java - 如何修复 java.lang.StringIndexOutOfBoundsException : length=225; regionStart=4; regionLength=-2

Question

这是我的错误:

`E/AndroidRuntime:致命异常:AsyncTask #2 进程:com.example.yasht.recyclerviewrss，PID:4097 java.lang.RuntimeException:执行 doInBackground() 时发生错误

    at android.os.AsyncTask$3.done(AsyncTask.java:325)
    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
    at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
    at java.util.concurrent.FutureTask.run(FutureTask.java:242)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)

    at java.lang.Thread.run(Thread.java:761)
Caused by: java.lang.StringIndexOutOfBoundsException: length=225; regionStart=4; regionLength=-2
    at java.lang.String.substring(String.java:1931)
    at com.example.yasht.recyclerviewrss.m_Rss.RssParser.parseRSS(RssParser.java:107)
    at com.example.yasht.recyclerviewrss.m_Rss.RssParser.doInBackground(RssParser.java:47)
    at com.example.yasht.recyclerviewrss.m_Rss.RssParser.doInBackground(RssParser.java:21)`      

我发生错误的来源:

case XmlPullParser.END_TAG:

                    if(!isSiteMeta)
                    {
                        if(tagName.equalsIgnoreCase("title"))
                        {
                            article.setTitle(tagValue);
                        }else if(tagName.equalsIgnoreCase("description"))
                        {
                            String desc=tagValue;

                            //EXTRACT IMAGE FROM DESC
                            // error in this line =>  
                             String 
 imageUrl=desc.substring(desc.indexOf("src=")+5,desc.indexOf("jpg")+3);
                            article.setImageurl(imageUrl);`

Answer 1

似乎jpg不在desc中，因此desc.indexOf("jpg")返回-1，+3给出-2!