對於每個文本框循環

Question

我想做一個foreach循環，檢查面板中的每個文本框，並更改BackColor，如果它的文本是什麼。我已經試過如下：

Dim c As TextBox 
For Each c In Panel1.Controls 
    if c.Text = "" Then 
    c.BackColor = Color.LightYellow 
    End If 
Next 

，但我得到的錯誤：

Unable to cast object of type System.Windows.Forms.Label to type System.windows.forms.textbox

Answer 1

你可以嘗試這樣的事情，而不是：

Dim ctrl As Control 
    For Each ctrl In Panel1.Controls 
    If (ctrl.GetType() Is GetType(TextBox)) Then 
     Dim txt As TextBox = CType(ctrl, TextBox) 
     txt.BackColor = Color.LightYellow 
    End If 

Answer 2

試試這個。它會把色彩回來時，你輸入的數據以及

For Each c As Control In Panel1.Controls 
     If TypeOf c Is TextBox Then 
      If c.Text = "" Then 
       c.BackColor = Color.LightYellow 
      Else 
       c.BackColor = System.Drawing.SystemColors.Window 
      End If 
     End If 
    Next 

還有一種不同的方式來做到這一點，涉及創建繼承TextBox控件和使用您的形式：

Public Class TextBoxCompulsory 
    Inherits TextBox 
    Overrides Property BackColor() As Color 
     Get 
      If MyBase.Text = "" Then 
       Return Color.LightYellow 
      Else 
       Return DirectCast(System.Drawing.SystemColors.Window, Color) 
      End If 
     End Get 
     Set(ByVal value As Color) 

     End Set 
    End Property 
End Class 

Answer 3

假設沒有出現任何嵌套控件：

For Each c As TextBox In Panel1.Controls.OfType(Of TextBox)() 
    If c.Text = String.Empty Then c.BackColor = Color.LightYellow 
Next