无法将“System.Windows.Forms.Button"类型的对象强制转换为类型 >'System.Windows.Forms.TextBox' [英] Unable to cast object of type 'System.Windows.Forms.Button' to type > 'System.Windows.Forms.TextBox'

问题描述

我编写了一个函数来清空表单中的所有文本框:

I wrote a function that empty all TextBox in my form:

Private Sub effacer()
        For Each t As TextBox In Me.Controls
            t.Text = Nothing
        Next
    End Sub

但是我遇到了这个问题:

But I had this problem :

无法将类型为System.Windows.Forms.Button"的对象转换为类型'System.Windows.Forms.TextBox'.

Unable to cast object of type 'System.Windows.Forms.Button' to type 'System.Windows.Forms.TextBox'.

我尝试添加此 If TypeOf t Is TextBox Then 但我遇到了同样的问题

I tried to add this If TypeOf t Is TextBox Then but I had the same problem

推荐答案

Controls 集合包含表单的所有控件，而不仅仅是 TextBox.

The Controls collection contains all controls of the form not only TextBoxes.

相反，您可以使用 Enumerable.OfType 来查找和转换所有 TextBoxes:

For Each txt As TextBox In Me.Controls.OfType(Of TextBox)()
    txt.Text = ""
Next

如果你想以老派"的方式做同样的事情:

If you want to do the same in the "old-school" way:

For Each ctrl As Object In Me.Controls
    If TypeOf ctrl Is TextBox
        DirectCast(ctrl, TextBox).Text = ""
    End If
Next

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