I want to create datatable array dynamically. according to i number, a table from datagridview will be saved to a datatable (like table1, table2 table3 etc). At another form, if user writes the i number to textbox, datagridview will be filled using the right table (table1, table2...)
But if I declare table(i) as new datatable, I get "Arrays cannot be declared with 'New'" error
If I declare table(i) as datatable, I get "system.nullreferenceexception object reference not set to an instance of an object" error while adding columns
Sub add newtable()
Dim i As Integer = TextBox1.Text
Dim table(i) As New DataTable '!
With table(i).Columns
.Add("sample1", Type.GetType("System.String"))
.Add("sample2", Type.GetType("System.String"))
End With
table(i).Rows.Add("a", "b")
table(i).Rows.Add("c", "d")
End sub
then
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
DataGridView1.DataSource = table(i)
End Sub
First, now and forever, turn on Option Strict. Project Properties -> Compile tab. Also for future projects Tools -> Options -> Projects and Solutions -> VB Defaults
A DataSet is made to hold DataTables. A List(Of DataTable) might be easier to use because you wouldn't have to keep track of the index. If you really need an array then declare it at the Class level. I like to use the plural for names of collections.
Private tables As DataTable()
Sub addnewtable()
Dim i As Integer = CInt(TextBox1.Text)
tables(i) = New DataTable
With tables(i).Columns
.Add("sample1", Type.GetType("System.String"))
.Add("sample2", Type.GetType("System.String"))
End With
tables(i).Rows.Add("a", "b")
tables(i).Rows.Add("c", "d")
End Sub
Related
I have a DataGridView that is bound to a datatable with hundred of rows, the database is a simple flatfile database written to a txt file. Whenever I scroll to the bottom the DGV starts stuttering. I am thinking of solutions but cannot find a way to code them
Here are my proposed solution:
Use Paging to lessen the numbers of row being rendered. Here's is a similar solution but they are using sql
Using doublebuffer which I've never touched before. I've tried doing DGV.doublebuffer = true but it said DGV is protected
Any help or clarification on my problem are greatly appreciated
Edit: Here is a GIF of how my DGV is stutteting
The Datatable is named Tbl_Sample
Here is how I insert rows of data into data table. It gets data using System.IO on the Flatfile database(.txt file), split each line then send it to InputTbl as a row
Public Sub Update_Table(InputTbl As DataTable, InputFile As String)
InputTbl.Rows.Clear()
Dim lines() As String
Dim vals() As String
lines = File.ReadAllLines(InputFile)
For i = 0 To lines.Length - 1
vals = lines(i).ToString().Split("|")
Dim row(vals.Length - 1) As String
For j = 0 To vals.Length - 1
row(j) = vals(j).Trim()
Next j
InputTbl.Rows.Add(row)
Next i
End Sub
I set the table as Data Source for the DGV by DGV.DataSource = Tbl_Sample
The Datatable is created as Follow
Public Sub Sample_Table()
'Method For creating database file
Create_DBFile("Sample.db")
Try
Tbl_Sample.Columns.Add("ID", Type.GetType("System.Int32"))
Tbl_Sample.Columns.Add("Name", Type.GetType("System.String"))
Tbl_Sample.Columns.Add("Username", Type.GetType("System.String"))
Tbl_Sample.Columns.Add("Account_Type", Type.GetType("System.String"))
Tbl_Sample.Columns.Add("Date", Type.GetType("System.String"))
Tbl_Sample.Columns.Add("Time", Type.GetType("System.String"))
Catch ex As Exception
End Try
Update_Table(Tbl_Sample, "Sample.db") 'populate table
End Sub
The way I create columns is not the best. I just copied it from my old program
Solution link here
Imports System.Reflection
Public Sub EnableDoubleBuffered(ByVal dgv As DataGridView)
Dim dgvType As Type = dgv.[GetType]()
Dim pi As PropertyInfo = dgvType.GetProperty("DoubleBuffered", _
BindingFlags.Instance Or BindingFlags.NonPublic)
pi.SetValue(dgv, True, Nothing)
End Sub
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
EnableDoubleBuffered(MyDataGridView, True)
End Sub
I have two Comboboxes with Master Detail Relationship Table Bank and Branch
My VB code behind:-
