I'm just starting with MVVM light, but so far it allowed me to solve some of my issues. Infortunately I'm struggling with relatively sime issues in Silverlight.
Let's assume the following button with EventToCommand:
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseEnter">
<GalaSoft_MvvmLight_Command:EventToCommand Command="{Binding UpdateAccountsCommand, Mode=OneWay}" CommandParameter="{Binding SelectedIndex, ElementName=lstLedgers}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</Button>
How to assign this code to SelectedIndexChanged event?
Futher issue - how to assign a command in C# code? The problem is as follows: I'm developing Windows Phone 7 app. Application Bar needs to be initiated in C# (as far as I know there is no xaml code for application bar at this stage). As a result I have no idea how to bind a command to a application bat button in from c#, now xaml.
Thanks in advance your your help.
How to assign this code to SelectedIndexChanged event
The event name is in the trigger's initial xaml line. The EventName is what triggers something to happen. You'll need to make sure that you have this trigger on an object with a SelectedIndexChanged event. Button doesn't have that event.
...
<i:EventTrigger EventName="SelectedIndexChanged">
...
If you are breaking mvvm for the application bar, I don't know why you'd want to create a trigger. You might as well go the direct route by accessing the events you want directly. You can do it, don't get me wrong... just this code is a lot cleaner:
ApplicationBarButton.Click += new RoutedEventHandler(OnApplicationBarButton_Click);
Related
I have a UI with a few controls.
Initially when form loads, search button will be disabled, once all
search criteria are given, search button will be enabled
automatically.
On click on search button, I want to call the method
using MVVM pattern and bind the result in grid
XAML:
<Button Name="btnGetDetails" Content="Get Details" Grid.Row="2" Command="{Binding SearchCommand}"/>
What code is required in model, view model and XAML?
Command will be executed only when the button will be clicked on. If you need to do something to the button then you should do it to the Window that contains the button (assuming your button is in a Window). Now if you want to stick with the MVVM pattern then you should not use the Window.OnLoaded, because that would put code in your code behind. One option is to use System.Windows.Interactivity, which you have download seperately. Here is what it will look like:
<Window x:Class="..."
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:i="clr
-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Loaded">
<i:InvokeCommandAction Command="{Binding ...}" />
</i:EventTrigger>
</i:Interaction.Triggers>
</Window>
As for what your Model, View and ViewModel should be, I think you should check out some tutorials on the web. There are some very good explanations on how to implement the MVVM pattern. I found this youtube video pretty informative myself:
http://www.youtube.com/watch?v=EpGvqVtSYjs
So some MVVM basics here. You're on the right track, just missing a step. Your Command implementation in your view model should (potentially) accept two inputs: An Action representing the executing code, and a Predicate that returns true/false on whether you can execute the code in the Action block. So, in your view model, define your command along the lines of (note: this is a sample from one of my projects):
this.executeCommand = new RelayCommand(this.OnExecuteClicked, this.OnCanExecuteChanged);
The OnCanExecuteChanged method will return a bool based on whatever criteria you set up. So, if you want the submit button enabled when property A and property B have been properly set up, then return true, else return false. The internal workings of your command implementation will take care of the rest. Do a search for a RelayCommand implementation (if you don't have it already) or a DelegateCommand for further samples.
I'm attempting to use a Command, defined in my view model with EventTriggers as defined in xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
I have changed the control from a Microsoft.Surface.Presentation.Controls.SurfaceSlider-derived control to a regular WPF Button. With the Button, the same ConfirmOrderCommand gets fired if I use the EventName="MouseEnter", but if I use EventName="Click" nothing happens. The XAML for the Button is here.
<Button Name="ConfirmButton"
IsEnabled="{Binding IsEnabled}"
Style="{StaticResource ConfirmButtonStyle}"
>
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<i:InvokeCommandAction Command="{Binding ConfirmOrderCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</Button>
I want the user to be able to click the button to fire the command. Can I get the Click event to work for a Button, or do I need to look for another event? I've also failed to get MouseLeftButtonUp to work.
Try EventName="Button.Click". Anyways, you can just set the Command Property of the Button itself, and remove the Interaction.Triggers part.
