On Dec 16, 9:05 am, "William.lw.w" <[email protected]> wrote:
> When I run it, it report below error:
> 12-16 23:49:54.307: WARN/dalvikvm(653): JNI WARNING: method declared
> to return 'Ljava/nio/ByteBuffer;' returned 'Ljava/nio/
> ReadWriteDirectByteBuffer;'
> 12-16 23:49:54.307: WARN/dalvikvm(653): failed in Lcom/lw/
> mupdf/PdfViewer;.readPage ('Ljava/nio/ByteBuffer;' not found)
>
> What's the meaning of "failed in Lcom/lw/mupdf/PdfViewer;.readPage
> ('Ljava/nio/ByteBuffer;' not found)? And how to solve it?
The JNI checks are trying to ensure that the type of object you're
returning matches up with what the method was declared to return. In
this case, a direct byte buffer is a ByteBuffer, so it should succeed.
The problem is that the class lookup on java.nio.ByteBuffer failed.
The CheckJNI code is assuming that ByteBuffer must already be loaded,
which is a reasonable assumption since loading a class will pull the
superclasses in. ReadWriteDirectByteBuffer extends DirectByteBuffer
extends BaseByteBuffer extends ByteBuffer.
As it turns out, the CheckJNI code is mildly broken, in that it
assumes the class has been loaded *by the current class loader*, which
for JNI is the class loader associated with the method at the top of
the stack. Until something causes the app's class loader to touch
ByteBuffer, and thereby get added as an initiating class loader, the
test will fail.
You can work around the problem by using ByteBuffer once in your app
before calling into the JNI code; that will ensure it's loaded. For
example, do this during initialization:
ByteBuffer dummy = ByteBuffer.allocate(0); dummy = null;
Also: please post any further questions about JNI development on the
android-ndk mailing list.
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