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• WPF - Binding a variable in an already bound ListBox?

  - by Corey Ogburn

  I really don't know how to title this question, but I need some help with binding to a ListBox. I have an object, that contains (among other information) 2 properties that need to be bound in one ListBox. One of these is an ObservableCollection of objects, called Layers, and the other property holds an enum value of either Point, Line or Polygon, called SpatialType. These are to act as a legend to a map application. I have bound Layers to a ListBox, no problem, but inside the ListBox.ItemTemplate, I need to bind the single variable SpatialType to every Item in the ListBox. The problem I'm running into is that when I try to bind while inside the ListBox, the only variables I have access to are the properties of each Layer and I can't access any properties of the original bound class that holds the Layers (and the needed SpatialType property). What can I do to get that piece of information bound inside the ItemTemplate without messing up a good MVVM architecture?

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• WPF Drag and Drop - Get original source info from DragEventArgs

  - by Quinn351

  I am trying write Drag and Drop functionality using MVVM which will allow me to drag PersonModel objects from one ListView to another. This is almost working but I need to be able to get the ItemsSource of the source ListView from the DragEventArgs which I cant figure out how to do. private void OnHandleDrop(DragEventArgs e) { if (e.Data != null && e.Data.GetDataPresent("myFormat")) { var person = e.Data.GetData("myFormat") as PersonModel; //Gets the ItemsSource of the source ListView .. //Gets the ItemsSource of the target ListView and Adds the person to it ((ObservableCollection<PersonModel>)(((ListView)e.Source).ItemsSource)).Add(person); } } Any help would be greatly appreciated. Thanks!

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• How do I detect when a cell's value has changed in Silverlight?

  - by jvenema

  Hey folks, I'm working in Silverlight, trying to figure out how to set a grid cell font color based on the contents of the cell. I have an ObservableCollection bound to a DataGrid, and my items implement INotifyPropertyChanged so the grid updates as I change the values; it's all working perfectly, including letting me sort items and keep the sorting while I update the underlying items. I know I can use the LoadingRow event to change colors, but the only way I can get the event to fire is by changing the grids datasource, in which case my sorting goes out the window. So, what I really want is a way to either 1) loop the rows in the datagrid, find the cell I need, and change it's color or 2) implement a custom column that I can use to dynamically set the color. The problem is how to actually do either of those things :) All suggestions welcome.

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• WPF XAML: How to trigger style change in ListBoxItem ancestor to user class?

  - by dhovel

  I have an ObservableCollection of items of my class "PlaylistItem" that implements INotifyPropertyChanged. The collection is databound to a ListBox and everything else is working. I want to know what markup to use to trigger a style change of the wrapping ListBoxItem based on a property (e.g. "Playing", bool) of the PlaylistItem. How to I use FindAncestor to trigger the change? I can to this in code, but I know I that I can (somehow) do it in markup. Thanks in advance.

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• ComboBox ItemTemplate does not support values of type 'Image'

  - by Charlie

  I'm trying to bind a WPF combobox to an observable collection of images. Here is my collection: public class AvatarPhoto { public int AvatarId { get; set; } public BitmapImage AvatarImage { get; set; } } public ObservableCollection<AvatarPhoto> AvailableProfilePictures { get; private set; } Here is my xaml: Visual Studio gives me this compile time error: Property 'ItemTemplate' does not support values of type 'Image'. Why is this error seen? Thanks Update: thanks for the answer! It solved the problem. Now I have updated my code but I'm seeing this in the ComboBox: Why is it not displaying pictures correctly? In the debug window I can see my collection is correctly populated:

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• WPF update binding in a background thread

  - by Mark

  I have a control that has its data bound to a standard ObservableCollection, and I have a background task that calls a service to get more data. I want to, then, update my backing data behind my control, while displaying a "please wait" dialog, but when I add the new items to the collection, the UI thread locks up while it re-binds and updates my controls. Can I get around this so that my animations and stuff keep running on my "please wait" dialog? Or at least give the "appearance" to the user that its not locked up?

