Binding ComboBox and ObservableCollection<KeyValue> in wpf - wpf

Question

in My OpenViewModel i collect data:
private ObservableCollection<KeyValue> availableData;
public ObservableCollection<KeyValue> AvailableDatas
{
get { return availableData; }
set
{
if (value != availableData)
{
availableData= value;
NotifyOfPropertyChange("AvailableDatas");
}
}
}
method for collecting data:
public ObservableCollection<KeyValue> CollectData()
{
ConnectorClient client = null;
try
{
client = webservice.GetClient();
AvailableDatas = client.GetDatas();
client.Close();
}
catch (Exception ex)
{
webservice.HandleException(ex, client);
}
return AvailableDatas;
}
How to call the method CollectData in wpf and fill my COmboBox?
thx

Answer 1

You might simply call the method the first time the AvailableDatas property is accessed (e.g. from a binding in XAML):
private ObservableCollection<KeyValue> availableData;
public ObservableCollection<KeyValue> AvailableDatas
{
get
{
if (availableData == null)
{
availableData = CollectData();
}
return availableData;
}
set
{
if (value != availableData)
{
availableData = value;
NotifyOfPropertyChange("AvailableDatas");
}
}
}
Then you should change the CollectData method in a way that is does not also set the property:
public ObservableCollection<KeyValue> CollectData()
{
ConnectorClient client = null;
ObservableCollection<KeyValue> data = null;
try
{
client = webservice.GetClient();
data = client.GetDatas();
client.Close();
}
catch (Exception ex)
{
webservice.HandleException(ex, client);
}
return data;
}

Answer 2

You could override the OnActivated() event assuming you are using an IScreen implementation and load data in there, or just do it in the constructor or a custom Initialise method if you want to roll your own (or in the property accessor as someone has already said).
You can also use coroutines if you want some visual context for the user and a better tie in with CM actions
There is a nice simple implementation of a Loader class here which helps provide visual context to the user:
https://caliburnmicro.codeplex.com/wikipage?title=IResult%20and%20Coroutines&referringTitle=Documentation
This searches the visual tree for a BusyIndicator control and activates it whilst the content is loading e.g. ...
public class SomeViewModel : Screen
{
protected override void OnActivate()
{
RefreshData();
}
public void RefreshData()
{
Coroutine.BeginExecute(LoadData(), new ActionExecutionContext() { Target = this });
}
public IEnumerable<IResult> LoadData()
{
yield return Loader.Show("Loading Data...");
yield return new LoadSomeDataRoutine(client.GetDatas);
yield return Loader.Hide();
}
}
The reason to have a RefreshData method is that this also allows you to bind CM actions and allows the coroutine can grab more contextual information.
Obviously you have less need to worry about the async->sync benefits this gives in Silverlight because you are using WPF (but it still applies to async web service calls), however it still has many benefits and it also helps you to write reusable routines which become part of your application framework (e.g. some level of error handling/logging encapsulated in the IResult implementation etc)
You also mentioned filling the combobox... all you would need to do in CM is place a combobox on your control, and set it's Name property to the name of the property on your VM:
public class SomeViewModel : Screen
{
public ObservableCollection<MyObject> MyProperty { //blah blah... }
}
<UserControl .... blah>
<ComboBox x:Name="MyProperty" />
</UserControl>
This will fill the combobox with the items. You will still need to set the binding for SelectedItem/SelectedValue
I assume you know this already though - if not CM has some decent documentation:
https://caliburnmicro.codeplex.com/wikipage?title=Basic%20Configuration%2c%20Actions%20and%20Conventions&referringTitle=Documentation