0

我遵循了有关如何在 Android 应用程序上解析 XML(RSS) 文件的教程。下面是我的代码，它正在运行，但需要很长时间。我是在做不正确的事情还是会减慢它的速度？加载 30-35 篇文章需要 7-10 秒……看起来太长了，而且用户每次切换部分时都等待太久（这会引入另一个提要）

我确实有办法每小时只提取新数据......等等......但第一次通常仍然需要 10 秒，这 - 到那时，用户认为他们的应用程序已经崩溃......等等。

  • 我在 AsyncTask 中这样做
  • 我现在不下载图像
  • 这是代码的慢部分（不是互联网，或显示......等）

TLDR：
这段代码太慢了——为什么？：

package com.mysite.utilities;

import java.util.ArrayList;

import org.xml.sax.Attributes;
import org.xml.sax.helpers.DefaultHandler;

public class RSSHandler extends DefaultHandler
{

    // creats a news item class to hold data within loop
    public class NewsItem
    {
        public String title;
        public String subhead;
        public String link;
        public String byline;
        public String description;
        public String storytext;
        public String cmsstoryid;
        public String pubDate;
        public String keyword;
        public String category;
        public String subcategory;
        public String slotreference;
        public String lastModTime;
        public ArrayList<PhotoItem> photos = new ArrayList<PhotoItem>();

        @Override
        public String toString()
        {
            return title;
        }
    }

    //creates a photo item class to hold image data within loop
    public class PhotoItem
    {
        public String photoid; //tribs id
        public String caption;
        public String height;
        public String width;
        public String photo; //full path to photo
        public String thumbnail; //full path to thumbnail
        public int articleid;
        public String photolastmodified;

        @Override
        public String toString()
        {
            return photo;
        }
    }

    //creates instances of classes to be used in loop
    private StringBuffer buf; //to hold element characters with loop
    private ArrayList<NewsItem> feedItems;
    private NewsItem item;
    private PhotoItem photoitem;

    //initialize variables of whether or not it's within an item (or photo item)
    private boolean inItem = false;
    private boolean inPhotoItem = false;

    //
    public ArrayList<NewsItem> getParsedItems() {
        return feedItems;
    }

    //Called at the head of each new element
    @Override
    public void startElement(String uri, String name, String qName, Attributes atts)
    {
        //creates an array of news items
        if ("channel".equals(name))
        {
            feedItems = new ArrayList<NewsItem>();
        }
        //creates a news item and toggles "in news item" to on
        else if ("item".equals(name))
        {
            item = new NewsItem();
            inItem = true;
        }
        //creates a photo item and toggles "in photo item" to on
        else if ("image".equals(name))
        {
            photoitem = new PhotoItem();
            inPhotoItem = true;
        }
        //starts a new string buffer if matches an elemnt we want from news item
        else if (
            ("title".equals(name) ||
            "subhead".equals(name) ||
            "link".equals(name) ||
            "byline".equals(name) ||
            "description".equals(name) ||
            "storytext".equals(name) ||
            "keyword".equals(name) ||
            "cmsstoryid".equals(name) ||
            "pubDate".equals(name) ||
            "category".equals(name) ||
            "subcategory".equals(name) ||
            "lastModTime".equals(name) ||
            "slotreference".equals(name)
            )
            && inItem)
        {
            buf = new StringBuffer();
        }
        //starts an a new string buffer if it matches an element we want from image item
        else if(
            ("caption".equals(name) ||
            "photoid".equals(name) ||
            "height".equals(name) ||
            "width".equals(name) ||
            "photo".equals(name) ||
            "photolastmodified".equals(name) ||
            "thumbnail".equals(name)
            )
            && inPhotoItem)
        {
            buf = new StringBuffer();
        }
    }

    //Called at the tail of each element end
    @Override
    public void endElement(String uri, String name, String qName)
    {       
        if ("item".equals(name))
        {
            feedItems.add(item);
            inItem = false;
        }
        else if ("image".equals(name))
        {
            try {
                item.photos.add(photoitem);
            } catch (Exception e) {
                System.out.println(e);
            }
            inPhotoItem = false;
        }
        else if (inItem)
        {
            if (inPhotoItem)
            {
                if ("caption".equals(name)) { photoitem.caption = buf.toString(); }
                else if ("photoid".equals(name)) { photoitem.photoid = buf.toString(); }
                else if ("height".equals(name)) { photoitem.height = buf.toString(); }
                else if ("width".equals(name)) { photoitem.width = buf.toString(); }
                else if ("photo".equals(name)) { photoitem.photo = buf.toString(); }
                else if ("photolastmodified".equals(name)) { photoitem.photolastmodified = buf.toString(); }
                else if ("thumbnail".equals(name)) { photoitem.thumbnail = buf.toString(); }
            }
            else if ("title".equals(name)) { item.title = buf.toString(); }
            else if ("subhead".equals(name)) { item.subhead = buf.toString(); }
            else if ("link".equals(name)) { item.link = buf.toString(); }
            else if ("byline".equals(name)) { item.byline = buf.toString(); }
            else if ("description".equals(name)) { item.description = buf.toString(); }
            else if ("storytext".equals(name)) { item.storytext = buf.toString(); }
            else if ("keyword".equals(name)) { item.keyword = buf.toString(); }
            else if ("cmsstoryid".equals(name)) { item.cmsstoryid = buf.toString(); }
            else if ("pubDate".equals(name)) { item.pubDate = buf.toString(); }
            else if ("category".equals(name)) { item.category = buf.toString(); }
            else if ("subcategory".equals(name)) { item.subcategory = buf.toString(); }
            else if ("lastModTime".equals(name)) { item.lastModTime = buf.toString(); }
            else if ("slotreference".equals(name)) { item.slotreference = buf.toString(); }