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Using con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\New\Test.accdb")
Using cmd As New OleDbCommand("Select Bank, ID from Bank", con)
Dim da As New OleDbDataAdapter(cmd)
Dim dt As New DataTable
da.Fill(dt)
ComboBox1.DataSource = dt
ComboBox1.DisplayMember = "Bank"
ComboBox1.ValueMember = "ID"
ComboBox1.Text = "Select"
End Using
End Using
End Sub
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
Dim bankId = ComboBox1.SelectedValue.ToString
Using con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\New\Test.accdb")
Using branch_cmd As New OleDbCommand("Select Branch from Branch where Bank_id ='" & bankId & "'", con)
Dim da As New OleDbDataAdapter(branch_cmd)
Dim dt As New DataTable
da.Fill(dt)
ComboBox2.DataSource = dt
ComboBox2.DisplayMember = "Bank"
ComboBox2.ValueMember = "ID"
End Using
End Using
End Sub
End Class
I want to populate in second combo box based on first combobox selected value, but the code got error on
ComboBox1_SelectedIndexChanged function:
And, from debugging the branch_cmd sql is:
Select Branch from Branch where Bank_id ='System.Data.DataRowView'
EDIT:
I was about to add a note and then I realised that this note is actually the solution to your actual problem. You are setting the DataSource first and then the DisplayMember and ValueMember afterwards. That is wrong and the reason for your issue. When you set the DataSource you have done the binding, so everything happens then and there. The first item in the list is selected so your SelectedIndexChanged handler is executed. You haven't set the DisplayMember or ValueMember yet, so the SelectedValue won't return the appropriate value. ALWAYS set the DataSource last, as I have done in my example below.
ORIGINAL:
Unless you have a large amount of data, you should just get all the data from both tables upfront, bind the data and then let the binding take care of the filtering automatically. You do that using BindingSources and binding the child to a DataRelation rather than a DataTable. Behold!
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim parentTable = GetParentTable()
Dim childTable = GetChildTable()
Dim data As New DataSet
'Create a foreign key relation between the tables.
data.Tables.Add(parentTable)
data.Tables.Add(childTable)
data.Relations.Add("ParentChild", parentTable.Columns("ParentId"), childTable.Columns("ParentId"))
'Bind the parent BindingSource to the parent table.
parentBindingSource.DataMember = "Parent"
parentBindingSource.DataSource = data
'Bind the child BindingSource to the relation.
childBindingSource.DataMember = "ParentChild"
childBindingSource.DataSource = parentBindingSource
parentComboBox.DisplayMember = "ParentName"
parentComboBox.ValueMember = "ParentId"
parentComboBox.DataSource = parentBindingSource
childComboBox.DisplayMember = "ChildName"
childComboBox.ValueMember = "ChildId"
childComboBox.DataSource = childBindingSource
End Sub
Private Function GetParentTable() As DataTable
Dim table As New DataTable("Parent")
table.PrimaryKey = {table.Columns.Add("ParentId", GetType(Integer))}
table.Columns.Add("ParentName", GetType(String))
table.Rows.Add(1, "Parent 1")
table.Rows.Add(2, "Parent 2")
table.Rows.Add(3, "Parent 3")
Return table
End Function
Private Function GetChildTable() As DataTable
Dim table As New DataTable("Child")
table.PrimaryKey = {table.Columns.Add("ChildId", GetType(Integer))}
table.Columns.Add("ChildName", GetType(String))
table.Columns.Add("ParentId", GetType(Integer))
table.Rows.Add(1, "Child 1.1", 1)
table.Rows.Add(2, "Child 1.2", 1)
table.Rows.Add(3, "Child 1.3", 1)
table.Rows.Add(4, "Child 2.1", 2)
table.Rows.Add(5, "Child 2.2", 2)
table.Rows.Add(6, "Child 2.3", 2)
table.Rows.Add(7, "Child 3.1", 3)
table.Rows.Add(8, "Child 3.2", 3)
table.Rows.Add(9, "Child 3.3", 3)
Return table
End Function
If you do that, selecting a parent will automatically filter the children displayed for selection.
In case it's not obvious, you would get the parent and child tables by querying a database rather than building them manually, as I have done in my example.
