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WinForms (C#) input field with database-driven autocomplete

I am trying to create a text input field with autocomplete functionality. The list of available options is huge (50,000+) and will need to be queried on TextChanged (after the first 3 characters have been entered).
I have a 99%-working solution with TextBox, setting AutoCompleteCustomSource to my new AutoCompleteStringCollection in the TextChanged event, but that results in occasional memory access violations due to a well-documented bug in the underlying AutoComplete implementation...
Microsoft Support say "Do not modify the AutoComplete candidate list dynamically during key events"...
Several SO threads: 1, 2, 3
These threads have some suggestions on how to prevent the exceptions but nothing seems to completely eliminate them, so I'm looking for an alternative. have tried switching to a ComboBox-based solution but can't get it to behave as I want.
After the user types the third character, I update the ComboBox's DataSource but the first item is automatically selected. The user is not able to continue typing the rest of the name.
The ComboBox items are not visible until the user clicks the triangle to expand the list
If the user selects the text they have entered and starts typing, I set DataSource to null to remove the list of suggestions. Doing this puts the cursor at the start of the text, so their characters appear in completely the wrong order!
My View:
public event EventHandler SearchTextChanged;
public event EventHandler InstrumentSelected;
public Instrument CurrentInstrument
{
get { return comboBoxQuickSearch.SelectedItem as Instrument; }
}
public IEnumerable<Instrument> Suggestions
{
get { return comboBoxQuickSearch.DataSource as IEnumerable<Instrument>; }
set
{
comboBoxQuickSearch.DataSource = value;
comboBoxQuickSearch.DisplayMember = "Name";
}
}
public string SearchText
{
get { return comboBoxQuickSearch.Text; }
}
private void comboBoxQuickSearch_TextChanged(object sender, EventArgs e)
{
if (SearchTextChanged != null)
{
SearchTextChanged(sender, e);
}
}
private void comboBoxQuickSearch_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter && InstrumentSelected != null)
{
InstrumentSelected(sender, e);
}
}
My Presenter:
private void SearchTextChanged(object sender, EventArgs e)
{
lock (searchLock)
{
// Do not update list of suggestions if:
// 1) an instrument has already been selected
// (the user may be scrolling through suggestion list)
// 2) a search has taken place within the last MIN_SEARCH_INTERVAL
if (DateTime.Now - quickSearchTimeStamp < minimumSearchInterval
|| (view.Suggestions != null && view.Suggestions.Any(i => i.Name == view.SearchText)))
{
return;
}
string searchText = view.SearchText.Trim();
if (searchText.Length < SEARCH_PREFIX_LENGTH)
{
// Do not show suggestions
view.Suggestions = null;
searchAgain = false;
}
// If the prefix has been entered or changed,
// or another search is needed to display the full sublist
else if (searchText.Length == SEARCH_PREFIX_LENGTH
|| searchText.Substring(0, SEARCH_PREFIX_LENGTH) != searchTextPrefix
|| searchAgain)
{
// Record the current time and prefix
quickSearchTimeStamp = DateTime.Now;
searchTextPrefix = searchText.Substring(0, SEARCH_PREFIX_LENGTH);
// Query matches from DB
IList<Instrument> matches = QueryMatches(searchText);
// Update suggestions
view.Suggestions = matches;
// If a large number of results was received, search again on the next chararacter
// This ensures the full match list is presented
searchAgain = matches.Count() > MAX_RESULTS;
}
}
}
(The searchAgain bit is left over from the TextBox implementation, where the AutoCompleteCustomSource wouldn't always show the complete list if it contained too many items.)
Can I get the ComboBox to work as I want it to, providing suggestions as the user types, given my requirement to query those suggestions on TextChanged?
Is there some other combination of controls I should use for a better user experience, e.g. ListBox?

Way to format Form with dynamic text fields c#

Right, so I have 13 textboxes with corresponding labels that are assigned after a user decides the name from a different form (instantiated by the 'Add field...' button). The issue arises when the user wishes to delete a textbox with previously entered data, as this results in an empty space where the textbox and label originally were as visualized by the following image:
My question is: how do I make it so that when a user chooses to delete a textbox, the textbox-label pair(s) that follow it replace the deleted textbox AND shift the remaining textboxes accordingly.
Textbox-label pairs in designer:
I've thought about this problem intensively over the past few days, and have concluded that with my current knowledge of C# I am limited to solving this issue with a horrendously tedious amount of if-statements (talking hundreds - thousands here). Any and all help would be appreciated!
Current code on the X-button for first textbox-label pair:
private void xButton1_Click(object sender, EventArgs e)
{
label14.Text = "";
textBox1.Text = "";
if (label14.Text.Equals(""))
{
label14.Visible = false;
textBox1.Visible = false;
xButton.Visible = false;
label14.Text = "";
textBox1.Text = "";
}
if (!textBox2.Text.Equals(""))
{
label14.Text = label15.Text;
textBox1.Text = textBox2.Text;
}
if (!textBox2.Text.Equals("") && (textBox3.Text.Equals("")))
{
label15.Visible = false;
textBox2.Text = "";
textBox2.Visible = false;
xButton2.Visible = false;
}
}

