vb.net函数的HTML百分比

Question

I have some articles saved in database.On certain pages I wanted to show certain percentage of the article based on some settings. eg 80% of the article

Problem is that as html is not plain text if I take certain percentage of the string length then formatting get disturbed Can any help me in some function where I provide string and new length (which will be less then the old string length) And it will return me truncated html without disturbing the formating I have tried with

Private Function HtmlSubstring(html As String, maxlength As Integer) As String
        'initialize regular expressions
        Dim htmltag As String = "</?\w+((\s+\w+(\s*=\s*(?:"".*?""|'.*?'|[^'"">\s]+))?)+\s*|\s*)/?>"
        Dim emptytags As String = "<(\w+)((\s+\w+(\s*=\s*(?:"".*?""|'.*?'|[^'"">\s]+))?)+\s*|\s*)/?></\1>"

        'match all html start and end tags, otherwise get each character one by one..
        Dim expression As Regex = New Regex(String.Format("({0})|(.?)", htmltag))
        Dim matches As MatchCollection = expression.Matches(html)

        Dim i As Integer = 0
        Dim content As New StringBuilder()
        For Each match As Match In matches
            If match.Value.Length = 1 AndAlso i < maxlength Then
                content.Append(match.Value)
                i += 1
                'the match contains a tag
            ElseIf match.Value.Length > 1 Then
                content.Append(match.Value)
            End If
        Next

        Return Regex.Replace(content.ToString(), emptytags, String.Empty)
    End Function

But didn't work always

Answer 1

I'm pretty sure that there is no built-in .NET method to do what you ask. However, consider the following method:

Your HTML page is probably structured, ie, it has paragraphs, headings, etc.:

<h1>...</h1>
<p>...</p>
<h2>...</h2>
<p>...<more tags>...</more tags></p>
<h2>...</h2>
<p>...</p>
...

What you could do is:

1. Use a HTML parser (the HTML agility pack is often mentioned in this context) and parse your HTML into a data structure.

2. Take the first 80% of the top-level tags . For example, if the root node of your HTML content has ten children, take the first eight:

    <h1>...</h1> <p>...</p> <p>...</p> <h2>...</h2> <p> ... <more tags> ... </more tags> ... </p> <p>...</p> <p>...<more tags>...</more tags>...</p> <p>...</p> --------------- <h2>...</h2> <p>...</p> 

If your article is approximately evenly spaced (ie, your long and short paragraphs average out over the course of the article), this will give you approximately 80% of the text without breaking any HTML formatting. As an additional benefit, you won't be splitting the text mid-line or mid-paragraph.

Answer 2

Finally following has work quite well for me

 Private Function HtmlSubstring(ByRef html As String, maxlength As Integer) As String
    'initialize regular expressions
    Const htmltag As String = "</?\w+((\s+\w+(\s*=\s*(?:"".*?""|'.*?'|[^'"">\s]+))?)+\s*|\s*)/?>"
    'match all html start and end tags, otherwise get each character one by one..
    Dim expression As Regex = New Regex(String.Format("({0})|(.?)", htmltag))
    Dim matches As MatchCollection = expression.Matches(html)
    Dim i As Integer = 0
    Dim isEndingSet As Boolean = False
    Dim content As StringBuilder = New StringBuilder()
    For Each match As Match In matches
        If match.Value.Length = 1 AndAlso i < maxlength Then
            content.Append(match.Value)
            'the match contains a tag
            i += 1
        ElseIf match.Value.Length > 1 Then
            If (isEndingSet AndAlso (match.Value.ToLower() = "<br />" OrElse match.Value.ToLower() = "<br>")) Then
                Continue For
            End If
            content.Append(match.Value)
        End If
        If (i = maxlength AndAlso Not isEndingSet) Then
            content.Append("....")
            isEndingSet = True
        End If
    Next

    Return content.ToString()
End Function