UITextView subclass to handle up/down cursor movement

gistfile1.m

// Code to handle up/down cursor motion in a UITextView.
//
// Based on code from OmniGroup's OUITextView
// https://github.com/omnigroup/OmniGroup/blob/master/Frameworks/OmniUI/iPad/OUITextView.m
//
 
#import "TextView.h"
 
@interface TextView ()
 
@property (strong, nonatomic) NSArray *textCommands;
@property (nonatomic) UITextLayoutDirection verticalMoveDirection;
@property (nonatomic) CGRect verticalMoveStartCaretRect;
@property (nonatomic) CGRect verticalMoveLastCaretRect;
 
@end
 
@implementation TextView
 
- (id)initWithCoder:(NSCoder *)decoder
{
    self = [super initWithCoder:decoder];
    if (self) {
        self.verticalMoveStartCaretRect = CGRectZero;
        self.verticalMoveLastCaretRect = CGRectZero;
    }
    return self;
}
 
- (NSArray *)keyCommands
{
    if (!self.textCommands) {
        UIKeyCommand *upCommand = [UIKeyCommand keyCommandWithInput:UIKeyInputUpArrow modifierFlags:0 action:@selector(moveUp:)];
        UIKeyCommand *downCommand = [UIKeyCommand keyCommandWithInput:UIKeyInputDownArrow modifierFlags:0 action:@selector(moveDown:)];
        self.textCommands = @[upCommand, downCommand];
    }
    return self.textCommands;
}
 
- (BOOL)canPerformAction:(SEL)action withSender:(id)sender
{
    if (action == @selector(moveUp:) || action == @selector(moveDown:)) {
        return YES;
    }
    return [super canPerformAction:action withSender:sender];
}
 
#pragma mark -
 
- (void)moveUp:(id)sender
{
    UITextPosition *p0 = self.selectedTextRange.start;
    if ([self isNewVerticalMovementForPosition:p0 inDirection:UITextLayoutDirectionUp]) {
        self.verticalMoveDirection = UITextLayoutDirectionUp;
        self.verticalMoveStartCaretRect = [self caretRectForPosition:p0];
    }
 
    if (p0) {
        UITextPosition *p1 = [self closestPositionToPosition:p0 inDirection:UITextLayoutDirectionUp];
        if (p1) {
            self.verticalMoveLastCaretRect = [self caretRectForPosition:p1];
            UITextRange *r = [self textRangeFromPosition:p1 toPosition:p1];
            self.selectedTextRange = r;
        }
    }
}
 
- (void)moveDown:(id)sender
{
    UITextPosition *p0 = self.selectedTextRange.end;
    if ([self isNewVerticalMovementForPosition:p0 inDirection:UITextLayoutDirectionDown]) {
        self.verticalMoveDirection = UITextLayoutDirectionDown;
        self.verticalMoveStartCaretRect = [self caretRectForPosition:p0];
    }
 
    if (p0) {
        UITextPosition *p1 = [self closestPositionToPosition:p0 inDirection:UITextLayoutDirectionDown];
        if (p1) {
            self.verticalMoveLastCaretRect = [self caretRectForPosition:p1];
            UITextRange* r = [self textRangeFromPosition:p1 toPosition:p1];
            self.selectedTextRange = r;
        }
    }
}
 
- (UITextPosition *)closestPositionToPosition:(UITextPosition *)position inDirection:(UITextLayoutDirection)direction
{
    // Currently only up and down are implemented.
    NSParameterAssert(direction == UITextLayoutDirectionUp || direction == UITextLayoutDirectionDown);
 
    // Translate the vertical direction to a horizontal direction.
    UITextLayoutDirection lookupDirection = (direction == UITextLayoutDirectionUp) ? UITextLayoutDirectionLeft : UITextLayoutDirectionRight;
 
    // Walk one character at a time in `lookupDirection` until the next line is reached.
    UITextPosition *checkPosition = position;
    UITextPosition *closestPosition = position;
    CGRect startingCaretRect = [self caretRectForPosition:position];
    CGRect nextLineCaretRect;
    BOOL isInNextLine = NO;
    while (YES) {
        UITextPosition *nextPosition = [self positionFromPosition:checkPosition inDirection:lookupDirection offset:1];
        if (!nextPosition || [self comparePosition:checkPosition toPosition:nextPosition] == NSOrderedSame) {
            // End of line.
            break;
        }
 
        checkPosition = nextPosition;
        CGRect checkRect = [self caretRectForPosition:checkPosition];
        if (CGRectGetMidY(startingCaretRect) != CGRectGetMidY(checkRect)) {
            // While on the next line stop just above/below the starting position.
            if (lookupDirection == UITextLayoutDirectionLeft && CGRectGetMidX(checkRect) <= CGRectGetMidX(self.verticalMoveStartCaretRect)) {
                closestPosition = checkPosition;
                break;
            }
            if (lookupDirection == UITextLayoutDirectionRight && CGRectGetMidX(checkRect) >= CGRectGetMidX(self.verticalMoveStartCaretRect)) {
                closestPosition = checkPosition;
                break;
            }
            // But don't skip lines.
            if (isInNextLine && CGRectGetMidY(checkRect) != CGRectGetMidY(nextLineCaretRect)) {
                break;
            }
 
            isInNextLine = YES;
            nextLineCaretRect = checkRect;
            closestPosition = checkPosition;
        }
    }
    return closestPosition;
}
 
- (BOOL)isNewVerticalMovementForPosition:(UITextPosition *)position inDirection:(UITextLayoutDirection)direction
{
    CGRect caretRect = [self caretRectForPosition:position];
    BOOL noPreviousStartPosition = CGRectEqualToRect(self.verticalMoveStartCaretRect, CGRectZero);
    BOOL caretMovedSinceLastPosition = !CGRectEqualToRect(caretRect, self.verticalMoveLastCaretRect);
    BOOL directionChanged = self.verticalMoveDirection != direction;
 
    BOOL newMovement = noPreviousStartPosition || caretMovedSinceLastPosition || directionChanged;
    return newMovement;
}
 
@end