How do I find controls inside class using ASP.NET C#

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Hey All,
Why FindControl not working in class. findcontrol not even appears in intelsense.How can i find a control inside class using ASP.NET C#.
Regards

What I have tried:

C#

public class FormDesign
{
public Panel mypanel { get; set; }
public TextBox findTbox()
        {
            TextBox tbox = new TextBox();
            tbox.ID = "tbox";
            mypanel.Controls.Add(tbox);
            TextBox temp = (TextBox)FindControl("tbox");
            temp.Text = "control found";
            return tbox;
        }
}

Posted 26-Sep-20 20:12pm

Aftab Iqbal Clips

Updated 26-Sep-20 22:57pm

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3 solutions

Solution 2

As Griff shared, you can find controls from an defined object like Page or a Control.

Following should explain more and help:
Page.FindControl(String) Method (System.Web.UI) | Microsoft Docs[^]
Control.FindControl Method (System.Web.UI) | Microsoft Docs[^]

Base is, you need to use FindControl to some sort of container that can hold controls. With such containers, you will get 'intellisense' too.

Posted 26-Sep-20 22:10pm

Sandeep Mewara

Solution 3

myPanel is never instantiated ! maybe seeing how you'd do something like this in WinForms will give you some ideas:

using System;
using System.Collections.Generic;
using System.Windows.Forms;

namespace YourNameSpace
{
    public class FormDesign
    {
        // ctor
        public FormDesign()
        {
            mypanel = new Panel();
            
            TextBox tbox = new TextBox();
            tbox.Name = "TextBox 1";  // use ID in ASP.NET
            tbox.Text = "tbox";

            mypanel.Controls.Add(tbox);
        }

        public Panel mypanel { get; set; }
    
        public Control findControl(string cname)
        {
            if (mypanel.Controls.ContainsKey(cname))
            {
                return mypanel.Controls[cname];
            }

            throw new KeyNotFoundException($"{cname} is not a valid key");
        }
    }
}

test:

YourNameSpace.FormDesign fd = new YourNameSpace.FormDesign();

Control tbx = fd.findControl("TextBox 3");

Posted 26-Sep-20 22:57pm

BillWoodruff

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OriginalGriff · Accepted Answer · 2020-09-26T20:32:00

Because your class is not explicitly derived from anything, it's inheritance is only from object.

As a result, the only "built in" methods you can use are object methods:

Equals
Finalize
GetHashCode
GetType
MemberwiseClone
ReferenceEquals
ToString

Since you are trying to deal with controls like Panel and TextBox, you probably need to derive you class from Form- which means adding a Form to your project, instead of a class as that add the "behind the scenes" code which makes it all work.
A class based on object alone can never be displayed directly: you need to derive it from a Form or Control to do that.

Quote:
after inheriting control class it's working now.but now getting error on
temp.Text = "control found";
the error says
Object reference not set to an instance of an object.
will deeply appreciate your help

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!
And since you aren't searching the Panel you added it to, I'm just guessing that the Panel isn't in the form / page Controls array either ...