i've got a textbox which text is binded to a listview selecteditem as follows:
<TextBox x:Name="txtAdditional" Width="300" Text="{Binding ElementName=lstPersons, Path=SelectedItem.Additional, Mode=OneWay}" />
Now i like to implement a mechanism to add new items to the listview using this textbox to get the actual data. So i would like to bind the text of the textbox to a property of the viewmodel so it can be processed by a command.
So it the textboxes text has to be binded to the listviews selecteditem and additionally to a property of my viewmodel.
I've searched around and found some approaches but i can't help to think that there should be some simpler mechanism to archive this goal.
What I found by now:
Using MultiBindung with some kind of ValueConverter? So it seems to me that this is primary for displaying and not for updating a viewmodels property.
The use of some selfdefined custom control?
The use of an BindingProxy with in- and out-dependencyproperties like in Impossible WPF Part 1: Binding Properties?
Is there another, simpler solution to this or would i have to use one of those above?
And if one should use one of those approaches, which one whould you choose?
I can't help but thinking that this issue hasn't been given some thoughts already, using an mvvm pattern?! ;-)
yes thanks to the hint from BionicCode.
We, or better I should have to think the MVVM concept out. Of course no - or at least as little code behind as possible.
I added the property "selectedPerson" to my viewmodel and bound the SelectedItem of the listview to this property. So the object related properties were at hand directly through the "selected" object in my viewmodel and there was no need anymore to access the textbox content at all.
Thanks to BionicCode for the hint!
Related
I have a accustom control bound to a model class. So if any change in UI for textbox it updates ViewModel.model instance. but it doesnot work the other way. What is the necessary thing I need to look for? or troubleshoot steps pls.
Thanks.
You mean the value is displayed in the Textbox but a new typed value isn't?
If so you need to set two way binding on the Textbox binding:
<Textbox Text={Binding myTextProperty, Mode="TwoWay", UpdateSourceTrigger="ProprtyChanged"/>
This will enable both read & write functionality to your binding.
As #Ganesh says, you also need to make sure you're implementing the INotifyPropertyChanged interface in your ViewModel.
I have a WPF Data Grid bound to an observable collection, which is working as intended.
What I am trying to do now is add text below it to say: "Number of selected rows: {count goes here}"
What's the proper way to do this? I could add a new property in the View Model called SelectedCount or something similar and bind to that, but it doesn't feel right. It seems redundant. Also, I could set the label text dynamically in the code behind, but I'm not sure if that's the "right" place to do this either.
Here's an example below.
EDIT:
Please pretend there's a checkbox column header whose intention is to provide check/uncheck all functionality. The state of this header checkbox should not count towards the final count.
You could use element binding to declaratively bind to the SelectedItems.Count property in XAML:
<TextBlock Text="{Binding ElementName=MyDataGrid,
Path=SelectedItems.Count, StringFormat=Number of selected rows: {0}}" />
Update
Presumably you're using MVVM, so adding a SelectedXCount property to your view model is a perfectly reasonable application of the view model. The advantage of having it in the view model is that you could unit test based on the number of selected items. E.g. if you want to check that the user can only progress (a CanNext property returns true) if the user has selected some items.
The SelectedItems property is not a DependencyProperty so can't be bound to, but there are many articles online that get around the issue when using the DataGrid in MVVM. Most of the solutions involve using a mechanism for calling a view model command on the invocation of the DataGrid's SelectionChanged event.
I have a bit of a problem with my Silverlight application, and my usage of the MVVM pattern.
In my View I have a DataGrid. The ItemsSource would normaly be bound to the ViewModel, but in my specific case I need the columns to be dynamic and my items collection consists of a Dictionary for each item, so I have no class properties to show. My solution was to generate all this in codebehind, since the actual design of the DataGrid has nothing to do with my ViewModel. This was the only solution I could think of since the columns can't be databound.
I have got all of this to work. My problem is that I'm using RIA and the view has no idea when the items collection has finished loading. I tried my design out by putting an ordinary button on the view to trigger the codebehind function, but obviously this solution is no good. I need my codebehind function to run as soon as my item collection has finished loading.
