DataGridView.La colonne(ColumnName comme une Chaîne de caractères) donne une erreur “la référence d'Objet n'est pas définie à une instance d'un objet”

Deux conseils:

1 - Par défaut, les Winforms designer crée un objet dans vos formulaires de Classe pour chaque colonne qui existe dans un DataGridView. Donc, si vous avez une colonne nommée MyIdColumn, par exemple, vous devriez être en mesure d'accéder à la colonne sous la forme d'un code comme ceci:

Me.MyIdColumn.Visible = False

Si vous souhaitez accéder à un élément de la DataGridView, vous pourriez faire quelque chose comme ceci:

Dim value = dgv.Item(MyIdColumn.Index, rowIndex).Value

À l'aide de cette astuce, si le nom de la colonne changements, il n'y a pas de problème parce que vous faites référence à la colonne directement au lieu d'une chaîne de caractères représentant le nom d'une colonne qui pourrait changer.

2 - Votre GetColName méthode pourrait être mieux; je voudrais la transformer en une méthode d'extension:

<System.Runtime.CompilerServices.Extension()> _
Private Function GetColByHeaderText(ByVal dgv As DataGridView, ByVal name As String) As DataGridViewColumn

    For Each col As DataGridViewColumn In dgv.Columns
        If col.HeaderText = name Then
            Return col
        End If
    Next

    Return Nothing

End Function

Utilisation:

dgv.GetColByHeaderText("ID").Visible = False

Beaucoup plus agréable de l'OMI!

OriginalL'auteur Meta-Knight

Public Class Form2
Privé de la liste Comme une Liste(D'une Personne)
Private Sub Form2_Load(ByVal sender as System.Object, ByVal e as System.EventArgs) Handles MyBase.Charge
CreateDGV()
PopulatingDGV()

End Sub
Private Sub CreateDGV()
dataGridView1.AllowUserToAddRows = False
dataGridView1.RowHeadersVisible = False
dataGridView1.Columns.Add("col1", "Column 1")
Dim column2 As DataGridViewComboBoxColumn = CreateComboBoxColumn1()
Dim column3 As DataGridViewComboBoxColumn = CreateComboBoxColumn2()
dataGridView1.Columns.Add(column2)
dataGridView1.Columns.Add(column3)
'adding an event:
'DataGridView1.EditingControlShowing += New DataGridViewEditingControlShowingEventHandler(AddressOf dataGridView1_EditingControlShowing)
'DataGridView1.DataError += New DataGridViewDataErrorEventHandler(AddressOf dataGridView1_DataError)
End Sub
Private Function CreateComboBoxColumn1() As DataGridViewComboBoxColumn
Dim column As New DataGridViewComboBoxColumn()
If True Then
column.Name = "column2"
column.HeaderText = "Column 2"
column.DropDownWidth = 120
column.Width = 120
column.MaxDropDownItems = 3
column.Items.AddRange(New String() {"First name", "Last name", "E-mail"})
column.FlatStyle = FlatStyle.Flat
End If
Return column
End Function
Private Function CreateComboBoxColumn2() As DataGridViewComboBoxColumn
Dim column As New DataGridViewComboBoxColumn()
If True Then
column.Name = "column3"
column.HeaderText = "Column 3"
column.DropDownWidth = 150
column.Width = 150
column.MaxDropDownItems = 3
column.FlatStyle = FlatStyle.Flat
End If
Return column
End Function
Private Sub PopulatingDGV()
'1.ST COLUMN: some test data to populate dgv
Dim companies As String() = {"Indian Info", "Cybex", "Admin"}
For i As Integer = 0 To companies.Length - 1
dataGridView1.Rows.Add(companies(i))
Next
'2.ND COLUMN: creating a generic list (of your data from the file):
'I will not populate it from the file, only invent some example data:
Dim persons As Person() = New Person() {New Person("Monica", "Trotsky", "[email protected]"), New Person("Budh", "sagar", "[email protected]")}
list = New List(Of Person)()
For Each p As Person In persons
list.Add(p)
Next
End Sub
Private Sub DataGridView1_EditingControlShowing(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles DataGridView1.EditingControlShowing
Try
If DataGridView1.CurrentCell.ColumnIndex = 1 Then
Dim combo As ComboBox = TryCast(e.Control, ComboBox)
If combo IsNot Nothing Then
RemoveHandler combo.SelectedIndexChanged, New EventHandler(AddressOf comboBox_SelectedIndexChanged)
AddHandler combo.SelectedIndexChanged, New EventHandler(AddressOf comboBox_SelectedIndexChanged)
End If
End If
Catch ex As Exception
MessageBox.Show("Error:" & vbLf & vbLf & ex.Message)
End Try
End Sub
Private Sub comboBox_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
Try
Dim cb As ComboBox = DirectCast(sender, ComboBox)
Dim selection As String = cb.Text
If selection <> [String].Empty Then
For Each dgvColumn As DataGridViewColumn In dataGridView1.Columns
If dgvColumn.Name = "column3" Then
Dim row As Integer = dataGridView1.CurrentCell.RowIndex
Dim cell As DataGridViewComboBoxCell = DirectCast(dataGridView1(2, row), DataGridViewComboBoxCell)
'cell.Items.Clear();
Select Case selection
Case "First name"
If True Then
cell.DataSource = list
cell.DisplayMember = "firstName"
cell.ValueMember = cell.DisplayMember
Exit Select
End If
Case "Last name"
If True Then
cell.DataSource = list
cell.DisplayMember = "lastName"
cell.ValueMember = cell.DisplayMember
Exit Select
End If
Case "E-mail"
If True Then
cell.DataSource = list
cell.DisplayMember = "eMail"
cell.ValueMember = cell.DisplayMember
Exit Select
End If
End Select
End If
Next
End If
Catch ex As Exception
MessageBox.Show("Error:" & vbLf & vbLf & ex.Message)
End Try
End Sub
Friend Class Person
Public Property firstName() As String
Get
Return m_firstName
End Get
Set(ByVal value As String)
m_firstName = Value
End Set
End Property
Private m_firstName As String
Public Property lastName() As String
Get
Return m_lastName
End Get
Set(ByVal value As String)
m_lastName = Value
End Set
End Property
Private m_lastName As String
Public Property eMail() As String
Get
Return m_eMail
End Get
Set(ByVal value As String)
m_eMail = Value
End Set
End Property
Private m_eMail As String
Public Sub New(ByVal _fn As String, ByVal _ln As String, ByVal _em As String)
firstName = _fn
lastName = _ln
eMail = _em
End Sub
End Class
Private Sub DataGridView1_DataError(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewDataErrorEventArgs) Handles DataGridView1.DataError
If e.Exception IsNot Nothing AndAlso e.Context = DataGridViewDataErrorContexts.Commit Then
MessageBox.Show("CustomerID value must be unique.")
End If
End Sub

Fin De La Classe

OriginalL'auteur budh sagar