R – Setting AssociatedControlID on label fails

asp.netcomposite-controls

I have a composite control that adds a TextBox and a Label control to its Controls collection. When i try to set the Label's AssociatedControlID to the ClientID of the Textbox i get this error

Unable to find control with id 
'ctl00_MainContentPlaceholder_MatrixSetControl_mec50_tb'
that is associated with the Label 'lb'.

Ok so a little background. I got this main-composite control that dynamically adds a number of 'elements' to its control collection. One of these elements happen to be this 'MatrixTextBox' which is the control consisting of a TextBox and a Label.

I hold the Label and TextBox as protected class variables and init them in CreateChildControls:

    ElementTextBox = new TextBox();
    ElementTextBox.ID = "tb";
    Controls.Add(ElementTextBox);

    ElementLabel = new Label();
    ElementLabel.ID = "lb";
    Controls.Add(ElementLabel);

I tried setting the

ElementLabel.AssociatedControlID = ElementTextBox.ClientID;

both right after adding the controls to the Controls collection and even in PreRender – both yield the same error. What am i doing wrong?

Best Answer

I think you mustn't use the ClientID property of the ElementTextBox, but the ID. ClientID is the page-unique ID you'd have to use in Javascript, e.g. in the document.getElementyById and is not the same as the server-side ID - especially if you have a masterpage and/or controls in controls etc.

So it should be:

ElementLabel.AssociatedControlID = ElementTextBox.ID;

Hope this helps.

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