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• Save VM properties with EF code first

  - by Julien

  I thought this would be simple but can't find any good examples. public Class BookVm : ImplementsPropertyChanged { public int BookId {get;set;} private bool _favorite; public bool Favorite { get { return _favorite; } set { _favorite = value; OnPropertyChanged("Favorite"); MyDbContext.SaveChanges() // this does not work } } Then in my XAML bound to Book <CheckBox Content="Favorite" IsChecked="{Binding Favorite}" /> How and when do I call SaveChanges() on my DatabaseContext? I don't want to implement a save button. If I intercept the PropertyChange event and call SaveChanges, nothing seems to happen. My object is modified in memory but the database does not see a change. My BookVm class is created on application startup like so: foreach (var book in MyDbContext.Books) Books.Add(book); Where Books is an ObservableCollection<Book> in my MainWindowVm

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• Binding Navigation Property with Entity Framework

  - by JSmaga

  Hi, I have another question about binding using C# and the entity framework. Here, I'm looking to bind a navigation property to a listbox or a listview. I saw on different posts that if I update the collection using code behind the list would not be notified because the collection does not handle notification (it's always the same problem anyway). People suggested to use an ObservableCollection for example, but, and here is my question, this comes down to basically duplicate the collection and hence, if I modify it, I'd have to handle in code-behind the fact that the change has also to be applied to the "original" navigation property right? If that's the case, I was thinking: why not create a custom property called, say, MyObservableNavigationProperty in a partial class. I could then interact only with this collection, catch the event when the collection is changed and apply the change to the "original" collection. Is that a nice way to do the trick? or am I getting all confused here....

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• Overrided ToString doesn't show in debug

  - by marco.ragogna

  I have a collection similar to: Public Class MyCollection Inherits ObservableCollection(Of MyCollection) Private _Name As String Public Property Name() As String Get Return _Name End Get Set(ByVal value As String) _Name = value End Set End Property Public Overrides Function ToString() As String Return "Name: " & _Name End Function End Class I have overrided ToString method in order to help in debug, but it doesn't show up. In the code that follow if, during debug, I move the mouse over coll it shows me Count = 0 Private Sub Window1_Loaded(ByVal sender As Object, ByVal e As System.Windows.RoutedEventArgs) Handles Me.Loaded Dim coll As New MyCollection coll.Name = "Test" End Sub Do you know what could be the problem?

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• What is the best practice for accessing Model using MVVM pattern

  - by Dzenand

  I have a database that communicates with webservices with my Model (own thread) and exposes Data Objects. My UI application consists of different Views and ViewModels and Custom Controls. I'm using ServiceProvider (IServiceProvider) to access the Model and route the events to the UI thread. Communication between the ViewModels is handeled by a Messenger. Is this way to go? I was also wondering what is the best way to strucutre the DataObjects At the moment i have the DataObjects that have a hierarchy structure but does not support INotifyProperty though the children list are of type of ObservableCollection. I have no possiblity to implement notifypropertychange on the properties. I was wondering the best way of making them MVVM friendly. Implementing a partial class and adding all the properties or commands that are necessary or wrapping all the DataObjects and keep the Model list and MVVM list in sync. All thoughts and ideas are appreciated.

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• List<string> doesn't update the UI when change occurs [WPF]

  - by Hard Turner

  <ListBox x:Name="MainList" HorizontalAlignment="Left" Height="468" Margin="10,10,0,0" VerticalAlignment="Top" Width="100" ItemsSource="{Binding Items,Mode=TwoWay}" DisplayMemberPath="Name"/> [Serializable()] public class MYcontainer : INotifyPropertyChanged,ISerializable { private List<MYClass> _items = new List<MYClass>(); public List<MYClass> Items { get{ return _items;} set { this._items =value; OnPropertyChanged("Items"); } public event PropertyChangedEventHandler PropertyChanged; public void OnPropertyChanged(string propertyName = null) { var eventHandler = this.PropertyChanged; if (eventHandler != null) eventHandler(this, new PropertyChangedEventArgs(propertyName)); } } when i add an item to "Items" the UI doesnt update, the binding is working fine, since if i closed the window and opened it again, the new items appear correctly what am i doing wrong? i know if i used observablecollection it will work fine, but shouldn't it work with List<? , i already have in another window a string[] property and it update fine

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• Sharing state/changes across ViewModels

  - by joshperry

  I have an App which has a Tasks tab and a Projects tab. I decided to make a separate ViewModel for each of the tabs, TasksViewModel and ProjectsViewModel. The Tasks tab has a new task area with an associated project pulldown and the Projects tab (obviously) has a list of projects. What I'd like is for the pulldown on the Tasks tab to share the same collection as the Projects tab list so that any time I add or remove a project on the Projects tab the list on the Tasks tab is up to date automatically. This worked well with a single ViewModel but it was beginning to become quite unruly. Should I not have split into two ViewModels? Is there a common method of sharing data like this? Perhaps pass the same ObservableCollection<Project> into each of the ViewModels? Perhaps some type of notification back to the TasksViewModel along the lines of ICollectionChanged. Appreciate any insight/input!

