I'm working with treeviews in Powershell - I have a different node for each of our buildings. In my code I'm grabbing variables, Joining them together, and using that as the variable name - but my code is seeing the variable as a string instead of the name of a node that already exists... so I'm getting
You cannot call a method on a null-valued expression.
How can I do this? It would save me from hard-coding in every floor in every building. Here's what my code looks like:
$bldg = "SG1-1" //for example
function refreshPrinterList ( $bldg )
{
$bldg1 = $bldg.substring(0,3)
$floor = $bldg.substring(4,1)
$refreshNode = -join('$TreeNode_',$bldg1,'_',$floor)
$refreshNode.gettype() //Returns System.String`
if($bldg1 -eq "SG1") {
if($floor -eq "1") {
$count = $refreshNode.Nodes.Count
while($refreshNode.Nodes.Count -gt 0)
{
$refreshNode.Nodes.RemoveAt($count)
$count--
}
The -join operator is for strings, and dutifully gives you one back instead of a TreeNode that you want. If you are passing in a string ($bldg looks like a string from your example), then you can do all the string manipulation you want, but there is no TreeNode object in that function to assign a name to. So, we need to make a TreeNode that your function could use. What about something like this?
$newNodeName = -join('$TreeNode_',$bldg1,'_',$floor)
$refreshNode = New-Object System.Windows.Forms.TreeNode($newNodeName )
// do stuff with $refreshNode as it is a TreeNode object like you expect
This $refreshNode will have no Nodes inside of it since we just fabbed it up. Since it looks like you want to modify an existing TreeNode object, pass in the $refreshNode as an argument then modify its friendly description with the $newNodeName.
I was pointed in the right direction over on the Technet Social forum
My question on Technet
The answer was using 'Get-Variable'
I had the two variables $bldg1 and $floor which I joined into a string:
$newNodeName = -join('TreeNode_',$bldg1,'_',$floor)
and then I passed that using 'Get-Variable' - but I had to put the variable name within parantheses, like so:
$refreshNode = (Get-Variable ($newNodeName)).Value
Now, instead of returning a string type it returns my existing string!
Related
Is there a way to add a method to built-in/native powershell object (or type?/class¿)?
In particular, I'm looking at you [hashtable], but I suppose my question is also a general one... for instance, I could see wanting to add functionality to all my arrays...
For instance, I would like all my [hashtable] objects to have the method: .AddAndOverwrite(..) which would replace the value of the key if it exists; otherwise it creates a new key.
The only way I seem to be able to do this is to:
create an empty hashtable, $HashTableNew
add the ScriptMethod(s) to $HashTableNew (i.e. .AddAndOverwrite(..))
then when I use it, make a copy of $HashTableNew
$SomeOtherHashTable = $HashTableNew.PSObject.Copy()
This just seems like not "the way"...
Note: I will admit, this is not the best example use of a data type extension method (as #SantiagoSquarzon points out)... but it is a simple one, and it allows for a simple example in the accepted answer; so I'm intentionally leaving it as is, rather than changing question / the extension method to .foo() returning widgets...
There is indeed a better and easier way to update a type as a whole by using Update-TypeData.
Here is an example that add an .AddOrOverwrite method to the hashtable.
$TypeParam = #{
TypeName = 'System.Collections.Hashtable'
MemberType = 'ScriptMethod'
MemberName = 'AddOrOverwrite'
Value = { Param($Key, $Value) $this.$key = $Value }
}
Update-TypeData #TypeParam -Force
$SomeHashTable.AddOrOverwrite('aaa','2222222')
$this, in the scriptblock of the method definition, correspond to the object reference that is targeted, in this case, the hashtable.
-Force will overwrite the definition every time without error stating the type was already added.
That method is not super useful as it does something that the hashtable manage pretty well on its own by just using assignment but it demonstrates how to do it.
Bonus example
Here's an example on how you would apply this principle and create 2 script properties (readonly) for a string so you can convert to base 64 back and forth.
$TypeParam = #{
TypeName = 'System.String'
MemberType = 'ScriptProperty'
Force = $true
}
Update-TypeData #TypeParam -MemberName 'Base64' -Value { [Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes($this)) }
Update-TypeData #TypeParam -MemberName 'Base64Decoded' -Value { [System.Text.Encoding]::UTF8.GetString([Convert]::FromBase64String($this)) }
# Encode the string to base 64 (Output: U29tZVN0cmluZw==)
"SomeString".Base64
# Decode the string from Base64 (Output: SomeString)
"U29tZVN0cmluZw==".Base64Decoded
References
Msdocs - About-Types
Dr Scripto - Easily Update Powershell Type Data by Using a Cmdlet
I have a function that can either initialize itself and return an ordered dictionary with initial values, or if a collection is provided as an argument, it manipulates that collection. And that collection is a key within a parent collection.
In my actual code I am seeing an odd behavior, where a key in the initial collection is initially $Null or has a specified value, but when I try to revise that value I do NOT get an error, but I also do not get a changed value. However, when I try creating a minimally functional example to post here, it does work correctly, both in the console and the IDE.
