System.NullReferenceException:对象引用没有设置为对象的实例。在试图存储文本框值时发生错误。

Question

我想将文本框的文本存储到string变量中，但是出现了一个错误：

System.NullReferenceException:未设置为对象实例的对象引用

代码：

 Dim Name As String = txtName.Text
Dim Email As String = txtEmail.Text
Dim Password As String = txtPassword.Text
Dim Repassword As String = txtRepassword.Text
Dim Country As String = txtCountry.Text
Dim College As String = txtCollege.Text
Dim Phone As String = txtPhone.Text

它显示txtName.text为NULL；如何修复它？

我的控制代码在这里：

'''<summary>
'''txtName control.
'''</summary>
'''<remarks>
'''Auto-generated field.
'''To modify move field declaration from designer file to code-behind file.
'''</remarks>
Protected WithEvents txtName As Global.System.Web.UI.WebControls.TextBox
'''<summary>
'''txtEmail control.
'''</summary>
'''<remarks>
'''Auto-generated field.
'''To modify move field declaration from designer file to code-behind file.
'''</remarks>
Protected WithEvents txtEmail As Global.System.Web.UI.WebControls.TextBox
'''<summary>
'''txtPassword control.
'''</summary>
'''<remarks>
'''Auto-generated field.
'''To modify move field declaration from designer file to code-behind file.
'''</remarks>
Protected WithEvents txtPassword As Global.System.Web.UI.WebControls.TextBox
'''<summary>
'''txtRepasword control.
'''</summary>
'''<remarks>
'''Auto-generated field.
'''To modify move field declaration from designer file to code-behind file.
'''</remarks>
Protected WithEvents txtRepassword As Global.System.Web.UI.WebControls.TextBox
'''<summary>
'''txtCountry control.
'''</summary>
'''<remarks>
'''Auto-generated field.
'''To modify move field declaration from designer file to code-behind file.
'''</remarks>
Protected WithEvents txtCountry As Global.System.Web.UI.WebControls.TextBox
'''<summary>
'''txtCollege control.
'''</summary>
'''<remarks>
'''Auto-generated field.
'''To modify move field declaration from designer file to code-behind file.
'''</remarks>
Protected WithEvents txtCollege As Global.System.Web.UI.WebControls.TextBox
'''<summary>
'''txtPhone control.
'''</summary>
'''<remarks>
'''Auto-generated field.
'''To modify move field declaration from designer file to code-behind file.
'''</remarks>
Protected WithEvents txtPhone As Global.System.Web.UI.WebControls.TextBox

Answer 1

一些错误检查将帮助您避免堆栈跟踪。

If String.IsNullOrEmpty(txtName.Text) Then
Dim name As String = txtName.Text
End If