如何将巨大的文本文件读取到 ObservableCollection

Question

我有一个超过 200,000 行的 excel 文件。如果我使用 OleDbConnection 将其读入数据表或 ObservableCollection，然后在数据网格中显示，则需要一分钟以上。我将 xlsx 更改为制表符分隔的 txt。我发现将整个 txt 文件放入数据表中非常快。它需要不到 10 秒。如果我将整个 txt 直接放入 ObservableCollection，我想知道该怎么做。它不能逐行完成，因为它会再次花费一分钟以上。

'Define Product property    
     Public Class Product
                    Public Property Model As String
                    Public Property Opt As String
                    Public Property Description As String
                    Public Property Price As String               
     End Class

'define Products as ObservableCollection       
 Dim Products As New ObservableCollection(Of Product)()

'Read txt file to datatable
Private Sub LoadBound(ByVal fName As String)
Dim textLine As String = String.Empty
Dim splitLine As String()

CSVdata.Columns.AddRange({New DataColumn("Model"),
                          New DataColumn("Opt"),
                          New DataColumn("Description"),
                          New DataColumn("Price")})
                    CSVdata.Rows.Clear()

                    If System.IO.File.Exists(fName) Then
                        Dim objReader As System.IO.StreamReader = New System.IO.StreamReader(fName)
                        Dim contents = objReader.ReadToEnd()
                        Dim strReader = New System.IO.StringReader(contents)


        Do
            textLine = strReader.ReadLine()
            If textLine.Contains("""") Then
                textLine = textLine.Replace("""", "")

            End If
                            If textLine <> String.Empty Then
                                splitLine = textLine.Split(vbTab)

                                If splitLine(0) <> String.Empty OrElse splitLine(1) <> String.Empty Then
                                    CSVdata.Rows.Add(splitLine)

                                End If
                            End If
                        Loop While strReader.Peek() <> -1
                    End If

 End Sub

Answer 1

注释和解释。

Public Class Product
    Public Property Model As String
    Public Property Opt As String
    Public Property Description As String
    Public Property Price As String
    'Add a parameterized constructor to your class to make coding easier
    Public Sub New(Mdl As String, O As String, Desc As String, P As String)
        Model = Mdl
        Opt = O
        Description = Desc
        Price = P
    End Sub
End Class

Dim Products As ObservableCollection(Of Product)

Private Sub LoadBound(ByVal fName As String)
    'Build a List(Of Product) from the text file
    Dim lstProducts As New List(Of Product)
    Dim lines = File.ReadAllLines(fName)
    For Each line In lines
        Dim Props = line.Split(CChar(vbTab))
        Dim p As New Product(Props(0), Props(1), Props(2), Props(3))
        lstProducts.Add(p)
    Next
    'The constructor of an ObservableCollection can take a List(Of T)
    Products = New ObservableCollection(Of Product)(lstProducts)
End Sub

编辑

Public Class Product
    Public Property Model As String
    Public Property Opt As String
    Public Property Description As String
    Private strPrice As String
    Public Property Price As Double
    'Add a parameterized constructor to your class to make coding easier
    Public Sub New(Mdl As String, O As String, Desc As String, P As String)
        Model = Mdl
        Opt = O
        Description = Desc
        Dim ParsedDouble As Double
        Double.TryParse(P, ParsedDouble)
        Price = ParsedDouble
    End Sub
End Class

更改价格类型

1. 更改属性的类型

2. 调整 Sub New 以从字符串中获取双精度值。如果解析失败，价格将为 0。

   如果你真的想要一个 null（vb 中什么都没有），请参阅 https://docs.microsoft.com/en-us/dotnet/visual-basic/programming-guide/language-features/data-types/nullable-value-types