android中的ProgressDialog即使使用异步任务也未显示

大家好：） 我有点小问题。我想在单击Login时显示ProgressDialog，但没有显示任何内容。它只是在没有ProgressDialog的情况下执行任务。我正在使用AsyncTask并在该线程中打开ProgressDialog，但什么也没有出现。以下是我的源代码：

这就是所谓的：

ProgressDialog progress = new ProgressDialog(mainActivity);
progress.setMessage("Sie werden registriert...");

jsonParser = new JSONParser(progress, url_create_user, "POST", params);

这是JSONParser类：

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.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.util.Log;

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

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

    String url = "";
    String method = "";
    List<NameValuePair> parameters;
    ProgressDialog prog;

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

    private Handler handler = new Handler() {

        @Override
        public void handleMessage(Message msg) {
            if (msg.what == 0)
            {
                prog.show();
            }
            else
            {
                prog.dismiss();
            }

        }
    };

    @Override
    protected JSONObject doInBackground(Context... params) {
        try {
            handler.sendEmptyMessage(0);
            // 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(this.parameters));

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

            }else if(method == "GET"){
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(this.parameters, "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 beim parsen " + e.toString());
        }
        handler.sendEmptyMessage(1);
        // Das JSONObject zurückgeben
        return jObj;
    }
}

导入java.io.BufferedReader；
导入java.io.IOException；
导入java.io.InputStream；
导入java.io.InputStreamReader；
导入java.io.UnsupportedEncodingException；
导入java.util.List；
导入org.apache.http.HttpEntity；
导入org.apache.http.HttpResponse；
导入org.apache.http.NameValuePair；
导入org.apache.http.client.ClientProtocolException；
导入org.apache.http.client.entity.UrlEncodedFormEntity；
导入org.apache.http.client.methods.HttpGet；
导入org.apache.http.client.methods.HttpPost；
导入org.apache.http.client.params.ClientPNames；
导入org.apache.http.client.params.CookiePolicy；
导入org.apache.http.client.utils.URLEncodedUtils；
导入org.apache.http.impl.client.DefaultHttpClient；
导入org.json.JSONException；
导入org.json.JSONObject；
导入android.app.ProgressDialog；
导入android.content.Context；
导入android.os.AsyncTask；
导入android.os.Handler；
导入android.os.Looper；
导入android.os.Message；
导入android.util.Log；
公共类JSONParser扩展了异步任务{
静态InputStream为空；
静态JSONObject jObj=null；
静态字符串json=“”；
字符串url=“”；
字符串方法=”；
列出参数；
进程对话程序；
//建造师
公共JSONParser（ProgressDialog程序、字符串url、字符串方法、列表参数）{
this.url=url；
这个方法=方法；
this.parameters=param；
this.prog=prog；
}
私有处理程序=新处理程序（）{
@凌驾
公共无效handleMessage（消息消息消息）{
如果（msg.what==0）
{
prog.show（）；
}
其他的
{
程序解除（）；
}
}
};
@凌驾
受保护的JSONObject doInBackground（上下文…参数）{
试一试{
handler.sendEmptyMessage（0）；
//Überprüfen welche请求方法
如果（方法==“POST”）{
DefaultHttpClient httpClient=新的DefaultHttpClient（）；
httpClient.getParams（）.setParameter（ClientPNames.COOKIE_策略，
CookiePolicy.BROWSER_兼容性）；
HttpPost HttpPost=新的HttpPost（url）；
setEntity（新的UrlEncodedFormEntity（this.parameters））；
HttpResponse HttpResponse=httpClient.execute（httpPost）；
HttpEntity HttpEntity=httpResponse.getEntity（）；
is=httpEntity.getContent（）；
}else if（方法==“GET”）{
DefaultHttpClient httpClient=新的DefaultHttpClient（）；
String paramString=URLEncodedUtils.format（this.parameters，“utf-8”）；
url+=“？”+参数字符串；
HttpGet HttpGet=新的HttpGet（url）；
HttpResponse HttpResponse=httpClient.execute（httpGet）；
HttpEntity HttpEntity=httpResponse.getEntity（）；
is=httpEntity.getContent（）；
}          
}捕获（不支持的编码异常e）{
e、 printStackTrace（）；
}捕获（客户端协议例外e）{
e、 printStackTrace（）；
}捕获（IOE异常）{
e、 printStackTrace（）；
}
//ein字符串umwandeln中的流
试一试{
BufferedReader reader=新的BufferedReader（新的InputStreamReader(
is，“iso-8859-1”），8）；
StringBuilder sb=新的StringBuilder（）；
字符串行=null；
而（（line=reader.readLine（））！=null）{
sb.追加（第+行“\n”）；
}
is.close（）；
json=sb.toString（）；
}捕获（例外e）{
Log.e（“Fehler！”，“Fehler mein umwandeln von Stream in String:”+e.toString（））；
}
//JSON对象解析
试一试{
jObj=新的JSONObject（json）；
}捕获（JSONException e）{
e（“JSON解析器”，“错误beim parsen”+e.toString（））；
}
handler.sendEmptyMessage（1）；
//这是祖鲁克本的工作目标
返回jObj；
}
}