One simple thing you could do is give all your "dynamic" controls (label, textbox, button) a similar value in their Tag property (in my example, I used the string "dynamic" for all the control Tags. This enables you to query for them easily.
Next, you could follow the logic that, anytime you delete some controls, you move all controls below the deleted ones up a distance equal to the height of the control being deleted plus whatever padding you have between the controls.
For example, when a user clicks the X button, since you know the value of the Bottom of the control that's being deleted, you could find all controls that had a matching Tag property whose Top is greater than the x button Bottom, and you can move them up.
Here's an example (this assumes that all your X buttons are mapped to this same click event):
private void buttonX_Click(object sender, EventArgs e)
{
// This is represents the distance between the bottom
// of one control to the top of the next control
// Normally it would be defined globally, and used when you
// lay out your controls.
const int controlPadding = 6;
var xButton = sender as Button;
if (xButton == null) return;
var minTopValue = xButton.Bottom;
var distanceToMoveUp = xButton.Height + controlPadding;
// Find all controls that have the Tag and are at the same height as the button
var controlsToDelete = Controls.Cast<Control>().Where(control =>
control.Tag != null &&
control.Tag.ToString() == "dynamic" &&
control.Top == xButton.Top)
.ToList();
// Delete the controls
controlsToDelete.ForEach(Controls.Remove);
// Get all controls with the same tag that are below the deleted controls
var controlsToMove = Controls.Cast<Control>().Where(control =>
control.Tag != null &&
control.Tag.ToString() == "dynamic" &&
control.Top > minTopValue);
// Move each control up the specified amount
foreach (var controlToMove in controlsToMove)
{
controlToMove.Top -= distanceToMoveUp;
}
}

DevExpress Set XtraTab Selected Page

I was trying to set the XtraTab Selected page in the constructor it self as follows,
public frmInquiryManagement()
{
InitializeComponent();
tabInquiryManagement.SelectedTabPage = xtraTabPage3;
}
But it doesn't work that way. Please help me to do this.

XtraTabControl does not provide this method to directly set a selected page. What i see is, to implement this method, we need to implement a loop internally.
for(int i = 0; i < xtraTabControl1.TabPages.Count; i ++)
if(xtraTabControl1.TabPages[i].Name == "someName"){
xtraTabControl1.SelectedTabPage = xtraTabControl1.TabPages[i];
break;
}
Else this is one of the clear solutions :
tabpage1.Show();
tabpage1.pageVisible=true;
xtraTabControl1.tabPages[0].selected=true;
Hope it helps.
Cheers.

If you want to achieve that you must use PageEnabled property from XtraTabPage component.
xtraTabPage3.PageEnabled = true;

private void Form1_Load(object sender, EventArgs e)
{
SelectTabByTitle("xtraTabPage3",xtraTabControl1);
}
private void SelectTabByTitle(String tabTitle, XtraTabControl tabControl)
{
if (tabControl != null)
{
XtraTabPage pageToSelect = (from curPage in tabControl.TabPages
where curPage.Text == tabTitle
select curPage).FirstOrDefault();
if (pageToSelect != null)
{
tabControl.SelectedTabPage = pageToSelect;
}
}
}

xtraTabControl1.SelectedTabPageIndex = 0;, where 0 is the index of the page you wish to display.

