I have a couple of 'problems' with your implementation.
- PLEASE ditch DataTables. They are terrible to work with. Slow etc etc.
- You should not be newing the BLL here (in the form I assume this is). The business layer is a service and should be injected to decouple your form from the data source.
- You have to call FillCombo each time the data updates.
- If you want to seperate concerns, the form should not be getting the data from the BLL. It should only be presenting the data. Another class should be getting the data and making it available for presentation.
My suggestion is as follows (I tend to minimise code in the form down to only bindings and using DI):
Row represents the data you want to display in the combo:
Code:
public class Row
{
public long Id { get; set; }
public string Name { get; set; }
}
The Viewmodel is where the behaviour behind the form is controlled from. The form is only the presentation/visualisation of the data/behaviour/state of the viewmodel behind it. The INotifyPropertyChanged allows controls on the form to bind to its properties. You inject the IBLL into the viewmodel, so you can inject any implementation (local DB, remote DB, Azure, webservice, anything) as a source of the data. When you call the UpdateRows, the viewmodel will fetch the data from the source and update the property. This will fire the event that will make binding happen.
Code:
public class ViewModel:
INotifyPropertyChanged
{
public ViewModel(IBll bll)
{
this.bll = bll;
}
public event PropertyChangedEventHandler PropertyChanged;
public IList<Row> Rows
{
get { return rows; }
private set
{
rows = value;
OnPropertyChanged("Rows");
}
}
public void UpdateRows()
{
Rows = bll.GetRows();
}
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
private readonly IBll bll;
private IList<Row> rows = new List<Row>();
}
Your form code is purely concerned with presentation. You can see the binding of the form Rows property to the viewmodel Rows property. Each time the viewmodel's Rows property is updated, the event will fire. This will in turn execute the form's Rows property setter and fill the combo.
Code:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public IList<Row> Rows
{
get { return null; }
set
{
//Fill Combo here
}
}
public void CreateBindings(ViewModel dataContext)
{
this.dataContext = dataContext;
DataBindings.Add("Rows", dataContext, "Rows", true, DataSourceUpdateMode.Never);
}
private ViewModel dataContext;
}
To compose all of this you do this:
Code:
Form1 frm = new Form1();
Bll bll = new Bll();
ViewModel dataContext = new ViewModel(bll);
frm.CreateBindings(dataContext);
Application.Run(frm);
You might think that is a lot more code than yours. Yes it is, but each class does one thing only. Its pulls the concerns apart and makes everything more extensible. You can now use any BLL implementation. In the same way you bind fiedl edit controls to properties in the viewmodel so that the behaviours, validation etc happens in the viewmodel and not the form.
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