NSStringFromRangeを使用する必要がありますが、開始UITextPositionsと終了UITextPositionsしかありません。UITextPositionをNSRangeにどのように変換しますか。
NSMutableArray * wordArray = [[NSMutableArray alloc]init];
id<UITextInputTokenizer> tokenizer = tv.tokenizer;
UITextPosition *start = tv.beginningOfDocument;
while (![start isEqual:tv.endOfDocument]) {
UITextPosition *end = [tokenizer positionFromPosition:start toBoundary:UITextGranularityWord inDirection:UITextStorageDirectionForward];
NSString *word = [tv textInRange:[tv textRangeFromPosition:start toPosition:end]];
[wordArray addObject:NSStringFromRange(<#NSRange range#>)];
start = end;
}