I am using WPF with the MVVM Pattern and Prism, and I'm using InteractionRequests for showing dialogs.
When I define the InteractionTriggers and their actions, I define them like this:
<i:Interaction.Triggers>
[Other event triggers]
<i:EventTrigger EventName="Raised" SourceObject="{Binding SomeConfirmationInteractionRequest}">
<i:EventTrigger.Actions>
<windowActions:DialogWindowAction />
</i:EventTrigger.Actions>
</i:EventTrigger>
</i:Interaction.Triggers>
Now I was checking my EventTriggers, and realized, I am missing one of the <i:EventTrigger.Actions> tags inside of the <i:EventTrigger>:
<i:EventTrigger EventName="Raised" SourceObject="{Binding SomeConfirmationInteractionRequest}">
<windowActions:DialogWindowAction />
</i:EventTrigger>
I was more confused that this part of my code worked, and there was no problem with it.
My question:
Why can it simply be omitted?
Can I just leave it out? Or does leaving the EventTrigger.Actions tag out change something that I haven't realized/experienced yet?
Yes, it can be safely omitted.
If you look at the TriggerBase class (up the inheritance tree of EventTrigger), you'll see it has an attribute [ContentProperty("Actions")]. This tells WPF to treat the Actions property as the direct child of the element in XAML.
This is widely used in WPF, e.g. ContentControls have the Content property (so you can write <Button><Image/></Button> instead of <Button><Button.Content><Image/></Button.Content></Button>), Panels have the Children property as their content, etc.
Related
I have a WPF project (C#, MVVM Light, Visual Studio 2010).
I have a bit of a problem regarding separation of concerns (MVVM) which basically is this: I have a command in a view model. I have a context menu that I want to call that command. So far so good. The problem is that the command needs to coordinates that the mouse was clicked.
To be a little more specific, the ContextMenu only appears if you click on a particular Canvas control, and it's the coordinates within said Canvas control that I want.
The easy way to do this is to manage it all in the code behind of the XAML document (and I have been able to do it that way), but I'd rather have it within my ViewModel if I can do so. The reason is that there are calls to my data model within this command so we end up with a problem of separation.
I am aware of PassEventArgsToCommand, and I'm aware that it's a bad practise, however in this case I'm not sure I can see a way around it. So for the moment I did try that, and it looks like this:
<ContextMenu x:Key="BackgroundMenu">
<MenuItem Header="Add new node here">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<cmd:EventToCommand Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContextMenu}}, Path=PlacementTarget.DataContext.AddNewNodeAtLocationCommand}" PassEventArgsToCommand="True"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</MenuItem>
</ContextMenu>
So now my command, within the view model, looks like this:
void AddNewNodeAtLocationExecute(RoutedEventArgs e)
{
return;
}
Within that method I'd like to get those mouse coordinates, but I don't know if it's possible. e.OriginalSource is 'MenuItem', which doesn't help much.
So how can I do this? Can I do this? Or should I just have this one command handled by the code behind? Said code will involve a call to the database, which is why I'm being so particular about the separation.
Thanks in advance.
Well I stumbled across this question which speaks about separation of concerns and what not.
In the end I did a merging of the two ideas I had. Firstly, the ContextMenu simply links to the code behind. At that point I get the coordinates I want. Then that code behind gets the DataContext of the view (where the command I want is) and calls the Execute method (having first checked the 'can' method).
I suppose it's as ideal as you're going to get.
I'm little confused about RelayCommand and EventToCommand in Mvvmlight.
It seems that EventToCommand handle the EventTrigger and call a RelayCommand to do job.
Such as:
<i:Interaction.Triggers>
<i:EventTrigger x:Uid="i:EventTrigger_1" EventName="MouseLeftButtonUp">
<cmd:EventToCommand x:Uid="cmd:EventToCommand_1" Command="{Binding Form_MouseLeftButtonUpCommand}" PassEventArgsToCommand="True"/>
</i:EventTrigger>
</i:Interaction.Triggers>
Is my understanding correct?
So, can we use RelayCommand directly with EventTrigger, no need to use EventToCommand?
Thanks for your help!
EventToCommand is a custom behavior. It is first provided by Expression blend team and now Part of WPF 4. If you're not using WPF4. you require Blend SDK from here.
Behaviors encapsulates functionality as reusable components. These are to be used when feature is not present by default. For example Adding Command support to Label, Combobox etc.
can we use RelayCommand directly with EventTrigger, no need to use EventToCommand?
No. RelayCommand is a shortcut to avoid code redudnency to define custom commands.It extends ICommand whose delegates can be attached for Execute(T) and CanExecute(T). It is similar to DelegateCommand of Prism library.
<cmd:EventToCommand x:Uid="cmd:EventToCommand_1" Command="{Binding Form_MouseLeftButtonUpCommand}" PassEventArgsToCommand="True"/>
In above line cmd:EventToCommand is additional feature to the underlying control. Form_MouseLeftButtonUpCommand is the Command it executes. This command can be encapsulated as RelayCommand.
