iOS:在矩形中的某个点绘制文本

Question

我正在使用核心文本API在UI上绘制文本.(我不知道其他方法,因为大多数Google搜索结果都会引导我使用核心文本api).

我在线阅读了一些关于使用核心文本API的教程.在那些教程中,我逐步看到从矩阵,属性字符串到框架集的配置......但是它们都没有仔细解释每个步骤的含义,所以我不能自己修改.

下面的代码是屏幕上的功能绘制文本,(x,y)是我想要绘制的位置.这段代码一目了然地在屏幕上绘制.不过我不知道在哪里放x和y参数,所以文本将开始在矩形中绘制.

// draw text on screen.
+ (void)drawText:(CGContextRef)context bound:(CGRect)rect text:(NSString *)text x:(float)x y:(float) y color:(UIColor *)color size:(float)textSize{
    CGContextSaveGState(context);
    // always remember to reset the text matrix before drawing.
    // otherwise the result will be unpredictable like using uninitialize memory
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
    CGContextSetTextMatrix(context, CGAffineTransformMakeScale(1.0f, -1.0f));
    // Flip the coordinate system. because core Text uses different coordinate system with UI Kit
    CGContextTranslateCTM(context, 0, rect.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    // step 1: prepare attribute string
    NSDictionary *attributes;
    attributes = @{
            (NSString *) kCTFontAttributeName            : [UIFont fontWithName:@"Helvetica" size:textSize],
            (NSString *) kCTForegroundColorAttributeName : color
    };

    NSAttributedString *str = [[NSAttributedString alloc]
                               initWithString:text attributes:attributes];

    CFAttributedStringRef attrString = (__bridge CFAttributedStringRef)str;

    // step 2: create CTFFrameSetter
    CTFramesetterRef framesetter =
    CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrString);

    // step 3. create CGPath
    CGMutablePathRef path = CGPathCreateMutable();
    CGPathAddRect(path, NULL, rect);

    // step 4. get the frame
    // use the CGPath and CTFrameSetter to create CTFrame. then drawn it in currently context
    CTFrameRef frame = CTFramesetterCreateFrame
            (framesetter, CFRangeMake(0, 0), path, NULL);

    CTFrameDraw(frame, context);

    // step 5. release resource
    //CFRelease(attrString);
    CFRelease(framesetter);
    CFRelease(frame);
    CFRelease(path);

    CGContextRestoreGState(context);
}

此外,我看到有功能:CGContextSetTextPosition这似乎是我需要的,但我应该在哪里放入代码.我尝试了一些,但没有成功.请告诉我如何解决这个问题.

谢谢 :)

Answer 1

这不是CoreText解决方案,但根据您的问题发表评论后,我认为这将是一个正确的答案.

在视图上绘制基本文本.

.H

#import <UIKit/UIKit.h>

@interface aView : UIView
@end

.M

#import "aView.h"

@implementation aView

- (void)drawText:(CGFloat)xPosition yPosition:(CGFloat)yPosition canvasWidth:(CGFloat)canvasWidth canvasHeight:(CGFloat)canvasHeight
{
    //Draw Text 
    CGRect textRect = CGRectMake(xPosition, yPosition, canvasWidth, canvasHeight);
    NSMutableParagraphStyle* textStyle = NSMutableParagraphStyle.defaultParagraphStyle.mutableCopy;
    textStyle.alignment = NSTextAlignmentLeft;

    NSDictionary* textFontAttributes = @{NSFontAttributeName: [UIFont fontWithName: @"Helvetica" size: 12], NSForegroundColorAttributeName: UIColor.redColor, NSParagraphStyleAttributeName: textStyle};

    [@"Hello, World!" drawInRect: textRect withAttributes: textFontAttributes];
}


- (void)drawRect:(CGRect)rect {
    [self drawText:0 yPosition:0 canvasWidth:200 canvasHeight:150];
}

@end