我对此堆栈跟踪感到困惑（只显示了令人困惑的部分）：
-[NSXMLDocument length]: unrecognized selector sent to instance 0x10187e010
An uncaught exception was raised
-[NSXMLDocument length]: unrecognized selector sent to instance 0x10187e010
(
0 CoreFoundation 0x00007fff8f5d6286 __exceptionPreprocess + 198
1 libobjc.A.dylib 0x00007fff9213bd5e objc_exception_throw + 43
2 CoreFoundation 0x00007fff8f6624ce -[NSObject doesNotRecognizeSelector:] + 190
3 CoreFoundation 0x00007fff8f5c3133 ___forwarding___ + 371
4 CoreFoundation 0x00007fff8f5c2f48 _CF_forwarding_prep_0 + 232
5 CoreFoundation 0x00007fff8f548c66 CFDataGetLength + 118
6 CoreFoundation 0x00007fff8f5791df CFStringCreateFromExternalRepresentation + 31
7 asLJ 0x0000000100013828 +[stripHTML stripAllHtmlFromString:] + 212
特别是，我不明白对CFStringCreateFromExternalRepresentation的调用发生在哪里，所以我不知道我的代码的哪一部分（+[stripHTML stripAllHtmlFromString:]）导致异常。是什么导致了对CFStringCreateFromExternalRepresentation的调用？如果很明显，我做错了什么导致异常呢？将来，我该如何确定调用CFStringCreateFromExternalRepresentation的内容？
这是+[stripHTML stripAllHtmlFromString:]：
+ (NSString *)stripAllHtmlFromString:(NSString *)inputString
{
// based on code from http://sugarmaplesoftware.com/25/strip-html-tags/#comment-71
NSError *theError = NULL;
NSString *modifiedInputString = [NSString stringWithFormat:@"%@\n\n\n\n\n\n\n\n\n\n\n\n",inputString]; // adding some spare newlines at the end to ensure that things will work even with a short non-HTML string
NSXMLDocument *theDocument = [[NSXMLDocument alloc] initWithXMLString:modifiedInputString
options:NSXMLDocumentTidyHTML
error:&theError];
NSString *theXSLTString = @"<?xml version='1.0' encoding='utf-8'?>"
"<xsl:stylesheet version='1.0' xmlns:xsl='http://www.w3.org/1999/XSL/Transform' xmlns:xhtml='http://www.w3.org/1999/xhtml'>"
"<xsl:output method='text'/>"
"<xsl:template match='xhtml:head'></xsl:template>"
"<xsl:template match='xhtml:script'></xsl:template>"
"</xsl:stylesheet>";
NSData *theData = [theDocument objectByApplyingXSLTString:theXSLTString arguments:NULL error:&theError];
[theDocument release];
return [[[NSString alloc] initWithData:theData encoding:NSUTF8StringEncoding] autorelease];
}
答案 0 :(得分：3)
哦，实际上，-objectByApplyingXSLTString:arguments:error:可能会返回NSXMLDocument而不是NSData。因此，对-[NSString initWithData:encoding:]的调用正在调用它认为是-length的内容NSData，但NSXMLDocument无法识别。{/ p>
答案 1 :(得分：0)
Ken Thomases's answer似乎完全正确 - 出于某种原因，对于非常短的输入（特别是空字符串），给定XSLT的-objectByApplyingXSLTString:arguments:error:返回NSXMLDocument（即使我不要以为它应该）。要修复它，我首先检测我们是否得到NSXMLDocument，如果是，请将其转换为XML的字符串表示形式并将其反馈给方法;否则假设我们得到了我们原先预期的NSData。
用下面的代码替换给定方法的最后3行（来自NSData *theData = ... on）似乎解决了这个问题。
// Had a report of an exception that seemed to indicate objectByApplyingXSLTString:arguments:error: was returning an NSXMLDocument objectinstead of an NSData object, so let's guard against that. (discussed at https://stackoverflow.com/q/10669479/291280 )
NSObject *XSTLresult = [theDocument objectByApplyingXSLTString:theXSLTString arguments:NULL error:&theError];
[theDocument release];
if ([XSTLresult isKindOfClass:[NSXMLDocument class]]) {
// If the result is an NSXMLDocument, call XMLData to get an NSData object, turn it into a string, and feed that back into this method...
return [self stripAllHtmlFromString:[[[NSString alloc]
initWithData:[(NSXMLDocument *)XSTLresult XMLData]
encoding:NSUTF8StringEncoding]
autorelease]
];
} else {
// Otherwise, assume we have an NSData object.
return [[[NSString alloc] initWithData:(NSData *)XSTLresult encoding:NSUTF8StringEncoding] autorelease];
}