前言
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主要是使用 CTFramesetterSuggestFrameSizeWithConstraints 计算文本的高度和宽度，记得要给CTFramesetterRef 设置相关的属性（行间距和自动换行）。以下是使用 CoreText 绘制并计算文本高度的 Objective-C 代码示例:
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- (void)calculatedHeight:(CGSize)bounds
{
NSString *text = @"This\nis\nsome\nmulti-line\nsample\ntext.";
UIFont *uiFont = [UIFont fontWithName:@"Helvetica" size:17.0];
CTFontRef ctFont = CTFontCreateWithName((CFStringRef) uiFont.fontName, uiFont.pointSize, NULL);
// 设置行间距
CGFloat leading = uiFont.lineHeight - uiFont.ascender + uiFont.descender;
CTParagraphStyleSetting LineSpacing;
LineSpacing.spec = kCTParagraphStyleSpecifierLineSpacingAdjustment;
LineSpacing.value = &leading;
LineSpacing.valueSize = sizeof(CGFloat);
// 设置换行模式
CTParagraphStyleSetting lineBreakMode;
CTLineBreakMode lineBreak = kCTLineBreakByCharWrapping;
lineBreakMode.spec = kCTParagraphStyleSpecifierLineBreakMode;
lineBreakMode.value = &lineBreak;
lineBreakMode.valueSize = sizeof(CTLineBreakMode);
CTParagraphStyleSetting paragraphSettings[] = {lineBreakMode,LineSpacing};
CTParagraphStyleRef paragraphStyle = CTParagraphStyleCreate(paragraphSettings, 2);
CFRange textRange = CFRangeMake(0, text.length);
CFMutableAttributedStringRef string = CFAttributedStringCreateMutable(kCFAllocatorDefault, text.length);
CFAttributedStringReplaceString(string, CFRangeMake(0, 0), (CFStringRef) text);
// 设置字体行间距和大小
CFAttributedStringSetAttribute(string, textRange, kCTFontAttributeName, ctFont);
CFAttributedStringSetAttribute(string, textRange, kCTParagraphStyleAttributeName, paragraphStyle);
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(string);
CFRange fitRange;
// 计算文本需要的高度
CGSize frameSize = CTFramesetterSuggestFrameSizeWithConstraints(framesetter, textRange, NULL, bounds, &fitRange);
CFRelease(framesetter);
CFRelease(string);
}
总结
记录一些容易遗忘的代码