpClient httpClient = new DefaultHttpClient();
                httpClient.getParams().setParameter(ClientPNames.COOKIE_POLICY,
                        CookiePolicy.BROWSER_COMPATIBILITY);
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();

            } else if(method == "GET"){
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Fehler!", "Fehler mein umwandeln von Stream in String: " + e.toString());
        }

        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        return jObj;
    }

    @Override
    protected void onPostExecute(JSONObject obj) {
        // Now we have your JSONObject, play around with it.
    }       
}

编辑：

我忘了提到你也可以传入args，它是一个字符串数组。您可以在调用 AsyncTask 时创建 args 并传入它：

new JSONParser(url, method, params).execute(args);

你可以在doInBackground()访问args

这里有更多关于 AyncTask 的信息：http://developer.android.com/reference/android/os/AsyncTask.html