I'm using Mvvm pattern and in View when the UserControl-Initialized event is binding to InitializedCommand as below.
<i:Interaction.Triggers>
<i:EventTrigger EventName="Initialized">
<prism:InvokeCommandAction Command="{Binding Path=InitializedCommand}" />
</i:EventTrigger>
</i:Interaction.Triggers>
and ViewModel as below.
public DelegateCommand InitializedCommand
{
get
{
SelectedPopupType = PopupTypes.Downloading;
IsShowPopup = true;
return new DelegateCommand(delegate ()
{
*** DoSomething...***
}
}
}
Other events(Loaded,Unloaded..) return parts are working properly but Initialized Command return does not work (DoSomething not called)..
I wonder whats the reason...
As the event name clearly says, Initialized event will get triggered before your Triggers were set via a AttachedProperty. Whereas Loaded event will work, as it is triggered after all your property values were assigned and loaded. So, this won't work.
Microsoft documentation says:
If you do not need to read element properties, intend to reset properties, and do not need any layout information, Initialized might be the better event to act upon.
If you need all properties of the element to be available, and you will be setting properties that are likely to reset the layout, Loaded might be the better event to act upon.
Also, why do you want to invoke a ICommand for a Initialized event? Why can't you have a EventHandler at your code-behind for this?
Related
So right now I'm using a property on my control that binds to a bool property on my viewmodel called searcheditemfound (with its pair, searcheditemnotfound). I can't have just one property because even if I raise OnPropertyChanged("variableName), it will not activate the trigger unless there was an actual value change. This means that in the code for the view model, I have to do this really ugly looking:
SearchedItemNotFound = false;
SearchedItemNotFound = true;
private bool _SearchedItemNotFound;
public bool SearchedItemNotFound
{
get
{
return _SearchedItemNotFound;
}
set
{
if (value != _SearchedItemNotFound)
{
_SearchedItemNotFound = value;
OnPropertyChanged("SearchedItemNotFound");
}
}
}
when what I would really like is to just tie to an event in the view model. However, eventtriggers only trigger off routed events. Can I place routed events in the viewmodel? I think I have to inherit from control to do that.
One post here: How can I Have a WPF EventTrigger on a View trigger when the underlying Viewmodel dictates it should?
mentioned using
<i:Interaction.Triggers>
<samples:DataEventTrigger EventName="YourEvent">
<im:ControlStoryboardAction Storyboard="{StaticResource Storyboard1}"
ControlStoryboardOption="Play"/>
</samples:DataEventTrigger>
</i:Interaction.Triggers>
which looks perfect, except that it requires expression blend and I'm in visual studio 2008 where it isn't available. I'm wondering what other options I have. I don't even mind if it's not MVVM. I'm not a purist, I'm just trying to understand what my options are.
A RoutedEvent is a UI element and has no place in a view model. Personally, I can't really see the problem with changing your bool property from true to false and then back to true again... there is a valid reason for doing that. If it really bothers you, then just hide it away in a method and call that instead:
private StartSearchedItemNotFoundAnimation()
{
SearchedItemNotFound = false;
SearchedItemNotFound = true;
}
There's hardly any point in using any more complex and/or expensive ways to replicate the functionality that you already have.
I saw this example - Binding.UpdateSourceTrigger Property
in the example the UpdateSourceTrigger set to Explicit and then in the view code he call to UpdateSource of the TextBox name.
But if i use the MVVM dp i dont want to have names to my controls and source properties are in the VM and not in the view so what is the right way to bind controls to VM properties and set the UpdateSourceTrigger to explicit?
I want to do this because in my case its ShowDialog window and I want that the source will update only if the user click "ok"
Thanks in advance!
If you are using MVVM truely then your OK button click must be handled by some Command. This command must be coming from your ViewModel. The Expliticly bound properties must be coming from your ViewModel again. So whats stopping you.
Do not use Explicit binding but use OneWay binding.
