BBCode解析

| 分类 技术随笔 

一行文本，可以包含多种文字样式，比如粗体、斜体和颜色，这个叫富文本。

富文本的表示和编辑不是件容易的事情。一种比较简单的方法是使用BBCode。

BBCode是Bulletin Board Code的缩写，被用于论坛等程序中用于表示富文本。

它使用方括号表示标签。标签如果有属性，通常跟随在标签名后面，用等号连接。标签可以嵌套。

比如下面这个BBCode的示例：

[b]Hello [i][color=#ff0000]world[/color][/i][/b]!

可以得到下面这样的效果：

Hello world!

本文会使用B4J编写一个简单的BBCode解析器，可以处理粗体、斜体和颜色标签。

  1. 定义一个TextRun类型，包含所包含文本、粗体、斜体和颜色等属性。

    Type TextRun(text As String,bold As Boolean,italic As Boolean,color As String)

  2. 建立一个BBCodeParser类，并添加一个解析文本的公开方法和一个解析TextRun的内部方法。解析的结果是TextRun列表。如果文本的bbcode有误，则不解析。这里的验证方法比较简单，只比较标签对数量和名字对不对。

    Sub Class_Globals
    Private supportedBBCodes As List = Array As String("b","color","i")
End Sub
Public Sub Parse(str As String) As List
    Dim run As TextRun
    run.Initialize
    run.text = str
    If validBBCode(str) Then
        Return ParseRun(run)
    Else
        Return Array(run)
    End If
End Sub
   
Private Sub ParseRun(run As TextRun) As List
   
End Sub
   
private Sub validBBCode(str As String) As Boolean
    Dim count As Int = 0
    Dim matcher As Matcher = Regex.Matcher("\[/?(.*?)]",str)
    Do While matcher.Find
        Dim match As String = matcher.Group(1)
        If match.Contains("=") Then
            match = match.SubString2(0,match.IndexOf("="))
        End If
        If match.Contains("[") Or match.Contains("]") Then
            Return False
        End If
        If supportedBBCodes.IndexOf(match) <> -1 Then
            count = count + 1
        End If
    Loop
    If count > 0 Then
        If count Mod 2 = 0 Then
            Return True
        End If
    End If    
    Return False
End Sub

  3. 实现ParseRun方法。

    具体步骤如下：

    1. 从左开始遍历单个字符，如果检测到[，截取[到下一个]的标签内容。如果没检测到，则将文本存入一个StringBuilder。
    2. 如果截取到的标签是支持的BBCode，截取完整的标签对包含的内容，新建一个TextRun，设置其对应的格式属性，将字符index移到该标签对结束位置。TextRun的文本为该标签对文本，但不包含标签本身。如果StringBuilder有内容，在新建一个富文本TextRun之前，先建一个纯文本的TextRun。
    3. 一个TextRun里面可能还包含标签，使用递归进行解析，直到不包含标签为止。
    4. 遍历结束后，如果StringBuilder不为空，添加一个纯文本TextRun。

    代码：

    Private Sub ParseRun(run As TextRun) As List
    Dim runs As List
    runs.Initialize
    If run.text = "" Then
        Return runs
    End If
    Dim str As String = run.text
    Dim plainText As StringBuilder
    plainText.Initialize
    For index=0 To str.Length-1
        If CurrentChar(str,index)="[" Then
            Dim tagContent As String = TextUntil("]",str,index)
            Dim codeName As String = GetBBCodeName(tagContent)
            If codeName <> "" And tagContent.Contains("/") = False Then
                Dim text As String = plainText.ToString
                If text <> "" Then
                    runs.Add(CreateRun(text,run,"",""))
                End If
                plainText.Initialize
                Dim endTag As String = "[/"&codeName&"]"
                Dim runText As String = TextUntil(endTag,str,index)
                If runText<>"" Then
                    index = index + runText.Length - 1
                    runText = CodePairStripped(runText,tagContent,endTag)                
                    Dim richRun As TextRun = CreateRun(runText,run,codeName,tagContent)
                    Dim innerRuns As List
                    innerRuns.Initialize
                    parseInnerRuns(richRun,innerRuns)
                    runs.AddAll(innerRuns)
                End If
            End If
        Else
            plainText.Append(CurrentChar(str,index))
        End If
    Next
    Dim text As String = plainText.ToString
    If text <> "" Then
        runs.Add(CreateRun(text,run,"",""))
    End If
    Return runs
End Sub

Private Sub parseInnerRuns(run As TextRun,runs As List)
    Dim parsedRuns As List  = ParseRun(run)
    If parsedRuns.Size = 1 Then ' no tags
        runs.Add(parsedRuns.Get(0))
    Else
        For Each innerRun As TextRun In parsedRuns
            parseInnerRuns(innerRun,runs)
        Next
    End If
End Sub


'[b]Hello [i]world[/i][/b] -> Hello [i]world[/i]
Private Sub CodePairStripped(runText As String,tagContent As String,endTag As String) As String
    runText = runText.Replace(tagContent,"")
    runText= runText.Replace(endTag,"")
    Return runText
End Sub

'text:[color=#ff00ff]Red[/color],codeName:color,tagContent:[color=#ff00ff]
private Sub CreateRun(text As String,parentRun As TextRun,codeName As String,tagContent As String) As TextRun
    Dim run As TextRun
    run.Initialize
    run.text = text
       
    If parentRun.IsInitialized Then
        run.bold = parentRun.bold
        run.color = parentRun.color
        run.italic = parentRun.italic
    End If
       
    If codeName = "b" Then
        run.bold = True
    else if codeName = "i" Then
        run.italic = True
    else if codeName = "color" Then
        run.color = ParseColor(tagContent)
    End If
    Return run
End Sub

'parse [color=#ff0000] and return the rgb value 255,0,0
private Sub ParseColor(tagContent As String) As String
    Try
        Dim hex As String
        hex = tagContent.SubString2(tagContent.IndexOf("=")+1,tagContent.Length-1)
        Dim r As Int = Bit.ParseInt(hex.SubString2(1,3), 16)
        Dim g As Int = Bit.ParseInt(hex.SubString2(3,5), 16)
        Dim b As Int = Bit.ParseInt(hex.SubString2(5,7), 16)
        Return r&","&g&","&b
    Catch
        Log(LastException)
    End Try
    Return ""
End Sub
   
private Sub GetBBCodeName(str As String) As String
    Dim matcher As Matcher = Regex.Matcher("\[/?(.*?)]",str)
    If matcher.Find Then
        Dim match As String = matcher.Group(1)
        If match.Contains("=") Then
            match = match.SubString2(0,match.IndexOf("="))
        End If
        If supportedBBCodes.IndexOf(match) <> -1 Then
            Return match
        End If
    End If
    Return ""
End Sub

private Sub TextUntil(EndStr As String,str As String,index As Int) As String
    Dim sb As StringBuilder
    sb.Initialize
    Dim textLeft As String=str.SubString2(index,str.Length)
    If textLeft.Contains(EndStr) Then
        For i=index To str.Length - EndStr.Length
            Dim s As String=str.CharAt(i)
            If str.SubString2(i,i + EndStr.Length) = EndStr Then
                sb.Append(EndStr)
                Exit
            Else
                sb.Append(s)
            End If
        Next
    End If
    Return sb.ToString
End Sub

private Sub CurrentChar(str As String,index As Int) As String
    Return str.CharAt(index)
End Sub

测试项目代码：

https://github.com/xulihang/BBCodeRichText


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