I'm trying to implement this pattern in my WinForms application (I don't like it, but it was required by the customer):
I edit the properties of an object in a DetailsControl (UserControl developed by us), and when the user tries to leave the control, then it's validated and saved
If it's not valid, or an error occurs during save, then the control must not be left (it's in a List/Detail section)
My idea was this:
on Validating, I check if my object is fine, otherwise I cancel the event
on Validated, I save my object, and if an error occurs, I cancel the event
Unfortunately, Validated is not cancelable, and Leave is fired before Validating/Validated. Is there a cancelable event after Validated, that would prevent losing the focus?
If not, I will move all my logic inside Validating, but I would like to keep the formal validation separated from the save errors.
This article lists the usual order of events when a Validated/Validating event is raised. There are no cancelable events after Validating. I think that without some extra magic, you're out of luck.
If you're really concerned that people using the class might do other validation checks of their own in Validating event handlers, you could extend the class with another custom, cancelabe validating event. You could then raise this custom event during OnValidating before calling base.OnValidating.
Related
I have a WPF Custom control which I have been building as I happen to need a particular functionality and I want to learn how to do this properly. Most of the control has now come together nicely and is generally pretty usable. There is now one feature that I'd like to implement, however, I'm not sure if it's possible in the first place or if it is how I would or should go about implementing it.
So here goes by way of my explanation of what I have and what I would like. Feel free to ask for extra clarification if required.
My control raises a custom event which passes along some custom event args. The event is declared like so in the control.
Public Event RecordControlButtonClicked(sender As Object, e As VtlDataNavigatorEventArgs)
In most cases when this event is raised the end user has simply clicked the button, nothing other than raising the event will take place because the developer using the control will most likely want to decide how they handle the situation at that particular moment and the custom event args provide more than enough info to do that.
There are however a couple of buttons where in all honesty the developer will probably want to happen what I (as the developer of the control) envisage should happen most of the time but on the odd occasion might not and therefore needs the opportunity to cancel out of it. So what I'm wondering is how I might achieve the following:
The end user clicks a button
The control button raises my custom event
The developer using my custom controls decides they wish to ignore what I (the creator of the control) thinks should happen, so they do something like e.handled = true in the code where they handle my custom event.
Somehow that message gets back to the button that raised the event, it seems that it's been 'handled' or 'canceled' and as a result does nothing
My question is how do I create that sort of functionality and is the event that I currently have declared the correct sort of event to handle this?
Well just in case anyone stumbles across this looking for an answer.
It transpires that my basic mistake lay in the way that I'd Created my custom events class. Originally I'd followed several examples that I'd read about and had my custom events inherit from EventArgs;
Public Class MyCustomEventArgs
Inherits EventArgs
End Class
What I should have done was have it inherit from CancelEventArgs;
Public Class MyCustomEventArgs
Inherits System.ComponentModel.CancelEventArgs
End Class
That provides the Property that I was after. Now when the event is actually handled upstreap the developer can add an e.cancel = true and all I need to do back in the originating call to raise the event is listen out for e.cancel ;
RaiseEvent MyCustomEvent(sender, e)
if e.cancel = true
'presumably don't do something
Else
'do what needs to be done
End If
When I try to add Nokia Ad Exchange ad control in my page XAML, the overridden OnManipulationStarted event handler doesn't fire when I touch it. It is fired if I touch anything else, but if I touch it specifically, then it doesn't enter in the method code.
Is this a related issue to the control or should I add something else?
It's probably handled by the control, so it doesn't bubble up.
You can use the alternative control.AddHandler method rather than += to add an event handler. It takes a boolean that specifies if you want the event handler called even if it was handled by a sub-element.
For each UI control on wpf, there is a 'loaded' event. Suppose I have a user control with a list of other controls, like Combobox. Now, If I catch loaded event for both "usercontrol" and for "Combobox", then the the loaded event is first occurred for Usercontrol and then for Combo box, which means when the user control is already loaded, its child elements may not be loaded completed. But, I want to catch the global load event, that means that load event will be occurred only when all controls are loaded successfully. How to achieve this please? Thanks in advance.
There is no global Loaded event, you state that the 'loaded event is first occurred for Usercontrol and then for Combo box', this is probably due to the order in which you registered for these events. What exactly are you trying to achieve?
Other events that might be of use to you are LayoutUpdated, this fires each time the visual tree is modified. You can register a handler, catch the first time this event is raised, then check your UI state to determine when your UI is initially rendered.
However, you normally only need to use these techniques if you are doing something quite complex or special within the UI, like creating a complex new control. For most applications you do not need to handle either of these events.
Like the title says I am trying to architecture into my application a way to distinguish the source of a variable change, either from UI or code-behind.
My problem is that I need to trigger some action after a property changed its value, but I only need to do this when the change comes from the UI because otherwise I don-t want to perform that action. I am having some trouble because, for example when a checkbox(two way binding), changes state, my binded property gets updated and then I use the checked and uncheked events to trigger that action.The problem is that when I change the property in codebehind it also triggers those events and I do not want that. Right now, i am using a flag that enables, or not, the actions at the event handlers but I do not feel that this is a good idea.
Any sugestions or ideas?
I am considering using only one-way binding and control everything my self, using commands.
It looks like you have some confusion between your model and your controller. There shouldn't be any cases where it matters if the a change to the model comes from the user or not. If you want to have something like a confirm message it the user makes the change, then don't bind the view control directly to the model, but have the controller respond to the event.
That way, if the control is changed to be the same as the model, then the change is internal, and no confirm is required, but if the control is changed by the user, then the control state differs from the model, and a confirm can be shown.
I have several controls on my form and on changed event the logic entity properties are changed. Is it possible not to implement changed event for every control,but do it in one place and update my logic entity when user is making changes on the form?
You need to subscribe to Change event of every control, but use the same event handler for all controls. For example, all textboxes can subscribe to the same Change event handler. For other control types, event handlers may have different types, so you can write one event handler per control type. You can also write single function, like OnUpdate, and call it from all event handlers.