In you button, bind a command and bind a command parameter to the OneWay bound Dependency property.
In your Command's Execute handler (which must be some method from your ViewModel), change the ViewModel's property with the parameter coming.
Raise the NotifyPropertyChanged for that property from your ViewModel.
E.g.
Assume I need to update a TextBox's Text back into my model on OK button click.
So for that I have a EmployeeViewModel class that has EmployeeName property in it. The property is has a getter and a setter. The setter raises property changed notification. The view model also has another property of type ICommand named SaveNameCommand that return a command for me to execute.
EmployeeViewModel is the data context type of my view. Myview has a TextBox (named as x:Name="EmployeeNameTxBx") OneWay bound to the EmployeeName and a Button as OK. I bind Button.Command property to EmployeeViewModel.SaveNameCommand property and Button.CommandParameter is bound to EmployeeNameTxBx.Text property.
<StackPanel>
<TextBox x:Name="EmployeeNameTxBx"
Text="{Binding EmployeeName, Mode=OneWay}" />
<Button Content="OK"
Command="{Binding SaveNameCommand}"
CommandParameter="{Bidning Text, ElementName=EmployeeNameTxBx}" />
</StackPanel>
Inside my EmployeeViewModel I have OnSaveNameCommandExecute(object param) method to execute my SaveNameCommand.
In this perform this code...
var text = (string)param;
this.EmployeeName = text;
This way ONLY OK button click, updates the TextBox's text back into EmployeeName property of the model.
EDIT
Looking at your comments below, I see that you are trying to implement Validation on a UI. Now this changes things a little bit.
IDataErrorInfo and related validation works ONLY IF your input controls (such as TextBoxes) are TwoWay bound. Yes thats how it is intended. So now you may ask "Does this mean the whole concept of NOT ALLOWING invalid data to pass to model is futile in MVVM if we use IDataErrorInfo"?
Not actually!
See MVVM does not enforce a rule that ONLY valid data should come back. It accept invalid data and that is how IDataErrorInfo works and raises error notfications. The point is ViewModel is a mere softcopy of your View so it can be dirty. What it should make sure is that this dirtiness is not committed to your external interfaces such as services or data base.
Such invalid data flow should be restricted by the ViewModel by testing the invalid data. And that data will come if we have TwoWay binding enabled. So considering that you are implementing IDataErrorInfo then you need to have TwoWay bindings which is perfectly allowed in MVVM.
Approach 1:
What if I wan to explicitly validate certain items on the UI on button click?
For this use a delayed validation trick. In your ViewModel have a flag called isValidating. Set it false by default.
In your IDataErrorInfo.this property skip the validation by checking isValidating flag...
string IDataErrorInfo.this[string columnName]
{
get
{
if (!isValidating) return string.Empty;
string result = string.Empty;
bool value = false;
if (columnName == "EmployeeName")
{
if (string.IsNullOrEmpty(AccountType))
{
result = "EmployeeName cannot be empty!";
value = true;
}
}
return result;
}
}
Then in your OK command executed handler, check employee name and then raise property change notification events for the same property ...
private void OnSaveNameCommandExecute(object param)
{
isValidating = true;
this.NotifyPropertyChanged("EmployeeName");
isValidating = false;
}
This triggers the validation ONLY when you click OK. Remember that EmployeeName will HAVE to contain invalid data for the validation to work.
Approach 2:
What if I want to explicitly update bindings without TwoWay mode in MVVM?
Then you will have to use Attached Behavior. The behavior will attach to the OK button and will accept list of all items that need their bindings refreshed.
<Button Content="OK">
<local:SpecialBindingBehavior.DependentControls>
<MultiBinding Converter="{StaticResource ListMaker}">
<Binding ElementName="EmployeeNameTxBx" />
<Binding ElementName="EmployeeSalaryTxBx" />
....
<MultiBinding>
</local:SpecialBindingBehavior.DependentControls>
</Button>
The ListMaker is a IMultiValueConverter that simply converts values into a list...
