Differences in string handling for NSString and NSAttributedString
Differences in string handling for NSString and NSAttributedString
- Subject: Differences in string handling for NSString and NSAttributedString
- From: Pax <email@hidden>
- Date: Mon, 05 May 2014 17:27:34 +0100
I have a an NSAttributedString into which I would like to insert images. The images need to be inserted after specific line endings (I know which line endings in advance - they've been previously calculated).
I have written a function which returns an array of all line ending locations (or anything else that you'd care to search for) for a given string:
+(NSArray*)getLocationsOfString:(NSString*)stringToFind inString:(NSString*)sourceString {
NSMutableArray* returnArray = [[NSMutableArray alloc]init];
@autoreleasepool
{
NSMutableString* sourceToSearch = [[NSMutableString alloc]initWithString:sourceString];
unsigned long locationIterator=0;
while ([sourceToSearch rangeOfString:stringToFind].location!=NSNotFound) {
unsigned long foundLocation = [sourceToSearch rangeOfString:stringToFind].location+1;
[sourceToSearch deleteCharactersInRange:NSMakeRange(0, foundLocation)];
[returnArray addObject:[NSNumber numberWithUnsignedLong:foundLocation+locationIterator]];
locationIterator+=foundLocation;
}
}
return returnArray;
}
When I use this with a plain string it appears to work correctly. I can use it to chop up a string into constituent lines as follows (just a test - clearly there are better ways of achieving the same result):
NSArray* newLineArray = [StringTools getLocationsOfString:@"\n" inString:[attributedRTFString string]];
int oldLoc = 0;
for (NSNumber* locNum in newLineArray) {
NSLog(@"%@",[[attributedRTFString string] substringWithRange:NSMakeRange(oldLoc, [locNum intValue]-oldLoc)]);
oldLoc = [locNum intValue];
}
This proves, to my satisfaction at least, that the line endings are being identified correctly and in the right place.
When I try to use it with the attributed string, rather than the plain text representation of the attributed string, it goes wrong. In the interests of a quick test, I am trying to insert a string rather than an image.
NSArray* newLineArray = [StringTools getLocationsOfString:@"\n" inString:[attributedRTFString string]];
if (([imageLocations count]>0)&&([newLineArray count]>0)) {
for (NSDictionary* imageDetails in imageLocations) {
unsigned long loc = [[imageDetails objectForKey:@"image location"]unsignedLongValue];
unsigned long locationForInsert = [[newLineArray objectAtIndex:loc]unsignedLongValue];
NSAttributedString* testString = [[NSAttributedString alloc]initWithString:@"IMAGE HERE" attributes:nil];
[attributedRTFString insertAttributedString:testString atIndex:locationForInsert];
}
}
I believe that this should cause "IMAGE HERE" to be inserted at specific line endings. However, it often inserts into the middle of a paragraph instead - usually, but not always, close to where it should put the text. Furthermore, the positioning is usually at, or very close, to the correct location for the first instance of image insertion - and it gets progressively less accurate as it gets through the text. Is there some difference between the ways that strings are handled in NSAttributedString and NSString? Could there be some problem with characters like Non-Breaking Space?
Hoping that someone can help!
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