I'm looking for a bit of advice if possible. I am using event handlers to update a WPF application, it works fine but I was wondering if this was the best way to go? Would it be better practice to use data binding using XAML?
Thanks for your help as always.
Personally I would use data binding to do this and the MVVM pattern.
At the most basic you would bind your textbox to a property on your view model, in the setter you could call a method which executes your SQL query. Your View Model class would also need to implement INotifyPropertyChanged to allow the view model to update the UI if you wanted data to flow both ways.
Although depending on what you're doing you may be better having something that triggers the SQL update rather than every time the text changes. If you have a lot of different fields to update and you use the text changed event you're going to fire off a lot more SQL updates than you need. Maybe a save button or something which detects when changes are finished and makes them all at once would be more efficient?
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I need some help to architect an MVVM application. This time I want to do it in the right way.
My View is bound to the ViewModel which is bound to the Model. No problem there. Displaying data is not the problem, updating it is my problem.
So when the View asks the ViewModel to update the Model (with a Command), which need to handle the logic?
In my case updating the data is not trivial, there are many calculations with many files.
Also, I really want that the Model does not know the business logic. So how to do this? A property in the Model which indicates that the he wants to be updated? Or maybe the ViewModel have to know the business logic? Is it the Best practice?
The model is really a snapshot of the state of your business data. Your non-trivial calculations can be encapsulated in services that can be abstracted behind interfaces and injected into your view model. This way your view model knows nothing of these complex processes other than calling them via interface contracts. So your command fires and your view model provides orchestration, your service provides actual business calculations and an updated model would be produced representing the new state of the system.
Can anyone please explain difference between Triggers, Behaviors and Commands. I tried to search on this, but could not find anything useful.
And would also like to know in which scenario which one should be preferred and which one is used frequently among them?
Behavior is a way of interactivity without writing code. Behaviors makes interactivity much simpler for the designers. In short, a behavior is a reusable piece that encapsulates some functionality that can be attached to an object to extend its built-in interactivity capabilities.
Commands are used to encapsulate a piece of logic, which various Silverlight controls can bind to and execute in response to an event, such as a button being clicked. You can expose a command from a ViewModel as a property and bind the Command property of a control in the View to it. When the control is clicked, the command will be executed.
In MVVM scenarios, triggers are used to notifying the view of an event from a ViewModel.
For example, perhaps the view needs to navigate to another view once a save operation is
complete. You can implement this behavior by raising an event from the ViewModel that the view can listen for by doing either of the following:
• Wiring up an event handler in the view’s code-behind and writing some code to
respond to the event (Not recommended approach)
• Implementing a trigger in the view that listens for the event and responds accordingly
You can see this, this and this for more explanations.
Also, Pro Business Applications with Silverlight 5 is a very good reference for you.
Sometimes a Domain Model object with a business logic (DDD) when calling a method an event is fired.
In my situation, a viewmodel (for a given view) encapsulates the domain object and needs to register and react on those domain events (i must use events because that same domain object can be managed by many loosely coupled views along with their viewmodels).
I also need to unregister to those events when that particular context is hidden.
I can handle this register/unregister/dispose in parallel with show/hide/dispose of that view using databinding, programmatically or whatever if the scenario keeps simple enough...
The problem comes when visualization logic comes with DataTemplates.
How can I know when that datatemplate becomes hidden so that I can unregister my events? is it there a better way with wpf to handle this, instead of adding more events?
What is the best practice to handle this scenario in a good MVVM approach?
edit: ok, the problem is structural. sometimes choices made inside the project has forced us to work in an atypical manner... in a good mvvm approach this problem should not happen
I'd be careful in making the ViewModel dependent on the View for making things right.
So what I would do is provide a property (Show? Visible? Open?) on the ViewModel that has a TwoWay binding with the View so the ViewModel can monitor the property.
I am using a WCF service reference in a WPF project, and my entity framework data model resides in WCF project.
And I am using MVVM Light framework. I am doing the following things:
I use LINQ in the service to get data and then fetch it from WPF, obersvablecollections usually.
Everything works in view part like populating datagrid, views as required.
But I have following doubts:
Is this correct way of transferring data between wcf and wpf.
I haven't used the Model for anything yet, I have doubt about when to use it?
I also wanted to save data from datagrid. I was able to pass on the observablecollection of updated data of datagrid to the service's function. But how do i update the entity from this collection? by looping? doesnt sound right. Once I update the entity from this collection I will be able to use saveChanges to update into database.
When I need to show hierarchal data in a treeview, where to make that data hierarichal, from stored procedure xml? use a view to create a grouping criteria column? create this column in service? create this column/property in presentation?
1 - There is no correct way, it depends on your requirements and goals.
2 - With MVVM, the model should sit between WPF and the database. That means all calls to the database should go through the model, and all writes to the database should also go through the model. The WPF GUI should only bind to the model. This usually means that your WPF portion consists mostly of XAML code. All code that accesses the database should be in the model.
There are good reasons for separating this.
You can write unit tests that on the model.
The view model is independent from the look of the GUI. This means that you can easily change the GUI by dropping in different components and just binding to the model.
A quick google search can probably yield more reasons.
3 - I would try to send over only the entities that have changed. This can be done by passing the collection to your view model, and have your view model figure out what has changed.
4 - I don't quite understand what you want to do. Usually, to make a TreeView, you should create HierarchicalDataTemplate for each of your view models. The TreeView control will take care of the rest. You should really do some tutorials on this one, because it's kinda hard to wrap your head around.
I am trying to get into MVVM and away from the code behind approach in Silverlight, and I want to know the best practices around how to invoke view logic.
I have a very basic page where I have bound a listbox to a collection of domain objects, this is all using MVVM, so when I recieve my data back from the services, I want to fire off an animation and view changes on the screen.
Where/How is the best way to doing this? Silverlight (version 3, BTW) doesnt have triggers does it? I have seen blogs where people seem to be using them, but i think they must be rolling their own? Not sure... anyways, any thoughts ideas here is greatly appreciated
First of all, I think code behind is just fine as long as it only works with the view, i.e. it is concerned only with UI concerns. Don't struggle for no-code-behind when the easier way out is just as correct.
Secondly, of course sometime you need some sort of disconnected communication between your view and view-model (for example, getting multiple selected items from your view into your view-model). For these purposes you could use an aggregator like MVVMLight's Messenger, which is both simple and expresses the concept nicely. You can send a message from the view-model and have the view listen for it; also you can send messages from your view (when some events occur) and broadcast them.
MVVMLight also includes some utility classes which make it easy to bind events directly to Commands in your view-model, so that's the easier option in most cases I think.