Thank Tilak for your useful answer.
With the explanation from Tilak, I did mess up like putting a binding in a event handler (such as Button GotFocus="{Binding DoJob}") --> Build failed and found that Event Handler like this does not support Binding. We can only bind in Command (such as Button Command="{Binding DoJob}" /> and default event is invoked in this situation, with button, it should be Click event).
Do something stupid will help me to understand the life more - LOL
can we use RelayCommand directly with EventTrigger, no need to use
EventToCommand?
Actually, I intend NOT to use EventToCommand, and I found the solution for that: use InvokeCommandAction instead (belongs to System.Windows.Interactivity - Mvvm-light also refers to this assembly).
Does exist a similar EventToCommand (behavior's) on Android?
Example Silverlight/WPF:
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<Commanding:EventToCommand Command="{Binding DataContext.EditEventTypeCommand,
RelativeSource={RelativeSource AncestorType=telerik:RadGridView}}"
CommandParameter="{Binding}"
PassEventArgsToCommand="True" />
</i:EventTrigger>
</i:Interaction.Triggers>
If you are using mvvmcross, then bindings exist for all events which have EventHandler signatures - so you can just use bindings like:
'Click':{'Path':'MyViewModelCommand'}
There are plenty of examples of this in the samples, plus there are several questions oh here - search for MvvmCross and click.
If you need to bind to an event which has an EventHandler<T> signature then you can add this yourself - see mvvmcross touch command binding in android
I'm not sure I have understood your question (I don't know Silverlight) but you can do as follows:
In your XML:
<Button ...
android:onClick="onMyButtonClicked".../>
In your java file
public void onMyButtonClicked(View sender) { ... }
There are no other ways to specify event handlers in Android XML, I think. You can specify a lot of properties though.
I'm trying to create an action for an attached event which I don't think CM supports out of the box.
This question/answer shows how to do this
using attached events with caliburn micro Message.Attach
but it requires using the long CM ActionMessage syntax, however, when I try to do this I get an 'ActionMessage does not exist in the XML namespace ' where blah is the CM namespace.
All of the examples also show this syntax; at the moment I've just put the code into the view which casts the DataContext to the ViewModel type and calls the appropriate method (I don't like this approach though as it couples the view to the VM and it's inconsistent with the rest of the app)
Anyone have any ideas why I can't see the ActionMessage?
e.g.
<i:Interaction.Triggers>
<Helpers:RoutedEventTrigger RoutedEvent="Helpers:DataChanging.Changing">
<!-- this line throws the error -->
<cal:ActionMessage MethodName="SelectedDataChanged">
<cal:Parameter Value="$eventargs" />
</cal:ActionMessage>
</Helpers:RoutedEventTrigger>
</i:Interaction.Triggers>
I'm using SL5 and CM's SL5 assembly but no joy...
Interestingly, if I try to use 'ActionMessage' elsewhere it seems to be resolved correctly but of course it's not very useful outside of where I want it!
Update:
This is the view namespace def
xmlns:cal="http://www.caliburnproject.org"
I've tried the actual assembly qualified namespace and other combinations, all with the same issue
I've never had to use the ActionMessage syntax before, but as long as the control has an event that you're trying to attach to have you tried the following syntax:
<Button Content="Remove" cal:Message.Attach="[Event Click] = [Action Remove($dataContext)]" />
I've been able to use that on a wide variety of controls without any issues.
http://devlicio.us/blogs/rob_eisenberg/archive/2010/07/17/caliburn-micro-soup-to-nuts-pt-3-all-about-actions.aspx
I had similar issues I had to add an extra xaml tag before calling ActionMessage my corresponding sample to get it to work was:
<i:Interaction.Triggers>
<Helpers:RoutedEventTrigger RoutedEvent="Helpers:DataChanging.Changing">
<cal:Action.Target>
<cal:ActionMessage MethodName="SelectedDataChanged">
<cal:Parameter Value="$eventargs"/>
</cal:ActionMessage>
</cal:Action.Target>
</Helpers:RoutedEventTrigger RoutedEvent="Helpers:DataChanging.Changing">
</i:Interaction.Triggers>
I have a view containing a button. And i want to perform an action on Hold event. How can i do this in mvvm? For Tap event i can Bind it to a Command property. Is it possible to do this with same way?
I would go with Braulio's answer - MVVM Light is what I would use, but back in the Silverlight 3 days I used custom attached properties to achieve this. See here for an example of custom attached properties: http://umairsaeed.com/2010/04/22/custom-attached-properties-in-silverlight/
You could create a custom attached property for the hold event to bind the command to and then use it like so:
<Border local:MyTextBoxControl.HoldEventCommand="{Binding HoldCommand}"/>
This is a lot of work compared with including the mvvm light toolkit in your project and then doing this:
<i:Interaction.Triggers>
<i:EventTrigger EventName="Hold">
<GalaSoft_MvvmLight_Command:EventToCommand Command="{Binding YourCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
Not sure if it supports the command, if not you can use MVVM Light Toolkit (free and open source) behavior: EventToCommand