C#

<br />
ApplicationClass excel = new Microsoft.Office.Interop.Excel.ApplicationClass();<br />
Workbooks oBooks = excel.Workbooks;<br />
object nulo = System.Reflection.Missing.Value;<br />
<br />
//here u have open method, there's many parameteres, but they can be null.<br />
oBooks.Open("C:\\file.xls",nulo,false,nulo,nulo,nulo,nulo,nulo,nulo,true,nulo,nulo,nulo,nulo,nulo);	<br />
<br />
//A _workbook where the sheet lives<br />
_Workbook b = oBooks.get_Item(1);<br />

if ( this.DesignMode ) {
    this.ProcessDesignTimeClick(e);
}
else{
    this.ProcessRunTimeClick(e);
}

bool IsInDesignMode(Component component) {
    ISite site = component.Site;
    bool ret = ( site != null && site.DesignMode );
    return ret;
}

public class MyButton : Button {
    protected override void OnClick( EventArgs e ){
        if ( this.DesignMode ) { // use protected property
            MessageBox.Show( "This button is in design mode. Raising event 'Click' is verboten." );
        }
        else {
            base.OnClick( e );
        }
    }
}

public class MyForm : Form {
    private Button button1;
    ...
    ...
    ...
    private void button1_Click(object sender, EventArgs e){
        ISite site = this.button1.Site;
        if ( site != null && site.DesignMode ){
            MessageBox.Show("Button was clicked in design mode.");
        }
        else{
            MessageBox.Show("Button was clicked in run-time mode.");
        }
    }
}

<code>public class MyControl_A : UserControl{
    private MyControl_B myCtl_B;

    public MyControl_A(){
        this.myCtl_B = new MyControl_B();
        this.Controls.Add(this.myCtl_B);
    }
}

public class MyControl_B : UserControl{
    protected bool IsInDesignMode(){
        bool ret = false;

        Control ctl = this;
        while( ctl != null && ret == false ){
            ISite site = ctl.Site;
            if ( site != null ){
                ret = site.DesignMode;
            }
            
            ctl = ctl.Parent;
        }

        return ret;
    }
    protected override void OnClick(EventArgs e){
        if ( this.IsInDesignMode() ){
            MessageBox.Show("This control is in design mode.");
        }
        else{
            base.OnClick(e);
        }
    }
}