{"id":299,"date":"2009-04-22T19:05:07","date_gmt":"2009-04-23T00:05:07","guid":{"rendered":"http:\/\/vgable.com\/blog\/2009\/04\/22\/nsurl-isequal-gotcha\/"},"modified":"2009-04-23T01:51:32","modified_gmt":"2009-04-23T06:51:32","slug":"nsurl-isequal-gotcha","status":"publish","type":"post","link":"https:\/\/vgable.com\/blog\/2009\/04\/22\/nsurl-isequal-gotcha\/","title":{"rendered":"-[NSURL isEqual:] Gotcha"},"content":{"rendered":"

BREAKING UPDATE: Actually comparing the -absoluteURL<\/code> or -absoluteString<\/code> of two NSURL<\/code>s that represent a file is not good enough<\/em>. One may start file:\/\/\/<\/code>, and the other file:\/\/localhost\/<\/code>, and they will not be isEqual:<\/code><\/em>! A work around is to compare the path<\/code> of each NSURL<\/code>. I’m still looking into the issue, but for now I am using the following method to compare NSURL<\/code>s.<\/p>\n

@implementation NSURL (IsEqualTesting)\n- (BOOL) isEqualToURL:(NSURL*)otherURL;\n{\n\treturn [[self absoluteURL] isEqual:[otherURL absoluteURL]] || \n\t[self isFileURL] && [otherURL isFileURL] &&\n\t([[self path] isEqual:[otherURL path]]);\n}\n@end\n<\/pre>\n
[a isEqual:b]<\/code> may report NO<\/code> for two NSURL<\/code>s that both resolve to the same resource (website, file, whatever). So compare NSURL<\/code>s like [[a absoluteString] isEqual:[b absoluteString]]<\/code><\/strong>. It’s important to be aware of this gotcha, because URLs are Apple’s preferred way to represent file paths, and APIs are starting to require them. Equality tests that worked for NSString<\/code> file-paths may fail with NSURL<\/code> file-paths.<\/strong><\/p>\n
The official documentation says<\/a><\/p>\n
 two NSURLs<\/code> are considered equal if they both have the same base baseURL<\/code><\/a> and relativeString<\/code><\/a>.<\/p><\/blockquote>\n
Furthermore,<\/p>\n
An NSURL<\/code> object is composed of two parts\u2014a potentially nil base URL and a string that is resolved relative to the base URL. An NSURL<\/code> object whose string is fully resolved without a base is considered absolute; all others are considered relative.\n<\/p><\/blockquote>\n
In other words, two NSURL<\/code> objects can resolve to the same absolute URL, but have a different base URL, and be considered !isEqual:<\/code>.<\/p>\n
An example should make this all clear,<\/p>\n
\nNSURL *VGableDotCom = [NSURL URLWithString:@\"http:\/\/vgable.com\"];\nNSURL *a = [[NSURL alloc] initWithString:@\"blog\" relativeToURL:VGableDotCom];\nNSURL *b = [[NSURL alloc] initWithString:@\"http:\/\/vgable.com\/blog\" relativeToURL:nil];\nLOG_INT<\/a>([a isEqual:b]);\nLOG_INT<\/a>([[a absoluteURL] isEqual:[b absoluteURL]]);\nLOG_ID<\/a>([a absoluteURL]);\nLOG_ID<\/a>([b absoluteURL]);\n<\/pre>\n
\n[a isEqual:b] = 0
\n[[a absoluteURL] isEqual:[b absoluteURL]] = 1
\n[a absoluteURL] = http:\/\/vgable.com\/blog
\n[b absoluteURL] = http:\/\/vgable.com\/blog\n<\/p><\/blockquote>\n
Remember that collections use isEqual:<\/code> to determine equality, so you may have to convert an NSURL<\/code> to an  absoluteURL<\/code> to get the behavior you expect, especially with NSSet<\/code> and NSDictionary<\/code>.<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"
BREAKING UPDATE: Actually comparing the -absoluteURL or -absoluteString of two NSURLs that represent a file is not good enough. One may start file:\/\/\/, and the other file:\/\/localhost\/, and they will not be isEqual:! A work around is to compare the path of each NSURL. I’m still looking into the issue, but for now I am […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[18,6,203,3,4,13],"tags":[241,395,107,108,109,78,396],"class_list":["post-299","post","type-post","status-publish","format-standard","hentry","category-bug-bite","category-cocoa","category-iphone","category-macosx","category-programming","category-sample-code","tag-best-practices","tag-isequal","tag-nsarray","tag-nsdictionary","tag-nsset","tag-nsstring","tag-nsurl"],"_links":{"self":[{"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/posts\/299","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/comments?post=299"}],"version-history":[{"count":0,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/posts\/299\/revisions"}],"wp:attachment":[{"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/media?parent=299"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/categories?post=299"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vgable.com\/blog\/wp-json\/wp\/v2\/tags?post=299"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}