I am getting a url of a file when a user opens one from an NSOpenPanel for example like so:
/Users/Name/Documents/MyFile.png
So I just want this bit:
MyFile.png
However the user could have a file name of any length so how can I say, only get the string after the last forward slash (/)? I just want to get the file name.
NSString *fileName = [someStringContainingAPath lastPathComponent];
More general advice: spend a little time reading through the reference pages for NSString and NSString(UIStringDrawing). There are a lot of useful methods in there that you might not otherwise know to look for. In addition to -lastPathComponent demonstrated above, there's -pathComponents, -componentsSeparatedByString:, and many other handy tools.
Related
I need to sort a NSMutableArray containing NSURLs with localizedStandardCompare:
[array sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
NSString *f1 = [(NSURL *)obj1 absoluteString];
NSString *f2 = [(NSURL *)obj2 absoluteString];
return [f1 localizedStandardCompare:f2];
}];
This works fine, but I worry a bit about the performance: the block will be evaluated n log n times during the sort, so I'd like it to be fast (the array might have up to 100,000 elements). Since localizedStandardCompare is only available on NSString, I need to convert the URLs to strings. Above, I use absoluteString, but there are other methods that return a NSString, for example relativeString. Reading the NSURL class reference, I get the impression that relativeString might be faster, since the URL does not need to be resolved, but this is my first time with Cocoa and OS-X, and thus just a wild guess.
Additional constraint: in this case, all URLs come from a NSDirectoryEnumerator on local storage, so all are file URLs. It would be a bonus if the method would work for all kinds of URL, though.
My question: which method should I use to convert NSURL to NSString for best performance?
Profiling all possible methods might be possible, but I have only one (rather fast) OS-X machine, and who knows - one day the code might end up on iOS.
I'm using Xcode 4.5.2 on OS-X 10.8.2, but the program should work on older version, too (within reasonable bounds).
You may need to use Carbon's FSCatalogSearch, which is faster than NSDirectoryEnumerator. As for getting the path, I see no choice.
The only thing you may consider for speeding up the sorting is that the paths are partially sorted, because the file system will return all the files of the same folder in alphabetical order.
So you may want to take all the path of the same directory and merge them with the other results.
For example the home contents may be:
ab1.txt
bb.txt
c.txt
The documents directory may contain:
adf.txt
fgh.txt
So you just merge them with a customized algorithm, which just applies the merge part of a mergesort.
I benchmarked the sort. It turned out that absoluteString and relativeString are much faster that path or relativePath.
Sorting about 26000 entries:
relativeString 550ms
absoluteString 580ms
path 920ms
relativePath 960ms
field access 480ms
For field access, I put the value of absoluteString into a field prior to the sort and access that. So, the ...String accessors are almost as fast as field access, and thus a good choice for my use case.
I have an app (Cocoa Touch, Web Browser), however I need to be able to compare an NSString with thousands of other strings. Here's the deal.
When a WebView loads, I get the URL. I need to compare this URL with literally thousands of results (27,847). Each of those numbers represents a line of text in a plain text file.
I would like to know the best way to go about getting the data from the text file, and comparing it with the NSString. I need to know if the URL that the WebView is loading contains any of these strings.
The app needs to be very fast, so I can't just parse through every line in the text file, turn it into an array, and then compare each and every result.
Please share your ideas. Thanks.
I think the cleanest solution is to:
Create a web service that can offload the work to a server and return a response. Since it sounds like you're building a web protection service, your database may grow to be quite substantial over time, and you can just scale your server up to increase its speed. Furthermore, you don't want to have to update your app every time the lookup data changes.
Other options are:
Use a local SQLite database. SQL databases should perform lookups relatively fast.
If you don't want to use any database, have you tried putting all the search strings into an NSDictionary or NSMutableDictionary object? This way, you would just check if the valueForKey: for the string you're searching for is nil.
Sample code for this:
NSDictionary *searchDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], #"google.com",
[NSNumber numberWithBool:YES], #"yahoo.com",
[NSNumber numberWithBool:YES], #"bing.com",
nil];
NSString *searchString = #"bing.com";
if ([searchDictionary valueForKey:searchString]) {
// search string found
} else {
// search string not found
}
Note: if you want the NSDictionary to perform case-insensitive comparisons, pre-load all values lowercase, and make the search string lowercase when using valueForKey:.
How much memory this could take is a whole other story, but I don't see how this comparison could be made much faster locally. I strongly recommend the remove web service approach, though.
Create a string from the file and enumerate through the lines.
NSString *stringToCheck;
NSData *bytesOfFile = [NSData dataWithContentsOfFile:#"/path/myfile.txt"];
NSString *fileString = [[NSString alloc] initWithData:bytesOfFile
encoding:NSUTF8Encoding];
__block BOOL foundMatch = NO;
[fileString enumerateLinesUsingBlock:^(NSString *line, BOOL *stop){
if([stringToCheck isEqualToString:line]){
*stop = YES;
foundMatch = YES;
}
}];
This is a job for regular expressions. Take all of the substrings you're looking for/filtering against, escape them appropriately (escaping characters such as [, ], |, and \, among others, with \), and join them with a |. The resulting string is your regular expression, which you apply to each URL.
You could loop through an entire array full of substrings, doing rangeOfString:options: with each one, but that's the slow way. A good regular expression implementation is built for this sort of thing, and I would hope that Apple's implementation is suitable.
That said, profile the hell out of it. I've seen some regex implementations choke on the | operator, so you'll want to make sure that Apple's is not one of them.
If you need to compare each string in your text file, you are going to have to compare it, no way around it.