Can I make my codebehind listen to the ViewModel?
I have a feeling that you are messing up things somewhere.
For your question I think you can solve it by having an event in the ViewModel.
Subscribe to that event in your view's view_Loaded event and call the codebehind function in the handler.
I would recommend you to recheck your design and to see if this is really necessary.
I understand what you mean, we once had to do the same thing generating random columns which is a PIA in silverlight because you would need some kind of object that has a dynamic set of properties.
I see you've found the Dictionary solution. What I would suggest, which isn't per sé the cleanest solution but it is cleaner then putting the stuff in the code behind, is to add this in a converter. Then bind the collection to the itemssource of an itemscontrol and then when the list propertychanged is raised you assemble the datagrid in the converter.
small example:
<ItemsControl Grid.Row="1" ItemsSource="{Binding theListOfEntities, Converter={StaticResource theconverter}}"/>
I have a UserControl that contains - among other things - a ListView. The ListView has a different data context than the UserControl (this data context is not exposed). If someone consumes my control, I would like them to be able to (indirectly) bind to the ListView's ItemsSource dependency property. It should really feel like the user is binding to a typical ItemsSource.
I'm not sure what the best way to proceed is. Looking at how ItemsControl's ItemsSource property worked in Reflector showed some logic that seemed a bit more involved than ought to be necessary for simple forwarding.
My current best idea is to expose a collection as a dependency property on the outer control and, when it is updated, update the ListView's ItemsSource. But I'm not sure what type this collection should be (should I require an ObservableCollection<T>, for example), or if there are any gotchas I should look out for.
Any suggestions or advice would be much appreciated.
Thanks.
Use AddOwner to add your UserControl as an owner of the ItemsControl.ItemsSourceProperty. In the new property meta data, give a property changed callback that sets the ItemsSource of your ListView.
I'm learning MVVM through a project and I got stuck on something simple.
I have a Button that updates a ListView. I have a command in the ViewModel that make the right things but I want to select the new row and get the focus on a TextBox after I click the Button.
The question is: How do I update my UI after executing a command?
If I need to change my windows Title when an operation have been made, I use a property on the ViewModel that is binded to the Window's title and it's changed when I need it but, I don't know how to get focus on a control when a command has been executed.
Thank you.
To select the new row, add a new property to your ViewModel ("SelectedItem" for instance), and bind the ListView's SelectedItem property to it :
<ListView ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}">...
In the ViewModel, you just have to assign the new item to the SelectedItem property
To focus the TextBox, Mike's idea seems a good one
You could make an attached behavior. I'd suggest using the new Blend behavior framework, ie TriggerAction that contained this custom logic.
For your attached behavior you put on the button, give it a DP for an ICommand and maybe a DP of a ListView type.
On the "protected override void Invoke(object parameter)" of your TriggerAction, execute your ICommand, then you have reference to your ListView. Here you can do your custom code on it, like setting focus.
Your XAML may look something like this:
<Button>
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<Behaviors:CustomBehavior Command="CommandName" ListView="{Binding ElementName=myListView}" />
</i:EventTrigger>
</i:Interaction.Triggers>
<Button/>
I suggest looking at Mike Brown's ExecuteCommandAction behavior (download here), it's about almost 1/2 of what you need.
What about setting focus to the control in the code behind: textBox.Focus()
I consider everything you mention in your question to be GUI logic so I would add a Click event to the button to handle stuff that needs to happend in the GUI.
Hope this helps.
I think you need to use the Mediator pattern. Please see this:
Josh Smith's Mediator Prototype for WPF Apps
This is generally used in communicating with the View from the View-Model. Hope this helps.
In your case you need some way that the ViewModel notifies the View that it should set the focus on a specific control.
This could be done with an IView interface. The view implements this interface and the ViewModel can call a method of the View over this interface. This way you have still the View and ViewModel decoupled of each other.
How this can be done is shown here:
WPF Application Framework (WAF)
http://waf.codeplex.com