Question

我基本上有两种形式，一种名为'frmSettings'，另一种名称'frmXLExternalFile'，'frmXLExternalFile'是从'frmSettings'创建的，在这两种形式之间传递数据，当我使用属性返回它时，它返回为null。香港专业教育学院尝试通过将其设置为公开来返回它，但仍然似乎没有一些奇怪的原因。我设置了断点并跟踪变量（实际上是一个结构），它肯定不是'null'

frmXLExternalFile

    Dim XL_File As frmMain.XLSheetData
Public ReadOnly Property XLFile As frmMain.XLSheetData
        Get
            Return XL_File
        End Get
    End Property

Private Sub frmXLExternalFile_formClosing(sender As Object, e As EventArgs) Handles MyBase.FormClosing
            If txtFilepath.Text <> "" And cmboName.Text <> "" Then
                XL_File = New frmMain.XLSheetData
                XL_File.name = cmboName.Text
                XL_File.filePath = txtFilepath.Text
                frmMain.settings.setXLFile()
                frmMain.settings.cmboXLSheets.Text = txtFilepath.Text
            End If
            frmMain.settings.Enabled = True
        End Sub

frmMain（这是声明结构的地方）

Public Structure XLSheetData
        Dim name As String
        Dim filePath As String
    End Structure

frmSettings

Dim XL_FileList As List(Of frmMain.XLSheetData)

    Sub setXLFile()
        Dim file As frmMain.XLSheetData = frmXLExternalFile.XLFile
        XL_FileList.Add(file)
        cmboXLSheets.Items.Add(file.filePath)
    End Sub

基本上，一旦字段--XL_File - 被填充，顶部表单将这称为底部方法，然后使用属性 - 'XLFile' - 来'获取'对象并将其放在'frmSettings'类中。正如我所说，我已经尝试将'XL_File'设置为public并尝试直接访问它，但抛出相同的异常。它为null，用于填充对象的组合框和文本框不为null。任何帮助，将不胜感激。感谢。

Answer 1

通过传递“所有者”表单，这是使用Show()执行此操作的一种方法：

在frmSettings中：

Dim frmX As New frmXLExternalFile
' ... pass some data to frmX ...
frmX.Show(Me) ' <-- pass this form in as the "Owner"

在frmXLExternalFile中：

Private Sub btnSubmit_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
    If txtFilepath.Text <> "" And cmboName.Text <> "" Then
        XL_File = New frmMain.XLSheetData
        XL_File.name = cmboName.Text
        XL_File.filePath = txtFilepath.Text

        Dim main As frmSettings = DirectCast(Me.Owner, frmSettings) ' <-- use the instance passed in as the owner via Show()
        ' ... use "main" somehow ...
        main.settings.setXLFile()
        main.settings.cmboXLSheets.Text = txtFilepath.Text
        main.settings.Enabled = True
    Else
        ' ... possibly do something else ...
    End If
End Sub

此示例演示了ShowDialog()方法：

在frmSettings中：

Dim frmX As New frmXLExternalFile
' ... pass some data to frmX ...
If frmX.ShowDialog() = Windows.Forms.DialogResult.OK Then ' <-- execution in this Form STOPS until "frmX" is dismissed
    ' Retrieve the value from out "frmX" instance:
    Dim file As frmMain.XLSheetData = frmX.XLFile

    ' ... do something with "file" ...
    XL_FileList.Add(file)
    cmboXLSheets.Items.Add(file.filePath)
    cmboXLSheets.Text = file.filePath
End If

在frmXLExternalFile中：

Private Sub btnSubmit_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
    If txtFilepath.Text <> "" And cmboName.Text <> "" Then
        XL_File = New frmMain.XLSheetData
        XL_File.name = cmboName.Text
        XL_File.filePath = txtFilepath.Text

        ' Set DialogResult, returning execution to the ShowDialog() line:
        Me.DialogResult = Windows.Forms.DialogResult.OK
    Else
        ' ... possibly do something else ...
    End If
End Sub

如果不是，则返回null

1 个答案: