I have over 9,00,000 records in my Access database but only a fraction of that is being displayed in the listbox. How Many Rows Can A Listbox Hold? Around 65K is the answer I got from my research.
Thanks!
There is a bug in the native listbox control that was introduced at Vista time and is still present in Win7. It prevents you from scrolling properly past 65536 + number of visible items. The most visible part of the bug, beyond not seeing the later items, is the scrollbar thumb jumping back when you drag it to the bottom.
This bug doesn't get put to the test very often. Nobody ever expects his user to have enough patience to claw through tens of thousands of items. Such a program gets uninstalled quickly. ListBox capacity is otherwise only limited by the amount of available virtual memory. If you really want to pursue this then use ListView or DataGridView.
I'm not sure what the exact limit is (The url provided below gives some suggestions) I think the number of items you want to populate the listbox with will probably slow your computer down alot if it's populating it with that many records.
Maybe you should consider using a different control that allows paging like a DataGrid or something similar to display 100 results at a time?
This link might be useful to you: http://codeguru.earthweb.com/forum/showthread.php?p=1715288
Creating datagrid with paging: http://support.microsoft.com/kb/305271
I've found it preferable to use DataGridView over ListBox in winforms. The key is to use VirtualMode. I'd derive from DataGridView similar to:
class CustomDgv : DataGridView {
public CustomDgv() {
this.BackgroundColor = SystemColors.Window;
this.BorderStyle = BorderStyle.None;
this.Dock = DockStyle.Fill;
this.MultiSelect = false;
this.AutoGenerateColumns = false;
this.RowHeadersVisible = this.AllowUserToResizeRows = false;
this.ReadOnly = true;
this.AllowUserToAddRows = this.AllowUserToDeleteRows = false;
this.CellBorderStyle = DataGridViewCellBorderStyle.None;
this.VirtualMode = true;
this.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
this.RowTemplate.Height = this.FontHeight + this.FontHeight / 2;
}
}
and then implement the virtual part accordingly.
Related
I have successfully found an answer to every question I ever had since I started with VB.NET 2 years ago by trawling forums, but this time I failed, and I decided to join my favourite forum where I have always found the best answers. This one :-)
I am somewhat of a beginner, so load you flack-guns 'cause here we go...
In my main form I have a DGV (called "gridDisplay") to display data. This DGV is a read only one as it is only used to disply data, not to inteact with it.
I have any number copies of a class (called "TaskData") that holds data to be displayed, and the data to be shown in the main form is that of the active "TaskData" class.
I came up with the brilliant (I have my doubts now...) idea to let the TaskData class make a DGV as it knows what data is in it and how to display it, and then all I had to do in the main form was to set the DGV there to that of the Active TaskData Class (see code below)
With ActiveTask
'Assign the active DataDisplay to the one in the main form
Me.gridDisplay = .TaskData.DataDisplay
Me.gridDisplay.RowHeadersWidthSizeMode = DataGridViewRowHeadersWidthSizeMode.AutoSizeToAllHeaders
Me.gridDisplay.Refresh() 'Trying to make it update
Me.gridDisplay.Update() 'Trying to make it update
MsgBox("Row count: " & Me.gridDisplay.RowCount)
End With
Ok, so the DGV in the .TaskData.DataDisplay has one column and 500 rows. The One in the main form is set up with a default of 2 columns and no rows (set up in the designer)
After the code above, nothing happens visually in the main form. Still 2 columns and 0 rows. However, the text box says: "Row count: 500" And if I put a break point there I can inspect Me.gridDisplay and it has all the data that should be there.
Why doesn't it show up?
Am I doing something unwise by assigning one DGV to another?
Any help would be much appreciated.
Any constructive critizism equally so :-)
I think you should call the datasource again before
Me.gridDisplay.Refresh()Me.gridDisplay.Update()
Something like this,
gridDisplay.DataSource = dataset.Tables["your table"];
I am upgrading user control from vb6 to vb.net.
In the vb6 application I am loading 3000 labels using a label control array.
In vb.net I am doing same but it's taking too much time to load.
In vb6 it's taking 1-2 seconds, but in vb.net it's taking 30-40 seconds for same work.
What is problem? Why does it take too much time in vb.net for same work?
Code is given below, here Led is the label control array.