Convert(object[] values, ...)
{
return values.ToList();
}
In your SpecialBindingBehavior have a DependentControls property changed handler...
private static void OnDependentControlsChanged(
DependencyObject depObj,
DependencyPropertyChangedEventArgs e)
{
var button = sender as Button;
if (button != null && e.NewValue is IList)
{
button.Click
+= new RoutedEventHandler(
(object s, RoutedEventArgs args) =>
{
foreach(var element in (IList)e.NewValue)
{
var bndExp
= ((TextBox)element).GetBindingExpression(
((TextBox)element).Textproperty);
bndExp.UpdateSource();
}
});
}
}
But I will still suggest you use my previous pure MVVM based **Approach 1.
This is an old question but still I want to provide an alternative approach for other users who stumble upon this question...
In my viewmodels, I do not expose the model properties directly in the get/set Property methods. I use internal variables for all the properties. Then I bind all the properties two-way. So I can do all the validation as "usual" because only the internal variables are changed. In the view model constructor, I have the model object as parameter and I set the internal variables to the values of my model. Now when I click on the "Save" Button (-> Save Command fires in my view model fires) and there are no errors, I set all the properties of my model to the values of the correspondng internal variable. If I click on the "Canel/Undo"-Button (-> Cancel-Command in my view model fires), I set the internal variables to the values of my untouched model (using the setters of the view model properties so that NotifyPropertyChanged is called and the view shows the changes=old values).
Yet another approach would be to implement Memento-Support in the model, so before you start editing you call a function in the model to save the current values, and if you cancel editing you call a function to restore those values...that way you would have the undo/cancel support everywhere an not just in one view model...
I've implemented both methods in different projects and both work fine, it depends on the requirements of the project...
I realised that when using an InvokeCommandAcction associated to an EventTrigger, the original event was still routing up to the parent elements until it is handled. Well, I guess it is an expected behavior. But my question is how I can mark the event as Handled so it does not propagate up through the whole UI tree?
Actually, as you handle this event in a command, everything will be handled in this command, therefore it does not need to propagate. And in one corner case I found, it causes some unwanted behavior. For example, I open a new window when a user double click an element (MouseDoubleClick event). The problem is that the new windows opens and then the main window come back in front of the new one because the MouseDoubleClick event just reached the top element in the UI tree. The wanted behavior would be to keep the new window in front, but as the InvokeCommandAction lets the event propagate up, the main window takes back the focus...
What I could do is to use the CallMethodAction asset instead but as I am in a MVVM scenario, I don't want UI event arguments in my code. Even if this would let me implicitely mark the event as handled and fix the issue.
<UserControl x:Class="..."
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity">
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseDoubleClick">
<i:InvokeCommandAction Command="{Binding Path=DisplayReportCommand}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
...
</UserControl>
You could implement your own EventTrigger that marks events as handled.
public class HandlingEventTrigger : System.Windows.Interactivity.EventTrigger
{
protected override void OnEvent(System.EventArgs eventArgs)
{
var routedEventArgs = eventArgs as RoutedEventArgs;
if (routedEventArgs != null)
routedEventArgs.Handled = true;
base.OnEvent(eventArgs);
}
}
Then replace <i:EventTrigger EventName="MouseDoubleClick"> with <local:HandlingEventTrigger EventName="MouseDoubleClick"> and add
xmlns:local="clr-namespace:HandlingEventTrigger's namespace here"
to your usercontrol's atributes.
Add attached event to user control
CommandManager.PreviewCanExecute="PreviewCanExecute"
and in event handler
e.ContinueRouting = false;
Hope this will help!
MouseDoubleClick Event is actually not a bubbling routed event but a direct routed event.
However, this event is raised along the element tree, which can be checked with Snoop tool. Moreover, even if Handled for MouseDoubleClick is set to true, this event will occur along the element tree.