What you can do however is do it on a background thread while showing some loading or something, and it won't feel as if the app got stuck.
I would suggest you try with NSDictionary first. You can load up all your URLs into this, and internally it will use some sort of hash table/map for very quick (O(1)) lookup.
You can then check the result of [dictionary objectForKey:userURL], and if it returns something then the URL matched one in the dictionary.
The only problem with this is that it requires an exact string match. If your dictionary contains http://server/foobar and the user enters http://server/FOOBAR (because it's a case-insensitive server), you are going to get a miss on your lookup. Similarly, adding ?foobar queries to the end of URLs will result in a miss. You could also add an explicit port with server:80, and with %XX character encoding you can create hundreds of variations of the same URL. You will have to account for this and canonicalize both the URLs in your dictionary, and the URL entered by the user prior to lookup.
I want to define a constant file path that includes whoever's username (e.g. /Users/username/Desktop...in my specific case it's a directory I create at /var/spool/FolderICreate/username).
What's the best way of declaring this constant so my other classes can recognize it? I currently have a globals.h file to include for the classes that need to see the globals, but I'm not sure how to set the value. #define obviously needs a hardcoded string literal, and I'm not sure if I can or how I would set the string using extern const NSString*. I feel like this shouldn't be hard, but I'm at a loss.
-- EDIT --
As people have rightly pointed out, my code was unnecessary because I can get the username with NSUserName, etc, so I've removed it. But I think people are missing the point of my question. I can see there are multiple ways to get the pathname I want--how do I declare that as a constant?
To your revised question, as Kaelin notes, you don't want a constant. A constant in C is something defined at compile time, and you don't know what the value is at compile time.
You don't want a variable for this problem. You want a static function. Foundation provides many that do things similar to what you want. If you want something else, make your own static function MYDirectoryForStuff().
Do not create non-constant global variables. That way lies madness. You then have to verify that they get initialized before they are used, which leads to all kinds of subtle bugs. If you use a static function, then it can easily be self-initializing.
Have a look at NSPathUtilities before you re-implement a bunch of functionality that's already provided in Foundation framework. You'll find a bunch of methods there specifically for what you're trying to do.
To answer the question you actually asked, there's no straightforward way to declare a variable as a constant and then change its value at runtime... That sort of defeats the purpose of telling the compiler it's constant. Simply declare the variable in a header file as an extern NSString * and only set it once. :-)
You should never make any assumptions about where the user's home folder might be.
The correct way to retrieve the path to the current user's home folder is
NSHomeDirectory()
If you wish to access one of the standard subfolders of the user's home folder, don't make any assumption about their location either, but use
NSSearchPathForDirectoriesInDomain()
to retrieve them. For example, to get the documents folder:
NSArray *searchPaths = NSSearchPathForDirectoriesInDomain(
NSDocumentDirectory,
NSUserDomainMask,
YES
);
NSLog(#"The documents folder is at %#", [searchPaths objectAtIndex:0]);
The Foundation framework has a function for this: NSUserName().
Given an app called ExampleApp, I want to find "~/Library/Logs/ExampleApp" basically without using hard coded paths. There exists NSSearchPathForDirectoriesInDomains, which you can use to find things like "~/Library/Application Support/ExampleApp" using the NSApplicationSupportDirectory search term, but there doesn't seem to be a search term for logging.
I don't think ~/Library/Logs is non-standard, since CrashReporter puts its logs there.
Try this :
NSString* libraryPath = [NSHomeDirectory stringByAppendingPathComponent:#"Library/Logs"];
Update (~/Library/Logs/AppName) :
NSString* bundleName = [[[NSBundle mainBundle] infoDictionary] objectForKey:#"CFBundleName"];
NSString* logsPath = [NSString stringWithFormat:#"Library/Logs/%#",bundleName];
NSString* libraryPath = [NSHomeDirectory stringByAppendingPathComponent:logsPath];
Cocoa doesn't provide a means for finding all of the standard directories. The old FSFindFolder() function can provide many more, but does involve converting from an FSRef back to a path or URL. Apple discourages its use, but it's still the only way to get certain standard directories without hard-coding. That said, it won't ever incorporate your app name. You have to append that.
Edited to add: the link to the legacy docs.
I need to read a HTML file and search for some tags in it. Based on the results, some tags would need to be removed, other ones changed and maybe refining some attributes — to then write the file back.
Is NSXMLDocument the way to go? I don't think that a parser is really needed in this case, it could even mean more work. And I don't want to touch the entire file, all I need to do is to load the file in memory, change some things, and save it again.
Note that, I'll be dealing with HTML, and not XHTML. Could that be a problem for NSXMLDocument? Maybe some unmatched tags or un-closed ones could make it stop working.
NSXMLDocument is the way to go. That way you can use Xpath/Xquery to find the tags you want. Bad HTML might be a problem but you can set NSXMLDocumentTidyHTML and it should be OK unless it's really bad.
NSRange startRange = [string rangeOfString:#"<htmlTag>"];
NSRange endRange = [string rangeOfString:#"</htmlTag>"];
NSString *subStr = [string subStringWithRange:NSMakeRange(startRange.location+startRange.length, endRange.location-startRange.location-startRange.length)];
NSString *finalStr = [string stringByReplacingOccurencesOfString:substr];
and then write finalstr to the file.
This is what I would do, note that I don't exactly know what the advantages of using NSXMLDocument would be, this should do it perfectly.
NSXMLDocument will possibly fail, due to the fact that HTML pages are not well formed, but you can try with NSXMLDocumentTidyHTML/NSXMLDocumentTidyXML (you can use them both to improve results) as outlined here and also have a look a this for tan approach at modifying the HTML.