So, given this code
function Write-Data {
param (
[System.Collections.Specialized.OrderedDictionary]$Collection
)
foreach ($key in $Collection.Keys) {
try {
$type = $Collection.$key.GetType().FullName
} catch {
$type = 'NULL'
}
Write-Host "$key $type $($Collection.$key)"
}
Write-Host
}
function Manage-Data {
param (
[System.Collections.Specialized.OrderedDictionary]$Collection
)
if (-not $Collection) {
[System.Collections.Specialized.OrderedDictionary]$initialCollection = [Ordered]#{
initialNull = $null
initialString = 'initial string'
}
return $initialCollection
} else {
$Collection.initialNull = 'No longer null'
$Collection.initialString = 'New String'
}
}
CLS
$parentContainer = New-Object System.Collections.Specialized.OrderedDictionary
$parentContainer.Add('data', (Manage-Data))
Write-Data $parentContainer.data
Manage-Data -Collection $parentContainer.data
Write-Data $parentContainer.data
is there any obvious scenario where either of the lines revising values would not throw an error, but would also not change the value? For example, if there are actually more functions doing other things with that initialized collection object before the attempt to revise data? Or perhaps more generally, since I am depending on the default byReference behavior of complex objects, is there some situation where this behavior breaks down and I am effectively modifying a new complex object when I think I am modifying the original? Or is the fact that I am having problems with a simple data type within the complex type potentially the issue?
For what it is worth, the idea here is to basically be able to use Dependency Injection, but with functions rather than classes, and also mimic to some extent the the concept of a constructor and a method in a class, but again in a function. And that has generally been working well, if a little messy, which has reenforced in my mind that I need to move to classes eventually. But this particular issue has me worried that I will see the same problem in classes, and unless I can understand it now I will have issues. But since I can't seem to recreate the issue in a simplified example, I seem to be unable to figure anything out.
It occurs to me that one thing I haven't tried is to actually get the memory address of the collection I think I am modifying, or even of the individual key, so I can verify I actually am changing the same data that I initialized. But HOW to get the memory address of a variable escapes me, and is maybe not possible in PowerShell or .NET?
"the default byReference behavior of complex objects" concerns the properties of the object not the object itself:
The difference between (if):
[System.Collections.Specialized.OrderedDictionary]$initialCollection = [Ordered]#{
initialNull = $null
initialString = 'initial string'
}
and (else)
$Collection.initialNull = 'No longer null'
$Collection.initialString = 'New String'
Is that the later (else) statements indeed change the values of the parent values as $Collection refers to the same object as $parentContainer.data but the former (if) statement creates a new $initialCollection in the scope of the Manage-Data function which isn't visible in the parent (even if you assign it to $Collection, it would create a new object reference in the scope of the Manage-Data function).
You might return $initialCollection but then, how are you handling the different returns (either a $initialCollection or enumerable null ) in your parent function? Therefore I would just return $initialCollection for both conditions and reassign the object (where the properties are still by reference and only the $parentContainer.data reference will change/reset):
$parentContainer.data = Manage-Data -Collection $parentContainer.data
Potential problems
In other words, the potential issue in your Manage-Data function lies in the fact that parent function needs a different approach in calling it based on the condition if (-not $Collection) which is actually defined within the function. (What will be the value of this condition, as the caller already need to act differently on the condition?)
This leaves two pitfalls:
You call the function in the assumption that the argument is not a collection but it actually is:
$parentContainer = [Ordered]#{ data = [Ordered]#{} }
$parentContainer.Add('data', (Manage-Data))
In this case you get an error:
MethodInvocationException: Exception calling "Add" with "2" argument(s): "Item has already been added. Key in dictionary: 'data' Key being added: 'data'"
And the opposite (which is less obvious): you call the function in the assumption that the argument is a collection but it is actually not:
$parentContainer = [Ordered]#{}
Manage-Data $ParentContainer.Data
This will leave an unexpected object on the pipeline:
(See: PowerShell Pipeline Pollution)
Name Value
---- -----
initialNull
initialString initial string
And doesn't add anything to the $parentContainer object:
$parentContainer # doesn't return anything as it doesn't contain anything
Suggestions
See about scopes
Enable Set-StrictMode -Version Latest.
This will show you that a property is potentially empty.
Use ([ref]$MyVar).Value = 'new value' to replace a value in a parent scope.
(not related to the question) Use the IDictionary interface: [Collections.IDictionary]$Collection to accept a more general collection type in your functions.
I've searched a lot but can't find a clear answer anywhere for string list -> enum.
I've got a list of strings that I want to turn into an enum that I can select from in Unity inspector.
Specifically, I'm trying to make an enum list of all the currently set-up Input buttons from project settings. I've got all the names, just don't know how to make it an enum or similar. Ideally showing up like a KeyCode variable in inspector.
