This chapter is from the book
This chapter is from the book
This chapter is from the book
Making an Adapter
It may be a little difficult to remember to use the Items collection of the list box for some operations but not for others. For this reason, we might prefer to have a class that hides some of these complexities and adapts the interface to the simpler one we wish we had, rather like the ListBox interface in VB6. We'll create a simpler interface in a ListAdapter class that then operates on an instance of the ListBox class.
public class ListAdapter {
private ListBox listbox; //operates on this one
public ListAdapter(ListBox lb) {
listbox = lb;
}
//-----
public void Add(string s) {
listbox.Items.Add (s);
}
//-----
public int SelectedIndex() {
return listbox.SelectedIndex;
}
//-----
public void Clear() {
listbox.Items.Clear ();
}
//-----
public void clearSelection() {
int i = SelectedIndex();
if(i >= 0) {
listbox.SelectedIndex =-1;
}
}
}
Then we can make our program a little simpler.
private void btClone_Click(object sender, EventArgs e) {
int i = lskids.SelectedIndex ();
if( i >= 0) {
Swimmer sw = swdata.getSwimmer (i);
lsnewKids.Add (sw.getName() + "\t" + sw.getTime ());
lskids.clearSelection ();
}
}
Now let's recognize that if we are always adding swimmers and times spaced apart like this, maybe there should be a method in our ListAdapter that handles the Swimmer object directly.
public void Add(Swimmer sw) {
listbox.Items.Add (sw.getName() + "" + sw.getTime());
}
This simplifies the Click Event handler even more.
private void btClone_Click(object sender, EventArgs e) {
int i = lskids.SelectedIndex ();
if( i >= 0) {
Swimmer sw = swdata.getSwimmer (i);
lsnewKids.Add (sw);
lskids.clearSelection ();
}
}
What we have done is create an Adapter class that contains a ListBox class and simplifies how you use the ListBox. Next, we'll see how we can use the same approach to create adapters for two of the more complex visual controls.