Control cursor position in UITextField

I have a UITextField that I'm forcing formatting on by modifying the text inside the change notification handler. This works great (once I solved the reentrancy issues) but leaves me with one more nagging problem. If the user moves the cursor someplace other than the end of the string then my formatting change moves it to the end of the string. This means users cannot insert more than one character at a time into the middle of the text field. Is there a way to remember and then reset the cursor position in the UITextField?

Solution 1:

Controlling cursor position in a UITextField is complicated because so many abstractions are involved with input boxes and calculating positions. However, it's certainly possible. You can use the member function setSelectedTextRange:

[input setSelectedTextRange:[input textRangeFromPosition:start toPosition:end]];

Here's a function which takes a range and selects the texts in that range. If you just want to place the cursor at a certain index, just use a range with length 0:

+ (void)selectTextForInput:(UITextField *)input atRange:(NSRange)range {
    UITextPosition *start = [input positionFromPosition:[input beginningOfDocument] 
                                                 offset:range.location];
    UITextPosition *end = [input positionFromPosition:start
                                               offset:range.length];
    [input setSelectedTextRange:[input textRangeFromPosition:start toPosition:end]];
}

For example, to place the cursor at idx in the UITextField input:

    [Helpers selectTextForInput:input 
                        atRange:NSMakeRange(idx, 0)];

Solution 2:

Useful to position at index (Swift 3)

private func setCursorPosition(input: UITextField, position: Int) {
    let position = input.position(from: input.beginningOfDocument, offset: position)!
    input.selectedTextRange = input.textRange(from: position, to: position)
}