在vb.net中構建一個多維數組

Question

我試圖構建一個多維數組，它將爲數據庫中的每條記錄保存兩位信息id，說明。

這就是我目前正在做的。

Dim mArray(,) As String 
Dim i As Integer = 0 
While cmdReader.Read() 
    mArray(i,0) = cmdReader.Item("id") 
    mArray(i,1) = cmdReader.Item("description") 
    i = i + 1 
End While 

我這裏的問題是，它不喜歡在mArray(i,0)的i。任何人對此有任何想法？這是給出的錯誤Object reference not set to an instance of an object.

感謝您的任何和所有幫助。

Nalum

Answer 1

爲什麼不情願利用List Class和Dictionary Class

你可以而不是創建一個字典列表，用鍵和值兩個字符串。然後密鑰可以表示您的密鑰（您的示例中的ID和描述，並且該值可以是曾經存儲的值）。

喜歡的東西

Dim values As New List(Of Dictionary(Of String, String))() 

，然後在while循環類似

values.Add(New Dictionary(Of String, String)() From { _ 
    {"id", cmdReader.Item("id")} _ 
}) 
values.Add(New Dictionary(Of String, String)() From { _ 
    {"description", cmdReader.Item("description")} _ 
}) 

然後，您可以使用的foreach

For Each value As Dictionary(Of String, String) In values 
    Dim id As String = value("id") 
    Dim description As String = value("description") 
Next 

或A

For i As Integer = 0 To values.Count - 1 
    Dim value As Dictionary(Of String, String) = values(i) 
    Dim id As String = value("id") 
    Dim description As String = value("description") 
Next 

Answer 2

問題是你沒有初始化數組。

這應該工作，直到i將達不到在初始化中設置的限制。

Dim mArray(100,100) As String 
Dim i As Integer = 0 
While cmdReader.Read() 
    mArray(i,0) = cmdReader.Item("id") 
    mArray(i,1) = cmdReader.Item("description") 
    i = i + 1 
End While 

但是，如果不知道數組限制，我建議按照astander's suggestion。

Answer 3

試試這個

Dim mArray(1,1) As String 
Dim i As Integer = 0 
While cmdReader.Read() 
    mArray(i,0) = cmdReader.Item("id") 
    mArray(i,1) = cmdReader.Item("description") 
    i = i + 1 
    ReDim Preserve mArray(i,1) 
End While 

Answer 4

糾正此錯誤。

Dim mArray(,) As String = ""