I have used FindControl in the past, prior to .NET 2.0/3.0. It seems like now, for some reason, the ID's of my controls get a funky named assigned. For example I assigned an id "cbSelect" to a checkbox, but FindControl does not find it. When I view the HTML it was assigned ctl00_bodyPlaceHolder_ctl02_cbSelect.
I have not found one example of FindControl that mentions that. In fact everyone seems to just use find control like normal.
So, am I doing something wrong? Did .Net change? Can anyone shed some light onto this for me, it is really frustrating!
You are probably using a MasterPage or user controls (ascx) and this is the reason the for client ids change. Imagine you have a control in the master page with the same id as one in the page. This would result in clashes. The id changes ensures all ClientID properties are unique on a page.
FindControl needs some special attention when working with MasterPages. Have a look at ASP.NET 2.0 MasterPages and FindControl(). The FindControl works inside a naming container. The MastePage and the page are different naming containers.
You could write extender to find any control on page using recursion.
This could be in some Util/Helper class.
public static Control FindAnyControl(this Page page, string controlId)
{
return FindControlRecursive(controlId, page.Form);
}
public static Control FindAnyControl(this UserControl control, string controlId)
{
return FindControlRecursive(controlId, control);
}
public static Control FindControlRecursive(string controlId, Control parent)
{
foreach (Control control in parent.Controls)
{
Control result = FindControlRecursive(controlId, control);
if (result != null)
{
return result;
}
}
return parent.FindControl(controlId);
}
I've had pretty good luck working around this problem in "most" cases with a simple extension method
You can call it on whatever higher-level container control you think best, including the Page itself if you want to scan the entire control hierarchy.
private static Control FindControlIterative(this Control control, string id)
{
Control ctl = control;
LinkedList<Control> controls = new LinkedList<Control>();
while(ctl != null)
{
if(ctl.ID == id)
{
return ctl;
}
foreach(Control child in ctl.Controls)
{
if(child.ID == id)
{
return child;
}
if(child.HasControls())
{
controls.AddLast(child);
}
}
ctl = controls.First.Value;
controls.Remove(ctl);
}
return null;
}
When searching for a control in a control collection, always use the id you assigned the control, not the one you see in the source post render. If FindControl() does not find the control you know exists, there is a good chance that you are not searching in the right branch of the control hierarchy. A recursive function has been successful for me.
Here is my example of what I use for VB.NET 3.5:
Function FindControlRecursive(ByVal ctrl As Control, ByVal id As String) As Control
Dim c As Control = Nothing
If ctrl.ID = id Then
c = ctrl
Else
For Each childCtrl In ctrl.Controls
Dim resCtrl As Control = FindControlRecursive(childCtrl, id)
If resCtrl IsNot Nothing Then c = resCtrl
Next
End If
Return c
End Function
Here is an example of how I would topically implement this function in my base page class:
Dim form HtmlForm = CType(FindControlRecursive(Me, "Form"), HtmlForm)
This is the VB.NET code that worked for me:
<Extension()> _
Function FindChildControlById(ByVal controlToStartWith As Control, ByVal controlIdToFind As String) As Control
If controlToStartWith Is Nothing Then Return Nothing
If controlToStartWith.ID = controlIdToFind Then Return controlToStartWith
For Each childControl As Control In controlToStartWith.Controls
Dim resCtrl As Control = FindChildControlById(childControl, controlIdToFind)
If resCtrl IsNot Nothing Then Return resCtrl
Next childControl
Return Nothing
End Function ' Function FindChildControlById(ByVal controlToStartWith As Control, ByVal controlIdToFind As String) As Control
Credit goes to George for the initial VB.NET code. I only modified it a teeny bit, with 2 functional change: mine doesn't error if/when null/Nothing is passed as the input control, and mine is implemented as an Extension. My other 3 minor changes don't affect the functionality, but to me, they were code simplifications. But I know it's very subjective.
So this method can be used with:
Dim c1 As Control = Page.FindChildControlById("aspControlID")
And if you want to convert it into a specific child class of a Control, like this:
Dim c1 As Control = Page.FindChildControlById("aspControlID")
Dim c As HyperLink = TryCast(c1, HyperLink)
Update: My function is now named 'FindChildControlById' (previously was 'FindMiControl'). I liked SpeedNet's suggestion better.
When it's rendering the html, ASP.NET will prefix all the control IDs with the IDs of the naming containers (User Controls etc..) in a hierarchy going back all the way to the document root. This ensures that all the IDs are unique for post backs etc..
This does not effect using FindControl where you should use the ID in the original markup.
Here is a reference as to how web form controls are named...
