如何在多个类中提供数据表 [英] How to make a datatable available in more than one class

问题描述

这是我第一次使用CSV文件来保存我的数据。



我在我的一个类中创建了一个DataTable，如下所示;

This is the first time I have used CSV files to hold my data.

I have created a DataTable in one of my classes as follows;

Public Class New_Yellow_Ball_Competition
Public YBResultsTable As DataTable = New DataTable()
Private Sub ResultsTable()

    YBResultsTable.Columns.AddRange(New DataColumn() {
        New DataColumn("Date", GetType(Date)),
        New DataColumn("TeamNumber", GetType(Integer)),
        New DataColumn("Player1", GetType(String)),
        New DataColumn("P1Handicap", GetType(Integer)),
        New DataColumn("P1Hole1", GetType(Integer)),
        New DataColumn("P1Stab1", GetType(Integer)),
        New DataColumn("YB1Lost", GetType(Boolean)),
        New DataColumn("P1Hole2", GetType(Integer)),
.... some 230 plus columns
 })

End Sub
End Class

但是，我想将DataTable保存为另一个类中的CSV文件，如下所示;

However, I want to save the DataTable as a CSV file in another Class as follows;

Public Class MainMenu
Private Sub YellowBallNew_Click(sender As Object, e As EventArgs) Handles YellowBallNew.Click
    New_Yellow_Ball_Competition.MdiParent = Me
    New_Yellow_Ball_Competition.WindowState = FormWindowState.Maximized
    New_Yellow_Ball_Competition.Show()
End Sub
Private Sub YellowBallClose_Click(sender As Object, e As EventArgs) Handles YellowBallClose.Click
    Using writer As StreamWriter = New StreamWriter("dump.csv")
        Rfc4180Writer.WriteDataTable(YBResultsTable, writer, True)
    End Using
End Sub
End Class 

但我收到错误说明

未声明YBResultsTable。由于其保护级别，它可能无法访问。



那么如何让MainMenu类中的DataTable可用？

代码工作提供它是从创建DataTable的类中调用的。

but I get an error stating
YBResultsTable is not declared. It maybe inaccessible due to its protection level.

So how do I get the DataTable to be available in the MainMenu class?
The code works providing it is called from the class the DataTable was created in.

推荐答案

实现这一点的方法很少。最好的方法是创建界面 [ ^ ]。这取决于你想要达到的目标。



更多：

演练：创建和实现接口（Visual Basic） [ ^ ]

在类和接口之间选择 [ ^ ]

创建类在Visual Basic .NET中 [ ^ ]





第二次看...

<$的定义c $ c> New_Yellow_Ball_Competition 类错误：

There's few ways to achieve that. The best way to achieve that is to create Interface[^]. It depends on what you want to achieve.

More:
Walkthrough: Creating and Implementing Interfaces (Visual Basic)[^]
Choosing Between Classes and Interfaces[^]
Creating Classes in Visual Basic .NET[^]


On the second look...
The definition of New_Yellow_Ball_Competition class is wrong:

Public YBResultsTable As DataTable = New DataTable()
Private Sub ResultsTable()

在第一行中，您已声明公共成员 YBResultsTable 类型 DataTable ，但它从未正确启动（它确实不包含任何列）。您应该在类构造函数（ Public Sub New（））中调用 ResultsTable 过程来添加列。



还有其他一些可能的错误。

In the first line you have declared public member YBResultsTable type of DataTable, but it has been never properly initiated (it does contain none columns). You should call ResultsTable procedure in class constructor (Public Sub New()) to add columns.

There's few other possible errors.

关于这个问题，你至少有两个选择，你可以在一个模块中声明数据表，以便它是可见的，或者您可以将New_Yellow_Ball_Competition类的现有实例传递给MainMenu类。如果在程序中广泛使用单个数据表，则使用模块是有意义的，请参阅模块声明 [ ^ ]和类与模块 [ ^ ]。



其他一些观察结果：

- 您似乎只有一个包含数据的表，请考虑规范化以实现易于维护的数据结构，请参阅数据库规范化 - 维基百科，免费的百科全书 [ ^ ]

- 如果规范化数据并最终使用多个数据les，使用单个数据集来保存所有数据表。

- 为什么选择CSV？数据表本身支持读取和写入XML格式的数据，请参阅 DataTable.WriteXml方法（字符串）（System.Data） [ ^ ]

Concerning the question, you have at least two choices, you can declare the datatable in a module in order for it to be visible or you can pass an existing instance of the New_Yellow_Ball_Competition class to MainMenu class. If the single datatable is used widely in the program, it would make sense to use a module, see Module Statement[^] and Classes vs. Modules[^].

Some other observations:
- You seem to have only one table containing the data, consider normalization to achieve an easily maintainable data structure, see Database normalization - Wikipedia, the free encyclopedia[^]
- If you normalize the data and end up using several datatables, use a single dataset to hold all the data tables.
- Why CSV? data table natively supports reading and writing XML formatted data, see DataTable.WriteXml Method (String) (System.Data)[^]

通过阅读互联网上的一些注释解决了这个问题。我需要包含声明DataTable的类名。所以

Solved the problem by reading some notes on the internet. I need to include the class name that the DataTable is declared in. So

Rfc4180Writer.WriteDataTable(YBResultsTable, writer, True)

变为

becomes

Rfc4180Writer.WriteDataTable(New_Yellow_Ball_Competition.YBResultsTable, writer, True)

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