drawing on top of UIImageView

Discussion in 'iOS Programming' started by dok24, Jun 30, 2011.

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  1. dok24, Jun 30, 2011

    dok24 macrumors newbie

    Joined:
    Jun 30, 2011
    #1
    Hey all,

    I have a bit of a problem here. I am trying to draw shapes responding to touch events. My basic heirarchy is as follows:

    Viewcontroller
    -uiscrollview
    -uiimageview(inside uiscrollview)

    When somebody touches the uiimage view I want a shape to appear where they touched, and stay there even when the UISCrollview is panned, or zoomed away. Whenever I try to call drawRect in the uiimageview I get an invalid context error. Any suggestions?

    Thanks in advance..
     
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  2. xStep, Jul 1, 2011

    xStep macrumors 68000

    Joined:
    Jan 28, 2003
    Location:
    Less lost in L.A.
    #2
    I suggest you supply your drawRect: code.

    Likely you haven't got a line like this so that you can reference the context.
    Code:
    CGContextRef context = UIGraphicsGetCurrentContext();
    Something to be concerned about is that you can't safely draw within a drawRect method of a UIView and expect to draw over the content that was there before entering the method. You have to act like the rectangle you are drawing into has been cleared. A UIImageView is a subclass of UIView so this should still apply. The way around that is to have the image in a separate UIImage variable and draw that to the rect before drawing your shape. If you want multiple shapes to build up over time, then things get more complicated.
     
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  3. dok24, Jul 4, 2011

    dok24 thread starter macrumors newbie

    Joined:
    Jun 30, 2011
    #3
    I was able to remedy the problem by attaching a transparent UIView overtop of the UIImageView and drawing my shapes onto that.
     
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