asked on

Object reference not set to an instance of object error in vb.net

Hello,

I'm using below code but i got an error as i wrote on title.

I'm pretty sure it causing from this section where i am finding tab control and try to color it's child datagridviews cell.

Any help would be grateful. I dont understand why it can't find control.

                    Check.StyleOutputDataGridView(CType(GUI.Controls.Find(tabName, True).FirstOrDefault, TabPage))

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It can't find object wi

Full Code Block:

        Public Shared Sub MeasureForceMarker()
            Try
                Dim forceList As List(Of IScrForce) = ModelBase.GetForceList(CType(Base.Model, IScrModelBase), True)
                Dim tabCtrl As TabControl = CType(GUI.Controls.Find("tcCheckForceOut", True).FirstOrDefault, TabControl)

                If forceList.Count > 0 Then
                    Dim tabName As String = "tpCheckForceOutMeas"
                    Dim dgvName As String = "dgvCheckForceOutMeas"

                    If Check.CheckTabPage(tabCtrl, tabName) = False Then
                        Dim tabpage As New TabPage With {
                            .Name = tabName,
                            .Text = "Measurements"
                            }

                        Dim dgv As New DataGridView With {
                            .Dock = DockStyle.Fill,
                            .Name = dgvName,
                            .AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.None,
                            .AllowUserToResizeColumns = True,
                            .AllowUserToResizeRows = True,
                            .ColumnHeadersHeightSizeMode = DataGridViewColumnHeadersHeightSizeMode.AutoSize,
                            .AllowUserToAddRows = False,
                            .RowHeadersVisible = False,
                            .[ReadOnly] = False
                            }

                        Dim colClass As New DataGridViewTextBoxColumn With {
                          .[ReadOnly] = True, .HeaderText = "Class", .Frozen = True
                        }
                        Dim colName As New DataGridViewTextBoxColumn With {
                         .[ReadOnly] = True, .HeaderText = "Name", .Frozen = True
                        }
                        Dim colDistX As New DataGridViewTextBoxColumn With {
                         .[ReadOnly] = True, .HeaderText = "Dist. x [m]", .Tag = "m"
                        }
                        Dim colDistY As New DataGridViewTextBoxColumn With {
                         .[ReadOnly] = True, .HeaderText = "Dist. y [m]", .Tag = "m"
                        }
                        Dim colDistZ As New DataGridViewTextBoxColumn With {
                         .[ReadOnly] = True, .HeaderText = "Dist. z [m]", .Tag = "m"
                        }
                        Dim colDistM As New DataGridViewTextBoxColumn With {
                         .[ReadOnly] = True, .HeaderText = "Dist. mag. [m]", .Tag = "m"
                        }
                        Dim colAngAl As New DataGridViewTextBoxColumn With {
                         .[ReadOnly] = True, .HeaderText = "Ang. al [rad]", .Tag = "rad"
                        }
                        Dim colAngBe As New DataGridViewTextBoxColumn With {
                         .[ReadOnly] = True, .HeaderText = "Ang. be [rad]", .Tag = "rad"
                        }
                        Dim colAngGa As New DataGridViewTextBoxColumn With {
                         .[ReadOnly] = True, .HeaderText = "Ang. ga [rad]", .Tag = "rad"
                        }
                        dgv.Columns.Add(colClass)
                        dgv.Columns.Add(colName)
                        dgv.Columns.Add(colDistX)
                        dgv.Columns.Add(colDistY)
                        dgv.Columns.Add(colDistZ)
                        dgv.Columns.Add(colDistM)
                        dgv.Columns.Add(colAngAl)
                        dgv.Columns.Add(colAngBe)
                        dgv.Columns.Add(colAngGa)

                        tabpage.Controls.Add(dgv)

                        tabCtrl.TabPages.Add(tabpage)
                    Else
                        Dim existTp As TabPage = DirectCast(tabCtrl.Controls(tabName), TabPage)
                        Dim existDgv As DataGridView = DirectCast(existTp.Controls(dgvName), DataGridView)
                        existDgv.Rows.Clear()
                    End If

                    For Each force In forceList
                        Dim res() As String = EvalForceMarkerPosition(force)
                        Dim tp As TabPage = DirectCast(tabCtrl.Controls(tabName), TabPage)
                        Dim dgv As DataGridView = DirectCast(tp.Controls(dgvName), DataGridView)
                        dgv.Rows.Add(GetClass(CType(force, ScrNamedObject)), force.name, res(0), res(1), res(2), res(3), res(4), res(5), res(6))
                    Next
                    Check.StyleOutputDataGridView(CType(GUI.Controls.Find(tabName, True).FirstOrDefault, TabPage))
                End If
            Catch ex As Exception
                Tools.OutputLog.Print(Tools.OutputLog.Type.ERR, ex.Message)
            End Try

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ste5an

hmm, when working with objects and collections where you are looking by name, you need always to either ensure that the object exists beforehand or you need to cover the case that is not found. The latter in your case:

TabPage tabPage = GUI.Controls.Find(tabName, True)
If Not tabPage Is Nothing Then
  Check.StyleOutputDataGridView(tabPage)
End If

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btw, .FirstOrDefault is not necessary. Cause a name must be unique in opposite to e.g. a caption or tag.

When you're sure that the control must exist, then you need to inspect your object hierarchy at runtime. Maybe it does exist, but is in a different scope not covered by GUI.Controls.Find(tabName, True).

Skale

ASKER

Hi ste5an,

As you can see on the codeblock i'm using that tab and adding some controls before, and i'm sure it's existing but i don't know why it's not give error for that part.

ASKER CERTIFIED SOLUTION

ste5an

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Skale

ASKER

I'm trying with below code and it gives a message it's exists

        Dim test As TabPage = CType(Controls.Find("tpCheckForceOutMeas", True).Single, TabPage)
        If Not test Is Nothing Then
            MsgBox("Exists!")
        Else
            MsgBox("Not Exists!")
        End If

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I don't understand really.

ste5an

On what hierarchy are you now? In your OP you were on GUI.Controls. Now you're on the active form. Is it the same as GUI?

Skale

ASKER

The problem occurs from a different procedure calling with that now it's solved thank you ste5an.