核心文本中的垂直文本对齐

Question

编辑： 如果更具可读性，这里是以下代码的 Github 要点。

我正在编写一种使用 Core Text 在 PDF 中的矩形内绘制文本的方法。我所写的内容完成了我需要的一切，除了垂直对齐（顶部、中心、底部）。当前绘制文本的标准方式是顶部对齐，我特别需要底部对齐。

- (void)drawText:(NSString *)textToDraw inFrame:(CGRect)frameRect withFont:(UIFont *)originalFont textColor:(UIColor *)textColor alignment:(PDFTextAlignment)alignment verticalAlignment:(PDFTextVerticalAlignment)verticalAlignment {

    if (!textToDraw) {
        // If nil, give it an empty value to draw
        textToDraw = @"";
    }


    // Prepare font
    CTFontRef font = [self ctFontRefFromUIFont:originalFont];
    CGColorRef color = textColor.CGColor;

    // Paragraph
    CTTextAlignment ctAlignment;
    switch (alignment) {
        case PDFTextAlignmentLeft:
            ctAlignment = kCTTextAlignmentLeft;
            break;
        case PDFTextAlignmentCenter:
            ctAlignment = kCTTextAlignmentCenter;
            break;
        case PDFTextAlignmentRight:
            ctAlignment = kCTTextAlignmentRight;
            break;
        case PDFTextAlignmentJustified:
            ctAlignment = kCTTextAlignmentJustified;
            break;
        default:
            ctAlignment = kCTTextAlignmentLeft;
            break;
    }

    CTParagraphStyleSetting settings[] = {
    {kCTParagraphStyleSpecifierAlignment, sizeof(ctAlignment), &ctAlignment},
    };

    CTParagraphStyleRef paragraphStyle = CTParagraphStyleCreate(settings, sizeof(settings) / sizeof(settings[0]));

    // Create an attributed string
    CFStringRef keys[] = { kCTFontAttributeName, kCTForegroundColorAttributeName, kCTParagraphStyleAttributeName };
    CFTypeRef values[] = { font, color, paragraphStyle };
    CFDictionaryRef attr = CFDictionaryCreate(NULL, (const void **)&keys, (const void **)&values,
                                          sizeof(keys) / sizeof(keys[0]), &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);

    CFStringRef stringRef = (__bridge CFStringRef)textToDraw;
    // Prepare the text using a Core Text Framesetter.
    CFAttributedStringRef currentText = CFAttributedStringCreate(NULL, stringRef, attr);

    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(currentText);

    CGMutablePathRef framePath = CGPathCreateMutable();    

    CGPathAddRect(framePath, NULL, frameRect);

    // Get the frame that will do the rendering.
    CFRange currentRange = CFRangeMake(0, 0);
    CTFrameRef frameRef = CTFramesetterCreateFrame(framesetter, currentRange, framePath, NULL);
    CGPathRelease(framePath);

    // Get the graphics context.
    CGContextRef currentContext = UIGraphicsGetCurrentContext();

    // Put the text matrix into a known state. This ensures
    // that no old scaling factors are left in place.
    CGContextSetTextMatrix(currentContext, CGAffineTransformIdentity);

    // Core Text draws from the bottom-left corner up, so flip
    // the current transform prior to drawing.
    // Modify this to take into consideration the origin.
    CGContextTranslateCTM(currentContext, 0, frameRect.origin.y*2);
    CGContextScaleCTM(currentContext, 1.0, -1.0);

    // Draw the frame.
    CTFrameDraw(frameRef, currentContext);

    // Add these two lines to reverse the earlier transformation.
    CGContextScaleCTM(currentContext, 1.0, -1.0);
    CGContextTranslateCTM(currentContext, 0, (-1)*frameRect.origin.y*2);

    CFRelease(frameRef);
    CFRelease(stringRef);
    CFRelease(framesetter);
    CFRelease(font);
    CFRelease(paragraphStyle);
}

以下是当前如何在矩形中绘制文本的示例（请注意，用线条绘制的矩形与我传入的frameRect 相同）... 。我希望这个文本在这个矩形中显示为底部对齐，就像这样...... 。

我已经完成了这篇 SO post上的解决方案，但没有运气让文本正确对齐。

我正在传递垂直对齐的枚举值，因此理想情况下我将使用以下条件确定垂直对齐。

if (verticalAlignment == PDFTextVerticalAlignmentTop) {
    // Top align
} else if (verticalAlignment == PDFTextVerticalAlignmentCenter) {
    // Center (vertical) align
} else if (verticalAlignment == PDFTextVerticalAlignmentBottom) {
    // Bottom align
} else {
    // Default: Bottom alignment  
}

谢谢！

Answer 1

由于我不太确定您如何从链接的帖子中找到解决方案，因此我将根据其中一个答案提出一个解决方案。这可能正是您尝试过的，但也可能是合适的解决方案。

我假设存在一种方法来获取 CTFrameRef 的大小，只要返回适当的 CGSize，就可以将实现留给您。除了链接的 SO 帖子中显示的方法之外，还可能值得查看CTFramesetterSuggestFrameSizeWithConstraints。假设这个功能可用，调整这部分绘图功能应该就足够了

...
CGMutablePathRef framePath = CGPathCreateMutable();    

// Get the graphics context.
CGContextRef currentContext = UIGraphicsGetCurrentContext();

CGRect textRect = frameRect;  // Will also give you the default behavior for top align
CGSize textSize = [self measureFrame:frameref forContext:currentContext];

if (verticalAlignment == PDFTextVerticalAlignmentBottom) {
    // Bottom align
    textRect.size.height = textSize.height;
    textRect.origin.y = frameRect.origin.y + frameRect.size.height - textSize.height;
} else if (verticalAlignment == PDFTextVerticalAlignmentCenter) {
    // Center (vertical) align
    textRect.size.height = textSize.height;
    textRect.origin.y = frameRect.origin.y + (frameRect.size.height - textSize.height) / 2;
}

CGPathAddRect(framePath, NULL, textRect);
...