Web Forms Control Identification
Related
I have a user control that is dynamically loaded in the the page load:
protected void Page_Load(object sender, EventArgs e)
{
MyControl ctl = (MyControl)LoadControl(controlPath);
ctl.ID = "mycontrol";
this.MyControlPlaceHolder.Controls.Add(ctl);
}
Front End of the Page:
<asp:PlaceHolder runat="server" ID="MyControlPlaceHolder"></asp:PlaceHolder>
I have an click event on the page that initiates and postback and calls a method where I'm trying to find the control and set some properties:
MyControl ctl = (MyControl)FindControl("mycontrol");
if (ctl != null){
ctl.MyProperty = true;
Response.Write("success");
}
else
Response.Write("fail");
This is writing fail after the postback, so it seems like I'm doing something incorrectly in finding the control. What is the best way to do this?
EDIT:
I switched it to MyControl ctl = (MyControl)this.MyControlPlaceHolder.FindControl("mycontrol");
This made it so it was finding the control, however, when the control loads after the postback, it appears as though the property is not set.
You have to use a recursive FindControl implementation because FindControl will only find direct childs. Your control is inserted in a naming container at a lower level. A generic FindControlRecurisve from MSDN:
private Control FindControlRecursive(Control rootControl, string controlID)
{
if (rootControl.ID == controlID) return rootControl;
foreach (Control controlToSearch in rootControl.Controls)
{
Control controlToReturn =
FindControlRecursive(controlToSearch, controlID);
if (controlToReturn != null) return controlToReturn;
}
return null;
}
from MSDN
Or, if you only have one specific conatiner like in your sample:
MyControl ctl = this.MyControlPlaceHolder.FindControl("mycontrol");
if (ctl != null){
ctl.MyProperty = true;
Response.Write("success");
}
else
Response.Write("fail");
ViewState enable your control
public class MyControl:Control
{
public bool MyProperty
{
get
{
return ViewState["my"] != null? (bool) ViewState["my"]: false;
}
set
{
ViewState["my"] = value;
}
}
}
Try moving the code to dynamically add the control into Init instead of load. I can't be sure but there are a lot of things that happen between Init and Load and if your control is not present and accounted for it may cause issues like this.
You added the Control in the controls collection of a placeholder.
Apart of what control is your dynamically created control, if you want to looking for your dynamically added control in that way you have to do a recursive search starting from the root (maybe the page), so, if you surf over the net, you could find good solutions for that.
Personally I prefer solutions with: generics support and expressed as extension methods, so you could use the solution everywhere. These are some usefull links
Recursive Find Control with generics
Recursive Find Control with generics by extension method
Recursive Find Control with generics by extension method and linq support/example
hope this helps
In a master page I got a panel which I want to add controls to it from the master page's code behind as follow:
var cphRegionName = this.Page.FindControl("pnlLeft") as Panel;
cphRegionName.Controls.Add(uc);
but I get this error:
Object reference not set to an instance of an object at cphRegionName.Controls.Add(uc);
I have tried all possible other ways, but get the same error.
The reason I user FindControl to access the PANEL is the panel's name is dynamic ("pnlLeft"), reading from Database.
The FindControl method doesn't work recursively. This means that unless your control was added directly to the page, it would not find it.
If you know the container control, use FindControl on that and not on the Page.
If you don't, you could use a a function like this to solve the problem
private Control FindControlRecursive(Control root, string id)
{
if (root.ID == id)
{
return root;
}
foreach (Control c in root.Controls)
{
Control t = FindControlRecursive(c, id);
if (t != null)
{
return t;
}
}
return null;
}
FindControl is not recursive, so you have to make sure you're calling it on the correct container. It doesn't look like the panel is defined at the root based on the null reference.
Try calling FindControl on the parent of the panel
I have a login control and at is nested 2 deep in a header control
i.e Page --> Header Control --> Login Control. I cannot get a reference to the control on the page using FindControl. I want to be able to set the visible property of the control like
if (_loginControl != null)
_loginControl.Visible = false;
I ended up using a recursive FindControl method to find the nested control.
public static Control FindControlRecursive(Control root, string id)
{
if (root.ID == id)
{
return root;
}
foreach (Control c in root.Controls)
{
Control t = FindControlRecursive(c, id);
if (t != null)
{
return t;
}
}
return null;
}
Are you needing to disable/hide the User Control from the ASP.NET page it resides on (or does the User Control exist on a master page, say)? If it's in the same page, then in your ASP.NET page's code-behind you'd do:
MyUserControlsID.Visible = false
Where MyUserControl is the ID of your User Control. To determine the ID of your User Control look at the markup of your .aspx page and you will see something like this:
<uc1:UserControlName ID="MyUserControlsID" runat="server" ... />
Happy Programming!
A good way would be to use:
Page.FindControl()
if that yields null, the control is not there.
Try calling this.FindControl("_loginControl") or this.Page.FindControl("_loginControl").