Currently trying (and failing) with:
foreach (string s in names)
{
if (Enum.TryParse(s, true, out list))
Debug.Log(list);
else Debug.Log("FAILED");
}
"names" = static List<string> names;
"list" = static MyList list;
"MyList" = enum MyList { Null }
Returns "FAILED" 58 times for only 29 Input axis.
I want a simple solution, so if its not possible or relatively simple, I'll work out something else.
Code for getting the "names" list of strings (Works correctly):
var inputManager = AssetDatabase.LoadAllAssetsAtPath("ProjectSettings/InputManager.asset")[0];
SerializedObject obj = new SerializedObject(inputManager);
SerializedProperty axisArray = obj.FindProperty("m_Axes");
if (axisArray.arraySize == 0)
Debug.Log("No Axes");
for (int i = 0; i < axisArray.arraySize; ++i)
{
var axis = axisArray.GetArrayElementAtIndex(i);
var name = axis.FindPropertyRelative("m_Name").stringValue;
names.Add(name);
}
Normally you can do
foreach (string colorName in Enum.GetNames(typeof(Colors))) which will iterate the names of the enums.
In your code above you havent shown what list is, nor where names has come from. However.
enum Things
{
Item1 = 0,
Item2 = 1
}
You can get the name from string name = Enum.GetName(typeof(Things), (int)Things.Item2) and you can get values from names with int value = (int)Enum.Parse(typeof(Things), nameOfThing)
So depending on what you actually want in a list and what you start with, iterate through and pick the relevant one
I ended up making my own solution, since (and please correct me if I'm wrong) the TryParse() and Parse() methods appear to need the enum to already contain entries with the same name (or index int) as the string to parse. This defeats the purpose for me, since I am doing this because I don't have the names in there already.
My solution ended up being to switch to having a single string input variable instead of an enum, then use Odin Inspector's ValidateInput attribute to check (for spelling errors, and) if the input variable matches any of the string entries in my dynamic list of InputManager input names (which I update manually using Odin Inspector's Button attribute and the code in the original post).
It's slightly less clean than I wanted, but does the job, so I'm satisfied.
I want program a struct in Matlab for saving some parameters.
The struct's name has to change every iteration in a loop, thus in each iteration I make a new struct. Therefore I want something like this:
index={'01','02','03'};
letter={'aa','bb','cc'};
names={'Peter','John','Michael'};
for(i=1:numel(index)){
......
strcat(str, index{i}, letter{i})(i).name = names{i};
}
Then, when the loop has finished I have 3 structs with the next names:
- str01aa{
name = 'Peter'
}
- str02bb{
name = 'John'
}
- str03cc{
name = 'Michael'
}
My problem is that the strcat function with the bracket (i) is not good defined, and the structs are not created.
I hope you can help me.
Thanks.
strcat(str, index{i}, letter{i})(i).name isn't a valid operation, because strcat returns a sting object, which can't possess fields. You need to make that string into a variable name using genvarname (documentation), like so:
index={'01','02','03'};
letter={'aa','bb','cc'};
names={'Peter','John','Michael'};
for(i = 1:numel(index))
{
......
genvarname(strcat('str', index{i}, letter{i}))(i).name = names{i};
}
Note that I changed str to 'str' for consistency with your example. As a general rule, dynamically constructed variable names are bad practice because they make debugging a nightmare.
Let me make a suggestion; instead of having a bunch of structs with different, seemingly arbitrary names, why not try something like this:
index={'01','02','03'};
letter={'aa','bb','cc'};
names={'Peter','John','Michael'};
for(i = 1:numel(index))
{
......
yourStruct(i).id = strcat('str', index{i}, letter{i});
yourStruct(i).name = names{i};
}
Either way, good luck!
I have a simple function that creates a generic List:
function test()
{
$genericType = [Type] "System.Collections.Generic.List``1"
[type[]] $typedParameters = ,"System.String"
$closedType = $genericType.MakeGenericType($typedParameters)
[Activator]::CreateInstance($closedType)
}
$a = test
The problem is that $a is always null no matter what I try. If I execute the same code outside of the function it works properly.
Thoughts?
IMHO that's pitfall #1. If you return an object from the function that is somehow enumerable (I don't know exactly if implementing IEnumerable is the only case), PowerShell unrolls the object and returns the items in that.
Your newly created list was empty, so nothing was returned. To make it work just use this:
,[Activator]::CreateInstance($closedType)
That will make an one item array that gets unrolled and the item (the generic list) is assigned to $a.
Further info
Here is list of similar question that will help you to understand what's going on:
Powershell pitfalls
Avoiding Agnostic Jagged Array Flattening in Powershell
Strange behavior in PowerShell function returning DataSet/DataTable
What determines whether the Powershell pipeline will unroll a collection?
Note: you dont need to declare the function header with parenthesis. If you need to add parameters, the function will look like this:
function test {
param($myParameter, $myParameter2)
}
or
function {
param(
[Parameter(Mandatory=true, Position=0)]$myParameter,
... again $myParameter2)
...
An easier way to work with generics. This does not directly solve the [Activator] approach though
Function test
{
New-Object "system.collections.generic.list[string]"
}
(test).gettype()