Selecting a part of an entered Text in a UITextField is not as easy as it seems. You need to do several steps to get to the goal.
The word entered in the textField is: PHILADELPHIA
itemAEntry1 is the textField in which the selection should take place.
int startpointIndex = 2; //the starting point Index is 2 (meaning the selection starts at the 3rd letter, remember the index starts with 0, first letter in the UITextField is 0)
int lengthOfSelection = 5; //requested length is 5 (5 characters will be selected)
NSRange toBeSelectedRange = NSMakeRange(startpointIndex, lengthOfSelection); //this creates the Range for the later selection
[itemAEntry1 becomeFirstResponder]; //first the text field needs to become first responder
UITextPosition *zeroIndexOfTextfield = itemAEntry1.beginningOfDocument; //here we find the start of the text field
UITextPosition *startOfSelection = [itemAEntry1 positionFromPosition:zeroIndexOfTextfield offset:toBeSelectedRange.location]; //here we generate the starting point of the selection by offsetting the location of the Chosen Range
UITextPosition *endOfSelection = [itemAEntry1 positionFromPosition:startOfSelection offset:toBeSelectedRange.length]; //here we find the end point of the selection by offsetting the length of the Chosen Range
UITextRange *createdRange = [itemAEntry1 textRangeFromPosition:startOfSelection toPosition:endOfSelection]; //here we generate the text Range by using the found starting and ending Position
[itemAEntry1 setSelectedTextRange:createdRange]; //select the above created Range in the Text field
This code results in selecting the Part "ILADE" in the word PHILADELPHIA.