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• Change WPF Datagrid Row Color

  - by juergen d

  I have a WPF datagrid that is filled with an ObserverableCollection. Now I want to color the rows depending on the row content at the program start and if something changes during runtime. System.Windows.Controls.DataGrid areaDataGrid = ...; ObservableCollection<Area> areas; //adding items to areas collection areaDataGrid.ItemsSource = areas; areaDataGrid.Rows <-- Property not available. how to access rows here? CollectionView myCollectionView = (CollectionView)CollectionViewSource.GetDefaultView(areaDataGrid.Items); ((INotifyCollectionChanged)myCollectionView).CollectionChanged += new NotifyCollectionChangedEventHandler(areaDataGrid_Changed); ... void areaDataGrid_Changed(object sender, NotifyCollectionChangedEventArgs e) { //how to access changed row here? } How can I access the rows at start and runtime?

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• Count number of given object in a list with LINQ

  - by Aaginor

  I have a list which can contain multiple occurrences of the same object. Now I need to count, how often the given object is contained in this list. int count = 0; foreach (IMyObject item in myList) if (item == object2Count) count++; I am sure that this can be done nicer with LINQ, but LINQ is still a mystery to me. My first question is: How would I count the objects via LINQ and the second question: Will this LINQ version be slower or faster? I am using a ObservableCollection and the number of items in the list is usally rather small ... usally not more then 20. Thanks in advance, Frank

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• How do I know if a drag/drop has been cancelled in WPF

  - by Jon Mitchell

  I'm writing a user control in WPF which is based on a ListBox. One of the main pieces of functionality is the ability to reorder the list by dragging the items around. When a user drags an item I change the items Opacity to 50% and physically move the item in an ObservableCollection in my ViewModel depending on where the user wants it. On the drop event I change the Opacity back to 100%. The problem I've got is that if the user drags the item off my control and drops it somewhere else then I need to change the Opacity back to 100% and move the item back to where it was when the user started the drag. Is there an event I can handle to capture this action? If not is there any other cunning way to solve this problem?

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• how to create property of type generic class?

  - by Anish

  public class SelectionList<T> : ObservableCollection<SelectionItem<T>> where T : IComparable<T> { // Code } public class SelectionItem<T> : INotifyPropertyChanged { // Code } I need to create a property which is of the type SelectionList...as follows: public SelectionList<string> Sports { get; set; }. But when I replace string with DataRowView, as public SelectionList<DataRowView> Sports { get; set; }. I am getting error. Please help

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• Is it considered bad practice to have ViewModel objects hold the Dispatcher?

  - by stiank81

  My WPF application is structured using the MVVM pattern. The ViewModels will communicate asynchronously with a server, and when the requested data is returned a callback in the ViewModel is triggered, and it will do something with this data. This will run on a thread which is not the UI Thread. Sometimes these callbacks involve work that needs to be done on the UI thread, so I need the Dispatcher. This might be things such as: Adding data to an ObservableCollection Trigger Prism commands that will set something to be displayed in the GUI Creating WPF objects of some kind. I try to avoid the latter, but the two first points here I find to be reasonable things for ViewModels to do. So; is it okay to have ViewModels hold the Dispatcher to be able to Invoke commands for the UI thread? Or is this considered bad practice? And why?

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• [dynamic] Different behaviours between .NET 4.0 beta 2 and last release of .NET 4.0 !

  - by yogi4ever

  Hi. I've identified a difference of DLR between .NET 4.0 Beta 2 and the last release of .NET 4.0. In .NET 4.0 Beta 2, this code perfectly works at runtime : var dateTimeList = new List(); dynamic myDynamicObject = dateTimeList; object value = DateTime.Now; myDynamicObject.Add(value); Now, with last release of .NET 4.0, I have an exception at run time (to solve myDynamicObject.Add(value);) :-( In my real code, 'myDynamicObject' is a dynamic (but I know that it is always an ObservableCollection where T can be anything). 'value' is an instance which was got by some reflexions. As 'value' can have any type, the type of 'value' is Object. Do you see how can I solve this new limitation of .NET 4.0 ? Thanks

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• Combining XmlSerializer and XmlWriter?

  - by num3ric

  In addition to a list of objects I am serializing to an xml file using C#'s XmlSerializer, I would like to store a few more independent elements (mainly strings from textboxes) in the same xml. public static void SaveBehaviors(ObservableCollection<Param> listParams) { XmlSerializer _paramsSerializer = new XmlSerializer(listParams.GetType()); string path = Environment.GetFolderPath(Environment.SpecialFolder.Desktop); path += "\\test.xml"; using (TextWriter writeFileStream = new StreamWriter(path)) { _paramsSerializer.Serialize(writeFileStream, listParams); using (XmlWriter writer = XmlWriter.Create(writeFileStream)) { writer.WriteStartElement("Foo"); //test entry... writer.WriteAttributeString("Bar", "Some & value"); writer.WriteElementString("Nested", "data"); writer.WriteEndElement(); } } } However, deserializing "test.xml" results in an error because of the added element. I suppose writing in the serialized xml file is prohibited and should be avoided?

