Develop Reference

Edit a button by its given name

I am generating x amount of buttons and I give all of them a unique name.
After all those are generated, I want to edit one of them without regenerating them so I was wondering if I could get a component by its name?
I am using WinForms

Yes:
Control myControl = Controls.Find("textBox1");
Now, beware that you have to do proper casting hen found, because Find returns a control.

You can use Controls property of your form (or some container control on your form). With LINQ you can select buttons and then find first button with required name:
var button1 = Controls.OfType<Button>().FirstOrDefault(b => b.Name == "button1");
Or if you want to search child controls recursively
var button1 = Controls.Find("button1", true)
.OfType<Button>()
.FirstOrDefault();
Without LINQ you can use method Find(string key, bool searchAllChildren) of ControlCollection:
Control[] controls = Controls.Find("button1", true);
if (controls.Length > 0)
{
Button button1 = controls[0] as Button;
}

Button btn1 = (Button)(Controls.Find("btnName"));
This will get the required button and will save the button attributes into a new Button btn1

After all those are generated, I want to edit one of them without
regenerating them so I was wondering if I could get a component by its
name?
var myButton = Controls.Find("buttonName", true).FirstOrDefault(); //Gets control by name
if(myButton != null)
{
if (myButton.GetType() == typeof(Button)) //Check if selected control is of type Button
{
//Edit button here...
}
else
{
//Control isn't a button
}
}
else
{
//Control not found.
}
Make sure you add a reference to: linq.

How to determine the active control within a tabControl

I have a tab control through which the user can right-click within one of several richTextBoxes. The textBoxes use the same contextMenuStrip control, and I need to determine which textBox is the active one within the contextMenuStripCopyPaste_Opening event. I would think that the code to determine this would be
tabControl1.SelectedTab.ActiveControl.Name but the ActiveControl property is not available. this.ActiveControl.Name just gives me the name of the tabControl.
How can I determine which textBox is the active control within the tabControl?

You can use the sender paramter to get the ContextMenuStrip then call the ContextMenuStrip.SourceControl property to get the control that opened the context menu.
In this case you can try the following code.
private void contextMenuStrip1_Opening(object sender, CancelEventArgs e)
{
var ctxStrip = sender as ContextMenuStrip;
if (ctxStrip == null)
return;
var rtb = ctxStrip.SourceControl as RichTextBox;
if (rtb == null)
return;
}
This code simply casts the sender object to a ContextMenuStrip if this is null then return. (Although should never be). The next line captures the SourceControl and casts the control to a RichTextBox.
If the source control is not a RichTextBox then the result will be null and we cancel as this shouldn't be null unless you bind the context menu to other controls aswell.

I'm not finding anything that is there by default. I would create a list of the rich text boxes, and then use a LINQ statement as the LINQ Select statement would return only the rich text box that has the focus. Something like this.
List rtbList = new List {RichTextBox1, RichTextBox2, RichTextBox3, RichTextBox4}
var FocusedRTB = rtbList.Select(x => x.Focused == true);
switch (FocusedRTB.Name)
{Execute Code for each RichTextBox
}

Reading __EVENTTARGET causes event is not called

I want to use information on which control was clicked for setting up the page. I use this to set up a sortable table in code. I found through this forum that I can use Request.Form.Get("__EVENTTARGET") for that. However, as soon as I do something with that parameter, the callback function is no longer called. Is this expected behavior or am I making a mistake?
Here some snippets of my code. The code in Page_Load() is:
string sortRequest = Request.Form.Get("__EVENTTARGET");
bool isCurrentField = false;
if (sortRequest != null) isCurrentField = sortRequest.Contains(header.Field);
if (!isCurrentField)
{
// Add a hyperlink for sorting to the cell
LinkButton newLink = new LinkButton();
newLink.Text = header.Title;
newLink.Font.Bold = true;
newLink.ID = "link" + header.Field;
newLink.CommandName = "Sort";
newLink.CommandArgument = header.Field;
newLink.Command += new CommandEventHandler(LinkButton_Command);
hdrCell.Controls.Add(newLink);
}
else
{
hdrCell.Text = header.Title;
hdrCell.Font.Bold = true;
}
My callback:
public void LinkButton_Command(Object sender, CommandEventArgs e)
{
_sortOrder = e.CommandArgument.ToString();
}
I have also tried it with copying the sortRequest into a temporary variable, but that doesn't make a difference. As soon as I comment out the line if (sortRequest != null) isCurrentField = sortRequest.Contains(header.Field);, the callback is called again.

