CODEWITHSUNDEEP
iphone
YinHuanChen
YinHuanChen

Reputation:

Issue of CGContext

I want to draw a line in the rect of UIView when I touch screen. Please can someone help me to check the code!

- (void)drawRect:(CGRect)rect {
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(context, 5.0);
    CGContextSetStrokeColorWithColor(context, [UIColor greenColor].CGColor);
    CGContextSetFillColorWithColor(context, [UIColor greenColor].CGColor);
    CGContextMoveToPoint(context, 100.0, 30.0);
    CGContextAddLineToPoint(context, 200.0, 30.0);
    CGContextStrokePath(context);
}

Upvotes: 0

Views: 498

Answers (1)

kennytm
kennytm

Reputation: 523274

UIGraphicsGetCurrentContext() refers to the UIView's context only when you're inside the -drawRect: method. To draw a line when you touch the screen, you need to use a variable to keep track on the finger's status.

@interface MyView : UIView {
   BOOL touchDown;
}
...

-(void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
   touchDown = YES;
   [self setNeedsDisplay];
}
-(void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
   touchDown = NO;
   [self setNeedsDisplay];
}
-(void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
   touchDown = NO;
   [self setNeedsDisplay];
}

-(void)drawRect:(CGRect)rect {
   CGContextRef context = UIGraphicsGetCurrentContext();
   if(touchesDown) {
        CGContextSetLineWidth(context, 5.0);
        CGContextSetStrokeColorWithColor(context, [UIColor greenColor].CGColor);
        CGContextSetFillColorWithColor(context, [UIColor greenColor].CGColor);
        CGContextMoveToPoint(context, 100.0, 30.0);
        CGContextAddLineToPoint(context, 200.0, 30.0);
        CGContextStrokePath(context);
   }
}

Upvotes: 2

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