ReportLab目录页码因标题过长缩小消失的解决办法求助

我按照ReportLab文档中的示例添加目录，多数情况运行正常。但当章节标题接近页面满宽时，页码会被缩小以适配空间，有时甚至会缩小到完全不可见。请问是否有人找到解决办法，能让章节标题提前换行，为页码预留足够空间？

可以看到当标题末尾有3、4、5个i时，页码会缩小直至消失：

以下是问题演示代码：

from reportlab.lib.styles import ParagraphStyle as PS
from reportlab.platypus import PageBreak
from reportlab.platypus.paragraph import Paragraph
from reportlab.platypus.doctemplate import PageTemplate, BaseDocTemplate
from reportlab.platypus.tableofcontents import TableOfContents
from reportlab.platypus.frames import Frame
from reportlab.lib.units import cm


class MyDocTemplate(BaseDocTemplate):

    def __init__(self, filename, **kw):
        self.allowSplitting = 0
        BaseDocTemplate.__init__(self, filename, **kw)
        template = PageTemplate('normal', [Frame(2.5 * cm, 2.5 * cm, 15 * cm, 25 * cm, id='F1')])
        self.addPageTemplates(template)

    def afterFlowable(self, flowable):
        "Registers TOC entries."
        if flowable.__class__.__name__ == 'Paragraph':
            text = flowable.getPlainText()
            style = flowable.style.name
            if style == 'Heading1':
                self.notify('TOCEntry', (0, text, self.page))
            if style == 'Heading2':
                self.notify('TOCEntry', (1, text, self.page))


h1 = PS(name='Heading1',
        fontSize=14,
        leading=16)

h2 = PS(name='Heading2',
        fontSize=12,
        leading=14,
        leftIndent=10)

# Build story.
story = []
toc = TableOfContents()
# For conciseness we use the same styles for headings and TOC entries
toc.levelStyles = [h1, h2]
story.append(toc)
story.append(PageBreak())
story.append(Paragraph('Table of Contents Test', h1))
for i in range(10):
    story.append(Paragraph('XXXXX ' * 9 + 'i' * i, h2))

doc = MyDocTemplate('toc_test.pdf')
doc.multiBuild(story)

我查看了ReportLab源码，发现页码确实会被不断缩小，直到适配空间或字号变为1像素。

解决办法 #

通过自定义TableOfContents类，修改目录条目生成逻辑，为页码预留固定空间，让长标题自动换行而非压缩页码字号，具体实现如下：

修改后的完整代码 #

from reportlab.lib.styles import ParagraphStyle as PS
from reportlab.platypus import PageBreak
from reportlab.platypus.paragraph import Paragraph
from reportlab.platypus.doctemplate import PageTemplate, BaseDocTemplate
from reportlab.platypus.tableofcontents import TableOfContents
from reportlab.platypus.frames import Frame
from reportlab.lib.units import cm
from reportlab.lib.utils import simpleSplit


class CustomTOC(TableOfContents):
    def addEntry(self, level, text, pageNum):
        # 为页码预留固定宽度（可根据需求调整）
        page_reserved_width = 1.5 * cm
        style = self.levelStyles[level]
        # 计算标题可用显示宽度
        available_width = self._frame._width - style.leftIndent - page_reserved_width
        
        # 将长标题拆分为适配可用宽度的多行
        text_lines = simpleSplit(text, style.fontName, style.fontSize, available_width)
        if len(text_lines) > 1:
            # 第一行保留原缩进，后续行增加额外缩进保持层级美观
            first_line = text_lines[0]
            indented_lines = [' '*(style.leftIndent + 10) + line for line in text_lines[1:]]
            formatted_text = f"{first_line}<br/>{'<br/>'.join(indented_lines)}"
        else:
            formatted_text = text
        
        # 调用父类方法添加处理后的目录条目
        super().addEntry(level, formatted_text, pageNum)


class MyDocTemplate(BaseDocTemplate):

    def __init__(self, filename, **kw):
        self.allowSplitting = 0
        BaseDocTemplate.__init__(self, filename, **kw)
        template = PageTemplate('normal', [Frame(2.5 * cm, 2.5 * cm, 15 * cm, 25 * cm, id='F1')])
        self.addPageTemplates(template)

    def afterFlowable(self, flowable):
        "Registers TOC entries."
        if flowable.__class__.__name__ == 'Paragraph':
            text = flowable.getPlainText()
            style = flowable.style.name
            if style == 'Heading1':
                self.notify('TOCEntry', (0, text, self.page))
            if style == 'Heading2':
                self.notify('TOCEntry', (1, text, self.page))


h1 = PS(name='Heading1',
        fontSize=14,
        leading=16)

h2 = PS(name='Heading2',
        fontSize=12,
        leading=14,
        leftIndent=10)

# Build story.
story = []
toc = CustomTOC()
toc.levelStyles = [h1, h2]
story.append(toc)
story.append(PageBreak())
story.append(Paragraph('Table of Contents Test', h1))
for i in range(10):
    story.append(Paragraph('XXXXX ' * 9 + 'i' * i, h2))

doc = MyDocTemplate('toc_test.pdf')
doc.multiBuild(story)

核心逻辑说明 #

1. 重写addEntry方法，为页码提前预留固定宽度（可根据实际排版需求调整数值）
2. 使用simpleSplit工具将长标题拆分为适配可用宽度的多行文本
3. 对多行标题的后续行增加额外缩进，保证目录层级的视觉一致性
4. 处理后的标题会自动换行，页码始终保持原有字号显示，不会被压缩

内容的提问来源于stack exchange，提问作者Don Kirkby