Hello,
I wonder if anyone has done a Silverlight / Async data portal implementation with lazy loaded properties. The lazy loaded technique seems to be to call DataPortal.Fetch on the child if it doesn't exist, however the async data portal needs a call back handler. The handler could be cached from the call to the parent factory method I suppose. Dunno if that would work. Other than that, I'm wondering if there's a technique that's anyone's used successfully.
Here
is a thread on the subject.
http://forums.lhotka.net/forums/thread/32438.aspx
Sergey Barskiy
Principal Consultant
office: 678.405.0687 |
mobile: 404.388.1899
Microsoft Worldwide Partner of the Year | Custom
Development Solutions, Technical Innovation
From: esaulsberry
[mailto:cslanet@lhotka.net]
Sent: Friday, June 12, 2009 1:58 PM
To: Sergey Barskiy
Subject: [CSLA .NET] Lazy Loading and the Async Data Portal
Hello,
I wonder if anyone has done a Silverlight / Async data portal implementation
with lazy loaded properties. The lazy loaded technique seems to be to
call DataPortal.Fetch on the child if it doesn't exist, however the async data
portal needs a call back handler. The handler could be cached from the
call to the parent factory method I suppose. Dunno if that would
work. Other than that, I'm wondering if there's a technique that's
anyone's used successfully.
sergeyb:
private bool _loadingScore = false;
private static PropertyInfo<Score> ScoreInfoProperty = RegisterProperty(new PropertyInfo<Score>("ScoreInfo", "ScoreInfo"));
public Score ScoreInfo {
get {
if (!_loadingScore && (!FieldManager.FieldExists(ScoreInfoProperty) || ReadProperty(ScoreInfoProperty) == null)) {#if SILVERLIGHT
_loadingScore = true;
Score.GetScore(ReadProperty(ProfileIDProperty), ReadProperty(PersonNameProperty), ReadProperty(NicknameProperty), ReadProperty(TeamIDProperty),((TeamMemberInfoList)this.Parent).ParentTeam.Name, (o, e) => {LoadProperty(ScoreInfoProperty, e.Object);
OnPropertyChanged(ScoreInfoProperty.Name);
_loadingScore = false;
}
);#else
LoadProperty(ScoreInfoProperty, Score.GetScore(ReadProperty(ProfileIDProperty), ReadProperty(PersonNameProperty), ReadProperty(NicknameProperty), ReadProperty(TeamIDProperty), ((TeamMemberInfoList)this.Parent).ParentTeam.Name));
#endif
}return GetProperty(ScoreInfoProperty);
}
}
OK, If I grock this, you're providing a different silverlight and non-silverlight lazy loaders in the get, which call different factory methods in the child - the silverlight one takes a handler and the regular one doesn't. In this case you're providing the handler as a lamba, but it could be silverlight only code elsewhere in the object that accomplished the same thing. The _loading boolean keeps you from starting the process again before the first one finishes. The return will run before the data comes back so at first the value of the property is null, a property changed event happens when the data comes back so the UI can update itself. An enigma, wrapped in a mystery... but elegant.
It is also possible that the LoadPropertyAsync() method can help you in this case.
In any case, technically you don't need a different implementation for SL from Windows - but SL can only have the async implementation, and most .NET developers won't expect the async behavior.
Copyright (c) Marimer LLC