未调用AsyncTask的onPostExecute

Question

我对Android应用开发相对较新，并想知道我做错了什么。我有一个使用用户名和密码连接到我的Web服务器的AsyncTask，并将用户数据集作为json对象返回。不幸的是我无法获取json字符串，因为我的AsyncHttpReading类中的onPostExecute（）似乎没有被调用。为什么呢？

MainActivity.java 的

package com.alphavoice.sampleproject;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executor;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import android.app.Activity;
import android.content.SharedPreferences;
import android.graphics.Color;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import org.json.JSONException;
import org.json.JSONObject;

import com.alphavoice.sampleproject.community.user.User;
import com.alphavoice.sampleproject.util.HttpReader;

public class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        SharedPreferences appPrefs = PreferenceManager.getDefaultSharedPreferences(this);
        boolean isLoggedIn = (appPrefs.getInt("userId", 0) != 0) ? true : false;

        if (isLoggedIn) {    
            renderCommunityView();
        }
        else {
            setContentView(R.layout.activity_main);

            final Button btnLogin = (Button) findViewById(R.id.btn_login);
            final EditText etUsername = (EditText) findViewById(R.id.et_username);
            final EditText etPassword = (EditText) findViewById(R.id.et_password);

            btnLogin.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    String username = etUsername.getText().toString();
                    String password = etPassword.getText().toString();

                    String loginUrl = "http://example.com/websrv/get_user.php?username=" + username + "&password=" + password;

                    AsyncHttpReading httpReading = new AsyncHttpReading();

                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
                        int corePoolSize = 60;
                        int maximumPoolSize = 80;
                        int keepAliveTime = 10;

                        BlockingQueue<Runnable> workQueue = new LinkedBlockingQueue<Runnable>(maximumPoolSize);
                        Executor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, workQueue);
                        // httpReading.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, loginUrl);
                        httpReading.executeOnExecutor(threadPoolExecutor, loginUrl);
                    }
                    else {
                        httpReading.execute(loginUrl);
                    }

                    if (httpReading.getLoggedInUser() != null) {
                        // renderCommunityView();
                        btnLogin.setBackgroundColor(Color.GREEN);
                    }
                    else {
                        // wrong combination of username & password => try again
                        etUsername.setBackgroundColor(Color.rgb(255, 204, 204));
                        etPassword.setBackgroundColor(Color.rgb(255, 204, 204));
                    }
                }
            });
        }
    }

    private void renderCommunityView() {
        setContentView(R.layout.activity_community);
    }

    private class AsyncHttpReading extends AsyncTask<String, Void, String> {
        private String response = "";
        private User loggedInUser = null;

        public AsyncHttpReading() { }

        public String getResponse() {
            return response;
        }

        public User getLoggedInUser() {
            return loggedInUser;
        }

        @Override
        protected String doInBackground(String... urls) {
            HttpReader httpReader = new HttpReader(urls[0]);
            response = httpReader.getResponse();

            return response;
        }

        @Override
        protected void onPostExecute(String response) {
            try {
                JSONObject userData = new JSONObject(this.getResponse()).getJSONObject("0");

                if (userData != null) {
                    loggedInUser = new User(userData);
                }
            } catch (JSONException e) {
                Log.e("SAMPLEPROJECT", "Could not parse json data!");
            }
        }
    }
}

