每次我点击JEditorPane中的超链接时，hyperlinkUpdate（）给我NullPointerException？ [英] hyperlinkUpdate() gives me NullPointerException every time i click a hyperlink in the JEditorPane?

问题描述

我只想补充说，加载的初始文件是一个包含所有类名称的javadoc，当我点击带有它名字的超链接时，我希望它显示每个类的相应页面，当我打印时在控制台中我没有看到收集相应url的任何问题，但每次我尝试将它添加到JEditorPane时我都会得到NullPointerException。

I just want to add that the initial file loaded is a javadoc that has the names of all the classes, I want it to display the corresponding page for each class when I click on the hyperlink with it's name, when i did prints in the console I didn't see any problems with gathering the corresponding url however I get a NullPointerException every time I try to add it to the JEditorPane.

这是我的程序：

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.io.*;

public class Help implements HyperlinkListener
 {

     JEditorPane htmlPane;
       String url = "file:///F:/java%2012/Isp/help%20file%20try/doc%202/allclasses-frame.html";
    public void hyperlinkUpdate(HyperlinkEvent event) {
    if (event.getEventType() == HyperlinkEvent.EventType.ACTIVATED) {
      try {

        htmlPane.setPage(event.getURL());
         //url.setText(event.getURL().toExternalForm());
        //System.out.println(event.getURL().toString());

      } 
      catch(IOException ioe) {
       // System.out.print("err");
        // Some warning to user
      }
    }
  }
    public void frame()
    {
       JFrame frame = new JFrame("asdd");
     JLabel l = new JLabel("asdsada");

     try 
         {

  JEditorPane htmlPane = new JEditorPane(url);
  htmlPane.addHyperlinkListener(this);
       htmlPane.setEditable(false);
       frame.add(new JScrollPane(htmlPane));


         } 
catch(IOException ioe) {
  System.err.println("Error displaying " + url);
  } 
frame.setSize(1200,800);
       frame.setVisible(true);


    }

   public static void main(String[] args)
   {
     Help h =new Help();
    h.frame();
   }
 }

推荐答案

但是你在哪里得到这个 NullPointerException ？

But where are you getting this NullPointerException?

我运行你的示例代码，得到 NullPointerException on：

I run your example code, and got NullPointerException on:

htmlPane.setPage(event.getURL());

所以 htmlPage 字段 null 。

添加行时：

this.htmlPane = htmlPane;

in：

public void frame() {
    JFrame frame = new JFrame("asdd");
    JLabel l = new JLabel("asdsada");
    try {
        JEditorPane htmlPane = new JEditorPane(url);
        this.htmlPane = htmlPane;

我现在可以点击任何链接（在我的案例中是http://www.google。 com /）

I can now click on any link (in my case in "http://www.google.com/")

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