I found this answer on how to draw rotated text with NSString drawInRect:, but I'm not sure how it works since it only sort of works for me: https://discussions.apple.com/thread/1779814?start=0&tstart=0
My code looks like:
CGContextSaveGState(context);
CGContextDrawLinearGradient(context, gradient, CGPointMake(0, centY - halfWidth), CGPointMake(0, centY + halfWidth), 0);
// Add text
CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
NSString *str = @"some test string";
CGAffineTransform transform1 = CGAffineTransformMakeRotation(M_PI/4);
CGContextConcatCTM(context, transform1);
CGContextTranslateCTM(context, 0, 0);
UIFont *font = [UIFont systemFontOfSize:16.0];
[str drawInRect:CGRectMake(0, 0, 200, 100) withFont:font lineBreakMode:UILineBreakModeWordWrap alignment:UIBaselineAdjustmentNone];
So when I use this, I see text being drawn 45 degrees below the x-axis. I want to draw the text vertically along my lineargradient. So I thought I could do that by using M_PI/2 for 90 degrees. I do not see my text though. I have tried different transforms for the rotation, and only some seem to work like M_PI/4 and M_PI/8. I would think that if I used -M_PI/4 it would have the text 45 degrees above the x-axis and M_PI/2 would be 90 degrees below the x-axis. But both turn up with nothing.
Any thoughts? thanks.
I think what's happening is that you're rotating the text to a location outside of the view because it rotates the context by pivoting on the origin.
After your rotation you need to do a translation to move the context back into the view. In the example below, I rotate the context counterclockwise 90 degrees. Then I translate the tx of the context the distance of the height.
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
// Create the gradient
CGColorRef startColor = [UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:1.0].CGColor;
CGColorRef endColor = [UIColor colorWithRed:200.0/255.0 green:200.0/255.0 blue:200.0/255.0 alpha:1.0].CGColor;
NSArray *colors = [NSArray arrayWithObjects:(id)startColor, (id)endColor, nil];
CGFloat locations[] = { 0.0, 1.0 };
CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (CFArrayRef) colors, locations);
CGContextDrawLinearGradient(context, gradient, CGPointMake(rect.origin.x + rect.size.width / 2, rect.origin.y), CGPointMake(rect.origin.x + rect.size.width / 2, rect.origin.y + rect.size.height), 0);
// Create text
CGContextSetFillColorWithColor(context, [UIColor blackColor].CGColor);
NSString *string = @"some test string";
UIFont *font = [UIFont systemFontOfSize:16.0];
// Rotate the context 90 degrees (convert to radians)
CGAffineTransform transform1 = CGAffineTransformMakeRotation(-M_PI_2);
CGContextConcatCTM(context, transform1);
// Move the context back into the view
CGContextTranslateCTM(context, -rect.size.height, 0);
// Draw the string
[string drawInRect:rect withFont:font lineBreakMode:UILineBreakModeWordWrap alignment:UITextAlignmentLeft];
// Clean up
CGGradientRelease(gradient);
CGColorSpaceRelease(colorSpace);
CGContextRestoreGState(context);
}
Note that you can also get the size of how the string will be rendered, which can help in doing calculations for the alignment of the text.
CGSize stringSize = [string sizeWithFont:font];
I solve this problem in next way.
1) Declare category on NSString
@interface NSString (NMSchemeItemDraw)
-(void) drawWithBasePoint:(CGPoint)basePoint
andAngle:(CGFloat)angle
andFont:(UIFont*)font;
@end
This category will draw text with given central point, in one line and with given font and angle.
2) Implementation of this category is looks like:
@implementation NSString (NMSchemeItemDraw)
-(void) drawWithBasePoint:(CGPoint)basePoint
andAngle:(CGFloat)angle
andFont:(UIFont *)font{
CGSize textSize = [self sizeWithFont:font];
CGContextRef context = UIGraphicsGetCurrentContext();
CGAffineTransform t = CGAffineTransformMakeTranslation(basePoint.x, basePoint.y);
CGAffineTransform r = CGAffineTransformMakeRotation(angle);
CGContextConcatCTM(context, t);
CGContextConcatCTM(context, r);
[self drawAtPoint:CGPointMake(-1 * textSize.width / 2, -1 * textSize.height / 2)
withFont:font];
CGContextConcatCTM(context, CGAffineTransformInvert(r));
CGContextConcatCTM(context, CGAffineTransformInvert(t));
}
@end
3) Now i can use it in my [UIView drawRect:] method.