There is a fault in your logic. You have a dynamically created control LinkButton with LinkButton_Command event handler connected to it. For the server-side event to fire on postback, the control must be present in the page control tree. This means the dynamic LinkButton must be created, configured and added to hdrCell.Controls always, regardless of sortRequest value. Only then will it be able to pick up the fact that it was clicked from the Request and fire its Command event.

Setting ToolStripMenuItem.Visible to true doesn't work

I have a TreeView control for which each node in it I want to share a ContextMenuStrip which has two ToolStripMenuItems ie:
this.BuildTree = new MyApp.MainForm.TreeView();
this.ItemMenuStrip = new System.Windows.Forms.ContextMenuStrip(this.components);
this.DeleteMenuItem = new System.Windows.Forms.ToolStripMenuItem();
this.ShowLogMenuItem = new System.Windows.Forms.ToolStripMenuItem();
...
this.ItemMenuStrip.Items.AddRange(new System.Windows.Forms.ToolStripItem[] {
this.DeleteMenuItem,
this.ShowLogMenuItem});
So I show and hide these to items according to certain criteria on a right click in a MouseUp event. When both are hidden I hide the ContextMenuStrip itself. Problem is when I hide the ContextMenuStrip it seems the next time I want to show one of the menu items I have to click twice on the node. The strange thing is on the first click to reshow one or both of the the items I have the following code:
ItemMenuStrip.Visible = true;
ShowLogMenuItem.Visible = true;
The two lines above don't seem to do anything ie both remain false in the debugger view after stepping over each line.
I don't think I've got any events on these values being set at least I don't have any events attached.
What am I doing wrong?

I suggest you to set:
this.BuildTree.ContextMenuStrip = this.ItemMenuStrip;
to make the menu automatically open on tree right-click.
Then subscribe ItemMenuStrip.Opening event to change the visibility of items and the contextmenu itself:
void ItemMenuStrip_Opening(object sender, CancelEventArgs e)
{
if (something)
{
e.Cancel = true; // don't show the menu
}
else
{
// show/hide the items...
}
}
If you need to know the current position of the clicked point (e.g. to check if a tree node is clicked), you can use Control.MousePosition property. Note that MousePosition is a point in screen coordinates, so you need to call treeView1.PointToClient(position) to get the tree coordinates e.g. :
private void ItemMenuStrip_Opening(object sender, CancelEventArgs e)
{
var pointClicked = this.BuildTree.PointToClient(Control.MousePosition);
var nodeClicked = this.BuildTree.GetNodeAt(pointClicked);
if (nodeClicked == null)
{
// no tree-node is clicked --> don't show the context menu
e.Cancel = true;
}
else
{
// nodeClicked variable is the clicked node;
// show/hide the context menu items accordingly
}
}

So figured out what was going wrong I was setting Visible on this.ItemMenuStrip rather than the this.BuildTree.ContextMenuStrip.
This seems rather strange to me as I would have thought BuildTree.ContextMenuStrip was just a direct reference to the ItemMenuStrip but apparently not.