Although this routed event(MouseDoubleClick Event) seems to follow a bubbling route through an element tree, it actually is a direct routed event that is raised along the element tree by each UIElement.
If you set the Handled property to true in a MouseDoubleClick event handler, subsequent MouseDoubleClick events along the route will occur with Handled set to false. This is a higher-level event for control consumers who want to be notified when the user double-clicks the control and to handle the event in an application. (From MSDN)
As above, your problem may be not caused by the propagating as you mentioned. There is Window.ShowActivated property, which determines whether a window is activated when first shown. You can set the property in a sub window(xaml) as below but please note that though ShowActivated can give the focus to the main window, it cannot let the main window visually keep in front of the sub window. I have tried to find the solution but have no idea until now.
<Window ShowActivated="False" ....>
....
</Window>
i'm just starting with the mvvm model in Silverlight.
In step 1 i got a listbox bound to my viewmodel, but now i want to propagate a click in a button and a selecteditemchanged of the listbox back to the viewmodel.
I guess i have to bind the click event of the button and the selecteditemchanged of the listbox to 2 methods in my viewmodel somehow?
For the selecteditemchanged of the listbox i think there must also be a 'return call' possible when the viewmodel tries to set the selecteditem to another value?
i come from a asp.net (mvc) background, but can't figure out how to do it in silverlight.
Roboblob provides excellent step-by-step solution for Silverlight 4. It strictly follows MVVM paradigm.
I would not bind or tie the VM in any way directly to the events of controls within the View. Instead, have a separate event that is raised by the View in response to the button click.
[disclaimer: this code is all done straight from my head, not copy & pasted from VS - treat it as an example!!]
So in pseudo code, the View will look like this:
private void MyView_Loaded(...)
{
MyButton.Click += new EventHandler(MyButton_Click);
}
private void MyButton_Click(...)
{
//Raise my event:
OnUserPressedGo();
}
private void OnUserPressedGo()
{
if (UserPressedTheGoButton != null)
this.UserPressedTheGoButton(this, EventArgs.Empty);
}
public EventHandler UserPressedTheGoButton;
and the VM would have a line like this:
MyView.UserPressedTheGoButton += new EventHandler(myHandler);
this may seem a little long-winded, why not do it a bit more directly? The main reason for this is you do not want to tie your VM too tightly (if at all) to the contents of the View, otherwise it becomes difficult to change the View. Having one UI agnostic event like this means the button can change at any time without affecting the VM - you could change it from a button to a hyperlink or that kool kat designer you hire may change it to something totally weird and funky, it doesn't matter.
Now, let's talk about the SelectedItemChanged event of the listbox. Chances are you want to intercept an event for this so that you can modify the data bound to another control in the View. If this is a correct assumption, then read on - if i'm wrong then stop reading and reuse the example from above :)
The odds are that you may be able to get away with not needing a handler for that event. If you bind the SelectedItem of the listbox to a property in the VM:
<ListBox ItemSource={Binding SomeList} SelectedItem={Binding MyListSelectedItem} />
and then in the MyListSelectedItem property of the VM:
public object MyListSelectedItem
{
get { return _myListSelectedItem; }
set
{
bool changed = _myListSelectedItem != value;
if (changed)
{
_myListSelectedItem = value;
OnPropertyChanged("MyListSelectedItem");
}
}
}
private void OnPropertyChanged(string propertyName)
{
if (this.NotifyPropertyChanged != null)
this.NotifyPropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
To get that NotifyPropertyChanged event, just implement the INotifyPropertyChanged interface on your VM (which you should have done already). That is the basic stuff out of the way... what you then follow this up with is a NotifyPropertyChanged event handler on the VM itself:
private void ViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
switch (e.PropertyName)
{
case "MyListSelectedItem":
//at this point i know the value of MyListSelectedItem has changed, so
//i can now retrieve its value and use it to modify a secondary
//piece of data:
MySecondaryList = AllAvailableItemsForSecondaryList.Select(p => p.Id == MyListSelectedItem.Id);
break;
}
}
All you need now is for MySecondaryList to also notify that its value has changed:
public List<someObject> MySecondaryList
{
get { return _mySecondaryList; }
set
{
bool changed = .......;
if (changed)
{
... etc ...
