C# Web App: Assigning controls dynamically

[dmj07]

Hi all,

I am trying to reference these drop down lists I assign in the code behind but I keep getting a 'null reference error. Object is not instantiated'

Here is the code:

public DropDownList[] ComboBoxes = new DropDownList[4];
 
public void SetComponents()
{
 
ComboBoxes[0] = ddlH1;     //ddlH1 and so forth are controls in the page
ComboBoxes[1] = ddlH2;
ComboBoxes[2] = ddlH3;
ComboBoxes[3] = ddlH4;
 
}

When I run this line of code later on:

txtUpdateType.Text = ComboBoxes[tracker - 1].SelectedItem.Value;

I get the error :(

Many thanks for any help in advance

[nateraaaa]

Are your drop down list inside of a container such as a gridview or a panel?

Nathan

[MrMancunian]

Did you check wheter the value of "tracker - 1" isn't higher than the number of arrays you created?

Steven

[dmj07]

Drop down lists are inside a tab panel of a tab container. I thought this would be where it is going wrong!! How would I assign them to it if they are containted in there?

And yes tracker value is always above 0 so it does always reference a value within the array.

Many thanks for your replies.

[nateraaaa]

You will need to use the FindControl method of the container control that the drop down list reside in.

array[0] = (DropDownList)container.FindControl("dropdownlist1");

Nathan

[dmj07]

Yes I tried this before similar to what you suggested where if finds the control in the containers:

ComboBoxes[1] = (DropDownList)Panel2.FindControl("UpdatePanel20").FindControl("ddlH2");

However again when it comes to using the Dropdownlists like here:

txtUpdateType.Text = ComboBoxes[tracker - 1].SelectedItem.Value;

I still get the not set to instance error :(

Any more help will be greatly appreciated

[nateraaaa]

Try finding the updatepanel control 1st then finding the dropdownlist in your updatepanel control.

UpdatePanel updatePanel = (UpdatePanel)Panel2.FindControl("UpdatePanel20");
ComboBoxes[1] = (DropDownList)updatePanel.FindControl("ddlH2");

Also have you run your debugger to verify which object is throwing the null reference exception.
If this does not work you may need to post more of your code so that we can see what is going on in your code behind file.

Nathan

[dmj07]

Hey thanks for all your help on this. I managed to figure it out in the end it was more to do with page load event and how I had not set it correctly in there with the code prior to the stuff I gave here.

Many thanks for your time

[nateraaaa]

Hey thanks for all your help on this. I managed to figure it out in the end it was more to do with page load event and how I had not set it correctly in there with the code prior to the stuff I gave here.

Many thanks for your time

Would you mind posting the code that works so that others may be able to see a working example if they run into the same problem? Thanks.
Nathan