当我运行这个函数所在的程序时，我收到了一个对我来说没有意义的神秘错误。我不知道我在空值表达式上运行了一个方法。我突然想到，这要么是范围问题，要么是没有设置值。然而，我还没能弄清楚并向社区发布：
You cannot call a method on a null-valued expression.
At C:UsersAdministratorDesktopDCB Settings ModificationDCBxPowershell.ps1:747 char:21
+ If ($resetAdapter -eq $FAIL_RESULT){
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
You cannot call a method on a null-valued expression.
At C:UsersAdministratorDesktopDCB Settings ModificationDCBxPowershell.ps1:760 char:17
+ If ($resetAdapter -eq $FAIL_RESULT){
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull**
$FAIL_RESULT = 0
$PASS_RESULT = 1
Function Use-Menu
{
param($DCBmenuItems, $modificationCatagoryChoosen)
## Function Menu-Choose --## Holds choosen Network Interface Index to work with
$networkIndex = Menu-Choose $strippedNetworkIndex $networkChooseTitle
#$networkIndex[0] ### Debug -
$resetAdapter = $FAIL_RESULT
Start-Sleep -s .7
If ($result = $PASS_RESULT) {
## Find Current Config in order to display it to user
$dcbConfig = Find-Config $networkIndex
}
#The following 'DO WHILEs' are for the "Go back to previous Menu" functionality.
Do {
Do {
## Function Menu-Choose --## Let user choose which catagory of modification to perform
$modificationCatagoryChoosen = Menu-Choose $DCBmenuItems $DCBMenuTitle $networkIndex -scope global
If (($DCBmenuItems.count - 1) -eq $modificationCatagoryChoosen) {
$resetAdapter = $PASS_RESULT
}
# These If Then statements allow reset of adapter without changing settings
If ($resetAdapter -eq $FAIL_RESULT){
$DCBmenuItems2 = $xmlDCBoptions.MenuItems.MenuOptions[$modificationCatagoryChoosen].Option
$DCBMenuTitle2 = $xmlDCBoptions.MenuItems.MenuOptions[$modificationCatagoryChoosen].Name
Start-Sleep -s .7
## Function Menu-Choose --## Let user choose which modification to perform
$modificationChoosen = Menu-Choose $DCBmenuItems2 $DCBMenuTitle2 $networkIndex
}
} While (($modificationChoosen -eq $DCBmenuItems2.GetUpperBound(0)) -and ($resetAdapter -eq $FAIL_RESULT))
# These If Then statements allow reset of adapter without changing settings
If ($resetAdapter -eq $FAIL_RESULT){
## Changes the options to choose on Menu-Choose to last chosen catagory
$DCBmenuItems3 = $xmlDCBoptions.MenuItems.MenuOptions[$modificationCatagoryChoosen].SubMenu[$modificationChoosen].Option
$DCBMenuTitle3 = $xmlDCBoptions.MenuItems.MenuOptions[$modificationCatagoryChoosen].SubMenu[$modificationChoosen].Name
Start-Sleep -s .7
## Function Menu-Choose --## Let user choose how to modify DCB setting
$modificationOptionChoosen = Menu-Choose $DCBmenuItems3 $DCBMenuTitle3 $networkIndex
}
} While (($modificationOptionChoosen -eq $DCBmenuItems3.GetUpperBound(0)) -and ($resetAdapter -eq $FAIL_RESULT))
# These If Then statements allow reset of adapter without changing settings
If ($resetAdapter -eq $FAIL_RESULT){
Start-Sleep -s .7
## Function Set-RegistryValues --## Records modified DCB setting to registry
Set-RegistryValues $xmlDCBregEdits $modificationCatagoryChoosen $modificationChoosen $modificationOptionChoosen
}
Return $networkIndex
从最初的两个if-then语句改为在我的初始if-then声明后插入break，并在第二个Do循环中添加一个相同的语句，似乎解决了我的问题。我这样做的原因是，在进入菜单的一层，然后返回顶层后，我注意到在选择重置适配器时没有出现错误。
侧栏：我没有解释我在这里列出的函数是一个遍历$DCBmenuItems，尽管这可能从代码中已经很明显了。
我认为$resetAdapter由于某种原因没有正确设置。我不能100%确定为什么这解决了我的问题，以及为什么其他代码会抛出错误。这是修改后的代码：
$FAIL_RESULT = 0
$PASS_RESULT = 1
Function Use-Menu
{
param($DCBmenuItems, $modificationCatagoryChoosen)
## Function Menu-Choose --## Holds choosen Network Interface Index to work with
$networkIndex = Menu-Choose $strippedNetworkIndex $networkChooseTitle
#$networkIndex[0] ### Debug -
$resetAdapter = $FAIL_RESULT
$modificationCatagoryChoosen = $null
$modificationChoosen = $null
$modificationOptionChoosen = $null
$DCBmenuItems2 = $null
$DCBMenuTitle2 = $null
$DCBmenuItems3 = $null
$DCBMenuTitle3 = $null
Start-Sleep -s .7
If ($result = $PASS_RESULT) {
## Find Current Config in order to display it to user
$dcbConfig = Find-Config $networkIndex
}
#The following 'DO WHILEs' are for the "Go back to previous Menu" functionality.
