小编emv*_*vee的帖子

每次我编辑PDFRendererBasicFragment java代码

mFileDescriptor = context.getAssets().openFd("sample.pdf").getParcelFileDescriptor();

对于放在assets文件夹中的不同pdf,应用程序崩溃了..

Logcat报告:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.pdfrendererbasic/com.example.android.pdfrendererbasic.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.graphics.pdf.PdfRenderer.getPageCount()' on a null object reference

为什么会这样？我甚至尝试在构建之前将我的PDF重命名为sample.pdf并且它仍然崩溃..一切都与原始代码一起正常工作,只是不让我替换PDF.

堆栈跟踪:

02-11 11:11:50.130 18201-18201/com.example.android.pdfrendererbasic I/art: Not late-enabling -Xcheck:jni (already on)
02-11 11:11:50.130 18201-18201/com.example.android.pdfrendererbasic I/art: Late-enabling JIT
02-11 11:11:50.132 18201-18201/com.example.android.pdfrendererbasic I/art: JIT created with code_cache_capacity=2MB compile_threshold=1000
02-11 11:11:50.201 18201-18201/com.example.android.pdfrendererbasic W/System: ClassLoader referenced unknown path: /data/app/com.example.android.pdfrendererbasic-1/lib/x86
02-11 11:11:50.252 18201-18201/com.example.android.pdfrendererbasic W/System.err: java.io.IOException: cannot create document. Error: 3
02-11 11:11:50.253 18201-18201/com.example.android.pdfrendererbasic W/System.err:     at android.graphics.pdf.PdfRenderer.nativeCreate(Native Method)
02-11 11:11:50.253 …

select * from MYTABLE t 
where EQUIPMENT = 'KEYBOARD' and ROWNUM <= 2 or
EQUIPMENT = 'MOUSE' and ROWNUM <= 2 or
EQUIPMENT = 'MONITOR' and ROWNUM <= 2; 

我正在尝试运行一个返回字段(即设备)匹配的查询,并将每种类型设备的输出限制为每个设备类型2个记录或更少.我知道这可能不是使用多个where子句的最佳方法我过去使用过这个或者语句,但是不能用于rownum.它似乎只返回最后一个where语句.提前致谢..