The actual reason the Button.Click would not work, was determined after much pain and finally asking someone on the project after he woke up in the morning.
Our application was stealing almost all of the Button events with FrameworkElement Preview delegates.
public static void RegisterEvents(FrameworkElement parent)
{
parent.PreviewMouseDown += MouseDown;
parent.PreviewMouseUp += MouseUp;
// even more of these
}
The delegates would then use System.Window.Input.TouchDevice to ReportDown() in the case of MouseDown etc. All this time I just thought I didn't know how the standard WPF button usually works. I guess the moral of this story is events don't have to start at the child control and then propagate up to their containers until Handled = true. Preview allows the container to capture the events first.
So I am using GalaSoft's EventToCommand for binding my View's Loaded event to my command in my ViewModel. The binding is working great but my Command is never being executed. The only way I have been able to get this to work is to handle the Loaded event in my View's code behind and then cast my DataContent to my VM and tell it to run my code (which the command is trying to do). Obviously this isnt very nice when trying to do it all MVVM like. FYI I did try the MouseEnter event and that worked great so that makes me think its a timing issue. Also, my View is a user control.
View:
<i:Interaction.Triggers>
<i:EventTrigger EventName="Loaded">
<cmd:EventToCommand PassEventArgsToCommand="False" Command="{Binding Path=DownloadDataCommand}" />
</i:EventTrigger>
</i:Interaction.Triggers>
ViewModel:
public RelayCommand DownloadDataCommand
{
get { return new RelayCommand(() => DownloadDataAsync()); }
}
Ive tried calling simple methods that do pretty much nothing and my relay command is still not invoked. So I doubt its the action within the RelayCommand. Does anyone see what I am doing wrong?
There is a Silverlight UserControl which got an MouseLeftButtonUp event. In xaml I add two triggers for this event. In which order Silverlight xaml-parser will parse and attach those triggers and can I be sure that trigger above will invoke first?
...
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseLeftButtonUp">
<i:InvokeCommandAction Command="{StaticResource someCommand}"/>
<AttachedBehaviors:SomeBehavior Parameter="Apple"/>
</i:EventTrigger>
</i:Interaction.Triggers>
...
UPDATE: Found connected issue In WPF, does the order of Triggers matter? which says:
WPF is processing triggers in declared order.
Hope, Silverlight behave exactly that same.
Even if the order is defined I wouldn't do this. Add the order you want to the handler of the command.
void someCommand_Executed()
{
DoFirstThing();
DoSecondThing();
}
This kind of code will cause pain in the long run because the order is not easily enforced and you are creating a dependency between two methods.
I have a couple of Storyboards in my view that I would like to trigger from the ViewModel if possible. Is there a simple way or elegant way of doing this. Here is what I am trying to do.
Person Clicks on a Button-->RelayCommand (In the ViewModel), the Relay Command should then play the storyboard. Also one more thing, I would like to also trigger the storyboard animation by itself in the ViewModel without any interaction.
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseLeftButtonDown">
<cmd:EventToCommand Command="{Binding ButtonPress}" CommandParameterValue="RedButtonLight">
</cmd:EventToCommand>
</i:EventTrigger>
</i:Interaction.Triggers>
I know it's a long time ago. But I've written a detailed blog post about Triggering Storyboards and MVVM.
http://mark.mymonster.nl/2010/12/14/trigger-a-storyboard-on-viewmodel-changes/
If the button click is purely to power a view-related thing and isn't doing any actual application logic, then I would argue that you can do all this in the code-behind of the view class.
If this isn't the case then I would use a property on the Presentation (ViewModel) to signal that the Presentation is in a state, and have the view react to the PropertyChanged event and start the storyboard. This is assuming you are implimenting INotifyPropertyChanged on your Presentation class.
Have a look at the expression samples. There is a trigger for events from the datacontext. DataEventTrigger
You could use that to trigger a ControlStoryboardAction to start the story board whenever your viewmodel raises a particular event.
Your viewmodel could then raise the event as part of the command as well as at other times.
Heres how you can do it in blend without touching a line of xaml or code :
http://www.basarat.com/2011/05/expression-blend-starting-storyboard.html