在 VB.NET 中动态添加的事件处理程序未触发

Question

由于某种原因，当我单击“删除”按钮时，没有任何反应。我假设这与视图状态和在页面加载时丢失处理程序有关，尽管我仍然无法理解它。每次页面加载时我都在重新创建处理程序，为什么这不起作用？

Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load

    If IsPostBack Then
        If Not IsNothing(fileUpload.PostedFile) AndAlso fileUpload.PostedFile.ContentLength > 0 Then
            _files = TryCast(Session("FilesToSend"), List(Of document))
            _files.Add(New Document(fileUpload.FileName, fileUpload.FileBytes, fileUpload.FileBytes.Length))
            loadTable()
        End If
    Else
        Session("FilesToSend") = New List(Of document)
    End If

End Sub

Private Sub loadTable()

    Dim count As Integer = 0
    For Each doc In _files
        Dim r As New TableRow()

        'Add Filename Cell
        Dim filenameCell As New TableCell()
        filenameCell.Text = doc.filename
        r.Cells.Add(filenameCell)

        'Add Size Cell
        Dim sizeCell As New TableCell()
        sizeCell.Text = doc.fileSize
        r.Cells.Add(filenameCell)

        'Add Remove Button Cell
        Dim deleteButton As New Button
        Dim deleteCell As New TableCell()
        With deleteButton
            .Text = "Remove"
            '.ID = "deleteButton" + count.ToString()
            deleteCell.Controls.Add(deleteButton)
            AddHandler deleteButton.Click, AddressOf deleteRow_Click
        End With
        r.Cells.Add(deleteCell)
        'AddHandler deleteButton.Click, New EventHandler(AddressOf deleteRow_Click)

        'Add Row to Table
        uploadedDocumentsTable.Rows.Add(r)

        count += 1
    Next
End Sub

Protected Sub deleteRow_Click(sender As Object, e As System.EventArgs)
    _files = TryCast(Session("FilesToSend"), List(Of Document))
    Dim deleteButton = TryCast(sender, Button)
    _files.RemoveAt(sender.ID)
    loadTable()
End Sub

Answer 1

经过多次反复试验，我终于弄明白了。所以第一个问题是我需要添加“.CausesValidation = False”。这触发了回发，但随后我需要重新安排以确保控件仍在加载。这是有效的：

Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load

    If IsPostBack Then
        _files = TryCast(Session("FilesToSend"), List(Of Document))
        If Not IsNothing(fileUpload.PostedFile) AndAlso fileUpload.PostedFile.ContentLength > 0 Then
            _files.Add(New Document(fileUpload.FileName, fileUpload.FileBytes, fileUpload.FileBytes.Length))
        End If
    Else
        Session("FilesToSend") = New List(Of document)
    End If
    loadTable()

End Sub

Private Sub loadTable()
    uploadedDocumentsTable.Rows.Clear()
    Dim count As Integer = 0
    For Each doc In _files
        Dim r As New TableRow()

        'Add Filename Cell
        Dim filenameCell As New TableCell()
        filenameCell.Text = doc.filename
        r.Cells.Add(filenameCell)

        'Add Size Cell
        Dim sizeCell As New TableCell()
        sizeCell.Text = doc.fileSize
        r.Cells.Add(filenameCell)

        'Add Remove Button Cell
        Dim deleteButton As New Button
        Dim deleteCell As New TableCell()
        With deleteButton
            .Text = "Remove"
            .CausesValidation = False
            .ID = count.ToString()
            deleteCell.Controls.Add(deleteButton)
            AddHandler deleteButton.Click, AddressOf deleteRow_Click
        End With
        r.Cells.Add(deleteCell)

        'Add Row to Table
        uploadedDocumentsTable.Rows.Add(r)

        count += 1
    Next
End Sub

Protected Sub deleteRow_Click(sender As Object, e As System.EventArgs)
    _files.RemoveAt(sender.ID)
    loadTable()
End Sub

Answer 2

您忘记将按钮添加到表单。这样修改：

'Add Remove Button Cell
    Dim deleteButton As New Button
    Dim deleteCell As New TableCell()
    With deleteButton
        .Text = "Remove"
        '.ID = "deleteButton" + count.ToString()
        deleteCell.Controls.Add(deleteButton)
        AddHandler deleteButton.Click, AddressOf deleteRow_Click
    End With
    Me.Controls.Add(deleteButton)

惊喜，您的按钮现在位于位置 (0, 0)，并且现在可以监听事件。我猜你可能也想修改它的位置。

玩得开心！