Erro閱讀Android中的epub文件

Question

我想在我的Android應用程序中逐頁閱讀epub文件。

我都試過，但我在這行獲得一個空指針異常：

Bitmap coverImage = BitmapFactory.decodeStream(book.getCoverImage().getInputStream()); 

任何人都可以解釋爲什麼我收到此錯誤，或者怎麼做逐頁閱讀書籍頁面？

這裏是我的活動代碼：

public class LogTestBookInfo extends Activity 
{ 
    @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("assets/books/wodehouse.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()); 

    } 

    } 


    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); 

    } 

    } 

} 

這裏是我的logcat的信息：

12-04 11:12:08.606: I/AndroidLoggerFactory(334): Logger name 'nl.siegmann.epublib.epub.EpubReader' exceeds maximum length of 23 characters, using 'n*.s*.e*.e*.EpubReader' instead. 
12-04 11:12:08.635: I/AndroidLoggerFactory(334): Logger name 'nl.siegmann.epublib.domain.Resource' exceeds maximum length of 23 characters, using 'n*.s*.e*.d*.Resource' instead. 
12-04 11:12:08.886: I/AndroidLoggerFactory(334): Logger name 'nl.siegmann.epublib.epub.EpubProcessorSupport' exceeds maximum length of 23 characters, using 'n*.s*.e*.e*.EpubProces*' instead. 
12-04 11:12:08.996: I/AndroidLoggerFactory(334): Logger name 'nl.siegmann.epublib.epub.PackageDocumentReader' exceeds maximum length of 23 characters, using 'n*.s*.e*.e*.PackageDoc*' instead. 
12-04 11:12:09.336: I/AndroidLoggerFactory(334): Logger name 'nl.siegmann.epublib.epub.NCXDocument' exceeds maximum length of 23 characters, using 'n*.s*.e*.e*.NCXDocument' instead. 
12-04 11:12:09.565: I/epublib(334): author(s): [B., Gummere, Francis] 
12-04 11:12:09.565: I/epublib(334): title: Beowulf 
12-04 11:12:09.606: E/AndroidRuntime(334): FATAL EXCEPTION: main 
12-04 11:12:09.606: E/AndroidRuntime(334): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bookapp/com.bookapp.LogTestBookInfo}: java.lang.NullPointerException 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.os.Looper.loop(Looper.java:123) 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.app.ActivityThread.main(ActivityThread.java:3683) 
12-04 11:12:09.606: E/AndroidRuntime(334): at java.lang.reflect.Method.invokeNative(Native Method) 
12-04 11:12:09.606: E/AndroidRuntime(334): at java.lang.reflect.Method.invoke(Method.java:507) 
12-04 11:12:09.606: E/AndroidRuntime(334): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
12-04 11:12:09.606: E/AndroidRuntime(334): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
12-04 11:12:09.606: E/AndroidRuntime(334): at dalvik.system.NativeStart.main(Native Method) 
12-04 11:12:09.606: E/AndroidRuntime(334): Caused by: java.lang.NullPointerException 
12-04 11:12:09.606: E/AndroidRuntime(334): at com.bookapp.LogTestBookInfo.onCreate(LogTestBookInfo.java:80) 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
12-04 11:12:09.606: E/AndroidRuntime(334): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
12-04 11:12:09.606: E/AndroidRuntime(334): ... 11 more 

Answer 1

更改這樣的代碼

if(book.getCoverImage()!=null&&book.getCoverImage().getInputStream()!=null) 
Bitmap coverImage = BitmapFactory.decodeStream(book.getCoverImage().getInputStream());