从 .sdf 数据库在 ASP.NET 和 VB.net 中实现搜索引擎 [重复]

Question

我正在尝试在 ASP.NET 和 VB.net 中实现搜索引擎。搜索来自 .sdf 数据库。我不断收到：

System.NullReferenceException：对象引用未设置为对象的实例

错误发生就行了

myDA.SelectCommand = cm

但我无法指出错误的来源，因为我的代码看起来很干净。我会很感激一些帮助

Private Sub searchButton_click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles searchButton.Click
    registration.Visible = True
    con.Open()
    cm.Connection = con
    cm.CommandText = "SELECT * FROM records WHERE phone = " & phoneTextBox.Text
    cm.ExecuteNonQuery()
    myDA.SelectCommand = cm
    myDA.Fill(myDataSet, "records")

    If myDataSet.Tables("records").Rows.Count = 0 Then
        TextBox1.Text = ""
        TextBox2.Text = ""
        TextBox3.Text = ""
        TextBox4.Text = ""
        TextBox5.Text = ""
        TextBox6.Text = ""
        Response.Write("Record not Found")
    Else
        TextBox1.Text = myDataSet.Tables("Records").Rows(0).Item("phone")
        TextBox2.Text = myDataSet.Tables("Records").Rows(0).Item("name")
        TextBox3.Text = myDataSet.Tables("Records").Rows(0).Item("id")
        TextBox4.Text = myDataSet.Tables("Records").Rows(0).Item("pin")
        TextBox5.Text = myDataSet.Tables("Records").Rows(0).Item("area")
        TextBox6.Text = myDataSet.Tables("Records").Rows(0).Item("subscription")
    End If
End Sub

Answer 1

你的错误在这里

          cm.CommandText = "SELECT * FROM records WHERE phone = " +& phoneTextBox.Text

电话号码是字符串或 varchar 字段，这意味着它们必须放在“引号”中。因为您还没有执行查询并返回空结果（0 行）。当您尝试访问第一行时，即 row[0]，因为没有行，您会收到 nullrefrence 异常

像这样修改你的代码

     cm.CommandText = "SELECT * FROM records WHERE phone = '" +phoneTextBox.Text+"'"