See MSDN for method details:
http://msdn.microsoft.com/en-us/library/system.web.ui.control.findcontrol.aspx
The login control, if it's registered in the markup, will also be an instance member of your codebehind page; you can refer to it from the codebehind class as if it were a normal member, using the same name you provided as the ID (I do recommend using codebehinds for most logic, instead of inlining code in the markup, BTW).
You can also use the FindControl() method of your page, which will search its control subtree for a control with a given ID. That takes longer, so I would recommend the first option unless the logic control is added dynamically and you don't always know it's there.
private List<Control> GetAllNestedUserControl(Control ph)
{
List<Control> Get = new List<Control>();
foreach (var control in ph.Controls)
{
if (control is UserControl)
{
UserControl uc = control as UserControl;
if (uc.HasControls())
{
Get = GetAllNestedUserControl(uc);
}
}
else
{
Control c = (Control)control;
if (!(control is LiteralControl))
{
Get.Add(c);
}
}
}
return Get;
}
just call this code from you any parent page and then get any control by the following code
List<Control> Get = GetAllNestedUserControl(ph);
Label l = (Label)Get.Find(o => o.ID == "lblusername");
l.Text = "changed from master";
HEllo, I need to dynamically activate fields in a page according to the service that is going to be executed...
Let me explain:
There's a page with all the possible fields and a ListBox with all the selected services to be executed, then when the user selects which service to execute (change a car plate, for example), then I need to activate only the field(s) that the service require... (The realationship between Services and Fields are stored in a database).
public void CheckAll(int pService_Id, Control pPage)
{
foreach (Control control in pPage.Controls)
{
busExecutaServico vExecuta = new busExecutaServico();
if (vExecuta.EnableField(control.ID.ToString(), Convert.ToInt32(listBoxServices.SelectedValue)))
{
switch (control.GetType().ToString())
{
case "TextBox":
TextBox controleText = (TextBox)Page.FindControl(control.ID.ToString());
controleText.Enabled = true;
break;
Note that busExecutaServico is the class which contains the method (EnableField) for checking if the selected item matches any field on the database..
I can't seem to get the control.ID.ToString() to work properly (the ID always comes as NULL)
If anyone can help me solve this, or if there's another way (even if it's completely different from what i'm trying), it would be of great help. thanks
I like to use a recursive function for locating controls by either type or ID.
public Control FindControlRecursive(Control rootControl, string controlId)
{
if (rootControl.ID == controlId)
return rootControl;
foreach (Control control in rootControl.Controls)
{
Control foundControl = FindControlRecursive(control, controlId);
if (foundControl != null)
{
return foundControl;
}
}
return null;
}
public Control FindControlRecursive(Control rootControl, Type type)
{
if (rootControl.GetType().Equals(type))
return rootControl;
foreach (Control control in rootControl.Controls)
{
Control foundControl = FindControlRecursive(control, type);
if (foundControl != null)
{
return foundControl;
}
}
return null;
}
You can adapt these to first return a collection of controls, then process them later. Might be easier to keep track of what's happening.
I learned this technique here: http://www.west-wind.com/Weblog/posts/5127.aspx
Be aware that FindControl only searches the current naming container so Page.FindControl will only find controls that are added directly to Page. For example, if you had a repeater control that had the controls you were looking for and it was added to Page, you could find your repeater control via Page.FindControl but it wouldn't find child controls within your repeater, you'd have to recursively perform the FindControl on all container controls in the page.
This might seem a bit strange but it allows you to have controls with the same ID existing on the same page. For example, if you had 10 instances of a user control with textboxes within them called "MyName", you'd really want them to not being over-writing each other's 'MyName' fields!
Your code will come across a null for an ID unless every control has been given an ID.
Also why use:-
TextBox controleText = (TextBox)Page.FindControl(control.ID.ToString());
at all instead of:-
TextBox controleText = (TextBox)control;
and indeed since you only want to change the Enabled property consider:-
((WebControl)control).Enabled = False;
That I suspect will eliminate many case statements.
In your code you don't need to search any control - you already have it in 'control' variable. You even don't need to cast it to TextBox, just to a WebControl, just do this:
...
if (vExecuta.EnableField(control.ID.ToString(), Convert.ToInt32(listBoxServices.SelectedValue)))
((WebControl)control).Enabled = true;
P.S. control.ID is already string, so you should remove any ID.ToString() also.
I have a master page which is nested 2 levels. It has a master page, and that master page has a master page.
When I stick controls in a ContentPlaceHolder with the name "bcr" - I have to find the controls like so:
Label lblName =(Label)Master.Master.FindControl("bcr").FindControl("bcr").FindControl("Conditional1").FindControl("ctl03").FindControl("lblName");
Am I totally lost? Or is this how it needs to be done?