Set Focus to Any Control After PostBack

First I have 3 TextBoxes, a DropDownList, a CheckBox, and 2 LinkButtons in a table. The TextBoxes and DropDownList must do an AutoPostBack because there are some calculations being done on the server side which called by OnTextChanged.
My issue here is that after the content of any Control (which requires a PostBack) changes and you attempt to move focus to any other Control on the page (whether it be tabbing or using the mouse to click on any other Control) the focus does not move to the next Control or the Control you clicked.
I tried using a method which finds the current Control and based on the TabIndex, adds 1 which moves the focus to the next control. The problem here is that it does not allow for focus to be set on any other Control other than that one with the next TabIndex. To better explain here is an example of the situation.
Example: I have TextBox1, TextBox2, and TextBox3. I change the content in TextBox2 then want to move backwards to TextBox1. When I click in TextBox1 the focus is set to TextBox3 since the code is using the order of the TabIndex. ** A key factor here is that TextBox1 DOES get focus before the server side code fires but then loses focus and sets it on TextBox3 **
To me, it seems like the only way this can be accomplished would be to add a function on the client side which finds the Control with focus before the PostBack occurs, then reset the focus on that Control after the server side code completes. It does not seem like anything I do on the server side will work since the focus has already been lost when this occurs.
I have searched and searched but have not been able to find any solution to this particular issue, everything I have found deals with setting focus to the NEXT Control instead of the Control you want to have focus. Any help would be greatly appreciated. Thank you in advance.
Here is the code I am using to move to the next Control based on the TabIndex but this does not work in my situation.
protected void Page_Load(object sender, EventArgs e)
{
WebControl ctrl = GetPostBackControl() as WebControl;
if (ctrl != null && !SetNextFocus(Controls, ctrl.TabIndex + 1)) { ctrl.Focus(); }
}
public Control GetPostBackControl()
{
Control control = null;
string ctrlname = Request.Params.Get("__EVENTTARGET");
if (ctrlname != null && ctrlname != string.Empty)
{
control = FindControl(ctrlname);
control.Focus();
}
else
{
foreach (string ctl in Request.Form)
{
Control c = FindControl(ctl);
if (c is Button)
{
control = c;
break;
}
}
}
return control;
}
private bool SetNextFocus(ControlCollection controls, int tabIndex)
{
foreach (Control control in controls)
{
if (control.HasControls())
{
bool found = SetNextFocus(control.Controls, tabIndex);
if (found) { return true; }
}
WebControl webControl = control as WebControl;
if (webControl == null) { continue; }
if (webControl.TabIndex != tabIndex) { continue; }
webControl.Focus();
return true;
}
return false;
}

Try doing something like this to retain focus after postback:
/// <summary>
/// Overrides the OnLoad event moves the cursor to the appropriate control.
/// </summary>
/// <param name="e"></param>
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
int currentTabIndex = 1;
WebControl postBackCtrl = (WebControl)GetControlThatCausedPostBack(Page);
foreach (WebControl ctrl in Panel1.Controls.OfType<WebControl>())
{
ctrl.TabIndex = (short)currentTabIndex;
if (postBackCtrl != null)
{
if (ctrl.TabIndex == postBackCtrl.TabIndex + 1)
ctrl.Focus();
}
currentTabIndex++;
}
}
/// <summary>
/// Retrieves the control that caused the postback.
/// </summary>
/// <param name="page"></param>
/// <returns></returns>
private Control GetControlThatCausedPostBack(Page page)
{
//initialize a control and set it to null
Control ctrl = null;
//get the event target name and find the control
string ctrlName = Page.Request.Params.Get("__EVENTTARGET");
if (!String.IsNullOrEmpty(ctrlName))
ctrl = page.FindControl(ctrlName);
//return the control to the calling method
return ctrl;
}

Thank you for the help, it did get me a little closer. The only thing that was preventing it from working correctly is that my page has some variables which are being carried over from other pages. When the page loads, the override is causing the page to break since it is unable to locate those controls. I was able to fix the issue by adding a HiddenField on the .aspx page and adding the following code to the onload() function:
if (document.getElementById("HiddenField1").value != "") {
var contr = document.getElementById(document.getElementById"HiddenField1").value);
contr.focus();
document.getElementById("HiddenField1").value = "";
}
as well as adding a new function which is called on each of the TextBoxes:
function tabFocus(e) {
document.getElementById("HiddenField1").value = e.id;
}
I ended up not having to make any changes in the code behind. Once again, thank you for the help!