As it stands now I can see two errors. First, do not concatenate strings to build sql command texts. Use always a parameterized query, specifying exactly what is the datatype of the parameter that you are passing. Second error is in the DisplayMember and ValueMember for the second combo. You don't have here a Bank_Id or a Bank name but the Branch name
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
' Always check if you have a valid selection to avoid NRE.
if ComboBox1.SelectedValue Is Nothing Then
Return
End if
' If bankid is an integer then convert to an integer
Dim bankId as Integer = Convert.ToInt32(ComboBox1.SelectedValue)
Using con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\New\Test.accdb")
Using branch_cmd As New OleDbCommand("Select Branch from Branch where Bank_id =#id", con)
cmd.Parameters.Add("#id", OleDbType.Integer).Value = bankId
Dim da As New OleDbDataAdapter(branch_cmd)
Dim dt As New DataTable
da.Fill(dt)
ComboBox2.DataSource = dt
ComboBox2.DisplayMember = "Branch"
ComboBox2.ValueMember = "Branch"
End Using
End Using
End Sub
According to your comment below you get a System.Data.DataRowView as the element contained in the SelectedValue. This should not happen with the code shown in your question, so perhaps, there is something different that creates the problem. (For example, if the datatable fields names don't match with the ValueMember/DisplayMember properties)
In any case, from a DataRowView, you should be able to get the integer in this way
Dim drv = DirectCast(ComboBox1.SelectedValue, DataRowView)
if drv IsNot Nothing then
Dim bankid = Convert.ToInt32(drv("ID"))
...
End if
VB2010 I have created a DataTable manually so it does not come from a database. I have assigned it to a combobox and it displays my column of data. If I change the DataTable do I have to re-establish the link?
'assign first table
dt = GetFirstTable()
cbo.DataSource = dt
cbo.DisplayMember = "Time"
cbo.ValueMember = "Time"
'print out items in combobox
'assign second table
dt = GetSecondTable()
'cbo.DataSource = dt 'do i have to re-connect here?
'print out items in combobox
It seems if I do not re-establish the link I get the same items. I though since the cbo was already linked to the dt variable i didn't need to re-link it each time. Is that how that works or am I doing something wrong here?
When you assign cbo.DataSource = dt, and you then recreate dt, cbo.DataSource will keep pointing to the old table. This is pure pointer logic working here, same principle applies to all .NET code. It does not mean anything that you are re-using the same variable. You could have instead created dt2 and used that, behavior would be the same. So yes, if you recreate the DataTable, you need to reassign DataSource again. However, if you change the original dt, i.e. add rows, those will appear, so you will not need to reassign DataSource. Here is a code sample, to illustrate the approach:
Dim _dt As DataTable
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
_dt = New DataTable
With _dt.Columns
.Add("key")
.Add("value")
End With
With ComboBox1
.DisplayMember = "value"
.ValueMember = "key"
.DataSource = _dt
End With
End Sub
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
_dt.Rows.Add({"item_key", "item_value"})
End Sub
This is so simple, I must be stupid!
I have a simple access database that a log record gets written to a few times an hour.
I'm trying to make a DataGridView that shows that data as it arrives.
My "Solution" is simple;
when a user clicks the view -> read from the database (fill the datatable) -> update the view.
Not what I dreamed of, but functional, if totally sub-optimal.
However, my "solution" is a dud, using fill draws every single record from the database, even if there are already 599 on screen.
Really, I just want fill the datatable once, and add new records as they arrive (or on click if needs be).
Bonus point if you can also explain another way (that isn't called so often) to hide the ID column, and change the header of column 1 (named DateTimeStamp) to TimeStamp.
Public Class FormMain
Shared dataAdapter As OleDbDataAdapter
Shared logTable As New DataTable("log")
Shared commandBuilder As OleDbCommandBuilder
Shared queryString As String = "SELECT * FROM log"
Shared bindingSource As New BindingSource
Private Sub FormServerBridge_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Try
ConfigureDataSet()
ConfigureBindingSource()
ConfigureDataView()
Catch ex As Exception
' FIXME: Helpful for debugging purposes but awful for the end-user.
