我遵循了如何解析Android应用上的XML（RSS）文件的教程。下面是我的代码正在运行，但需要很长时间。我做错了什么或者会减慢它的速度吗？加载30-35篇文章需要7-10秒......看似太长了，而且用户每次切换部分时都会等待太长时间（拉入另一个进程）
我确实有适当的地方每小时只提取新数据......等等......但是第一次通常还需要10秒钟，然后用户会认为他们的应用程序崩溃了......等等。
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]);
}
}
}
}
到目前为止我的更新代码（仍然没有加速）：
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);
}
}
}
答案 0 :(得分：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。
如果您不是在后台线程上执行此操作，则可能会使此操作变得非常慢，因为系统正在努力保持用户界面继续运行。
至于为什么这很慢，有一个TON的分支。你拥有的if语句越多，你拥有的elses越多，分支预测器就越难以完成它的工作。
此外，我无法判断您是否在此处下载图像，但如果您是，则应在检索文本数据并向用户显示后异步完成（以使用户界面更具响应性）。< / p>