Do {
Do {
## Function Menu-Choose --## Let user choose which catagory of modification to perform
$modificationCatagoryChoosen = Menu-Choose $DCBmenuItems $DCBMenuTitle $networkIndex -scope global
If (($DCBmenuItems.count - 1) -eq $modificationCatagoryChoosen) {
$resetAdapter = $PASS_RESULT
break
}
# These If Then statements allow reset of adapter without changing settings
$DCBmenuItems2 = $xmlDCBoptions.MenuItems.MenuOptions[$modificationCatagoryChoosen].Option
$DCBMenuTitle2 = $xmlDCBoptions.MenuItems.MenuOptions[$modificationCatagoryChoosen].Name
Start-Sleep -s .7
## Function Menu-Choose --## Let user choose which modification to perform
$modificationChoosen = Menu-Choose $DCBmenuItems2 $DCBMenuTitle2 $networkIndex
} While (($modificationChoosen -eq $DCBmenuItems2.GetUpperBound(0)) -and ($resetAdapter -eq $FAIL_RESULT))
If (($DCBmenuItems.count - 1) -eq $modificationCatagoryChoosen) {
break
}
# These If Then statements allow reset of adapter without changing settings
## Changes the options to choose on Menu-Choose to last chosen catagory
$DCBmenuItems3 = $xmlDCBoptions.MenuItems.MenuOptions[$modificationCatagoryChoosen].SubMenu[$modificationChoosen].Option
$DCBMenuTitle3 = $xmlDCBoptions.MenuItems.MenuOptions[$modificationCatagoryChoosen].SubMenu[$modificationChoosen].Name
Start-Sleep -s .7
## Function Menu-Choose --## Let user choose how to modify DCB setting
$modificationOptionChoosen = Menu-Choose $DCBmenuItems3 $DCBMenuTitle3 $networkIndex
} While (($modificationOptionChoosen -eq $DCBmenuItems3.GetUpperBound(0)) -and ($resetAdapter -eq $FAIL_RESULT))
# These If Then statements allow reset of adapter without changing settings
If ($resetAdapter -eq $FAIL_RESULT){
Start-Sleep -s .7
## Function Set-RegistryValues --## Records modified DCB setting to registry
Set-RegistryValues $xmlDCBregEdits $modificationCatagoryChoosen $modificationChoosen $modificationOptionChoosen
}
Return $networkIndex
}
此错误的位置似乎不正确。我看不出PowerShell是如何在if ()条件下得到这种类型的错误的。然而，这条线可能会导致错误：
$DCBmenuItems3.GetUpperBound(0)
添加一个检查以确保$DCBmenuItems3不为空。此外，当调试问题时（或者像正常做法一样检查），我会将Set-StrictMode -version latest放在脚本的顶部。
FAIL_RESULT = 0
PASS_RESULT = 1
打字错误？
$FAIL_RESULT = 0
$PASS_RESULT = 1