I am about to work with a MultiView, which is inside of a conditional content control. So if I want to change the view I have to get a reference to that control right? Getting that reference is going to be even nastier! Is there a better way?
Thanks
Finding controls is a pain, and I've been using this method which I got from the CodingHorror blog quite a while ago, with a single modification that returns null if an empty id is passed in.
/// <summary>
/// Recursive FindControl method, to search a control and all child
/// controls for a control with the specified ID.
/// </summary>
/// <returns>Control if found or null</returns>
public static Control FindControlRecursive(Control root, string id)
{
if (id == string.Empty)
return null;
if (root.ID == id)
return root;
foreach (Control c in root.Controls)
{
Control t = FindControlRecursive(c, id);
if (t != null)
{
return t;
}
}
return null;
}
In your case, I think you'd need the following:
Label lblName = (Label) FindControlRecursive(Page, "lblName");
Using this method is generally much more convenient, as you don't need to know exactly where the control resides to find it (assuming you know the ID, of course), though if you have nested controls with the same name, you'll probably get some strange behavior, so that might be something to watch out for.
Firstly, you should know that MasterPages actually sit inside Pages. So much so that a MasterPage's Load event is actually called after your ASPX's Load event.
This means, the Page object is actually the highest control in the control hierarchy.
So, knowing this, the best way to find any control in such a nested environment, is to write a recursive function that loops through every control and child controls until it finds the one you're looking for. in this case, your MasterPages are actually child controls of the main Page control.
You get to the main Page object from inside any control like this:
C#:
this.Page;
VB.NET
Me.Page
I find that usually, the Control's class FindControl() method is pretty useless, as the enviroment is always nested.
Because if this, I've decided to use .NET's 3.5 new Extension features to extend the Control class.
By using the code below (VB.NET), in say, your AppCode folder, all your controls will now peform a recursive find by calling FindByControlID()
Public Module ControlExtensions
<System.Runtime.CompilerServices.Extension()> _
Public Function FindControlByID(ByRef SourceControl As Control, ByRef ControlID As String) As Control
If Not String.IsNullOrEmpty(ControlID) Then
Return FindControlHelper(Of Control)(SourceControl.Controls, ControlID)
Else
Return Nothing
End If
End Function
Private Function FindControlHelper(Of GenericControlType)(ByVal ConCol As ControlCollection, ByRef ControlID As String) As Control
Dim RetControl As Control
For Each Con As Control In ConCol
If ControlID IsNot Nothing Then
If Con.ID = ControlID Then
Return Con
End If
Else
If TypeOf Con Is GenericControlType Then
Return Con
End If
End If
If Con.HasControls Then
If ControlID IsNot Nothing Then
RetControl = FindControlByID(Con, ControlID)
Else
RetControl = FindControlByType(Of GenericControlType)(Con)
End If
If RetControl IsNot Nothing Then
Return RetControl
End If
End If
Next
Return Nothing
End Function
End Module
Although I love recursion, and agree with andy and Mun, one other approach you may want to consider is to have a strongly typed Master page. All you have to do is add one directive in your aspx page.
Instead of accessing a page's control from your master page, consider accessing a control in your master page from the page itself. This approach makes a lot of sense when you have a header label on your master page, and want to set its value from each page that uses the master.
I'm not 100% sure, but I think this would be simpler technique with nested master pages, as you would just point the VirtualPath to the master containing the control you wish to access. It might prove to be tricky though if you want to access two controls, one in each respective master page.
Here is a code that is more generic and works with a custom condition (that can be a lambda expression!)
Call:
Control founded = parent.FindControl(c => c.ID == "youdId", true);
Control extension
public static class ControlExtensions
{
public static Control FindControl(this Control parent, Func<Control, bool> condition, bool recurse)
{
Control founded = null;
Func<Control, bool> search = null;
search = c => c != parent && condition(c) ? (founded = c) != null :
recurse ? c.Controls.FirstOrDefault(search) != null :
(founded = c.Controls.FirstOrDefault(condition)) != null;
search(parent);
return founded;
}
}
I have used the <%# MasterType VirtualPath="~/MyMaster.master" %> method. I have a property in the main master page then in the detail master page other property with the same name calling the main master property and it works fine.
I have this in the main master page
public string MensajeErrorString
{
set
{
if (value != string.Empty)
{
MensajeError.Visible = true;
MensajeError.InnerHtml = value;
}
else
MensajeError.Visible = false;
}
}
this is just a div element that have to show an error message. I would like to use this same property in the pages with the detail master page(this is nested with the main master).
Then in the detail master I have this
public string MensajeErrorString
{
set
{
Master.MensajeErrorString = value;
}
}
Im calling the main master property from the detail master to create the same behavior.
I just got it working perfectly.
In contentpage.aspx, I wrote the following:
If Master.Master.connectsession.IsConnected Then
my coded comes in here
End If