Powershell Function elseif语句不起作用

Question

I have a powershell function that is not working the way it should. It is supposed to limit the choices given to it in $prm to a maximum of 5. More than 5 it should alert the user. If 0 is passed in the string then default to null.

Can someone advise what I need to do to fix this:

Function GetListValues($prm, $charCount){ 

$buildStr="Call db.Fruit(" 

#no selection
if ($charCount -eq 0 ){ 
    $buildStr = $buildStr + "NULL,NULL,NULL,NULL,NULL);"
    write $buildStr
}elseif($charCount -ge 1 -and $charCount -le 4 ){

#selections made with then 5 parameter range

$arr = $prm.split(",");
if ($arr[0]) { $buildStr = $buildStr  + $arr[0] + "," } else { $buildStr = $buildStr + "Null," }
if ($arr[1]) { $buildStr  = $buildStr + $arr[1] + "," } else { $buildStr = $buildStr + "Null," }
if ($arr[2]) { $buildStr  = $buildStr + $arr[2] + "," } else { $buildStr = $buildStr + "Null," }
if ($arr[3]) { $buildStr  = $buildStr + $arr[3] + "," } else { $buildStr = $buildStr + "Null," }
if ($arr[4]) { $buildStr  = $buildStr + $arr[4] + ");" } else {$buildStr =  $buildStr + "Null);" }

write $buildStr


}else{
# too many selections

[System.Windows.MessageBox]::Show('Too many selections! A maximum of 5 only!')


}


}
$prm = "'Apple','Orange','Pear','Banana','Grapes'"
$charCount = ($prm.ToCharArray() | Where-Object {$_ -eq ','} | Measure-Object).Count
GetListValues $prm, $charCount

Answer 1

Your problem is with your test code, not your Function. For powershell, you only use spaces to delimit parameters, not commas.

So if you change your test to

GetListValues $prm $charCount

Then the code works.

You can ignore my earlier comment, as I assumed that your $charCount value was being set to the number of elements. But on closer inspection I see that you are just counting the number of commas, and so the number of elements will be #commas + 1 (as long as you have >1 elements)

BTW, the $charCount is somewhat redundant, as the Function could work this out for itself, and would make the function more resilient as it would remove the possibility of the calling code passing inconsistent values.

Answer 2

DeanOC's helpful answer points out your immediate problem with the argument-passing syntax.

Additionally, as he suggests, you needn't determine the element count outside the function - it's easier and more robust to let the function itself handle that. Here's a PowerShell-idiomatic reformulation of your function that does just that:

function GetListValues {
  param(
    [ValidateCount(0,5)] # Allow between 0 and 5 values.
    [string[]] $Columns
  )
  # Create a 5-element array filled with the input column names
  # and 'Null' for any remaining elements.
  $allColumns = New-Object string[] 5
  for ($i = 0; $i -lt $allColumns.Count; ++$i) {
    $allColumns[$i] = if ($i -lt $Columns.Count) { $Columns[$i] } else { 'Null' }
  }
  # Use string expansion (interpolation) to construct the output string.
  "Call db.Fruit($($allColumns -join ','))"
}

Defining the parameter as [string[]] allows you to (a) pass the column names individually and (b) easily gives you access to their count and allows you to constrain the acceptable range of column names via the ValidateCount attribute.

Therefore you can call the function above as follows:

# Pass 5 column names.
# Note that with the simple names at hand you needn't even quote them.
PS> GetListValues Apple, Orange, Pear, Banana, Grapes

Call db.Fruit(Apple,Orange,Pear,Banana,Grapes)

# Pass no column names at all.
PS> GetListValues

Call db.Fruit(Null,Null,Null,Null,Null)

# Pass too many names -> ValidateCount triggers an error.
PS> GetListValues Apple, Orange, Pear, Banana, Grapes, TooMuch

GetListValues : Cannot validate argument on parameter 'Columns'. 
The parameter requires at least 0 value(s) and no more than 5 value(s)
- 6 value(s) were provided.

---

A variant solution (requested later by the OP) that:

• allows passing the max. number of columns as a parameter

• passes the column names as a single string with embedded quoting (eg, "'Apple', 'Orange', 'Pear', 'Banana', 'Grapes'" ).

function GetListValues {
  param(
    [string] $ColumnList,
    [int]    $MaxColumnCount
  )

  # Split something like "'Apple', 'Orange', 'Pear', 'Banana', 'Grapes'"
  # into an array of tokens.
  $Columns = $ColumnList -split "[, ']" -ne ''
  if ($Columns.Count -gt $MaxColumnCount) { Throw "Too many columns passed." }

  # Create an N-element array filled with the input column names
  # and 'Null' for any remaining elements.
  $allColumns = New-Object string[] $MaxColumnCount
  for ($i = 0; $i -lt $allColumns.Count; ++$i) {
    $allColumns[$i] = if ($i -lt $Columns.Count) { $Columns[$i] } else { 'Null' }
  }
  # Use string expansion (interpolation) to construct the output string.
  "Call db.Fruit($($allColumns -join ','))"
}

Example calls:

PS> GetListValues "'Apple', 'Orange', 'Pear', 'Banana', 'Grapes'" 5

Call db.Fruit(Apple,Orange,Pear,Banana,Grapes)

PS> GetListValues "" 3

Call db.Fruit(Null,Null,Null)