Implementing NSUndoManager with Paint Application - ios

Question

I am new to iOS and building a paint application.
Everything goes ok..but I am unable to implement NSUndoManager in my application for undo and redo purpose.
The problem is that I am unable to store the previous state of painting for undo.
Here is the code
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
mouseSwiped = NO;
UITouch *touch = [touches anyObject];
lastPoint = [touch locationInView:self.tempDrawImage];
[[self.undoManage prepareWithInvocationTarget:self]
touchesMoved:touches withEvent:event];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
mouseSwiped = YES;
UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:self.tempDrawImage];
UIGraphicsBeginImageContext(self.view.frame.size);
[self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width,
self.view.frame.size.height)];
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush );
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeNormal);
CGContextStrokePath(UIGraphicsGetCurrentContext());
self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
[self.tempDrawImage setAlpha:opacity];
UIGraphicsEndImageContext();
lastPoint = currentPoint;
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
UIGraphicsBeginImageContext(self.tempDrawImage.frame.size);
[self.tempDrawImage.image drawInRect:
CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)
blendMode:kCGBlendModeNormal alpha:1.0];
self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
[[self.undoManage prepareWithInvocationTarget:self] touchesMoved:touches
withEvent:event];
UIGraphicsEndImageContext();
}
-(void)undo
{
[self.undoManage undo];
}
-(void)redo
{
[self.undoManage redo];
}