OnNotifyPropertyChanged("MySecondaryList");
}
}
}
and anything bound to it will automatically be updated. Once again, it may seem that this is the long way to do things, but it means you have avoided having any handlers for UI events from the View, you have kept the abstraction between the View and the ViewModel.
I hope this has made some sense to you. With my code, i try to have the ViewModel knowing absolutely zero about the View, and the View only knowing the bare minimum about the ViewModel (the View recieves the ViewModel as an interface, so it can only know what the interface has specified).
Regarding binding the button click event I can recommend Laurent Bugnion's MVVM Light Toolkit (http://www.galasoft.ch/mvvm/getstarted/) as a way of dealing with this, I'll provide a little example, but Laurent's documentation is most likely a better way of understanding his framework.
Reference a couple of assemblies in your xaml page
xmlns:command="clr-namespace:GalaSoft.MvvmLight.Command;assembly=GalaSoft.MvvmLight.Extras"
xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
add a blend behaviour to the button
<Button Content="Press Me">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<command:EventToCommand Command="{Binding ViewModelEventName}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</Button>
and create the event within your viewmodel which will be called when the button is clicked
public RelayCommand ViewModelEventName { get; protected set; }
...
public PageViewModel()
{
ViewModelEventName = new RelayCommand(
() => DoWork()
);
}
This supports passing parameters, checking whether execution is allowed etc also.
Although I haven't used it myself, I think the Prism framework also allows you to do something similar.
I am following the M-V-VM pattern for my WPF UI. I would like to hook up a command to the TextChanged event of a TextBox to a command that is in my ViewModel class. The only way I can conceive of completing this task is to inherit from the TextBox control, and implement ICommandSource. I can then instruct the command to be fired from the TextChanged event. This seems to be too much work for something which appears to be so simple.
Is there an easier way (than subclassing the TextBox and implementing ICommandSource) to hook up the TextChanged event to my ViewModel class?
First off, you've surely considered two-way data binding to your viewmodel, with an UpdateSourceTrigger of PropertyChanged? That way the property setter of the property you bind to will be called every time the text is changed?
If that's not enough, then I would tackle this problem using Attached Behaviours. On Julian Dominguez’s Blog you'll find an article about how to do something very similar in Silverlight, which should be easily adaptable to WPF.
Basically, in a static class (called, say TextBoxBehaviours) you define an Attached Property called (perhaps) TextChangedCommand of type ICommand. Hook up an OnPropertyChanged handler for that property, and within the handler, check that the property is being set on a TextBox; if it is, add a handler to the TextChanged event on the textbox that will call the command specified in the property.
Then, assuming your viewmodel has been assigned to the DataContext of your View, you would use it like:
<TextBox
x:Name="MyTextBox"
TextBoxBehaviours.TextChangedCommand="{Binding ViewModelTextChangedCommand}" />
Using the event binding and command method might not be the right thing to use.
What exactly will this command do?
You might want to consider using a Databinding to a string field in your VM. This way you can make a call to a command or function from there rather than having the UI care at all.
<TextBox Text="{Binding WorldName}"/>
....
public string WorldName
{
get
{
return WorldData.Name;
}
set
{
WorldData.Name = value;
OnPropertyChanged("WorldName");
// CallYourCustomFunctionHere();
}
}
Can you not just handle the TextChanged event and execute the command from there?
private void _textBox_TextChanged(object sender, EventArgs e)
{
MyCommand.Execute(null);
}
The alternative, as you say, is to create a TextBox that acts as a command source, but that does seem like overkill unless it's something you're planning on sharing and leveraging in many places.