iOS:读取文件内容

Question

通过查阅Quartz 2D编程指南和一些文章，我拼凑了一些代码来读取PDF文件的内容。它在PDF扫描器部分失败了，我想。当我要释放扫描仪时，应用程序崩溃，并显示以下错误：

avi(2282,0x3de7bb88) malloc: *** error for object 0x693f7c0: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug

我正在通过电子邮件附件打开PDF文件。我知道它至少可以识别文件，因为我可以得到页数。有没有人可以看看我下面的代码，看看我的错误发生在哪里？谢谢。

- (void) readPDFFile:(NSURL *)PDFURL {

    //make a pdf document and point it to the url of our pdf file
    CGPDFDocumentRef pdfDocument;
    pdfDocument = CGPDFDocumentCreateWithURL((__bridge CFURLRef)(PDFURL));

    //release the url
    CFRelease((__bridge CFTypeRef)(PDFURL));


    if (pdfDocument) {

        //get page count
        int pageCount = CGPDFDocumentGetNumberOfPages (pdfDocument);

        //
        if (pageCount > 0) {

            //set up operator table
            CGPDFOperatorTableRef pdfOpTable;
            pdfOpTable = CGPDFOperatorTableCreate();

            //call backs for Op Table
            CGPDFOperatorTableSetCallback (pdfOpTable, "MP", &op_MP);
            CGPDFOperatorTableSetCallback (pdfOpTable, "DP", &op_DP);
            CGPDFOperatorTableSetCallback (pdfOpTable, "BMC", &op_BMC);
            CGPDFOperatorTableSetCallback (pdfOpTable, "BDC", &op_BDC);
            CGPDFOperatorTableSetCallback (pdfOpTable, "EMC", &op_EMC);

            for(int i=0; i<pageCount; i++) {

                //set up
                CGPDFPageRef thisPage;
                CGPDFScannerRef pdfScanner;
                CGPDFContentStreamRef thisContentStream;

                //get the page
                thisPage = CGPDFDocumentGetPage (pdfDocument, i + 1 );

                //get the page content stream
                thisContentStream = CGPDFContentStreamCreateWithPage (thisPage);

                //create a pdf scanner using our previously created table and callbacks
                pdfScanner = CGPDFScannerCreate (thisContentStream, pdfOpTable, NULL);

                //scan the pdf file
                CGPDFScannerScan (pdfScanner); //-->call backs happen here

                //release everything
                CGPDFPageRelease (thisPage);
                /*CGPDFScannerRelease (pdfScanner);
                CGPDFContentStreamRelease (thisContentStream);*/


            }
        }
    }

    //release the pdf document
    CGPDFDocumentRelease(pdfDocument);


}

static void op_MP (CGPDFScannerRef s, void *info) {

    const char *name;

    if (!CGPDFScannerPopName(s, &name))
        return;

    NSLog(@"MP /%s\n", name);
}

static void op_DP (CGPDFScannerRef s, void *info) {
    const char *name;
    if (!CGPDFScannerPopName(s, &name))
        return;
    NSLog(@"DP /%s\n", name);
}

static void op_BMC (CGPDFScannerRef s, void *info) {
    const char *name;
    if (!CGPDFScannerPopName(s, &name))
        return;
    NSLog(@"BMC /%s\n", name);
}

static void op_BDC (CGPDFScannerRef s, void *info) {
    const char *name;
    if (!CGPDFScannerPopName(s, &name))
        return;
    NSLog(@"BDC /%s\n", name);
}

static void op_EMC (CGPDFScannerRef s, void *info) {
    const char *name;
    if (!CGPDFScannerPopName(s, &name))
        return;
    NSLog(@"EMC /%s\n", name);
}

编辑: PDFURL来自这个过程:用户选择打开带有应用程序的电子邮件附件的PDF文件。在AppDelegate.m中：

- (BOOL)application:(UIApplication *)application openURL:(NSURL *)url sourceApplication:(NSString *)sourceApplication annotation:(id)annotation
{
   /* NSLog(@"Open URL:\t%@\n"
          "From source:\t%@\n"
          "With annotation:%@",
          url, sourceApplication, annotation);*/

    NSMutableDictionary* userData = [[NSMutableDictionary alloc] init];

    [userData setObject:@"Read PDF" forKey:@"Action"];
    [userData setObject:url forKey:@"File Path"];

    [[NSNotificationCenter defaultCenter] postNotificationName:@"theMessenger" object:self userInfo: userData];

    //NSString *filepath = [url path];
    //...
    return YES;
}

在视图控制器中。m

- (void) receiveNotification:(NSNotification* ) notification {
...
} else if ([strAction isEqualToString:@"Read PDF"]) {

            NSURL* documentURL = [[notification userInfo] objectForKey:@"File Path"];
            [self readPDFFile:documentURL];

        }
...

编辑:如果我不释放这个页面，应用程序仍然崩溃：

libobjc.A.dylib`objc_release: 0x3be89f20: cmp r0，#0 0x3be89f22: it eq 0x3be89f24: bxeq lr 0x3be89f26: ldr r1，r0 0x3be89f28: movs r2，#2 0x3be89f2a: ldr r1，r1，#16 0x3be89f2c: bfi r1，r2，#0，#2 0x3be89f30: ldrb r1，r1 0x3be89f32: tst.w r1，#2 0x3be89f36: bne 0x3be89f3e；objc_release + 30 0x3be89f38: movs r1，#0 0x3be89f3a: b.w 0x3be981c0；-NSObject版本0x3be89f3e: movw r1，#19326 0x3be89f42: movt r1，#507 0x3be89f46:添加r1，pc 0x3be89f48: ldr r1，r1 0x3be89f4a: b.w 0x3be875a0；objc_msgSend 0x3be89f4e:无

Answer 1

不要释放thisPage..您通过get调用而不是copy或create方法获取它，这意味着您不拥有它

--

不释放PDURL..你从外面得到它，但你并不拥有它

--

请务必释放operatorTable ..您可以创建它

和

不要在多台扫描仪中重复使用它