I'd like to know how to set a single ViewModel throughout a single UserControl. I'm using an Items container inside a user control (bound to ItemsSource) and it doesn't seem to update with the code-behind replacement of a DataContext (to a code-behind instantiated ViewModel)
What i'm trying to do is change the DataBound foreground color of every text Item in the userControl, and the items inside an Itemscontrol dont seem to change. forcing a datacontext change removed the collection items from display.
I think I'm conceptually Misunderstood here. could anyone help?
I could fix the problem by using Storyboards to change color but the problem was still the same. The eventual solution was to access the resources inside the templates, which is possible by browsing the Visual Tree as shown in this tutorial
http://windowsphonegeek.com/tips/how-to-access-a-control-placed-inside-listbox-itemtemplate-in-wp7
The peculiar thing though, was that I needed to look for my object inside the initial object returned, as it seems to return the System generated one, which you don't see yourself. Looking for the answer inside this one helped. Also, pushing them into a list of items for easy access later could be a general idea, but MS needs to fix the way of doing this pronto.
I would recommend binding the ItemsSource to a property in your ViewModel.
Related
I am using Monotouch dialog with Mvvmcross. My requirement is to have multiple textfield in single element/cell. But in Entryelement we have only one value property which has by default two way binding. Rest of the property are with only one way binding.
I have also tried with UIViewElement but same thing I can bind only one way. UI will update based on changes of ViewModel. But if something user will enter into textfield then how to fire ValueChange for it is challenge for me.
It would be good if somebody can point out rough steps to achieve it.
I am dynamically loading around 1000+ items which are translated to buttons in xaml.
The view model has an IsEnabled property that is binded to the IsEnabled property of the button in the View.
My question is, won't this affect performance? I only need the property on some of the items but all of them use the same viewmodel and it is quite hard to introduce a new view model just for that purpose.
I am using Windows Store 8.1.
Thank You!
1k bool bindings should not do any harm. I've seen applications with 5-10k bindings beeing populated at once, they can freeze a little bit if done in sync. Your item/list in viewmodel loading should be done async to avoid UI freeze if the collection of those items is bound instantly with all the items already there, that is why observable collection is a fundamental thing to bind to.
could someone help me with design/understanding the problem: what I need to achieve is page with Panorama/Pivot control, where its items (panos/pivots) will be set via binding, using standard MVVM pattern. Problem is I need to have different content (different user controls) on each pano/pivot, that means If I define a panorama/pivot item template, I doom all of them to be alike, which is not what I want.
I found this question here already asked: Databound windows phone panorama with MVVM design but its still not clear to me. Many thanks.
If you have a dynamic page count on panorama/pivot you could use selector to choose what template is right according to your content.
Implementing DataTemplateSelector
Also, Data Binding Pivot to MVVM may help you too
You could add a dependency property to the user control that you want to use as a data template, a dependency property named "Type" for example and depending on that property you can change the layout of your user control (data template) - for example you could have multiple grids inside your user control and you could show and hide them depending on the type.
I have a View that contains a Listbox. I'll call it CityListingPage.xaml. This list page has a CityListingViewModel, that is binded with the View like somewhat like this:
DataContext="{Binding CityListing, Source={StaticResource Locator}}"
This works nicely. Now I what to change my page to a Pivot Control, where the Pivot Items, would be instances of CityListingViewModel, but obviously with different constructor data (ie. Country)
I extracted the ListBox into a UserControl. Now I'm struggling how to make this work so that for each list I get a new instance of the CityListingViewModel.
I tried creating in the ViewModelLocator a collection of CityListingViewModels but how do I pass the a CityListingViewModel instance to the UserControls DataContext?
Perhaps there is a different, better way of doing this?
Without seeing your code, I'm going to do a little guessing, but I think you can do it directly via data binding. Since each pivot item is getting an instance of CityListingViewModel, you can just pass that binding along to the UserControl:
If you post a little more code showing what you're trying to do, we might be able to be of more help.
The following are two answers for using a collection to create panorama pages. But I am quite sure that the approach can be adapted to pivot pages:
Dynamically add eventtocommand actions to a listbox
Static and dynamic panorama items in a panorama wp7 mvvm
The second post should be more relevant.
If you are thinking of partitioning the same data over multiple views on a pivot page then I would suggest NOT using several view models, especially if it is the same datasource you are using for all the data.
Simply have a parameter which each view would bind to and use Linq to control what data is visible to that parameter.
So you will have the variable which will contain all the data to be displayed and one parameter per view querying that data.
In MVVM Light toolkit for Windows Phone, whenever I am to add a new MvvmLightView (WP) item, I end up with the template creating a PhoneApplicationPage for me.
What about cases, when I want to create a nested view, for example in case of a ListBox ItemTemplate view.
Before MVVM Light, every time I needed a view to separate markup to, I would have created a standard UserControl and that worked fine.
Should I only use MvvmLightView whenever creating a navigable pages?
The item template is a guidance, that produces some code for you. It is not, nor does it intend to be, the single way of creating views or sub views.
In the case you are mentioning, it is usual to create a user control hat is backed on its own view model. This sub-view view model is then included as a property in your main view model. To pass it to your sub-view (e.g. a user control) you bind this property to the user control's DataContext.
<ext:MyUserControl DataContext="{Binding MySubViewProperty}"/>
However, you do not need a separate view model, in some cases it is more appropriate to share the main view model. In this case you do not need to do the above binding, as it is do one implicitly. Also, when you are using the user control within an DataTemplate the templates DataContext is passed to the user control implicitly and you do not need the binding. In general you only need to set the data context when you want to bind to a property of the current context, or to another context.
MVVM is about freedom and MVVM Light about supporting the developer in using this freedom. All guidance are best practises and provide usually the easiest an/or most consistant way, but nothing stops you going down another route for a good reason. Especially the templates are just shortcuts that provide for one problem, but not for the general (meaning every) case.