如何在不使用VB.net Windows窗體應用程序中的“”的情況下將Textbox值設置為double並使其為空？

Question

這是代碼

Public Partial Class MainForm
Public Sub New()
    ' The Me.InitializeComponent call is required for Windows Forms designer support.
    Me.InitializeComponent()

    '
    ' TODO : Add constructor code after InitializeComponents
    '
End Sub

Sub Label4Click(sender As Object, e As EventArgs)

End Sub

Sub Button2Click(sender As Object, e As EventArgs)
    Dim poundInAKg As Double = 2.20462
    Dim KGInAPound As Double = 0.453592
    If pound.Text = " " Then
        MessageBox.Show("Please fill atleast one value Kilo or Pound : ")
    End If

    kilo.Text = Val(pound.Text) * 0.453592
    'pound.Text = Val(kilo.Text / 2.20462 )


End Sub

Sub MainFormLoad(sender As Object, e As EventArgs)

End Sub
End Class

錯誤是從“雙精度”到“字符串”的隱式轉換。 （BC42016）請幫助

Answer 1

您應該使用double.TryParse方法嘗試將用戶輸入（字符串）轉換為雙精度值，然后，如果轉換成功，請執行moltiplication並將所有內容重新轉換為字符串

Dim poundInAKg As Double = 2.20462
Dim KGInAPound As Double = 0.453592
Dim poundVal As Double
if double.TryParse(pound.Text, poundVal) Then
    kilo.Text = (poundVal * 0.453592).ToString()
else
    MessageBox.Show("Please fill atleast one value Kilo or Pound : ")
End If