Visual Basic DataGridView NullReferenceException

Question

我正在处理一个 Windows 窗体项目，并且遇到了其中一个窗体中的一个 DataGridView 对象的问题。这是我目前所拥有的：

Private Sub CustomerUsageForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Me.Tbl_usageTableAdapter1.Fill(Me.ClarityWaterDBMAINDataSet1.tbl_usage)

    Dim con As New OleDb.OleDbConnection
    Dim dbString As String
    Dim ds As New DataSet
    Dim da As OleDb.OleDbDataAdapter
    Dim sql As String

    dbString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\ClarityWaterDBMAIN.accdb"

    con.ConnectionString = dbString
    con.Open()

    sql = "SELECT * FROM tbl_usage"
    da = New OleDb.OleDbDataAdapter(sql, con)
    da.Fill(ds, "tbl_usage")
    con.Close()

然后当表单被激活时，这段代码就会运行：

    Private Sub CustomerUsageForm_Activated(sender As Object, e As EventArgs) Handles MyBase.Activated
    Dim GridInitializedBoolean As Boolean = False

    'Initialize the grid's binding
    If Not GridInitializedBoolean Then
        'bind and format the grid
        DataGridView1.DataSource = BindingSource1

        SetUpGridColumns()

        GridInitializedBoolean = True
    End If
End Sub

Private Sub SetUpGridColumns()
    'sets up the columns for the data grid view
    Try
        With DataGridView1
            .Columns!usage_id.Visible = False
            .Columns!reading_date.HeaderText = "Reading Date"
            .Columns!reading_cf.HeaderText = "Amount Used"
            .Columns!account_id.HeaderText = "Account ID"
        End With
    Catch ex As Exception
        MessageBox.Show("Error Setting up the grid." & ex.Message)
    End Try
End Sub

当我加载表单时，SetUpGridColumns() 方法会抛出 NullReferenceException。我不确定为什么会发生这种情况，我将这个表单设置为与另一个完美运行的表单完全一样：

 Private Sub InventoryForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    'TODO: This line of code loads data into the 'ClarityWaterDBMAINDataSet.tbl_customers' table. You can move, or remove it, as needed.
    Me.Tbl_customersTableAdapter.Fill(Me.ClarityWaterDBMAINDataSet.tbl_customers)

    Dim con As New OleDb.OleDbConnection
    Dim dbString As String
    Dim ds As New DataSet
    Dim da As OleDb.OleDbDataAdapter
    Dim sql As String

    dbString = "Provider=Microsoft.ACE.OLEDB.12.0;DataSource=|DataDirectory|\ClarityWaterDBMAIN.accdb"

    con.ConnectionString = dbString
    con.Open()

    sql = "SELECT * FROM tbl_customers"
    da = New OleDb.OleDbDataAdapter(sql, con)
    da.Fill(ds, "tbl_customers")

    con.Close()
    AccountNumberTextBox.Focus()


    CustomerUsageForm.CustomerUsageForm_Load(sender, e)
    CustomerUsageForm.Hide()
End Sub

那么这就是按钮点击事件上的事件

Private Sub SearchButton_Click(sender As Object, e As EventArgs) Handles SearchButton.Click
    'retrieve the customer search information
    Dim GridInitializedBoolean As Boolean = False

    'initialize the grids binding
    If Not GridInitializedBoolean Then
        'bind and format the grid
        CompanyIDLookupDataGridView.DataSource = CompanyLookupBindingSource

        SetUpGridColumns()

        GridInitializedBoolean = True
    End If

    Try
        CompanyLookupBindingSource.Filter = BuildSearchString()
    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try
End Sub

我很抱歉这么长的帖子。老实说，我不确定还能尝试什么。谁能帮助解释我为什么会遇到这些问题？

编辑：我所说的设置完全相同的意思是，两种形式都具有相同类型的对象，加载事件的编码相同，初始化网格的事件也相同。

如果我注释掉第一个 .Columns！ SetUpGridColumns() 方法中的行，错误将在下一行引发。

Answer 1

据我所见，您似乎在您的列的 with 语句中有一个额外的字符...您也说过...

“我不确定为什么会发生这种情况，我将这个表单设置为与另一个完美运行的表单完全一样”

如果是这样的话，这段代码在哪里，我很想看看这个表单的代码。

   'You have a ! that shouldn't be referenced for your columns...
   With DataGridView1
        .Columns!usage_id.Visible = False
        .Columns!reading_date.HeaderText = "Reading Date"
        .Columns!reading_cf.HeaderText = "Amount Used"
        .Columns!account_id.HeaderText = "Account ID"
   End With

这应该是它的样子......

    With DataGridView1
        .Columns(usage_id).Visible = False
        'And so on for the rest of your columns...
    End With