how to build an undo stack in iOS/core graphics - cocoa-touch

Question

I'm trying to add an undo / redo capability to a set of touches..
I have this code for touchesBegan and moved:
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
NSLog(#"%s", __FUNCTION__);
mouseSwiped = NO;
UITouch *touch = [touches anyObject];
if ([touch tapCount] == 2) {
[self eraseButtonTapped:self];
return;
}
lastPoint = [touch locationInView:self.view];
lastPoint.y -= 20;
[self.undoPath addObject:WHATGOESHERE];
// Remove all paths from redo stack
[self.redoStack removeAllObjects];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
//NSLog(#"%s", __FUNCTION__);
mouseSwiped = YES;
UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:self.view];
currentPoint.y -= 20;
UIGraphicsBeginImageContext(self.view.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, brush);
CGContextSetRGBStrokeColor(context, red, green, blue, 1.0);
CGContextBeginPath(context);
CGContextMoveToPoint(context, lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y);
CGContextStrokePath(context);
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
[self.undoPath addObject:WHATGOESHERE];
UIGraphicsEndImageContext();
NSLog(#"Touches Moved undoPath contains %i objects", [self.undoPath count]);
// Remove all paths from redo stack
[self.redoPath removeAllObjects];
lastPoint = currentPoint;
}
I think that if I can figure how to populate the undo stack, that I can iterate through the stack to undo redo touches.. Maybe I'm all wet. I sure would appreciate some help...
Thanks
..I have asked a similar question before, but I've restarted the project in a different form as the last way was not satisfactory.

Answer 1

I finally solved this by managing arrays.
For each stroke, there is an addition to a buffer array:
[self.currentColoredPath.path moveToPoint:[touch locationInView:self]];
[self.currentArray addObject:self.currentColoredPath];
// Remove all paths from redo stack
[self.redoStack removeAllObjects];
Then the Undo and Redo methods look like this:
-(void)undoButtonClicked
{
//NSLog(#"%s", __FUNCTION__);
if ([self.currentArray count] == 0) {
//nothing to undo
return;
}
DrawingPath *undonePath = [self.currentArray lastObject];
[self.currentArray removeLastObject];
[self.redoStack addObject:undonePath];
[self setNeedsDisplay];
}
-(void)redoButtonClicked
{
//NSLog(#"%s", __FUNCTION__);
if ([self.redoStack count] == 0) {
// nothing to redo
return;
}
DrawingPath *redonePath = [self.redoStack lastObject];
[self.redoStack removeLastObject];
[self.currentArray addObject:redonePath];
[self setNeedsDisplay];
}
I hope this helps others.
UPDATE - This is in response to the question below: "What is currentColoredPath?"
#property (strong,nonatomic) DrawingPath *currentColoredPath;
This refers to a class DrawingPath, which I wrote as follows:
.h
#import <Foundation/Foundation.h>
#interface DrawingPath : NSObject {
NSString *brushSize;
}
#property (strong, nonatomic) NSString *brushSize;
#property (strong,nonatomic) UIColor *color;
#property (strong,nonatomic) UIBezierPath *path;
- (void)draw;
- (void)brushChange;
.m
#import "DrawingPath.h"
#implementation DrawingPath
#synthesize path = _path;
#synthesize color = _color;
#synthesize brushSize = _brushSize;
float brush = 12;
- (id)init {
//NSLog(#"%s", __FUNCTION__);
if (!(self = [super init] ))
return nil;
brushSize = [[NSUserDefaults standardUserDefaults] objectForKey:#"brushKey"];
[self brushChange];
_path = [[UIBezierPath alloc] init];
_path.lineCapStyle=kCGLineCapRound;
_path.lineJoinStyle=kCGLineJoinRound;
[_path setLineWidth:brush];
return self;
}
- (void)draw {
//NSLog(#"%s", __FUNCTION__);
[self.color setStroke];
[self.path stroke];
}
- (void)brushChange { //from notification
//NSLog(#"%s", __FUNCTION__);
brushSize = [[NSUserDefaults standardUserDefaults] objectForKey:#"brushKey"];
//NSLog(#"DrawingPath - brushSize is %#: ", brushSize );
//NSLog(#"DrawingPath - brush is %f: ", brush );
}