Drawing half-circles with CoreGraphics

问题:

I know how to draw lines and shapes with CGPaths . But I couldn't figure out how to draw this symbol for a circuit diagram

What code should I write to get that half circle shape?

This is what I have so far:

- (void)drawRect:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(context, 5.0);
    CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
    CGContextMoveToPoint(context, 60, 80);
    CGContextAddLineToPoint(context, 120, 80);
    CGContextMoveToPoint(context, 120, 80);
    CGContextAddArc(120,80,M_PI,M_PI/2);
    CGContextMoveToPoint(context, 200, 80);
    CGContextAddLineToPoint(context, 300, 80);
    CGContextStrokePath(context);
}

回答1:

You could create a UIBezierPath, e.g. something like:

UIBezierPath *path = [UIBezierPath bezierPath];
CGPoint point = CGPointMake(0, 50);
CGFloat radius = 15.0;
CGFloat lineLength = 25.0;

[path moveToPoint:point];
point.x += lineLength;
[path addLineToPoint:point];
point.x += radius;
[path addArcWithCenter:point radius:radius startAngle:M_PI endAngle:M_PI * 2 clockwise:YES];
point.x += radius * 2;
[path addArcWithCenter:point radius:radius startAngle:M_PI endAngle:M_PI * 2 clockwise:YES];
point.x += radius * 2;
[path addArcWithCenter:point radius:radius startAngle:M_PI endAngle:M_PI * 2 clockwise:YES];
point.x += radius * 2;
[path addArcWithCenter:point radius:radius startAngle:M_PI endAngle:M_PI * 2 clockwise:YES];
point.x += lineLength + radius;
[path addLineToPoint:point];

You could have your view controller just create a CAShapeLayer and add it to your view's layer.

CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = [path CGPath];
layer.lineWidth = 2.0;
layer.fillColor = [[UIColor clearColor] CGColor];
layer.strokeColor = [[UIColor blackColor] CGColor];

[self.view.layer addSublayer:layer];

If you wanted to do it in the drawRect of a UIView subclass you could, stroke this path:

- (void)drawRect:(CGRect)rect
{
    UIBezierPath *path = [UIBezierPath bezierPath];
    CGPoint point = CGPointMake(0, 50);
    CGFloat radius = 20.0;
    CGFloat lineLength = 45.0;

    [path moveToPoint:point];
    point.x += lineLength;
    [path addLineToPoint:point];
    point.x += radius;
    [path addArcWithCenter:point radius:radius startAngle:M_PI endAngle:M_PI * 2.0 clockwise:YES];
    point.x += radius * 2.0;
    [path addArcWithCenter:point radius:radius startAngle:M_PI endAngle:M_PI * 2.0 clockwise:YES];
    point.x += radius * 2.0;
    [path addArcWithCenter:point radius:radius startAngle:M_PI endAngle:M_PI * 2.0 clockwise:YES];
    point.x += radius * 2.0;
    [path addArcWithCenter:point radius:radius startAngle:M_PI endAngle:M_PI * 2.0 clockwise:YES];
    point.x += lineLength + radius;
    [path addLineToPoint:point];

    path.lineWidth = 2.0;
    [[UIColor blackColor] setStroke];
    [[UIColor clearColor] setFill];

    [path stroke];
}

Or, as your revised question suggests, if you're more comfortable with CoreGraphics, you could do that, too:

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGPoint point = CGPointMake(0, 50);
    CGFloat radius = 20.0;
    CGFloat lineLength = 45.0;

    CGContextMoveToPoint(context, point.x, point.y);
    point.x += lineLength;
    CGContextAddLineToPoint(context, point.x, point.y);
    point.x += radius;
    CGContextAddArc(context, point.x, point.y, radius, M_PI, M_PI * 2.0, NO);
    point.x += radius * 2.0;
    CGContextAddArc(context, point.x, point.y, radius, M_PI, M_PI * 2.0, NO);
    point.x += radius * 2.0;
    CGContextAddArc(context, point.x, point.y, radius, M_PI, M_PI * 2.0, NO);
    point.x += radius * 2.0;
    CGContextAddArc(context, point.x, point.y, radius, M_PI, M_PI * 2.0, NO);
    point.x += lineLength + radius;
    CGContextAddLineToPoint(context, point.x, point.y);

    CGContextSetStrokeColorWithColor(context, [[UIColor blackColor] CGColor]);
    CGContextSetLineWidth(context, 2.0);

    CGContextDrawPath(context, kCGPathStroke);
}