package com.alphavoice.sampleproject; import java.util.concurrent.BlockingQueue; import java.util.concurrent.Executor; import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; import android.app.Activity; import android.content.SharedPreferences; import android.graphics.Color; import android.os.AsyncTask; import android.os.Build; import android.os.Bundle; import android.preference.PreferenceManager; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.Toast; import org.json.JSONException; import org.json.JSONObject; import com.alphavoice.sampleproject.community.user.User; import com.alphavoice.sampleproject.util.HttpReader; public class MainActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); SharedPreferences appPrefs = PreferenceManager.getDefaultSharedPreferences(this); boolean isLoggedIn = (appPrefs.getInt("userId", 0) != 0) ? true : false; if (isLoggedIn) { renderCommunityView(); } else { setContentView(R.layout.activity_main); final Button btnLogin = (Button) findViewById(R.id.btn_login); final EditText etUsername = (EditText) findViewById(R.id.et_username); final EditText etPassword = (EditText) findViewById(R.id.et_password); btnLogin.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { String username = etUsername.getText().toString(); String password = etPassword.getText().toString(); String loginUrl = "http://example.com/websrv/get_user.php?username=" + username + "&password=" + password; AsyncHttpReading httpReading = new AsyncHttpReading(); if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { int corePoolSize = 60; int maximumPoolSize = 80; int keepAliveTime = 10; BlockingQueue<Runnable> workQueue = new LinkedBlockingQueue<Runnable>(maximumPoolSize); Executor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, workQueue); // httpReading.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, loginUrl); httpReading.executeOnExecutor(threadPoolExecutor, loginUrl); } else { httpReading.execute(loginUrl); } if (httpReading.getLoggedInUser() != null) { // renderCommunityView(); btnLogin.setBackgroundColor(Color.GREEN); } else { // wrong combination of username & password => try again etUsername.setBackgroundColor(Color.rgb(255, 204, 204)); etPassword.setBackgroundColor(Color.rgb(255, 204, 204)); } } }); } } private void renderCommunityView() { setContentView(R.layout.activity_community); } private class AsyncHttpReading extends AsyncTask<String, Void, String> { private String response = ""; private User loggedInUser = null; public AsyncHttpReading() { } public String getResponse() { return response; } public User getLoggedInUser() { return loggedInUser; } @Override protected String doInBackground(String... urls) { HttpReader httpReader = new HttpReader(urls[0]); response = httpReader.getResponse(); return response; } @Override protected void onPostExecute(String response) { try { JSONObject userData = new JSONObject(this.getResponse()).getJSONObject("0"); if (userData != null) { loggedInUser = new User(userData); } } catch (JSONException e) { Log.e("SAMPLEPROJECT", "Could not parse json data!"); } } } }

HttpReader.java 的

package com.alphavoice.sampleproject.util;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;

import android.util.Log;

public class HttpReader {
    private String url = "";

    public HttpReader(String url) {
        this.url = url;
    }

    public String getURL() {
        return url;
    }

    public String getResponse() {
        URL urlObj = null;
        HttpURLConnection connection = null;

        // http request
        try {
            urlObj = new URL(url);

            connection = (HttpURLConnection) urlObj.openConnection();
            connection.setReadTimeout(10000);
            connection.setConnectTimeout(15000);
            connection.setRequestMethod("POST");
            connection.setDoInput(true);
            connection.setDoOutput(true);
        } catch (Exception e) {
            Log.e("SAMPLEPROJECT", "Could not connect to web server!");
        }

        // read stream
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(urlObj.openStream()));
            StringBuffer buffer = new StringBuffer();
            char[] chars = new char[1024];
            int read = 0;

            while ((read = reader.read(chars)) != -1) {
                buffer.append(chars, 0, read); 
            }

            reader.close();

            return buffer.toString();
        } catch (IOException e) {
            Log.e("SAMPLEPROJECT", "Could not open stream!");
        }

        return null;
    }
}

User.java 的 package com.alphavoice.sampleproject.util; import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.IOException; import java.net.HttpURLConnection; import java.net.URL; import android.util.Log; public class HttpReader { private String url = ""; public HttpReader(String url) { this.url = url; } public String getURL() { return url; } public String getResponse() { URL urlObj = null; HttpURLConnection connection = null; // http request try { urlObj = new URL(url); connection = (HttpURLConnection) urlObj.openConnection(); connection.setReadTimeout(10000); connection.setConnectTimeout(15000); connection.setRequestMethod("POST"); connection.setDoInput(true); connection.setDoOutput(true); } catch (Exception e) { Log.e("SAMPLEPROJECT", "Could not connect to web server!"); } // read stream try { BufferedReader reader = new BufferedReader(new InputStreamReader(urlObj.openStream())); StringBuffer buffer = new StringBuffer(); char[] chars = new char[1024]; int read = 0; while ((read = reader.read(chars)) != -1) { buffer.append(chars, 0, read); } reader.close(); return buffer.toString(); } catch (IOException e) { Log.e("SAMPLEPROJECT", "Could not open stream!"); } return null; } }