Can't use Control.FindControl on dynamically created System.Web.UI.WebControl - asp.net

Question

Why would the following code not work? I am creating a control, adding a child control and attempting to retrieve it by id using the .FindControl method.
[Test]
public void TryToFindControl()
{
var myPanel = new Panel();
var textField = new TextBox
{
ID = "mycontrol"
};
myPanel.Controls.Add(textField);
var foundControl = myPanel.FindControl("mycontrol");
// this fails
Assert.IsNotNull(foundControl);
}

Answer 1

Panel has not been added to Page yet, so you cannot use FindControl. Instead, you need to find it inside Panel.Controls
[TestMethod]
public void TryToFindControl()
{
var myPanel = new Panel();
var textField = new TextBox
{
ID = "mycontrol"
};
myPanel.Controls.Add(textField);
var foundControl = myPanel.Controls
.OfType<TextBox>()
.FirstOrDefault(x => x.ID == "mycontrol");
Assert.IsNotNull(foundControl);
}
Testing with Page
FindControl works only if container is added to Page.
public partial class Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
var myPanel = new Panel();
var textField = new TextBox
{
ID = "mycontrol"
};
myPanel.Controls.Add(textField);
Controls.Add(myPanel);
// foundControl is not null anymore!
var foundControl = myPanel.FindControl("mycontrol");
}
}

Answer 2

The control must be part of the server side Page control collection hierarchy to be found.
public void TryToFindControl()
{
var myPanel = new Panel();
// key line here
Page.Controls.Add(myPanel);
var textField = new TextBox
{
ID = "mycontrol"
};
myPanel.Controls.Add(textField);
var foundControl = myPanel.FindControl("mycontrol");
Assert.IsNotNull(foundControl);
}

Answer 3

First I'll start form the fact I don't know of System.UI.Control, Rather System.Web.UI.Control
Then I could not find TextField Control so I used Web TextBox instead. Please adjust your code as necessary. I also used VS Test attributes
[TestMethod()]
public void TryToFindControl()
{
var editContainer = new HtmlTableCell();
editContainer.Controls.Add(new TextBox
{
ID = "mycontrol",
});
System.Web.UI.Control foundControl = null;
foreach (System.Web.UI.Control ctrl in editContainer.Controls)
{
if (ctrl.ID == "mycontrol")
{
foundControl = ctrl;
break;
}
}
// This works
Assert.IsNotNull(foundControl);
}
Based on your exact wording, if you want to access the control you added, create an instance first as variable, so you can access it directly. Please keep in mind that I don't know what you are trying to achieve globally, so my answer(s) may not apply because of that, or there maybe be better solution.
[TestMethod()]
public void TryToFindControl()
{
var editContainer = new HtmlTableCell();
var foundControl = new TextBox
{
ID = "mycontrol"
};
editContainer.Controls.Add(foundControl);
// This works
Assert.IsNotNull(foundControl);
}