在字符串中使用 null

Question

我发现在 PowerShell 中对字符串使用 $null 是不可能的。虽然我使用了以下解决方法，但我想知道是否有更好的方法？

基本上我需要字符串$null、''（空）、'some string string' 的 3 种状态。

• 第一个表示 - 不执行。
• 第二个 - 明文
• 用新值替换文本

以下是我选择开关-ClearText 的解决方法代码。请记住，虽然如果字段为 $null，我不能添加 Set-WordTextText，但由于我在嵌套场景中执行此操作，因此我更愿意将其添加为 $null。

function Remove-WordText {
    Param(
        [parameter(ValueFromPipelineByPropertyName, ValueFromPipeline)][Xceed.Words.NET.InsertBeforeOrAfter] $Paragraph,
        [int] $Index = 0,
        [int] $Count = $($Paragraph.Text.Length),
        [bool] $TrackChanges,
        [bool] $RemoveEmptyParagraph,
        [bool] $Supress = $false
    )
    if ($Paragraph -ne $null) {
        Write-Verbose "Remove-WordText - Current text $($Paragraph.Text) "
        Write-Verbose "Remove-WordText - Removing from $Index to $Count - Paragraph Text Count: $($Paragraph.Text.Length)"
        $Paragraph.RemoveText($Index, $Count, $TrackChanges, $RemoveEmptyParagraph)
    }
    if ($Supress) { return } else { return $Paragraph }
}

function Set-WordTextText {
    param(
        [parameter(ValueFromPipelineByPropertyName, ValueFromPipeline)][Xceed.Words.NET.InsertBeforeOrAfter] $Paragraph,
        [alias ("S")] [AllowNull()][string] $Text,
        [switch] $ClearText,
        [bool] $Supress = $false
    )
    if ($Paragraph -ne $null) {
        if (-not [string]::IsNullOrEmpty($Text)) {
            if ($ClearText -eq $true) {
                Write-Verbose 'Set-WordTextText - Clearing Text $ClearText is True'
                $Paragraph = Remove-WordText -Paragraph $Paragraph
            }
            Write-Verbose "Set-WordTextText - Appending Value $Text"
            $Paragraph = $Paragraph.Append($Text)
        }
    }
    if ($Supress) { return } else { return $Paragraph }
}

我基本上是在函数中执行它：

$Paragraph[$i] = $Paragraph[$i] | Set-WordTextText -Text $Text[$i] -ClearText:$ClearText -Supress $false
$Paragraph[$i] = $Paragraph[$i] | Set-WordTextColor -Color $Color[$i] -Supress $false
$Paragraph[$i] = $Paragraph[$i] | Set-WordTextFontSize -FontSize $FontSize[$i] -Supress $false
$Paragraph[$i] = $Paragraph[$i] | Set-WordTextFontFamily -FontFamily $FontFamily[$i] -Supress $false
$Paragraph[$i] = $Paragraph[$i] | Set-WordTextBold -Bold $Bold[$i] -Supress $false
$Paragraph[$i] = $Paragraph[$i] | Set-WordTextItalic -Italic $Italic[$i] -Supress $false

只有值不为空时才会执行动作。所以“包装器”函数可以有 1 到 20 个参数，并且只有在给定参数时才执行。

Answer 1

如果您为参数指定类型[String]，则该参数将成为类型变量并且不能再为$null。即使您将$null 传递给参数，该值也会自动转换为空字符串。要允许参数是 $null 或字符串（空或非空），您需要这样的内容：

function Set-WordTextText {
    Param(
        ...
        [Parameter(Mandatory=$false)]
        [AllowNull()]
        $Text = $null,
        ...
    )

    if ($_ -ne $null -and $_ -isnot [String]) {
        throw 'Invalid argument for parameter -Text.'
    }

    ...
}

Answer 2

如果 $Paragraph 处于三种状态之一，则决定要做什么取决于您正在执行的功能。这样的事情可能会有所帮助

if ($null -eq $Paragraph) { 
    Write-Host "Paragraph is Null, do not execute"
    return
}
elseif ([string]::IsNullOrEmpty($Paragraph.Text)) { 
    # this depends on the function you are in.
    # if inside Remove-WordText() you don't have to do anything because it is already empty
    # you can check the function currently executed with $MyInvocation.MyCommand.Name
    if ($MyInvocation.MyCommand.Name -eq 'Remove-WordText') {
        Write-Host "Paragraph.Text is Null or Empty, clear text"
        $Paragraph.RemoveText($Index, $Count, $TrackChanges, $RemoveEmptyParagraph)
    else {
        # however, if you're inside Set-WordTextText() you need to decide if $Text
        # is not empty aswell and if not, you append the Text tp $Paragraph
        if (-not [string]::IsNullOrEmpty($Text)) {
            Write-Verbose "Set-WordTextText - Appending Value $Text"
            $Paragraph = $Paragraph.Append($Text)
        }
    }
}
else {
    Write-Host "Paragraph.Text has value, appending text"
    $Paragraph = $Paragraph.Append($Text)
}

希望有帮助