Member Avatar for C#Novice

[I have an application where , i have a radiobuttonlist having 2 radio buttons radiobuttons RB1 & RB2
and there are 6 checkBoxes CB1 thru CB6
If RB1 is selected then CB6 shld be disable /invisible and if RB2 is selected then all the CBs shld be enabled. How do i do this?

protected void rb_OnIndexChanged(object sender, System.EventArgs e)
	{				
if (rb.SelectedValue=="A")
	{
	cb6.Enabled=true;
	}
	}

i get an error Object reference not set to an instance of an object
plz help.
thank you

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Dani AI

Generated

Common causes of the "Object reference not set to an instance of an object" seen by are a mismatched control ID, a control missing runat="server", the event not being wired up, or the wrong event type (RadioButtonList uses SelectedIndexChanged, single RadioButton uses CheckedChanged). ’s per-radio handlers show the idea, but the RB2 handler actually disables all checkboxes (contrary to the requirement to enable all when RB2 is chosen).

A clean server-side pattern when using a RadioButtonList:

  • Markup: set runat="server" on the list and checkboxes and AutoPostBack="true" on the radio list (or wire the event in code).
  • In the handler cast sender to RadioButtonList and null-check it.
  • Change only the needed checkbox (CB6) and avoid repeating code by iterating a container (Panel/PlaceHolder) that holds the checkboxes.

Example server-side handler:

protected void RadioChoices_SelectedIndexChanged(object sender, EventArgs e)
{
    var rbl = sender as RadioButtonList;
    if (rbl == null) return;

    bool hideCb6 = rbl.SelectedValue == "A"; // RB1
    cb6.Visible = !hideCb6;

    foreach (Control c in checkboxPanel.Controls)
    {
        var cb = c as CheckBox;
        if (cb == null) continue;
        if (cb.ID == "cb6")
            cb.Enabled = !hideCb6;
        else
            cb.Enabled = true; // RB2 makes all enabled
    }
}

For a snappier UX, do this client-side with JavaScript: add onclick/onchange to the radio buttons and toggle the disabled or style.display of the checkboxes using their ClientID. That avoids postbacks entirely.

Quick troubleshooting checklist: confirm runat="server", verify IDs match the code-behind, set AutoPostBack="true" (if server-side), only bind lists inside if (!IsPostBack), and inspect the exception stack trace to see exactly which variable is null.

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Member Avatar for Jx_Man

try this :

private void RB1_CheckedChanged(object sender, System.EventArgs e)
{
	if (RB1.Checked == true)
	{
		C1.Enabled = true;
		C2.Enabled = true;
		C3.Enabled = true;
		C4.Enabled = true;
		C5.Enabled = true;
		C6.Enabled = false;
	}
}

private void RB2_CheckedChanged(object sender, System.EventArgs e)
{
	if (RB2.Checked == true)
	{
		C1.Enabled = false;
		C2.Enabled = false;
		C3.Enabled = false;
		C4.Enabled = false;
		C5.Enabled = false;
		C6.Enabled = false;
	}
}
Member Avatar for C#Novice

thnx Jx_Man. i will surely try this tomorrow. and let u know.

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