Android（Java）通过递归方法填充ArrayList

2 月 Questions & Answers 341

我正在开发可以打开epub文件的图书阅读器。我在互联网上搜索了很多，最后在这个tutorial link中找到了一个解决方案

但是现在我在使用这种方法时遇到了麻烦

内容的日志表（列表引用、int深度）

我把它从void改为String，这是我的代码

 private String logTableOfContents(List<TOCReference> tocReferences, int depth) {

    if (tocReferences == null) {




        return null;
    }

    for (TOCReference tocReference : tocReferences) {
        StringBuilder tocString = new StringBuilder();
        for (int i = 0; i < depth; i++) {
            tocString.append("\t");
        }

        tocString.append(tocReference.getTitle());

        //Toast.makeText(this, ""+ logTableOfContents(tocReference.getChildren(), depth + 1), Toast.LENGTH_SHORT).show();

        return tocString.toString();

    }

    return null;
}

可以清楚地看到，编写该教程的开发人员使用了递归方法来获取目录

我将方法void更改为String，以获取并存储在ArrayList中然而，无法从递归方法中单独获取该书的目录。尝试记录ArrayList的元素时出现nullPointerException

现在我想从某人那里得到帮助来解决这个问题，欢迎任何建议，提前谢谢

来自我使用的tutorial的代码

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
import nl.siegmann.epublib.domain.Book;
import nl.siegmann.epublib.domain.TOCReference;
import nl.siegmann.epublib.epub.EpubReader;
import 安卓.app.Activity;
import 安卓.content.res.AssetManager;
import 安卓.graphics.Bitmap;
import 安卓.graphics.BitmapFactory;
import 安卓.os.Bundle;
import 安卓.util.Log;
 
/**
 * Log the info of 'assets/books/testbook.epub'.
 *
 * @author paul.siegmann
 *
 */
public class LogTestBookInfo extends Activity {
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    AssetManager assetManager = getAssets();
    try {
      // find InputStream for book
      InputStream epubInputStream = assetManager
          .open("books/testbook.epub");
 
      // Load Book from inputStream
      Book book = (new EpubReader()).readEpub(epubInputStream);
 
      // Log the book's authors
      Log.i("epublib", "author(s): " + book.getMetadata().getAuthors());
 
      // Log the book's title
      Log.i("epublib", "title: " + book.getTitle());
 
      // Log the book's coverimage property
      Bitmap coverImage = BitmapFactory.decodeStream(book.getCoverImage()
          .getInputStream());
      Log.i("epublib", "Coverimage is " + coverImage.getWidth() + " by "
          + coverImage.getHeight() + " pixels");
 
      // Log the tale of contents
      logTableOfContents(book.getTableOfContents().getTocReferences(), 0);
    } catch (IOException e) {
      Log.e("epublib", e.getMessage());
    }
  }
 
  /**
   * Recursively Log the Table of Contents
   *
   * @param tocReferences
   * @param depth
   */
  private void logTableOfContents(List<TOCReference> tocReferences, int depth) {
    if (tocReferences == null) {
      return;
    }
    for (TOCReference tocReference : tocReferences) {
      StringBuilder tocString = new StringBuilder();
      for (int i = 0; i < depth; i++) {
        tocString.append("\t");
      }
      tocString.append(tocReference.getTitle());
      Log.i("epublib", tocString.toString());
 
      logTableOfContents(tocReference.getChildren(), depth + 1);
    }
  }
}

Python中文网

有 Java 编程相关的问题?

Android（Java）通过递归方法填充ArrayList

共 (1) 个答案

# 1 楼答案