How can we access dynamically created controls in C# windows application?

Question

I am designing C# windows application using 3-Tier architecture, Basically i am making management system for super market in which i have created a form for generating BILL. I have used FlowLayout panel for generating 4 ComboBoxes, 3 TextBoxes and 2 Numeric UpDown respectively to hold Bill values accordingly. I have supplied add button with which we can create these controls dynamically on each button click, so, for example, when user clicks on the add button to add new item, new row will be generated with 4 CBs, 3 TBs and 2 NUpDowns. Having mentioned the scenario, I have following queries:

1. How can i access each and every of the control in each row in turn? So, for example, I want to access 3rd ComboBox of 5th row, How can I access that in particular.
2. I am using 3-tier application architecture to design the application. I have placed their functions in BusinessLogicLayer and have called them in UI in button event. Am i alright with this approach?
3. I want each ComboBox, in each row, to be connected with the first one. for example first one indicates main category when user selects anything from that, second combo box(sub category) should show items connected with the first one and so on. How can i do that?

Thanks

Answer 1

I don't know the very architecture of your application, but let me try and help you. Assumed you have some sort of Customer, Product and Order objects for your business logic the workflow could be the following

void ButtonFindCustomer_Click(object sender, EventArgs e)
{
    m_order.Customer = Customer.Find(TextBoxFirst.Text, TextBoxLast.Text, TextBoxCustomerID.Text);
}

void ButtonAddProduct_Click(object sender, Event args)
{
    m_order.AddArticle(Product.Find(TextBoxArticleNumber.Text), NumericUpDownArticleAmount.Value);
}

void ButtonSubmit_Click(object sender, EventArgs e)
{
    m_order.Place();
}

I used the prefix for the member variable here just for clarity, for the lack on context. In your real code you should avoid it. Furthermore I have omitted the check if the user exists in ButtonFindCustomer_Click, this case should be handled, too. In ButtonAddProduct_Click the case a product is added is handled. Again the existence of the product is assumed, thus you'll have to introduce some error handling here, for example by using something like

if(Product.Exists(productNumber))
{
    // add to order
}
else
{
    // emit error message
}

The actual transaction is performed in the ButtonSubmit_Click handler. The order is validated and then sent to the data access layer (for example written to a SQL-Database). Once again the error handling is missing, please keep that in mind.

To get to your actual questions:

1) You'll somehow have to keep track the controls you created. If you are always creating them in the same groups, you should consider a user control, which avoids keeping track of which controls belong together. The control could - for example - contain a drop down box for categories, a drop down box for products and a numeric up down for the amount.

class ProductSelector : UserControl
{
    ... //add controls to user control

    public event EventHandler CategoryChanged;
    public event EventHandler ProductChanged;
    ...

    public void PopulateCategories(list<string> names, list<string> ids)
    {
        ...
    }

    public void PopulateProducts(list<string> names, list<string ids)
    {
        ...
    }
}

Now any time anything about the product is changed, you'll receive an event and can directly access your user control and all necessary data (if you wrote the functions in ProductSelector). If you want to access the controls in turn, you can either get all controls of type ProductSelector from MainForm.Controls or create a list of all ProductControls you added.

2) Yes, I think you'll be alright with this approach. Somewhere you'll have to access the functions of your BLL and UI event handlers are a good starting point for.

3) Please see me answer to 1).

I hope my explanation met your requirements and answered you questions. Feel free to ask, if I may help you any further.