Your code should normally work, but it seems that the problem is that the Form has not loaded yet and the Tabs are not visible yet. Try setting the SelectedTabPage on the Load event, or the Shown event

Use the following code in the Form's Load event handler:
tabInquiryManagement.SelectedTabPage = xtraTabPage3;
tabInquiryManagement.MakePageVisible(xtraTabPage3);

Searching ListBox control and programmatically selecting closest match

I have a ListBox control populated with branches of a large retail chain. The staff using the system have to log in to the relevant branch, and I would like them to be able to search the ListBox to find their branch.
I have created an event handler for when text in the search box changes, and attempted to use code sound on StackOverflow already:
private int lastMatch = 0;
private void txtSearch_TextChanged(object sender, EventArgs e)
{
int x = 0;
string match = txtSearch.Text;
if (txtSearch.Text.Length != 0)
{
bool found = true;
while (found)
{
if (lbBranches.Items.Count == x)
{
lbBranches.SetSelected(lastMatch, true);
found = false;
}
else
{
lbBranches.SetSelected(x, true);
match = lbBranches.SelectedValue.ToString();
if (match.Contains(txtSearch.Text))
{
lastMatch = x;
found = false;
}
x++;
}
}
}
}
When I compile and start typing into the search box, I get this error:
Object reference not set to an instance of an object.
The line in question is:
match = lbBranches.SelectedValue.ToString();
I have no idea what could be wrong there, anyone got an idea?
Thanks!

SelectedValue of the listbox will only return a value if you have specified the ValueMember property of the listbox to indicate a property from which you would like to read the value for the selected item. The property you want to use in this case is SelectedItem:
match = lbBranches.SelectedItem.ToString();

when the user is entering text it's possible that no value has been selected (hence the error) -- keep in mind that what is being entered by the user has no mandatory or direct association with selections in the controls listbox sub-element
it's possible what you're doing might be simpler to implement with a full combo-box control and I think some of the examples at MSDN could be very helpful for you as well

Can I display links in a ListView's detail mode?

I'm displaying a set of search results in a ListView. The first column holds the search term, and the second shows the number of matches.
There are tens of thousands of rows, so the ListView is in virtual mode.
I'd like to change this so that the second column shows the matches as hyperlinks, in the same way as a LinkLabel shows links; when the user clicks on the link, I'd like to receive an event that will let me open up the match elsewhere in our application.
Is this possible, and if so, how?
EDIT: I don't think I've been sufficiently clear - I want multiple hyperlinks in a single column, just as it is possible to have multiple hyperlinks in a single LinkLabel.

You can easily fake it. Ensure that the list view items you add have UseItemStyleForSubItems = false so that you can set the sub-item's ForeColor to blue. Implement the MouseMove event so you can underline the "link" and change the cursor. For example:
ListViewItem.ListViewSubItem mSelected;
private void listView1_MouseMove(object sender, MouseEventArgs e) {
var info = listView1.HitTest(e.Location);
if (info.SubItem == mSelected) return;
if (mSelected != null) mSelected.Font = listView1.Font;
mSelected = null;
listView1.Cursor = Cursors.Default;
if (info.SubItem != null && info.Item.SubItems[1] == info.SubItem) {
info.SubItem.Font = new Font(info.SubItem.Font, FontStyle.Underline);
listView1.Cursor = Cursors.Hand;
mSelected = info.SubItem;
}
}
Note that this snippet checks if the 2nd column is hovered, tweak as needed.

Use ObjectListView -- an open source wrapper around a standard ListView. It supports links directly:
This recipe documents the (very simple) process and how you can customise it.

The other answers here are great, but if you don't want to have to hack some code together, look at the DataGridView control which has support for LinkLabel equivalent columns.
Using this control, you get all the functionality of the details view in a ListView, but with more customisation per row.

You can by inheriting the ListView control override the method OnDrawSubItem.
Here is a VERY simple example of how you might do:
public class MyListView : ListView
{
private Brush m_brush;
private Pen m_pen;
public MyListView()
{
this.OwnerDraw = true;
m_brush = new SolidBrush(Color.Blue);
m_pen = new Pen(m_brush)
}
protected override void OnDrawColumnHeader(DrawListViewColumnHeaderEventArgs e)
{
e.DrawDefault = true;
}
protected override void OnDrawSubItem(DrawListViewSubItemEventArgs e)
{
if (e.ColumnIndex != 1) {
e.DrawDefault = true;
return;
}
// Draw the item's background.
e.DrawBackground();
var textSize = e.Graphics.MeasureString(e.SubItem.Text, e.SubItem.Font);
var textY = e.Bounds.Y + ((e.Bounds.Height - textSize.Height) / 2);
int textX = e.SubItem.Bounds.Location.X;
var lineY = textY + textSize.Height;
// Do the drawing of the underlined text.
e.Graphics.DrawString(e.SubItem.Text, e.SubItem.Font, m_brush, textX, textY);
e.Graphics.DrawLine(m_pen, textX, lineY, textX + textSize.Width, lineY);
}
}

You can set HotTracking to true so that when the user hovers mouse over the item it appears as link.