        }
        else
        {
            buf = null;
        }

    }

    //Called with character data inside elements
    @Override
    public void characters(char ch[], int start, int length)
    {
        //Don't bother if buffer isn't initialized
        if(buf != null)
        {
            for (int i=start; i<start+length; i++)
            {
                buf.append(ch[i]);
            }
        }
    }
}

到目前为止我更新的代码（仍然没有速度增加）：

package com.sltrib.utilities;

import java.util.ArrayList;

import org.xml.sax.Attributes;
import org.xml.sax.helpers.DefaultHandler;

import android.util.Log;

public class RSSHandler extends DefaultHandler
{

    // creats a news item class to hold data within loop
    public class NewsItem
    {
        public String title;
        public String subhead;
        public String link;
        public String byline;
        public String description;
        public String storytext;
        public String cmsstoryid;
        public String pubDate;
        public String keyword;
        public String category;
        public String subcategory;
        public String slotreference;
        public String lastModTime;
        public ArrayList<PhotoItem> photos = new ArrayList<PhotoItem>();

        @Override
        public String toString()
        {
            return title;
        }
    }

    //creates a photo item class to hold image data within loop
    public class PhotoItem
    {
        public String photoid; //tribs id
        public String caption;
        public String height;
        public String width;
        public String photo; //full path to photo
        public String thumbnail; //full path to thumbnail
        public int articleid;
        public String photolastmodified;

        @Override
        public String toString()
        {
            return photo;
        }
    }

    //creates instances of classes to be used in loop
    private StringBuilder buf; //to hold element characters with loop
    private ArrayList<NewsItem> feedItems;
    private NewsItem item;
    private PhotoItem photoitem;

    //initialize variables of whether or not it's within an item (or photo item)
    private boolean inItem = false;

    private int currentTagId = 0;

    //
    public ArrayList<NewsItem> getParsedItems() {
        return feedItems;
    }


    @Override
    public void startDocument()
    {
        feedItems = new ArrayList<NewsItem>(); //creates an array to hold feed items
    }


    //Called at the head of each new element
    @Override
    public void startElement(String uri, String name, String qName, Attributes atts)
    {
        //gets the id of the current tag
        currentTagId = 0;
        String tmpId = atts.getValue("id");
        if(tmpId != null)
        {
            currentTagId = Integer.parseInt(tmpId);
        }

        //creates a news item
        if (currentTagId == 99) // <item>
        {
            item = new NewsItem();
            inItem = true;
        }

        //creates a photo item
        else if (currentTagId == 21) { // <image>
            photoitem = new PhotoItem();
        }

        //creates a string builder if it's a tag within an article or a photo
        else if (inItem && currentTagId > 0 && currentTagId < 29)
        {
            buf = new StringBuilder();
        }
    }


    //Called at the tail of each element end
    @Override
    public void endElement(String uri, String name, String qName)
    {

        // it's not getting the tag id - how?

        Log.d("XML", "endElement:" + Integer.toString(currentTagId));

        if (currentTagId == 99)  // </item>
        {
            Log.d("XML", "Should be adding item: " + item.title);
            feedItems.add(item);
            inItem=false;
        }

        else if (currentTagId == 21) // </image>
        {
            try {
                item.photos.add(photoitem);
            } catch (Exception e) {
                System.out.println(e);
            }
        }
        else
        {
            switch(currentTagId)
            {
                case 1: item.title = buf.toString(); break;
                case 2: item.subhead = buf.toString(); break;
                case 3: item.link = buf.toString(); break;
                case 4: item.byline = buf.toString(); break;
                case 5: item.description = buf.toString(); break;
                case 6: item.storytext = buf.toString(); break;
                case 11: item.cmsstoryid = buf.toString(); break;
                case 14: item.pubDate = buf.toString(); break;
                case 15: item.lastModTime = buf.toString(); break;
                case 16: item.keyword = buf.toString(); break;
                case 17: item.category = buf.toString(); break;
                case 18: item.subcategory = buf.toString(); break;
                case 19: item.slotreference = buf.toString(); break;
                case 22: photoitem.caption = buf.toString(); break;
                case 23: photoitem.photoid = buf.toString(); break;
                case 24: photoitem.photolastmodified = buf.toString(); break;
                case 25: photoitem.height = buf.toString(); break;
                case 26: photoitem.width = buf.toString(); break;
                case 27: photoitem.photo = buf.toString(); break;
                case 28: photoitem.thumbnail = buf.toString(); break;
                default: if(!inItem) buf = null;
            }
        }
    }

    //Called with character data inside elements
    @Override
    public void characters(char ch[], int start, int length)
    {
        if(buf != null)
        {
            String chars = new String(ch, start, length); // get all text value inside the element tag
            chars = chars.trim(); // remove all white-space characters
            buf.append(chars);
        }
    }
}
4

1 回答 1

2

也许你已经这样做了，但我只是想重申这应该在另一个线程上完成。如果您显示进度指示器（微调器）并保持 GUI 响应，用户不会认为应用程序已崩溃。

如果您不在后台线程上执行此操作，则可能会人为地使其变慢，因为系统正在努力保持用户界面正常运行。

至于为什么这很慢，有大量的分支。您拥有的 if 语句越多，拥有的 else （等）越多，分支预测器执行其工作的难度就越大。

另外，我不知道您是否在此处下载图像，但如果是，则应在检索到文本数据并将其显示给用户后异步完成（以使用户界面更具响应性）。

于 2012-07-25T15:44:59.177 回答