Ways to trigger a sub on all objects in the list?

Question

Hallo,

I have a following class and i have a List of Box. In the form i have option to change Unit system to SI or Imperial. I have a Boolean property and String property called UnitChanged and Unit. In the form start SI will be set as default unit. if user change the unit by clicking a button Unit property will be set to "SI" or "IM" and UnitChanged will be set to True and i want all the Length and Width values has to be converted to Imperial unit and vice versa.

I am looking for a way to trigger a sub when user changes the Unit in the form. Is there a way i can trigger it for all the objects in the list?

I can listen to the unitchange by using readonly property in the Box object but with readonly property i cant execute the sub.

Public Class Box

    Public Property Length As Integer
    Public Property Width As Integer

    Public Sub ChangeUnit()
        If Form1.UnitChanged Then
            If Form1.Unit.Equals("SI") Then
                Length = Length * 25.400013716
            Else
                Length = Length * 0.0393701
            End If
        Else
    End Sub

End Class

Thanks

Answer 1

Here is a possible solution (full source)

Unit types

Namespace Classes  
	Public Enum Unit  
		SI  
		IM  
	End Enum  
End Namespace  

Container

Imports System.ComponentModel  
Imports System.Runtime.CompilerServices  
  
Namespace Classes  
	Public Class Box  
		Implements INotifyPropertyChanged  
  
		Private _unit As Unit  
		Private _length As Double  
  
		Public Property Length() As Double  
			Get  
				Return _length  
			End Get  
			Set  
				_length = Value  
			End Set  
		End Property  
  
		Public Property Width() As Integer  
  
		Public Property Unit() As Unit  
			Get  
				Return _unit  
			End Get  
			Set  
				_unit = Value  
				OnPropertyChanged()  
  
				If Unit = Unit.SI Then  
					Length *= 25.400013716  
				Else  
					Length *= 0.0393701  
				End If  
  
			End Set  
		End Property  
  
		Public Overrides Function ToString() As String  
			Return Length.ToString()  
		End Function  
  
		Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged  
		Protected Overridable Sub OnPropertyChanged(<CallerMemberName> Optional ByVal propertyName As String = Nothing)  
			PropertyChangedEvent?.Invoke(Me, New PropertyChangedEventArgs(propertyName))  
		End Sub  
  
	End Class  
End Namespace  
  

Mocked data

Namespace Classes  
	Public Class MockedData  
		Public Shared Function Boxes() As List(Of Box)  
			Return New List(Of Box)() From {  
				New Box() With {  
					.Length = 25,  
					.Unit = Unit.IM  
				},  
				New Box() With {  
					.Length = 26,  
					.Unit = Unit.IM  
				},  
				New Box() With {  
					.Length = 27,  
					.Unit = Unit.IM  
				}  
			}  
		End Function  
	End Class  
End Namespace  

Form code

Note that each RadioButton has it's Tag property set eg.

Imports System.ComponentModel  
Imports System.Windows.Forms  
Imports Classes  
  
Partial Public Class Form1  
    Inherits Form  
  
    Private ReadOnly _dataSource As New BindingList(Of Box)()  
    Public Sub New()  
        InitializeComponent()  
  
        _dataSource = New BindingList(Of Box)(MockedData.Boxes())  
  
        listBox1.DataSource = _dataSource  
  
        AdjustUnits()  
  
        AddHandler radioButtonIM.CheckedChanged, AddressOf RadioButtonOnCheckedChanged  
        AddHandler radioButtonSI.CheckedChanged, AddressOf RadioButtonOnCheckedChanged  
  
    End Sub  
  
    Private Sub RadioButtonOnCheckedChanged(ByVal sender As Object, ByVal e As EventArgs)  
        Dim rb = DirectCast(sender, RadioButton)  
  
        If rb IsNot Nothing Then  
            If rb.Checked Then  
                AdjustUnits()  
            End If  
        End If  
  
    End Sub  
  
    Private Sub AdjustUnits()  
        Dim unitType As String = Controls.OfType(Of RadioButton)().FirstOrDefault(Function(r) r.Checked).Tag.ToString()  
  
        Dim unit As Unit  
  
        [Enum].TryParse(unitType, unit)  
  
        For index As Integer = 0 To listBox1.Items.Count - 1  
            Dim item As Box = _dataSource(index)  
            item.Unit = unit  
        Next  
  
    End Sub  
End Class  

Answer 2

Hi @Hobbyist_programmer ,
If you want to update all objects in a list, you can use List.ForEach(Sub(c) c.PropertyToChange = value)
The code looks like:

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click  
        Dim boxes As List(Of Box) = New List(Of Box) From { ...}  
  
        If Form1.UnitChanged Then  
            If Form1.Unit.Equals("SI") Then  
                boxes.ForEach(Sub(c) c.Length *= 25.400013716)  
            Else  
                boxes.ForEach(Sub(c) c.Length *= 0.0393701)  
            End If  
        Else  
            ...  
        End If  
    End Sub  

Hope it could be helpful.

Best Regards,
Xingyu Zhao
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