Question

我该怎么解决这个问题？

我正在做一个简单的数据库项目，我有一个搜索字段，我编写了以下代码，用于在DataGridView中搜索和显示数据，但是 Null Reference Exception一直显示，因为我没有任何内容初始化表，但如果我不这样做，我会在初始化之前使用警告。

问题是：如何正确初始化表格。

Private Sub txtSearch_TextChanged(ByVal sender As System.Object, ByVal e As    System.EventArgs) Handles txtSearch.TextChanged
    Dim searchText As String = txtSearch.Text
    Dim matchText As String = ""
    Dim rowMatch As Boolean = False
    Dim foundRows As DataTable = Nothing 'this initializig causes the   problem of null exception,But how can i Initialize it then?????


For Each rw As DataRow In dataSet.Tables(0).Rows

        Dim cl As String = rw.Item(1).ToString '  this cell is FirstName  Cell
        If searchText.Length > cl.ToString.Length Then
            matchText = cl.ToString
        Else
            matchText = cl.ToString.Substring(0, searchText.Length)
        End If

        'bellow it adds the Found Row (rw) to the table 
        If (searchText.Equals(matchText) And searchText <> "" And Not foundRows Is Nothing) Then foundRows.Rows.Add(rw)

Next


    'to shows data if the search text field is not empty then show the found matching rows
    If (searchText <> "") Then
        contactView.DataSource = foundRows
    Else ' else show the original tavle again 
        contactView.DataSource = dataSet.Tables(0)
    End If
    contactView.Refresh() 'refresh 
End Sub

i also tried this

我尝试使用

Dim foundRows As DataTable = New DataTable

但它显示 ArgumentException

此行已属于另一个表

但是你可以看到没有任何效果，请帮助！

Answer 1

是我终于明白了

我的栏目有问题

Dim foundRows As DataTable = New DataTable("PseuContact")  'this initializig causes the problem of null exception,But how can i Initialize it then?????
   foundRows.Columns.Add("ID")
    foundRows.Columns.Add("First Name")
    foundRows.Columns.Add("Last Name")
    foundRows.Columns.Add("Phone Number")
    foundRows.Columns.Add("Mobile Number")
    foundRows.Columns.Add("Email Address")

在声明新表

时，

初始化列很重要

这是最好的

＆＃39;在使用前初始化数据表＆＃39;

1 个答案: