在从控制面板卸载第三方应用程序的过程中，我得到了这个错误。不能在空值表达式PowerShell上调用方法。

Question

我有脚本卸载Veeam软件从控制面板通过PowerShell。在卸载最后一个Veeam组件的过程中，我得到了以下错误：

You Cannot call a method on a null-valued expression PowerShell : line 15 char:1
+ $console.Uninstall()
+ CategoryInfo         : InvalidOperation: (:) [], RuntimeException
+FullyQualifiedErrorId : InvokeMethodOnNull

我不知道，专家帮我修好了。我在等你的答复。我已经把我的剧本附在下面。

function uninstallvm
{
$veeamConsole = 'Veeam Backup & Replication Console'
$objects = Get-WmiObject -Class win32_product
$veeamComponents = $objects | where {$_.Name -like 'Veeam*' -and $_.Name -ne $veeamConsole}
foreach ($object in $veeamComponents) {
  Write-Output "Uninstalling $($object.Name)"
  $object.Uninstall()
}
Start-Sleep -Seconds 5
$console = $objects | where {$_.Name -eq $veeamConsole}
Write-Output "Uninstalling $($console.Name)"
$console.Uninstall() 
}
uninstallvm

Answer 1

之所以会出现这个错误，是因为在此之后：

$console = $objects | where {$_.Name -eq $veeamConsole}

您的$console变量是$null，这意味着在名称属性中没有找到对象，该属性等于Veeam备份和复制控制台

PS /> $null.Uninstall()
You cannot call a method on a null-valued expression.
At line:1 char:1
+ $null.Uninstall()
+ ~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

在尝试调用uninstall方法之前添加一个条件可以很容易地解决这个问题。

function uninstallvm
{
    $veeamConsole = 'Veeam Backup & Replication Console'
    $objects = Get-WmiObject -Class win32_product
    $veeamComponents = $objects | where {$_.Name -like 'Veeam*' -and $_.Name -ne $veeamConsole}
    
    foreach ($object in $veeamComponents)
    {
        Write-Output "Uninstalling $($object.Name)"
        $object.Uninstall()
    }
    
    Start-Sleep -Seconds 5
    
    $console = $objects | where {$_.Name -eq $veeamConsole}
    
    if(-not $console)
    {
        return "No object found with name: $veeamConsole"
    }

    Write-Output "Uninstalling $($console.Name)"
    $console.Uninstall() 
}

uninstallvm