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• Region or ItemsSource for large data set in ListBox

  - by Ryan

  I'm having trouble figuring out what the best solution is given the following situation. I'm using Prism 4.1, MEF, and .Net 4.0. I have an object Project that could have a large number (~1000) of Line objects. I'm deciding whether it is better to expose an ObservableCollection<LineViewModel> from my ProjectViewModel and manually create the Line viewmodels there OR set the ListBox as it's own region and activate views that way. I'd still want my LineViewModel to have Prism's shared services (IEventAggregator, etc.) injected, but I don't know how to do that when I manually create the LineViewModel. Any suggestions or thoughts?

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• connecting to multiple resources

  - by Dudu

  I would like to know if there is a way to connect to multiple resources: Specifically I have the following problem abstact class BaseClass { ObservableCollection<BaseClass>; } class GrandSonClass:BaseClass{} class SonClass:BaseClass{} class FatherClass:BaseClass { CollectionViewSource col = new CollectionViewSource ; col.Source = Items.SelectMany(p => p.Items); } FatherClass's Items are of ChildrenClass type, and ChildrenClass's Items are of GrandSonClass type; I want FatherClass to bind to all the GrandSonClass's items it possesses. The solution of using SelectMany is not good as I need this to be dynamically updated whenever FatherClass adds more Items and whenever its Items(SonClasses) add more Items. Now I could go on and write notifiaction events but I was wondering if there is a smarter way to do it -i.e. simply define the sources as the Items of each Item FatherClass posses

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• WPF Prism deactivate ?

  - by 2Fast4YouBR

  Hi all, I have an problem and would like to know if it is common problem or jsut with me. I am using Wpf with Prism and Unity, all with the pattern MvvM. I am loading a viewModel that has a reference to a dropdown with few items, my idea is that each time that the user click in some place to open the view that has this dropdown is that the dropdown will be shown with diferent values. The problem is that I see is that after I show the view for the first time and after the first DEACTIVATE, when I try to load it again looks like it is already in the memory (was not deactivated/disposed), so as is already in memory, it not call the constructor again of the modelView and the dropdown is shown with tha same old values. public BranchSelectionViewModel(IUnityContainer unityContainer) { this.unityContainer = unityContainer; User user = this.unityContainer.Resolve<User>(); this.branches = new ObservableCollection<Department>(user.Departments .Where(department => department.DepartmentId != user.SelectedDepartment.DepartmentId)); }

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• how to update off screen pivot item

  - by Yama moto

  I want to have a pivot with many PivotItems. However, doing so will impact memory. So I bind pivot to my ViewModel, which has 3 item, and pivot will generate 3 PivotItems. My ViewModel is of type ObservableCollection and my item does implement INotifyPropertyChanged. This works fine. But when I update my ViewModel, only the current PivotItem, and the right PivotItem is updated. The left PivotItem, which is off screen, is not updated. You can see it when you drag pivot to the left. How to fix this? Or WP7 doesnot update off screen PivotItem ?

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• Should I use ObservableCollections in my Model in M-V-VM

  - by Bill Jeeves

  I'm completely new to M-V-VM and very new to Silverlight, just reading about it for the first time today. As a sample, I am creating a model containing a list of items. My (Silverlight 4) View contains a listbox and my ViewModel will look to the model to retrieve the collection that the listbox will bind to. My question is this. I think it would be good to use an ObservableCollection to hold the items that the listbox binds to. This would be an ObseravleCollection in the ViewModel. Should I also use this type of collection in the model, or should I use another collection type and do smoe conversion between model and viewmodel?

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• Freezing a listboxitem while items are being added

  - by siz

  We have a ListBox that has a number of items. Items are inserted into the ListBox via an ObservableCollection. Some of these items can be edited right in the ListBox. However, if an item is added at an index < the edited item's index, the entire content of the ListBox moves down. What we'd like to do is the following: if an item is in edit mode, we'd like to freeze its position on the screen. It is fine if items are added to the collection and the UI around the item changes. But the position of the item should remain constant on the screen. The only thing I've been able to do so far is attach to the ScrollChanged event and, at most, use either BringIntoView or ScrollIntoView methods to ensure that the item is always displayed somewhere in the UI, but I am unable to lock down its position. Has anyone done something like this and help out?

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