For example, in a next way:
-(void)drawRect:(CGRect)rect{
NSString* example = @"Title";
[example drawWithBasePoint:CGPointMake(0.0f, 0.0f)
andAngle:M_PI
andFont:[UIFont boldSystemFontOfSize:16.0]];
}
Here'a an updated and simplified version of KoNEW's answer. It preserves the state of the graphics context as a bonus. This is also a simple function instead of a String extension.
func drawRotatedText(_ text: String, at p: CGPoint, angle: CGFloat, font: UIFont, color: UIColor) {
// Draw text centered on the point, rotated by an angle in degrees moving clockwise.
let attrs = [NSFontAttributeName: font, NSForegroundColorAttributeName: color]
let textSize = text.size(attributes: attrs)
let c = UIGraphicsGetCurrentContext()!
c.saveGState()
// Translate the origin to the drawing location and rotate the coordinate system.
c.translateBy(x: p.x, y: p.y)
c.rotate(by: angle * .pi / 180)
// Draw the text centered at the point.
text.draw(at: CGPoint(x: -textSize.width / 2, y: -textSize.height / 2), withAttributes: attrs)
// Restore the original coordinate system.
c.restoreGState()
}
KoNew's Solution in Swift:
extension NSString {
func drawWithBasePoint(basePoint:CGPoint, angle:CGFloat, font:UIFont) {
var attrs: NSDictionary = [
NSFontAttributeName: font
]
var textSize:CGSize = self.sizeWithAttributes(attrs as [NSObject : AnyObject])
// sizeWithAttributes is only effective with single line NSString text
// use boundingRectWithSize for multi line text
var context: CGContextRef = UIGraphicsGetCurrentContext()
var t:CGAffineTransform = CGAffineTransformMakeTranslation(basePoint.x, basePoint.y)
var r:CGAffineTransform = CGAffineTransformMakeRotation(angle)
CGContextConcatCTM(context, t)
CGContextConcatCTM(context, r)
self.drawAtPoint(CGPointMake(-1 * textSize.width / 2, -1 * textSize.height / 2), withAttributes: attrs as [NSObject : AnyObject])
CGContextConcatCTM(context, CGAffineTransformInvert(r))
CGContextConcatCTM(context, CGAffineTransformInvert(t))
}
}
To use:
let fieldFont = UIFont(name: "Helvetica Neue", size: 14)
myNSString.drawWithBasePoint(CGPointMake(bounds.width/2, bounds.height/2), angle: CGFloat(-M_PI_2), font: fieldFont!)
Thank for this post, and Chris's answer, and Arkadiusz's answer at another post.
Finally, I solve this problem by a UILabel subclass, named MyVerticalLabel, and make it draw vertical text.
@implementation MyVerticalLabel
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
// Drawing code
CGContextRef context = UIGraphicsGetCurrentContext();
CGAffineTransform transform = CGAffineTransformMakeRotation(-M_PI_2);
CGContextConcatCTM(context, transform);
CGContextTranslateCTM(context, -rect.size.height, 0);
// The drawing rect should be applied with transform to.
CGRect newRect = CGRectApplyAffineTransform(rect, transform);
newRect.origin = CGPointZero;
NSMutableParagraphStyle *textStyle = [[NSMutableParagraphStyle defaultParagraphStyle] mutableCopy];
textStyle.lineBreakMode = self.lineBreakMode;
textStyle.alignment = self.textAlignment;
// Apply current label attributes for drawing function.
NSDictionary *attributeDict =
@{
NSFontAttributeName : self.font,
NSForegroundColorAttributeName : self.textColor,
NSParagraphStyleAttributeName : textStyle,
};
[self.text drawInRect:newRect withAttributes:attributeDict];
}
@end
来源：https://stackoverflow.com/questions/10289898/drawing-rotated-text-with-nsstring-drawinrect