drawing on the iPhone in objective c [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

Drawing on the iPhone in objective c

I have written this...

In the .h file:

#import <UIKit/UIKit.h>

@interface DrawView : UIView {
    CGPoint gestureStartPoint,currentPosition;
    CGContex开发者_开发百科tRef c;
    UIBezierPath *currentPath;
}

@property(nonatomic,retain)UIBezierPath *currentPath;

@end

And in the .m file:

#import "DrawView.h"

@implementation DrawView

@synthesize currentPath;

- (id)initWithFrame:(CGRect)frame {
    [self drawRect:CGRectMake(0, 0, 320, 480)];
    self = [super initWithFrame:frame];
    if (self) {
        currentPath = [[UIBezierPath alloc]init];
        currentPath.lineWidth=3;
    }
    return self;
}




- (void)drawRect:(CGRect)rect {
    [[UIColor redColor] set];
    [currentPath strokeWithBlendMode:kCGBlendModeNormal alpha:1.0];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    currentPosition = [touch locationInView:self]; 
    [currentPath addLineToPoint:(currentPosition)];
    [self setNeedsDisplay];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    gestureStartPoint = [touch locationInView:self];
    [currentPath moveToPoint:(gestureStartPoint)];
}

- (void)dealloc {
    [super dealloc];
}


@end

I want to let the user draw an image on the iPhone screen and then use that image for the game... but this doesn't draw anything...

---

This is because your currentPath is not allocated. If you instantiate the view in the resource [UIView initWithFrame:] will never be called. Implement [UIView initWithCoder:] and allocate it there.

- (void)commonInit
{
    currentPath = [[UIBezierPath alloc] init];
    currentPath.lineWidth=3;
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {
        [self commonInit];
    }
    return self;
}

- (id)initWithCoder:(NSCoder*)aDecoder
{
    self = [super initWithCoder:aDecoder];
    if (self)
    {
        [self commonInit];
    }
    return self;
}

Alternatively you can make the path in the touchesBegan if it is nil.

- (UIBezierPath*)currentPath
{
    if (currentPath = nil)
    {
        currentPath = [[UIBezierPath alloc] init];
        currentPath.lineWidth=3;
    }
    return currentPath;
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    gestureStartPoint = [touch locationInView:self];

    [[self currentPath] moveToPoint:(gestureStartPoint)];
}

However, there are some problems in the code.

1. You call [self drawRect:CGRectMake(0, 0, 320, 480)] before self = [super initWithFrame:frame]. You must not call any method there. You can write your code only inside

   if (self ! =nil) { // your code }

2. currentPath leaks. Release it in dealloc.

3. Never call drawRect directly. Call [UIView setNeedsDisplay] instead.