How to find a pixel-positon of a cursor in UITextView?

Question

I'm developing a simple writing app for iPad.

I'm trying to compute the pixel-position of the cursor in UITextView. I spend a few weeks to design this, but I still couldn't figure out to do it.

In stackoverflow, Tony wrote one good algorithm to find the pixel-position of the cursor.

Pixel-Position of Cursor in UITextView

I implemented this with a little modification, and it almost works that it gives the correct pixel-position of the cursor. However, it only works with English alphabets.

If there is Chinese or Japanese character at the end of line, UITextView performs character-wrapping, instead of word-wrapping, even though there is no space between Chinese characters. I think Tony's algorithm works when UITextView performs only word-wrapping (with English alphabets).

Is there any other way to find the pixel-position of the cursor in UITextView?

Or is there a way to determine whether a particular character follows character-wrapping like Chinese characters or word-wrapping like English?

Addition:

Here's my implementation based on Tony's algorithm. I placed one UITextView in a landscape mode, so its width is 1024, and I used the custom font with size 21. You should change sizeOfContentWidth and sizeOfContentLine appropriately. sizeOfContentWidth is smaller than the actual width, and sizeOfContentLine is larger than the actual font size (line height > font size).

Sorry about messy code and comments! There are still some small bugs, and it gives wrong position if you type Chinese characters at the end of line (no word-wrap).

#define sizeOfContentWidth 1010
#define sizeOfContentHeight 1000
#define sizeOfContentLine 25

    // Stores the original position of the cursor
NSRange originalPosition = textView.selectedRange;    

// Computes textView's origin
CGPoint origin = textView.frame.origin;

// Checks whether a character right to the current cursor is a non-space character
unichar c = ' ';

if(textView.selectedRange.location != [textView.text length])
    c = [textView.text characterAtIndex:textView.selectedRange.location];

// If it's a non-space or newline character, then the current cursor moves to the end of that word
if(c != 32 && c != 10){
    NSRange delimiter = [textView.text rangeOfCharacterFromSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]
                                                       options:NSLiteralSearch
                                                         range:NSMakeRange(textView.selectedRange.location, [textView.text length] - textView.selectedRange.location)];

    if(delimiter.location == NSNotFound){
        delimiter.location = [textView.text length];
    }

    textView.selectedRange = delimiter;
}

// Deviation between the original cursor location and moved location
int deviationLocation = textView.selectedRange .location - originalPosition.location;

// Substrings the part before the cursor position
NSString* head = [textView.text substringToIndex:textView.selectedRange.location];

// Gets the size of this part
CGSize initialSize = [head sizeWithFont:textView.font constrainedToSize:CGSizeMake(sizeOfContentWidth, sizeOfContentHeight)];

// Gets the length of the head
NSUInteger startOfLine = [head length];

// The first line
BOOL isFirstLine = NO;

if(initialSize.height / sizeOfContentLine == 1){
    isFirstLine = YES;
}

while (startOfLine > 0 && isFirstLine == NO) {
    // 1. Adjusts startOfLine to the beginning of the first word before startOfLine
    NSRange delimiter = [head rangeOfCharacterFromSet:[NSCharacterSet whitespaceAndNewlineCharacterSet] options:NSBackwardsSearch range:NSMakeRange(0, startOfLine)];

    // Updates startsOfLine
    startOfLine = delimiter.location;

    // 2. Check if drawing the substring of head up to startOfLine causes a reduction in height compared to initialSize. 
    NSString *tempHead = [head substringToIndex:startOfLine];

    // Gets the size of this temp head
    CGSize tempHeadSize = [tempHead sizeWithFont:textView.font constrainedToSize:CGSizeMake(sizeOfContentWidth, sizeOfContentHeight)];

    // Counts the line of the original
    int beforeLine = initialSize.height / sizeOfContentLine;

    // Counts the line of the one after processing
    int afterLine = tempHeadSize.height / sizeOfContentLine;

    // 3. If so, then you've identified the start of the line containing the cursor, otherwise keep going.
    if(beforeLine != afterLine)
        break;
}

// Substrings the part after the cursor position
NSString* tail;

if(isFirstLine == NO)
    tail = [head substringFromIndex:(startOfLine + deviationLocation)];
else {
    tail = [head substringToIndex:(startOfLine - deviationLocation)];
}

// Gets the size of this part
CGSize lineSize = [tail sizeWithFont:textView.font forWidth:sizeOfContentWidth lineBreakMode:UILineBreakModeWordWrap];

// Gets the cursor position in coordinate
CGPoint cursor = origin;    
cursor.x += lineSize.width;
cursor.y += initialSize.height - lineSize.height;

// Back to the original position
textView.selectedRange = originalPosition;

// Debug
printf("x: %f,   y: %f\n", cursor.x, cursor.y);

Answer 1

If you target to IOS7 only you could use UITextView method:

- (CGRect)caretRectForPosition:(UITextPosition *)position;

Short sample:

NSRange range; // target location in text that you should get from somewhere, e.g. textview.selectedRange
UITextView textview; // the text view

UITextPosition *start = [textview positionFromPosition:textview.beginningOfDocument offset:range.location];
CGRect caretRect = [self caretRectForPosition:start]; // caret rect in UITextView

Answer 2

This is probably rather inefficient, but could you take the same basic principal of the code you have posted and take the line of text the cursor is on, and loop through each individual character and do [NSString sizeWithFont:forWidth:lineBreakMode:] to calculate each character's width, and you could add all those up for your x position? Just an idea, but may help fix the issue with word wrapping.