Ios 创建pdf时字符串拆分？

我必须生成pdf文件。我的pdf文件页面大小是固定的。但是字符串文本的高度比pdf页面文件的高度大。但字符串只在页面内绘制，不拆分到下一页

 float height = 40;
    CGRect rectFrame = CGRectMake(x, y, width-kMarginInset, height);
    CGContextSetRGBFillColor(currentContext, 0.0, 0.0, 0.0, 1.0);
    NSString *textToDraw =text;
    CGSize stringSize = [textToDraw sizeWithFont:font
                               constrainedToSize:CGSizeMake(width, 100000)
                                   lineBreakMode:NSLineBreakByWordWrapping];

    CGRect renderingRect = rectFrame;
    if (height<stringSize.height)
    {
        height=stringSize.height+height;
        renderingRect = CGRectMake(kBorderInset + kMarginInset, kBorderInset + kMarginInset + 50.0, pageSize.width - 2*kBorderInset - 2*kMarginInset, stringSize.height);
    }

    renderingRect.origin.y=rectFrame.origin.y+((height - stringSize.height)/2);
    renderingRect.size.height=height;
    renderingRect.origin.x+=kMarginInset;
    rectFrame.size.height=height+height*.5;

    [textToDraw drawInRect:renderingRect
                  withFont:font
             lineBreakMode:NSLineBreakByWordWrapping
                 alignment:NSTextAlignmentLeft];

    pdfCurrentPoint.x+=width;

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谁能帮帮我

非常感谢。。现在开始工作了。