For l = 1 To 3000
Led.Load(ledCounter)
ColLed.Add(Led(ledCounter))
Led(ledCounter).BackColor = System.Drawing.ColorTranslator.FromOle(LedColor)
Led(ledCounter).Top = VB6.TwipsToPixelsY(15)
Led(ledCounter).Left = VB6.TwipsToPixelsX(15)
Led(ledCounter).Height = VB6.TwipsToPixelsY(LedHeight)
Led(ledCounter).Width = VB6.TwipsToPixelsX(LedWidth)
Led(ledCounter).BorderStyle = Windows.Forms.BorderStyle.None
Led(ledCounter).BackColor = System.Drawing.ColorTranslator.FromOle(LedColor)
Led(ledCounter).Visible = True
Next
In VB6, a label is a windowless (lightweight) control. It doesn't have a window handle and therefore does not exist as far as the OS is concerned. The code behind this control just checks where the mouse is and does some drawing on the parent control.
In VB.NET, however, a label is a full-fledged control that has a window handle and therefore "exists." Creating several thousands of these is a bad idea, because number of available window handles is limited (and because it's slow).
You should revise your design and consider using a grid of some sort.
I have over 9,00,000 records in my Access database but only a fraction of that is being displayed in the listbox. How Many Rows Can A Listbox Hold? Around 65K is the answer I got from my research.
Thanks!
There is a bug in the native listbox control that was introduced at Vista time and is still present in Win7. It prevents you from scrolling properly past 65536 + number of visible items. The most visible part of the bug, beyond not seeing the later items, is the scrollbar thumb jumping back when you drag it to the bottom.
This bug doesn't get put to the test very often. Nobody ever expects his user to have enough patience to claw through tens of thousands of items. Such a program gets uninstalled quickly. ListBox capacity is otherwise only limited by the amount of available virtual memory. If you really want to pursue this then use ListView or DataGridView.
I'm not sure what the exact limit is (The url provided below gives some suggestions) I think the number of items you want to populate the listbox with will probably slow your computer down alot if it's populating it with that many records.
Maybe you should consider using a different control that allows paging like a DataGrid or something similar to display 100 results at a time?
This link might be useful to you: http://codeguru.earthweb.com/forum/showthread.php?p=1715288
Creating datagrid with paging: http://support.microsoft.com/kb/305271
I've found it preferable to use DataGridView over ListBox in winforms. The key is to use VirtualMode. I'd derive from DataGridView similar to:
class CustomDgv : DataGridView {
public CustomDgv() {
this.BackgroundColor = SystemColors.Window;
this.BorderStyle = BorderStyle.None;
this.Dock = DockStyle.Fill;
this.MultiSelect = false;
this.AutoGenerateColumns = false;
this.RowHeadersVisible = this.AllowUserToResizeRows = false;
this.ReadOnly = true;
this.AllowUserToAddRows = this.AllowUserToDeleteRows = false;
this.CellBorderStyle = DataGridViewCellBorderStyle.None;
this.VirtualMode = true;
this.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
this.RowTemplate.Height = this.FontHeight + this.FontHeight / 2;
}
}
and then implement the virtual part accordingly.
I know that the data grid isn't designed to directly access each row. My problem is I need to highlight rows based on certain conditions but not just at loading time. After the grid has been loaded there can be changes that occur on a collection that is not the collection that the grid is populated from so changes to this collection obviously won't affect the grid.
Sample Data Diagram:
[GridCollection] [SecondaryCollection]
{ID = 0, Name = "Test A"} {ID = 0, GridCollectionID = 0, Name = "Test A Linked"}
{ID = 1, Name = "Test B"}
So in this case GridCollection item 0 would be highlighted in the grid. But if I add another item to the SecondaryCollection this item would be should highlighted in the grid.
Now I can force an update to the grid's ItemsSource but this seems hacky. Anyone got any ideas on how to approach this issue?
This would be really easy to achieve by using Prism's EventAggregator:
Make sure the items in GridCollection implement INotifyPropertyChanged
Add a boolean IsHighlight property to the class of items in GridCollection
When an item is added to SecondaryCollection, fire an event using the event aggregator, using the GridCollectionID as payload.
Subscribe to this event on GridCollection and set IsHighlight to true.
On the DataGrid, set your conditional format to be on when IsHighlight is true.
This methodology is decoupled and robust and it let's you make the highlight look as you want and change any time, even using animations.
Am I going mad/blind? Probably a combination of the two.
How does one go about removing the data labels from a pie chart with the new chart control in .net 4?
I can get these to display as tooltips absolutely fine, but ultiamtely I'd like the labels not to be present as it looks rather busy.
I've searched previous answers and seen code behind resolutions but surely there must be some sort of code infront option to turn these labels off?
Apologies for being thick/blind.
EstadoPie2.Series("EstadoSummarySeries")("PieLabelStyle") = "Disabled"
This worked for me.
for (var i = 0; i < Chart.Series.Count; i++)
{
Chart.Series[i]["PieLabelStyle"] = "Disabled";
}