Question

我正在尝试从表中获取数据并将其插入到数组中。但是，当我调试我的代码时，Visual Studio会返回此错误：

Microsoft.VisualBasic.dll中出现未处理的“System.MissingMemberException”类型异常

其他信息：找不到类型为“DBNull”的默认成员。

运行并导致此错误的过程如下：

Sub characterChecked(ByVal pronunciation As String)
    Dim query As String = "SELECT Character FROM [Hiragana List] WHERE Pronunciation='" & pronunciation & "';" 'Selects the character from the SQL table
    Dim instruction = New SqlCommand(query, sqlCon)
    Dim da As New SqlDataAdapter
    da.SelectCommand = instruction
    HiraganaList = New DataTable
    da.Fill(HiraganaList)
    dataArray(columnCount, rowCount) = HiraganaList.NewRow(0)("column") 'fills the first column in a row with the charater
    columnCount += 1 'Increments the coulmn count so that the pronunciation is in the same row as the character

    Dim query2 As String = "SELECT Pronunciation FROM [Hiragana List] WHERE Pronunciation='" & pronunciation & "';"
    Dim instruction2 = New SqlCommand(query, sqlCon)
    Dim da2 As New SqlDataAdapter
    da2.SelectCommand = instruction
    HiraganaList = New DataTable
    da2.Fill(HiraganaList)
    dataArray(columnCount, rowCount) = HiraganaList.NewRow(0)("row")
    rowCount += 1

调试在这一行中断：

dataArray(columnCount, rowCount) = HiraganaList.NewRow(0)("column") 'fills the first column in a row with the charater

数组，数据表等的声明在这里：

Dim connectionString As String = "Server=my_server;Database=name_of_db;User Id=user_name;Password=my_password"
Dim sqlCon = New SqlConnection("Data Source=(LocalDB)\v11.0;AttachDbFilename='J:\Computing Coursework\real project\KES\KES\Kana List.mdf';Integrated Security=True;Connect Timeout=30")
Dim HiraganaList As DataTable
Dim KanjiList As DataTable
Dim Katakana As DataTable
Dim YoonList As DataTable
Dim YoonKataList As DataTable
Dim columnCount As Integer = 1 'initialising the column and row counter for when data is inserted
Dim rowCount As Integer = 1
Dim varFileName As String = "J:\Computing Coursework\real project\KES\Resources\csv.txt"
Dim dataArray(1, 1) As String

如果有人能在我的代码中帮助发现问题，那将非常有帮助。就个人而言，我认为错误是由于没有以正确的方式将数据插入到数组中引起的，但是我不知道我在做什么是不正确的还是确实有效。

Answer 1

你要做的事情并不是很清楚，但NewRow电话似乎完全错了。它不仅创建了一个最初为空的新行，而且似乎没有接受参数的重载所以也许这就是你想要做的。（不测试数组中可用的空间来复制返回的值）

Sub characterChecked(ByVal pronunciation As String)
    Dim query As String = "SELECT Character FROM [Hiragana List] WHERE Pronunciation=@pro"
    Dim instruction = New SqlCommand(query, sqlCon)
    instruction.Parameters.AddWithValue("@pro", pronunciation)
    Dim da As New SqlDataAdapter(instruction)
    HiraganaList = New DataTable
    da.Fill(HiraganaList)
    if HiraganaList.Rows.Count > 0 Then
        dataArray(0, rowCount) = HiraganaList.Rows(0)("Character") 
        dataArray(1, rowCount) = pronunciation
    End If
End Sub

但在这一点上，我怀疑你是否真的需要它 DataTable已经是一个美化的数组，具有比简单数组更多的功能。所以只需要调用

Function characterChecked(ByVal pronunciation As String) As DataTable
    Dim query As String = "SELECT Pronunciation, Character " & _ 
                          "FROM [Hiragana List] WHERE Pronunciation=@pro"
    Dim instruction = New SqlCommand(query, sqlCon)
    instruction.Parameters.AddWithValue("@pro", pronunciation)
    Dim da As New SqlDataAdapter(instruction)
    HiraganaList = New DataTable
    da.Fill(HiraganaList)
    return HiraganaList
End Function

将为您提供一个DataTable，其中包含查询返回的多行和两列（索引0处为Pronunciation，索引处为Character）

Dim hira As DataTable = characterChecked(pronciation.Text)
Dim hiraChar = hira.Rows(0)("Character")

VB - 在将数据插入数组时，未找到类型“DBNull”的默认成员

1 个答案: