管理android中进度对话框的显示时间

Question

问题是，如果用户有缓慢的互联网连接，那么我想要显示进度对话框期间从网站加载数据。我使用AsyncTask类来实现这一点。但是当我运行我的代码时，当数据已经加载到屏幕上时，我的对话框就会显示。在加载过程中，我看到模拟器上有黑屏。请给出建议如何在加载开始时显示进度对话框，并在加载结束时自动关闭。我不想一开始就看到黑屏。这是我的主要java文件。请帮帮忙.........

package com.androidhive.xmlparsing;

import java.util.ArrayList;
import java.util.HashMap;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.DialogInterface.OnCancelListener;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.SimpleAdapter;
import android.widget.TextView;

public class AndroidXMLParsingActivity extends ListActivity {


TextView textView;
ArrayList<HashMap<String, String>> menuItems;
// All static variables
static final String URL = "http://feeds.bbci.co.uk/news/rss.xml" ;
// XML node keys
static final String KEY_ITEM = "item"; // parent node
static final String KEY_ID = "id";
static final String KEY_NAME = "title";
//static final String KEY_COST = "cost";
static final String KEY_DESC = "description";
static final String KEY_IMAGE = "media:thumbnail";



@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    new HeavyWorker(AndroidXMLParsingActivity.this).execute();

System.out.println("you are on print line 1");  
    menuItems = new ArrayList<HashMap<String, String>>();

    XMLParser parser = new XMLParser();
    String xml = parser.getXmlFromUrl(URL); // getting XML
    Document doc = parser.getDomElement(xml); // getting DOM element
    System.out.println("you are on print line 2");
    NodeList nl = doc.getElementsByTagName(KEY_ITEM);
    // looping through all item nodes <item>
    for (int i = 0; i < nl.getLength(); i++) {
        // creating new HashMap
        HashMap<String, String> map = new HashMap<String, String>();
        Element e = (Element) nl.item(i);
        // adding each child node to HashMap key => value
        map.put(KEY_ID, parser.getValue(e, KEY_ID));
        map.put(KEY_NAME, parser.getValue(e, KEY_NAME));
    //  map.put(KEY_COST, "Rs" + parser.getValue(e, KEY_COST));
        map.put(KEY_DESC, parser.getValue(e, KEY_DESC));
        map.put(KEY_IMAGE, parser.getValue(e, KEY_IMAGE));

        // adding HashList to ArrayList
        menuItems.add(map);
    }

    System.out.println("you are on print line 3");


    // Adding menuItems to ListView
    ListAdapter adapter = new SimpleAdapter(this, menuItems,
            R.layout.list_item,
            new String[] { KEY_NAME, KEY_DESC,  KEY_IMAGE}, new int[] {
                    R.id.name, R.id.desciption,   R.id.image });

    setListAdapter(adapter);



    // selecting single ListView item
    ListView lv = getListView();

    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.cost)).getText().toString();
            String description = ((TextView) view.findViewById(R.id.desciption)).getText().toString();


            // Starting new intent
            Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class);
            in.putExtra(KEY_NAME, name);
            //in.putExtra(KEY_COST, cost);
            in.putExtra(KEY_DESC, description);
            startActivity(in);

        }
    });

/*       }
    }).start();

     */    
         }

public class HeavyWorker extends AsyncTask < Void , Integer, Object > {


    ProgressBar progressBar = (ProgressBar)findViewById(R.id.progress);
    int progress_status;

    private ProgressDialog      progressDialog ;
    private Context             targetCtx ;

    public HeavyWorker ( Context context ) {
        this.targetCtx = context ;
      //  this.needToShow = true;
        progressDialog = new ProgressDialog ( targetCtx ) ;
        progressDialog.setCancelable ( false ) ;
        progressDialog.setMessage ( "Retrieving data..." ) ;
        progressDialog.setTitle ( "Please wait" ) ;
        progressDialog.setIndeterminate ( true ) ;
        System.out.println("you are on print line 5");
    }







    @Override
    protected void onPostExecute(Object result) {
         if(progressDialog != null && progressDialog.isShowing()){
                progressDialog.dismiss ( ) ;
            }
        System.out.println("you are on print line 6");
    }
    @Override
    protected Object doInBackground(Void... params) {
        // TODO Auto-generated method stub
       while (progress_status<100)
             {
                 progress_status+=2;
                 setProgress(progress_status);
                 try {
                     Thread.sleep(3000);
                 } catch (InterruptedException e) {
                     e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
                 }
             }
        System.out.println("you are on print line 7");

        return null;
    }
    @Override
    protected void onProgressUpdate(Integer... values) {
        // TODO Auto-generated method stub
        super.onProgressUpdate(values);
        progressBar.setProgress(values[0]);
             textView.setText("downloading " +values[0]+"%");
             System.out.println("you are on print line 8");

    }







    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
         progressDialog.show ( ) ;
        super.onPreExecute();
        System.out.println("you are on print line 9");
    }


}


}

Answer 1

当你从服务器加载大型数据时，你必须管理后台线程。看，我会试着向你解释。

See Here为例链接

在线程启动前调用%1完成任务。

 @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub

        super.onPreExecute();
// This will call before the loading the URL data. so if you want to get data from locally that logic should be written here.
    }

}

调用2在后台加载数据 @Override protected Object doInBackground(无效...params) { // TODO自动生成的方法存根

   while (progress_status<100)
         {
             progress_status+=2;
             setProgress(progress_status);
             try {
                 Thread.sleep(3000);
             } catch (InterruptedException e) {
                 e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
             }
         }
    System.out.println("you are on print line 7");

    return null;
}

调用3这是UI线程，它将根据重试数据更新UI。

  @Override
    protected void onProgressUpdate(Integer... values) {
        // TODO Auto-generated method stub

// show your dialog here progressDialog.show ( ) ;

        super.onProgressUpdate(values);
        progressBar.setProgress(values[0]);
             textView.setText("downloading " +values[0]+"%");
             System.out.println("you are on print line 8");

    }

调用线程的4结束。因此显示最终输出或释放控制。

 @Override
    protected void onPostExecute(Object result) {

         if(progressDialog != null && progressDialog.isShowing()){
                progressDialog.dismiss ( ) ;
            }
        System.out.println("you are on print line 6");
    }