We got a requirement from our client that, when
user clicks on the “All” option from a Silverlight list box, and then all Items
from that Listbox should be selected.
Here below are the three scenarios.
·
User
Clicks on “All” option to select All Items, then all items in the list to be
selected.
·
User
can select all items individually using Ctl key, then the option “All” also to
be selected, even the user not selects it.
·
If
any of the Items got unselected, then “All” option also to be unselected.
Here we are trying to write the logic in List Box
Selection Changed event, there is a possibility that we may end in infinite
loop, if we are trying to implement it without taking care. As selection and de
selection will raise Selection Changed event, we should do something to avoid
it.
Even if Selection Changed event logic is having
some code to be executed, when user really changes selection, that code will be
executed unnecessarily because of our newly added code. So it will create
latency and performance will be down.
After some research, I have come up with below
solution.
void LstGeographics_SelectionChanged(object sender, SelectionChangedEventArgs
e)
{
ListBox lstBox = sender as
ListBox;
if (lstBox.Tag != null
&& (bool)lstBox.Tag == false)
{
lstBox.Tag = true;
return;
}
SetRegionListBoxSelection((ListBox)sender, e);
DoSomething();
}
In the above event handler, we are checking for
ListBox’s tag property, which we are setting to false, when our code itself
changing the selection, without user interaction.
So if it is false, then we can avoid unnecessary execution
of the method “Dosomething”
public void SetRegionListBoxSelection(ListBox lstBox, SelectionChangedEventArgs
e)
{
try
{
if (e.AddedItems.Count == 0 &&
e.RemovedItems.Count == 0)
return;
if (lstBox.SelectedItems.Count ==
lstBox.Items.Count - 1)
{
if (!e.AddedItems.Cast<ClassName>().Contains(lstBox.Items.Cast<ClassName>().First()))
if (!e.RemovedItems.Cast<ClassName>().Contains(lstBox.Items.Cast<ClassName>().First()))
{
lstBox.Tag = false;
lstBox.SelectAll();
return;
}
else
{
lstBox.Tag = false;
lstBox.SelectedItems.Clear();
}
}
if (e.AddedItems.Cast<ClassName>().Contains(lstBox.Items.Cast<ClassName>().First()))
{
lstBox.Tag = false;
lstBox.SelectAll();
return;
}
if (lstBox.SelectedItems.Count <=
lstBox.Items.Count - 1)
{
lstBox.Tag = false;
lstBox.SelectedItems.Remove(lstBox.Items.Cast<ClassName>().First());
}
}
catch (Exception
ex)
{
}
lstBox.Tag = true;
}
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