WPF 中的变量与 PropertyChanged 绑定

Question

我在 PowerShell 脚本中实现了 WPF 接口。 当窗口打开时，将显示变量 MyFolder.SelectedFolder 的值。 但是当修改值时，并没有更新。

Class cFolder {
    [String] $Path
    [String] $SelectedFolder
} 

$MyFolder = [cFolder]::new()
$MyFolder.Path = "C:\temp"
$MyFolder.SelectedFolder = "temp"

<Label x:Name ="Lbl_SelFolder" Content="{Binding Path, UpdateSourceTrigger=PropertyChanged}"/>

$XMLReader = (New-Object System.Xml.XmlNodeReader $Form)
$XMLForm = [Windows.Markup.XamlReader]::Load($XMLReader)
$XMLForm.DataContext = $MyFolder
$LblSelFolder = $XMLForm.FindName('Lbl_SelFolder')

感谢您的帮助

Answer 1

问题是没有人观察您稍后对

$MyFolder

对象的属性所做的更改。

解决此问题的一种方法是将对象存储在

System.Collections.ObjectModel.ObservableCollection<T>

实例中，并将后者分配给 WPF 表单（窗口）的

.DataContext

属性：

$XMLForm.DataContext = 
  [System.Collections.ObjectModel.ObservableCollection[cFolder]] $MyFolder

然后根据

$MyFolder

的更新触发标签控件的更新：

• 更新

  $MyFolder

  的数据绑定属性，例如

  .SelectedFolder

  ：

  $MyFolder.SelectedFolder = 'tempNEW'
  

• 然后将

  $MyFolder

  重新分配给可观察集合，作为其唯一的元素；这就是触发标签更新的原因：

  $XMLForm.DataContext[0] = $MyFolder
  

---

一个独立的示例，它在循环中更新数据上下文对象的 .SelectedFolder

 属性，以演示标签已响应更新：

using namespace System.Windows
using namespace System.Windows.Data
using namespace System.Windows.Controls
using namespace System.Windows.Markup
using namespace System.Xml
using namespace System.Collections.ObjectModel
# Note: `using assembly PresentationFramework` works in Windows PowerShell,
#       but seemingly not in PowerShell (Core) as of v7.3.5
Add-Type -AssemblyName PresentationFramework
Add-Type -AssemblyName System.Windows.Forms

Class cFolder {
  [String] $Path
  [String] $SelectedFolder
} 

$MyFolder = [cFolder]::new()
$MyFolder.Path = "C:\temp"
$MyFolder.SelectedFolder = "temp"

# Define the XAML document defining the WPF form with a single label.
[xml] $xaml = @"
  <Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Label data-binding demo"
    Height="80" Width="350"
  >
      <Label x:Name ="Lbl_SelFolder" Content="{Binding Path=SelectedFolder}"/>
  </Window>
"@

# Parse the XAML, which returns a [System.Windows.Window] instance.
$form = [XamlReader]::Load([XmlNodeReader] $xaml)

# Use an observable collection as the data context.
# with $MyFolder as the first and only element.
$form.DataContext = [ObservableCollection[cFolder]] $MyFolder

# Show the window non-modally and activate it.
$null = $form.Show()
$form.Activate()

# While the window is open, process pending GUI events
# and update the selected folder.
$i = 0
while ($form.IsVisible) {
  # Note: Even though this is designed for WinForms, it works for WPF too.
  [System.Windows.Forms.Application]::DoEvents()
  # Sleep a little.
  Start-Sleep -Milliseconds 100
  # Update the selected folder.
  $MyFolder.SelectedFolder = 'temp' + ++$i
  # It is through *re-assigning* the object as the first (and only)
  # element of the observable collection that the control update
  # is triggered.
  $form.DataContext[0] = $MyFolder
}