我是 android 应用程序开发的新手。
我面临的问题是，第一次运行我的应用程序显示空白屏幕，当我关闭它并立即重新打开它时，它工作正常。
我想知道为什么它没有在第一次加载时加载。
任何帮助深表感谢....
应用详情：
我编写了一个应用程序来读取 XML 源并将其显示在屏幕上。为了显示，我动态创建了 LinearLayout、ScrollView、buttons 和 textviews。我曾使用异步任务通过 SAX Parser 读取 XML 数据。
MainActivity.Java
package com.example.thehindu_topstories;
import java.net.MalformedURLException;
import java.net.URL;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.InputSource;
import org.xml.sax.XMLReader;
import android.net.ParseException;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.graphics.Color;
import android.text.Html;
import android.text.method.LinkMovementMethod;
import android.view.Menu;
import android.view.ViewGroup;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.ScrollView;
import android.widget.TextView;
public class MainActivity extends Activity
{
NewsList newsList = null;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
ScrollView sv = new ScrollView(this);
LinearLayout layout = new LinearLayout(this);
sv.addView(layout);
layout.setOrientation(LinearLayout.VERTICAL);
new FetchFeed().execute();
Button title[];
TextView pubDate[];
newsList = NewsXMLHandler.newsList;
title = new Button[newsList.getTitle().size()];
pubDate = new TextView[newsList.getpubDate().size()];
for (int i = 1; i <= (newsList.getTitle().size()); i++)
{
try{
title[i] = new Button(this);
title[i].setText(i+"."+newsList.getTitle().get(i)+"\n");
title[i].append(Html.fromHtml( String.format("<a href=\"%s\">(..Read more..)</a> ",newsList.getLink().get(i))));
title[i].setMovementMethod(LinkMovementMethod.getInstance());
title[i].setBackgroundColor(Color.LTGRAY);
pubDate[i]= new TextView(this);
pubDate[i].setText(newsList.getpubDate().get(i)+"\n");
pubDate[i].setTextSize(10);
layout.addView(title[i]);
layout.addView(pubDate[i]);
}
catch(Exception e)
{
System.out.println(e.toString());
}
}
setContentView(sv);
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
private class FetchFeed extends AsyncTask<Void, Void, Void>
{
protected Void doInBackground(Void... params)
{
try
{
SAXParserFactory spf=SAXParserFactory.newInstance();
SAXParser sp= spf.newSAXParser();
XMLReader xr = sp.getXMLReader();
URL SourceUrl = new URL ("http://beta.thehindu.com/news/?service=rss");
NewsXMLHandler myXMLHandler = new NewsXMLHandler();
xr.setContentHandler(myXMLHandler);
xr.parse(new InputSource(SourceUrl.openStream()));
}
catch (ParseException e)
{
System.out.println("XML Parsing Exception="+ e);
}
catch (MalformedURLException e)
{
System.out.println("XML Parsing Exception="+ e);
}
catch (Exception e)
{
System.out.println("XML Parsing Exception="+ e);
}
return null;
/**/
}
protected void onPostExecute(Void param)
{
}
}
}
新闻列表.Java
package com.example.thehindu_topstories;
import java.util.ArrayList;
public class NewsList
{
private ArrayList<String> title = new ArrayList<String>();
private ArrayList<String> link = new ArrayList<String>();
private ArrayList<String> pubDate = new ArrayList<String>();
public ArrayList<String> getTitle()
{
return title;
}
public void setTitle(String title)
{
this.title.add(title);
}
public ArrayList<String> getLink()
{
return link;
}
public void setLink(String link)
{
this.link.add(link);
}
public ArrayList<String> getpubDate()
{
return pubDate;
}
public void setpubDate(String pubDate)
{
this.pubDate.add(pubDate);
}
}
新闻XMLHandler.java
package com.example.thehindu_topstories;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
public class NewsXMLHandler extends DefaultHandler
{
Boolean currentElement = false;
String currentValue = null;
public static NewsList newsList = new NewsList();
public static NewsList getNewsList()
{
return newsList;
}
public static void setNewsList(NewsList newsList)
{
NewsXMLHandler.newsList = newsList;
}
@Override
public void startElement(String uri, String localName, String qName,
Attributes attributes) throws SAXException
{
currentElement = true;
if (localName.equals("channel"))
{
newsList = new NewsList();
}
}
@Override
public void endElement(String uri, String localName, String qName)
throws SAXException
{
currentElement = false;
if (localName.equalsIgnoreCase("title"))
newsList.setTitle(currentValue);
else if (localName.equalsIgnoreCase("link"))
newsList.setLink(currentValue);
else if (localName.equalsIgnoreCase("pubDate"))
newsList.setpubDate(currentValue);
}
@Override
public void characters(char[] ch, int start, int length)
throws SAXException
{
if (currentElement)
{
currentValue = new String(ch, start, length);
currentElement = false;
}
}
}
activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
</RelativeLayout>