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POObjective-C costum drawing with draw: (CGContextRef *)context
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  1. POObjective-C costum drawing with draw: (CGContextRef *)context
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    copied!<p>I have a home work which our professor told us to make circle, square, and triangle confirm to a protocol called </p> <p><code>Shape.h</code>:</p> <pre><code>#import &lt;Foundation/Foundation.h&gt; @protocol Shape &lt;NSObject&gt; @required - (void)draw:(CGContextRef) context; - (float)area; @end </code></pre> <p>and use <code>UIBotton</code> to call different class to draw..</p> <p>I call the draw function from my view controller </p> <p><code>XYZController.m</code>:</p> <pre><code>- (IBAction)rectButton:(id)sender { CGRect frame = [myView bounds]; MyRect *rectView = [[MyRect alloc] initWithFrame:frame]; [rectView draw: UIGraphicsGetCurrentContext()]; [myView addSubview:rectView]; } </code></pre> <p>where <code>myView</code> is a <code>UIView</code> I dragged onto <code>.xib</code> </p> <p>and perform draw in <code>MyRect</code> class </p> <p><code>MyRect.h</code>:</p> <pre><code>@interface MyRect : UIView &lt;Shape&gt; </code></pre> <p>I changed the super class from NSObject to UIView... Not sure if I did it correctly..</p> <p><code>MyRect.m</code>:</p> <pre><code>- (id)initWithFrame:(CGRect)frame { self = [super initWithFrame:frame]; if (self) { [self setNeedsDisplay]; } return self; } - (void)draw : (CGContextRef) context { CGRect bounds = [self bounds]; CGRect originRect = CGRectMake(25.0, 25.0, 50.0, 75.0); CGContextAddRect(context, originRect); CGContextStrokePath(context); [[UIColor greenColor] setFill]; CGContextFillRect(context, originRect); } </code></pre> <p>But then I got the error:</p> <pre><code>[...] &lt;Error&gt;: CGContextSetFillColorWithColor: invalid context 0x0 [...] &lt;Error&gt;: CGContextAddRect: invalid context 0x0 [...] &lt;Error&gt;: CGContextFillRects: invalid context 0x0 </code></pre> <p>I guess it's from <code>[rectView draw: UIGraphicsGetCurrentContext()];</code></p> <p>Any idea of how to fix this?</p> <p>Thanks!</p>
 

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