Question

I just started breaking up my GUI application into UserControls. I have a TabControl with a bunch of TagePages. Obviously my MainForm.cs file was filled up with tons of events and controls etc and it got very messy quick.

So a previous question gained me the insight of how to create a UserControl. I intend on creating a UserControl for each TabPage and I was wondering how I can interact with Components on the main form or other UserControls.

Here is an example of a TabPage that I have made using a UserControl, which needs to Enable or Disable a button depending which TabPage is currently selected. Is this proper usage or is there a better way?

public partial class TabDetails : UserControl
{
    private RequestForm fRequestForm;
    public TabDetails()
    {
        InitializeComponent();
    }

    public void CustomInitialization(RequestForm pRequestForm)
    {
        fRequestForm = pRequestForm;
        pRequestForm.TabControl_Main.SelectedIndexChanged += SelectedTabIndexChanged;
    }

    private void SelectedTabIndexChanged(object pSender, EventArgs pEvents)
    {
        fRequestForm.Button_SubmitRequest.Enabled = fRequestForm.TabControl_Main.SelectedTab != fRequestForm.Tab_Details;
    }
}

In the MainForm.cs constructor I call:

this.tab_Details1.CustomInitialization(this);

Answer 1

This doesn’t look like a good use of a user control. The user control should not decide how things in the form should behave when something is changed in the user control. A user control should be unaware of its container and should operate in any container.

The user control should notify the form that something has changed without telling what’s the internal implementation and the form should decide what to do.

Example:
A user control named “NameUserControl” consists of TitleComboBox, FirstNameTextBox and LastNameTextBox. The user control wants to notify when one of the values has changed.

Wrong Way:

Create events:

TitleComboBox – SelectedIndexChanged.
FirstNameTextBox, LastNameTextBox – TextChanged.

The problems here:

1. You expose the internal controls behavior. What will happen if you want to change the TitleComboBox to TextBox? You’ll have to change the event name and implementation.
2. You expose the fact that you use exactly 3 different controls. What will happen if you want to use the same text box for first and last name? You’ll have to delete one event and change the name of the other.

Good Way:

Create only a single event: NameChanged and expose 1 property of FullName or three different properties for the values.

Either way the form subscribe to the event and decide what to do next.

Another thing to think about: the more you add more functionality to your user control, you either make it less reusable or you make its code more complex. For example, if you add validation inside the user control, you’ll find one day that you need it without validation, so you’ll add a property “bool ValidateData” or it will be so complicated that you’ll need to build another control. One way to solve that is to build very small user controls, but combine them in one or more bigger user controls that fit all your current needs.