MessageBox.Show(ex.Message)
End Try
End Sub
Private Sub ConfigureDataSet()
dataAdapter = New OleDbDataAdapter(queryString, _Config.ConnectionString)
commandBuilder = New OleDbCommandBuilder(dataAdapter)
commandBuilder.GetUpdateCommand()
dataAdapter.Fill(logTable)
With logTable
.Locale = System.Globalization.CultureInfo.InvariantCulture
.PrimaryKey = New DataColumn() {logTable.Columns("ID")}
End With
End Sub
Private Sub ConfigureBindingSource()
With bindingSource
.DataSource = logTable
End With
End Sub
Private Sub ConfigureDataView()
With DataGridView
.DataSource = bindingSource
End With
End Sub
Private Sub DataGridView_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGridView.Click
UpdateUI()
End Sub
Sub UpdateUI()
dataAdapter.Fill(logTable)
End Sub
Private Sub DataGridView_DataBindingComplete(ByVal sender As Object, ByVal e As DataGridViewBindingCompleteEventArgs) Handles DataGridView.DataBindingComplete
' FIXME: This code gets run as many times as there are rows after dataAdapter.Fill!
With DataGridView
.Columns("ID").Visible = False
.Columns(1).HeaderText = "Timestamp"
.Columns(1).AutoSizeMode = DataGridViewAutoSizeColumnMode.AllCells
.Columns(2).AutoSizeMode = DataGridViewAutoSizeColumnMode.AllCells
.Columns(3).AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill
End With
End Sub
End Class
p.s. Links to websites and books will be appreciated, even the right MSDN page (if you know where it is, I admit I find it uncomfortable to peruse, I regularly get lost).
Assuming your IDs are sequential, the way I would approach this is:
1) Record the last id that you retrieved
2) When the user presses view, only get records whose IDs are greater than the last one record
3) Retrieve the records into a new datatable and then merge that with your existing data set.
Here is how I would make the changes (only changed info included):
Public Class FormMain
Shared logTable As DataTable
Shared bindingSource As New BindingSource
Private m_wLastID As Integer
Private Sub FormServerBridge_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
Try
ConfigureDataSet()
ConfigureBindingSource()
ConfigureDataView()
Catch ex As Exception
' FIXME: Helpful for debugging purposes but awful for the end-user.
MessageBox.Show(ex.Message)
End Try
End Sub
Private Sub ConfigureDataSet()
Dim queryString As String
queryString = "SELECT * FROM log WHERE ID > " & m_wLastID.ToString & " ORDER BY ID"
Using dataAdapter As New OleDbDataAdapter(queryString, _Config.ConnectionString)
Using commandBuilder As New OleDbCommandBuilder(dataAdapter)
Dim oDataTable As New DataTable("log")
commandBuilder.GetUpdateCommand()
dataAdapter.Fill(oDataTable)
With oDataTable
.Locale = System.Globalization.CultureInfo.InvariantCulture
.PrimaryKey = New DataColumn() {.Columns("ID")}
End With
' Record the last id
If oDataTable.Rows.Count <> 0 Then
m_wLastID = CInt(oDataTable.Rows(oDataTable.Rows.Count - 1)("ID"))
End If
If logTable Is Nothing Then
logTable = oDataTable
Else
logTable.Merge(oDataTable, True)
logTable.AcceptChanges()
End If
End Using
End Using
End Sub
Sub UpdateUI()
ConfigureDataSet()
End Sub
' Rest of the form code here
I face a stupid problem here. Cannot find an error and do not really know how to fix this.
I'm adding an item into datatable on selected index changed. Everything works, except only the last item is shown in dt. I always has the latest item and all others are gone. i suppose this is because I initialize it in the wrong place but still cannot find a solution.
Dim dt As DataTable = New DataTable()
Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Page.Load
dt.Columns.Add("dr1")
dt.Columns.Add("dr2")
End Sub
Protected Sub ddlTest_SelectedIndexChanged(sender As Object, e As System.EventArgs) Handles ddlTest.SelectedIndexChanged
Dim row As DataRow = dt.NewRow()
row(0) = "Test!"
row(1) ="Test"
dt.Rows.Add(row)
End If
End Sub
This always shows only last item in list. How do I do this correct way?
Unless I am mistaken, you create a new DataTable every time a user hits the page.
You need to persist the row to a real database or perhaps make your DataTable shared (static in C#) instead.
Shared dt As DataTable = New DataTable()