是否可以将事件附加到PSObject？ [英] Is it possible to attach an event to a PSObject?

问题描述

说我有一个这样的psobject：

  $ o =新对象PSObject -Property @ {value = 0} 
添加成员-MemberType ScriptMethod -NameSqrt-Value {
 echo$（$ this.value）的平方根是$（[Math] :: Round（[Math ] :: Sqrt（$ this.value），2））
} -inputObject $ o 
  

是否可以附加事件，以便在value属性更改时执行方法Sqrt（）？即：

  PS> $ o.value = 9 
  

将生成

  9的平方根为3 
  

更新

根据@Richard的回答，这是工作食谱：

  $ o =新对象PSObject -property @ {_ val= 1} 
添加成员-MemberType ScriptMethod -NameSqrt-Value {
 write-host$（$ this._val）的平方根是$（[Math] :: Round（[Math] :: Sqrt（$ this。 _val），2））
} -inputObject $ o 
 
 
添加成员-MemberType ScriptProperty -Name'val'-Value {$ this._val} -SecondValue { $ this._val = $ args [0]; $ this.Sqrt（）} -inputObject $ o 
  

解决方案

而不是使值 a NoteProperty 使其成为 ScriptProperty ，这包括定义单独的get和set方法，而不是直接修改一个字段。

  $ theObject | Add-Member -MemberType ScriptProperty -Name'Value'
 -Value {$ this._value} 
 -SecondValue {$ this._value = $ args [0]; $ this.Sqrt} 
  

（价值定义get方法 SecondValue 集合。）

注意，由于PowerShell不提供封装数据的任何能力，呼叫者仍然可以访问基础字段。在C＃（或其他.NET语言）中编码自定义类型，并使用 Add-Type 可以避免这种情况，但不大可能值得，除非您真的有呼叫者将不遵守规则。

第二期

在ScriptProperty中没有输出管道（任何输出都被丢弃），所以 echo （作为 Write-Output 的别名）不会做任何有用的事情使用 Write-Host 替换它。一般来说，在获取或设置属性（包括输出）中的副作用是不好的做法（使用它们时期望低开销）。

Say I've a psobject like this :

$o=New-Object PSObject -Property @{"value"=0}
Add-Member -MemberType ScriptMethod -Name "Sqrt" -Value {
    echo "the square root of $($this.value) is $([Math]::Round([Math]::Sqrt($this.value),2))"
} -inputObject $o

Is it possible to attach an event so that the method Sqrt() is executed when the value attribute change ? ie :

PS>$o.value=9

will produce

the square root of 9 is 3

update

As per @Richard answer this is the working recipe :

$o=New-Object PSObject -property @{"_val"=1}
Add-Member -MemberType ScriptMethod -Name "Sqrt" -Value {
    write-host "the square root of $($this._val) is $([Math]::Round([Math]::Sqrt($this._val),2))"
} -inputObject $o


Add-Member -MemberType ScriptProperty -Name 'val' -Value{ $this._val }  -SecondValue { $this._val=$args[0];$this.Sqrt() } -inputObject $o

解决方案

Rather than making value a NoteProperty make it a ScriptProperty, this includes defining separate get and set methods that are called rather than directly modifying a field.

$theObject | Add-Member -MemberType ScriptProperty -Name 'Value' 
                        -Value{ $this._value }
                        -SecondValue { $this._value = $args[0]; $this.Sqrt }

(Value defines the get method, SecondValue the set.)

Note as PowerShell doesn't provide any ability to encapsulate data, the underlying field is still accessible to callers. Coding a custom type in C# (or other .NET language) and use of Add-Type can avoid this, but is unlikely to be worth it unless you really have callers who will not follow the rules.

Second Issue

In a ScriptProperty there is no output pipe (any output is thrown away), so echo (being an alias for Write-Output) won't do anything useful. Replacing it with Write-Host works. In general side effects in a property get or set (including output) are poor practice (there is an expectation of low overhead when using them).

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