Ios 从某些UIView创建PDF会导致崩溃

我一直试图将某些UIView保存为PDF格式，在某些情况下，它会崩溃。。请注意，特定UIView上的崩溃。在这段代码中，崩溃开始于

UIGraphicsEndPDFContext

我在这里做错什么了吗？。。这使得某些UIView上的错误不一致

   NSMutableData *pdfData = [NSMutableData data];

        UIGraphicsBeginPDFContextToData(pdfData,CGRectMake(0, 0, 0,0   ), nil);
        // Points the pdf converter to the mutable data object and to the UIView to be converted


        // draws rect to the view and thus this is captured by UIGraphicsBeginPDFContextToData
        [contentViews enumerateKeysAndObjectsUsingBlock: // Enumerate content views
         ^(id key, id object, BOOL *stop) {

             ReaderContentView *contentView = object;

             UIGraphicsBeginPDFPage();
             CGContextRef pdfContext = UIGraphicsGetCurrentContext();

             [contentView.theContentView.layer renderInContext:pdfContext];

         }];    

        UIGraphicsEndPDFContext();

事故发生在第一行

0x33e69884:  ldr    r2, [r0], #4
0x33e69888:  beq    0x33e6989c               ; strlen + 36

谢谢大家