您无法比较两个字符串之间的==值

使用：

请参阅以下带有异步任务的JSON解析器示例代码
包com.androidhive.json解析；
导入java.io.BufferedReader；
导入java.io.IOException；
导入java.io.InputStream；
导入java.io.InputStreamReader；
导入java.io.UnsupportedEncodingException；
导入java.util.ArrayList；
导入java.util.HashMap；
导入org.apache.http.HttpEntity；
导入org.apache.http.HttpResponse；
导入org.apache.http.client.ClientProtocolException；
导入org.apache.http.client.methods.HttpPost；
导入org.apache.http.impl.client.DefaultHttpClient；
导入org.json.JSONArray；
导入org.json.JSONException；
导入org.json.JSONObject；
导入android.app.ListActivity；
导入android.app.ProgressDialog；
导入android.content.Intent；
导入android.os.AsyncTask；
导入android.os.Bundle；
导入android.util.Log；
导入android.view.view；
导入android.widget.AdapterView；
导入android.widget.AdapterView.OnItemClickListener；
导入android.widget.ListAdapter；
导入android.widget.ListView；
导入android.widget.simpledapter；
导入android.widget.TextView；
公共类AndroidJSONParsingActivity扩展了ListActivity{
//发出请求的url
专用静态字符串url=”http://api.androidhive.info/contacts/";
//JSON节点名称
专用静态最终字符串标记_CONTACTS=“CONTACTS”；
私有静态最终字符串标记\u ID=“ID”；
私有静态最终Strin
method.equals("POST");

see the following example code of JSON parser with async task

package com.androidhive.jsonparsing;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.HashMap;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;

public class AndroidJSONParsingActivity extends ListActivity {

    // url to make request
    private static String url = "http://api.androidhive.info/contacts/";

    // JSON Node names
    private static final String TAG_CONTACTS = "contacts";
    private static final String TAG_ID = "id";
    private static final String TAG_NAME = "name";
    private static final String TAG_EMAIL = "email";
    private static final String TAG_ADDRESS = "address";
    private static final String TAG_GENDER = "gender";
    private static final String TAG_PHONE = "phone";
    private static final String TAG_PHONE_MOBILE = "mobile";
    private static final String TAG_PHONE_HOME = "home";
    private static final String TAG_PHONE_OFFICE = "office";
    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // contacts JSONArray
    JSONArray contacts = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        new GetEventsTask().execute("");
    }

    protected class GetEventsTask extends
            AsyncTask<String, Integer, ArrayList<HashMap<String, String>>> {
        protected ArrayList<HashMap<String, String>> contactList;

        private final ProgressDialog dialog = new ProgressDialog(
                AndroidJSONParsingActivity.this);

        //PreExecute Method

        protected void onPreExecute() {
            this.dialog.setMessage("Loading, Please Wait..");
            this.dialog.setCancelable(false);
            this.dialog.show();
        }

        //doInBackground Method

        @Override
        protected ArrayList<HashMap<String, String>> doInBackground(
                String... params) {
            contactList = new ArrayList<HashMap<String, String>>();
            // Making HTTP request
            try {
                // defaultHttpClient
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);

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

            // try parse the string to a JSON object
            try {
                jObj = new JSONObject(json);
                Log.i("json objects",""+json);
            } catch (JSONException e) {
                Log.e("JSON Parser", "Error parsing data " + e.toString());
            }
            try {
                // Getting Array of Contacts
                contacts = jObj.getJSONArray(TAG_CONTACTS);

                // looping through All Contacts
                for (int i = 0; i < contacts.length(); i++) {
                    JSONObject c = contacts.getJSONObject(i);

                    // Storing each json item in variable
                    String id = c.getString(TAG_ID);
                    String name = c.getString(TAG_NAME);
                    String email = c.getString(TAG_EMAIL);
                    String address = c.getString(TAG_ADDRESS);
                    String gender = c.getString(TAG_GENDER);

                    // Phone number is agin JSON Object
                    JSONObject phone = c.getJSONObject(TAG_PHONE);
                    String mobile = phone.getString(TAG_PHONE_MOBILE);
                    String home = phone.getString(TAG_PHONE_HOME);
                    String office = phone.getString(TAG_PHONE_OFFICE);

                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    map.put(TAG_ID, id);
                    map.put(TAG_NAME, name);
                    map.put(TAG_EMAIL, email);
                    map.put(TAG_PHONE_MOBILE, mobile);

                    // adding HashList to ArrayList
                    contactList.add(map);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return contactList;
        }

        //onPostExecute Method 


        protected void onPostExecute(ArrayList<HashMap<String, String>> result) {

            ListAdapter adapter = new SimpleAdapter(getApplicationContext(),
                    contactList, R.layout.list_item, new String[] { TAG_NAME,
                            TAG_EMAIL, TAG_PHONE_MOBILE }, new int[] {
                            R.id.name, R.id.email, R.id.mobile });
            // selecting single ListView item
            ListView lv = getListView();
            lv.setAdapter(adapter);



            // Launching new screen on Selecting Single ListItem
            lv.setOnItemClickListener(new OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view,
                        int position, long id) {
                    // getting values from selected ListItem
                    String name = ((TextView) view.findViewById(R.id.name)).getText().toString();
                    String cost = ((TextView) view.findViewById(R.id.email)).getText().toString();
                    String description = ((TextView) view.findViewById(R.id.mobile)).getText().toString();

                    // Starting new intent
                    Intent in = new Intent(getApplicationContext(),SingleMenuItemActivity.class);
                    in.putExtra(TAG_NAME, name);
                    in.putExtra(TAG_EMAIL, cost);
                    in.putExtra(TAG_PHONE_MOBILE, description);
                    startActivity(in);
                }
            });
            if (this.dialog.isShowing()) {
                this.dialog.dismiss();
            }
        }

    }

}