本文介绍了如何访问动态创建的控件的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我已经动态创建了一个带有模板字段的GridView. .问题是我想访问那些动态创建的控件，但是当我说找到控件时，就会给它NUllEXCEPTIONERROR错误对象引用未设置为对象的实例."
Hi i Have Created A GridView with Template Fields Dynamically. . The Problem is I Want to Acces those Dynamically Created Controls but when i Say Find Control its Giving NUllEXCEPTIONERROR error "Object reference not set to an instance of an object."
For i = 0 To AuthorsGridView.Rows.Count - 1
Dim txt As TextBox = AuthorsGridView.Rows(i).Cells(0).FindControl("firstName")
'' Error Run Time
txt.Text = ""
If txt.Text = "SomeValue" Then
'txt.ForeColor = Drawing.Color.Red
txt.Font.Bold = True
Else
txt.Font.Italic = True
End If
Next i
请帮我一个忙
Plz Help me Out
推荐答案
' Here my Code is
Public Class GridViewTemplate
Implements ITemplate
Private templateType As DataControlRowType
Private columnName As String
Sub New(ByVal type As DataControlRowType, ByVal colname As String)
templateType = type
columnName = colname
End Sub
Sub InstantiateIn(ByVal container As System.Web.UI.Control) _
Implements ITemplate.InstantiateIn
' Create the content for the different row types.
Select Case templateType
Case DataControlRowType.Header
' Create the controls to put in the header
' section and set their properties.
Dim lc As New Literal
lc.Text = " " & UCase(columnName) & ""
' Add the controls to the Controls collection
' of the container.
container.Controls.Add(lc)
Case DataControlRowType.DataRow
' Create the controls to put in a data row
' section and set their properties.
Dim firstName As New TextBox
firstName = New TextBox
Dim lastName As New Label
firstName.ID = "txtFName"
Dim spacer = New Literal
spacer.Text = "--"
' To support data binding, register the event-handling methods
' to perform the data binding. Each control needs its own event
' handler.
AddHandler firstName.DataBinding, AddressOf FirstName_DataBinding
AddHandler lastName.DataBinding, AddressOf LastName_DataBinding
lastName.Visible = False
' Add the controls to the Controls collection
' of the container.
container.Controls.Add(firstName)
container.Controls.Add(spacer)
container.Controls.Add(lastName)
' Insert cases to create the content for the other
' row types, if desired.
Case Else
' Insert code to handle unexpected values.
End Select
End Sub
Private Sub FirstName_DataBinding(ByVal sender As Object, ByVal e As EventArgs)
' Get the Label control to bind the value. The Label control
' is contained in the object that raised the DataBinding
' event (the sender parameter).
Dim l As TextBox = CType(sender, TextBox)
' Get the GridViewRow object that contains the Label control.
Dim row As GridViewRow = CType(l.NamingContainer, GridViewRow)
' Get the field value from the GridViewRow object and
' assign it to the Text property of the Label control.
l.Text = DataBinder.Eval(row.DataItem, "Doctor_Name").ToString()
End Sub
Private Sub LastName_DataBinding(ByVal sender As Object, ByVal e As EventArgs)
' Get the Label control to bind the value. The Label control
' is contained in the object that raised the DataBinding
' event (the sender parameter).
Dim l As Label = CType(sender, Label)
' Get the GridViewRow object that contains the Label control.
Dim row As GridViewRow = CType(l.NamingContainer, GridViewRow)
' Get the field value from the GridViewRow object and
' assign it to the Text property of the Label control.
l.Text = DataBinder.Eval(row.DataItem, "SlNo").ToString()
End Sub
End Class
Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Label1.Text = "Entered"
Dim dt As DataTable
Dim dr As DataRow
dt = New DataTable()
dt.Columns.Add(New DataColumn("Doctor_Name"))
dt.Columns.Add(New DataColumn("SlNo"))
dr = dt.NewRow()
dr("Doctor_Name") = "Val1"
dr("Slno") = "1001"
dt.Rows.Add(dr)
Label1.Text = "1 add"
dr = dt.NewRow()
dr("Doctor_Name") = "Val2"
dr("Slno") = "1002"
dt.Rows.Add(dr)
Label1.Text = "2 add"
dr = dt.NewRow()
dr("Doctor_Name") = "Val3"
dr("Slno") = "1003"
dt.Rows.Add(dr)
dr = dt.NewRow()
dr("Doctor_Name") = "val4"
dr("Slno") = "1004"
dt.Rows.Add(dr)
Label1.Text = "4 add"
Dim customField As New TemplateField
Dim CustomField1 As New TemplateField
' Create the dynamic templates and assign them to
' the appropriate template property.
customField.ItemTemplate = New GridViewTemplate(DataControlRowType.DataRow, "Author Name")
customField.HeaderTemplate = New GridViewTemplate(DataControlRowType.Header, "Employees")
'CustomField1.ItemTemplate = New GridViewTemplate(DataControlRowType.DataRow, "Author Name 2")
'CustomField1.HeaderTemplate = New GridViewTemplate(DataControlRowType.Header, "Author Name 2")
' Add the field column to the Columns collection of the
' GridView control.
AuthorsGridView.Columns.Add(customField)
'AuthorsGridView.Columns.Add(CustomField1)
AuthorsGridView.DataSource = dt
Label1.Text = " DataSource Set"
AuthorsGridView.DataBind()
ViewState("table") = dt
Label1.Text = "Binded"
' Here This Code Works it Shows Me the Value I Can Access it But Out side this Fun i Cant Access all Controls just Goes of
For i = 0 To AuthorsGridView.Rows.Count - 1
Dim txt As TextBox = AuthorsGridView.Rows(i).Cells(0).FindControl("txtFName")
'' Error Run Time
'txt.Text = ""
Label1.Text = txt.Text
If txt.Text = "VAl2" Then
'txt.ForeColor = Drawing.Color.Red
txt.Font.Bold = True
Else
txt.Font.Italic = True
End If
Next
End Sub
' Here on Other Control click i want to Access it But its Not Happening
Protected Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button2.Click
Dim dt As DataTable
dt = ViewState("table")
'AuthorsGridView.Columns.Add(CustomField1)
AuthorsGridView.DataSource = dt
'Label1.Text = " DataSource Set"
AuthorsGridView.DataBind()
Label1.Text = AuthorsGridView.Rows.Count
For i = 0 To AuthorsGridView.Rows.Count - 1
Dim txt As TextBox = AuthorsGridView.Rows(i).Cells(0).FindControl("txtFName")
Label1.Text = txt.Text
If txt.Text = "Val2" Then
txt.Font.Bold = True
Else
txt.Font.Italic = True
End If
Next
End Sub
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