Question

早上好我想解析rss xml文件。我使用一个线程来实现这个操作，但通常应用程序崩溃，我收到了这条消息Java.lang.NullPointerException....

package com.example.albir;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;
import android.os.Bundle;
import android.widget.ListView;
import android.app.Activity;
import android.util.Log;
import android.view.Menu;

public class MainActivity extends Activity {
     private PostData[] listData;
     int i =0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listData =new PostData[100];

                Thread thread = new Thread()
                {
                    @Override
                    public void run() { 

                try {
                    PostData data = null;
                        URL url = new URL("http://######.org/?feed=rss2");
                        XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
                        factory.setNamespaceAware(false);
                        XmlPullParser xpp = factory.newPullParser();
                            // We will get the XML from an input stream
                        xpp.setInput(getInputStream(url), "UTF_8");
                        boolean insideItem = false;

                            // Returns the type of current event: START_TAG, END_TAG, etc..
                        int eventType = xpp.getEventType();
                        while (eventType != XmlPullParser.END_DOCUMENT) {


                            if (eventType == XmlPullParser.START_TAG) {

                                if (xpp.getName().equalsIgnoreCase("item")) {
                                    data = new PostData();
                                    data.postThumbUrl = null;
                                    insideItem = true;
                                } 
                                else if (xpp.getName().equalsIgnoreCase("title")) {
                                    if (insideItem)
                                        data.postTitle=xpp.nextText();

                                } 
                                else if (xpp.getName().equalsIgnoreCase("pubDate")) {
                                    if (insideItem)

                                        data.postDate=xpp.nextText();

                                }
                                }

                            else if(eventType==XmlPullParser.END_TAG && xpp.getName().equalsIgnoreCase("item")){
                                insideItem=false;
                                listData[i] = data;
                                i++; 
                            }

                            eventType = xpp.next(); //move to next element
                        }

                        // Binding data



                    } catch (MalformedURLException e) {
                        e.printStackTrace();
                    } catch (XmlPullParserException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    }
                };      
         thread.start(); 
        Log.v("AAAA",String.valueOf(i));
        for (int j=0;j<i;j++)
         Log.v(listData[j].postTitle,"  ");

         // Binding data

        ListView listView = (ListView) this.findViewById(R.id.postListView);
        PostItemAdapter itemAdapter = new PostItemAdapter(this,
                R.layout.postitem, listData);
        listView.setAdapter(itemAdapter);


    }

    @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;
    }
    public InputStream getInputStream(URL url) {
           try {
               return url.openConnection().getInputStream();
           } catch (IOException e) {
               return null;
             }
        }


}

Slass postitem适配器

package com.example.albir;
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class PostItemAdapter extends ArrayAdapter<PostData> {
    private Activity myContext;
    private PostData[] datas;

    public PostItemAdapter(Context context, int textViewResourceId,
            PostData[] objects) {
        super(context, textViewResourceId, objects);
        // TODO Auto-generated constructor stub
        myContext = (Activity) context;
        datas = objects;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        View rowView;


        if(convertView == null) {
            LayoutInflater inflater = myContext.getLayoutInflater();
            convertView = inflater.inflate(R.layout.postitem, null);
        }

        rowView = convertView;
        ImageView thumbImageView = (ImageView) rowView
                .findViewById(R.id.postThumb);
        if (datas[position].postThumbUrl == null) {
            thumbImageView.setImageResource(R.drawable.ic_launcher);
        }

        TextView postTitleView = (TextView) rowView
                .findViewById(R.id.postTitleLabel);
        postTitleView.setText(datas[position].postTitle);

        TextView postDateView = (TextView) rowView
                .findViewById(R.id.postDateLabel);
        postDateView.setText(datas[position].postDate);

        return rowView;
}
}

我需要一个帮助来解析RSS feed而不会出现此问题，或者是否有更高效的其他解决方案。

Answer 1

获取LayoutInflater对象的方法多于直接来自Activity的方法。事实上，getLayoutInflater（）可能只是一个方便的方法：你可以

LayoutInflater inflater = (LayoutInflater) myContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    convertView = inflater.inflate(R.layout.postitem, parent, false);

或

LayoutInflater inflater = myContext.getLayoutInflater(null);
convertView = inflater.inflate(R.layout.postitem, parent, false);

而不是

LayoutInflater inflater = myContext.getLayoutInflater();
            convertView = inflater.inflate(R.layout.postitem, null);

阅读doc

Answer 2

将此用于inflater：

LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

使用适用于ViewHolder方法的适配器，效率更高

使用rss feed填充listview

2 个答案: