Draw Line using CGContext

Question

I want to draw line in table view cell so that I can place textfield & switch in single cell. I increased the height of cell. How can I draw line in cell?

I have subclass of UIView which contains following code

 //Get the CGContext from this view
 CGContextRef context = UIGraphicsGetCurrentContext();
 //Set the stroke (pen) color
 CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
 //Set the width of the pen mark
 CGContextSetLineWidth(context, 1.0);

 // Draw a line
 //Start at this point
 CGContextMoveToPoint(context, 10.0, 30.0);

 //Give instructions to the CGContext
 //(move "pen" around the screen)
 CGContextAddLineToPoint(context, 310.0, 30.0);


 //Draw it
 CGContextStrokePath(context);

Then I have a tableViewController with grouped table style. In cellForRowAtIndexPath I have following code

//code to add textfield
DrawLineView *drawLine = [[DrawLineView alloc]init];
[cell addSubview:drawLine];
//code add switch

But it is not drawing any line. I can't use 2 different cells. I have to Please help me. This is my first to deal with graphics i iphone. Thanks

score 20 · Answer 1 · edited Feb 06 '12 at 03:24

20

If all you want to do is draw a line, it would be a lot better to use a CAShapeLayer, pass it a path with a line, and then attach that as a sublayer of the cells content view. The table should perform better than using a view with a custom drawRect.

Example of drawing a line via CALayer and a path:

// You'll also need the QuartzCore framework added to the project
#import <QuartzCore/QuartzCore.h>

CAShapeLayer *lineShape = nil;
CGMutablePathRef linePath = nil;
linePath = CGPathCreateMutable();
lineShape = [CAShapeLayer layer];

lineShape.lineWidth = 4.0f;
lineShape.lineCap = kCALineCapRound;;
lineShape.strokeColor = [[UIColor blackColor] CGColor];

int x = 0; int y = 0;
int toX = 30; int toY = 40;                            
CGPathMoveToPoint(linePath, NULL, x, y);
CGPathAddLineToPoint(linePath, NULL, toX, toY);

lineShape.path = linePath;
CGPathRelease(linePath);
[self.layer addSublayer:lineShape];

edited Feb 06 '12 at 03:24

pheelicks

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answered Mar 20 '11 at 18:56

Kendall Helmstetter Gelner

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Can u explain how can do this? – iOSAppDev Mar 20 '11 at 18:58
Drawing with CoreAnimation and CoreGraphics seems to be largely dispused. I just watched a video from Apple, presented at WDC2011 where the presenter noticed that CoreGraphics would be faster than CoreAnimation. Are there any benchmarks available to back up these claims? – Brian Aug 07 '12 at 19:11
1

I'm not really sure it makes sense to compare CoreGraphics and CoreAnimation, since CoreGraphics is about rendering graphics and CoreAnimation is built on top, meant for adjusting properties of graphics over time... What was the session title and name? – Kendall Helmstetter Gelner Aug 08 '12 at 03:27

score 0 · Answer 2 · answered Jul 08 '16 at 10:49

I think a very simplified way of drawing a line is to create a UIView and fill it with desired color, then choose its width accordingly, and setup height to be 1 pixel like so:

var lineView : UIView = {
     let view = UIView()
     view.backgroundColor = UIColor.blackColor()
     view.translatesAutoresizingMaskIntoConstraints = false
     return view
}()


self.view.addSubview(lineView)
self.view.addConstraints(NSLayoutConstraint.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|[view]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["view": lineView])))
self.view.addConstraints(NSLayoutConstraint.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-50-[view(1)]", options: NSLayoutFormatOptions(), metrics: nil, views: ["view": lineView])))

amattn · Accepted Answer · 2011-03-20T19:11:30.847

Two things... First, you usually don't draw into the cell itself.

You normally draw into the content view. Sometimes it makes sense draw into the cell's backgroundView or selectedBackgroundView.

[cell.contentView addSubview:drawLine];

Second, the default cell text labels cell.textLabel and cell.detailTextLabel have non-transparent background. Try setting their background colors to [UIColor clearColor].

Edit: one more thing: you need to set a proper frame for your drawLine

DrawLineView *drawLine = [[DrawLineView alloc]initWithFrame:cell.contentView.bounds];

Draw Line using CGContext

3 Answers3

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