I am binding my entities to an edit form in WPF. Within a DataTemplate, I want to be able to set the background color of the root container within a DataTemplate to show it has been changed and these changes have not yet been submitted to the database.
Here's a very simple sample that demonstrates what I'm talking about (forgive errors):
<Page ...>
<Page.DataContext>
<vm:MyPageViewModel /> <!-- Holds reference to the DataContext -->
</Page.DataContext>
<ItemsControl
ItemsSource = {Binding Items}>
<ItemsControl.Resources>
<DataTemplate
DataType="Lol.Models.Item"> <!-- Item is L2S entity -->
<!-- In real life, I use styles to set the background color -->
<TextBlock Text="{Binding IsDirty, StringFormat='Am I dirty? /{0/}'}"/>
</DataTemplate>
</ItemsControl.Resources>
</ItemsControl>
</Page>
The example just prints out "Am I dirty? yes" or "Am I dirty? no", but you get the idea.
To do this, I'll need to add a public property to my Item (partial class, simple) that can determine if the entity is dirty or not. This is the tough bit.
public partial class Item
{
public bool IsDirty
{
get
{
throw new NotImplementedException("hurf durf");
}
}
}
Outside of the entity, it's pretty simple (as long as you have the DataContext the entity is attached to). Inside, not so much.
What are my options here?
Edit: I don't think there's one good solution here, so suggestions for workarounds are welcome.
(Okay, similar questions exist, but they are all about how to determine this from outside of the entity itself and use the DataContext the entity is attached to.)
If you are using the dbml generated classes, you should be able to implement a couple of partial methods like this:
public partial class SampleEntity
{
partial void OnCreated()
{
this.IsDirty = true;
}
partial void OnLoaded()
{
this.PropertyChanged += (s, e) => this.IsDirty = true;
this.IsDirty = false;
}
public bool IsDirty { get; private set; }
}
Related
I'm writing WPF application with MVVM structure using MVVM Light.
I have class Foo in the Model:
class Foo: ObservableObject
{
private string _propA = String.Empty;
public string PropA
{
get => _propA ;
set
{
if (_propA == value)
{
return;
}
_propA = value;
RaisePropertyChanged("PropA");
}
}
// same for property PropB, PropC, PropD, etc.
}
And I have some collection of Foo objects in the Model:
class FooCollection: ObservableObject
{
private ObservableCollection<Foo> _items = null;
public IEnumerable<Foo> Items
{
get { ... }
set { ... }
}
public string Name { get; set; }
// ...
// and other methods, properties and fields
}
Now I have a ViewModel where this list is populated via some injected provider:
class MainWindowModel: ViewModelBase
{
private FooCollection _fooList;
public FooList
{
get => _fooList;
set
{
_fooList = value;
RaisePropertyChangedEvent(FooList);
}
}
public MainWindowModel(IFooListProvider provider)
{
FooList = provider.GetFooList();
}
}
And the View, with MainWindowModel as data context:
<TextBlock Text={Binding FooList.Name} />
<ItemsControl ItemsSource="{Binding FooList.Items}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text={Binding PropA} />
<Button Content={Binding PropB} />
<!-- other controls with bindings -->
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Everything works fine, I can delete and add new items, edit them and etc. All changes in View reflects automatically in ViewModel and Model via bindings and observable objects, and vice versa.
But now I need to add ToggleButton to data template of ItemsControl, which controls visibility of particular item in other part of window. I need IsChecked value in ViewModel, because control in other part of window is Windows Forms control and I can't bind IsChecked directly without ViewModel.
But I don't want to add new property (Visibility, for example) in model classes (Foo, FooCollection), because it is just an interface thing and it doesn't need to be saved or passed somewhere outside ViewModel.
So my question: what is the best way to add new property to Model collection in ViewModel?
I could create new collection of wrappers in ViewModel (some sort of class Wrapper { Foo item, bool Visibility }) and bind it to ItemsControl. But in this case I have to control adding, removing and editing manually and transfer all changes from List<Wrapper> to FooList.Items, so I don't like this solution. Is there any more simple way to achieve this?
Edition to clarify the question. Now I have:
<ItemsControl ItemsSource="{Binding FooList.Items}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text={Binding PropA} />
<Button Content={Binding PropB} />
<ToggleButton IsChecked={Binding ????????????} />
<!-- other controls with bindings -->
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
I have no field in class to bind IsChecked and I don't want to add it to class, because it's only interface thing and not data model field. How can I, for example, create another collection of bools and bind it to this ItemControl alongside with FooList.Items?
The best place to add the property is of course in the Foo class.
Creating another collection of some other type, add an object per Foo object in the current collection to this one, and then bind to some property of this new object seems like a really bad solution compared to simply adding a property to your current class.
Foo is not an "interface thing", or at least it shouldn't be. It is view model that is supposed to contain properties that the view binds to. There is nothing wrong with adding an IsChecked property to it. This certainly sounds like the best solution in your case.
I'm not sure if I understand why you would need to add a property in the model.
Can't you just use the command property or add an EventTrigger to your toggle button?
(See Sega and Arseny answer for both examples Executing a command on Checkbox.Checked or Unchecked )
This way, when you check the toggleButton, there is a method in your viewModel which enable or disable the visibility property of your Winform control.
To change the visibility of your control from a command in your viewModel, you could use the messenger functionnality of MVVM LIGHT
MVVM Light Messenger - Sending and Registering Objects
The ViewModel sends a message to you're Windows Forms and this one handles the visibility of your control.
First of all, I'm newbie in WPF and specially in MVVM. I have a window with diferent tabs and a very large ViewModel with the business logic of the content of every tab. I know it is not right, so now I'm trying to do it more elegant:
As I see googling, an idea is to do a collection of a "base" viewmodel from wich inherit the sub-viewmodels of every tab, and a collection on this "base" viewmodel in the viewmodel of the window.
TabBaseViewModel
Tab1ViewModel inherits TabBaseViewModel
Tab2ViewModel inherits TabBaseViewModel
MainWindow ViewModel --> Collection of TabBaseViewModel
The contents the tabs do not have anything in common along each other.
How I have to proceed?
You should consider using an MVVM framework if you're using MVVM. With Caliburn.Micro for example, you can define your main view as:
<TabControl x:Name="Items">
<TabControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding DisplayName}" />
</DataTemplate>
</TabControl.ItemTemplate>
</TabControl>
Where the data context is a Conductor type that has a collection. The Items property will expose a collection of your view models:
public class MainViewModel : Conductor<IScreen>.Collection.OneActive
{
private OneOfMyViewModels oneOfMyViewModels;
private AnotherViewModel anotherViewModel;
protected override void OnInitialise()
{
// Better to use constructor injection here
this.oneOfMyViewModels = new OneOfMyViewModels();
this.anotherViewModel = new AnotherViewModel();
this.Items.Add(this.oneOfMyViewModels);
this.Items.Add(this.anotherViewModel);
}
protected override void OnActivate()
{
base.OnActivate();
this.ActivateItem(this.oneOfMyViewModels);
}
}
public class OneOfMyViewModels : Screen
{
public OneOfMyViewModels()
{
this.DisplayName = "My First Screen";
}
}
I posted an answer to a different question which shows how to do exactly this: How to Get a Reference to a ViewModel
It's a very simple example, but hopefully should get you started along the right track.
I made a main window that displays various user controls in a content control. In this window, I have the user controls and their accompanying view models in the XAML as DataTemplate Resources. This window has a button that needs to display the user control in the contentcontrol and instantiate the view model for it. How can i pass the resource to my RelayCommand, so that i can tell the command which user control and view model to use? I figured out how to pass a hard-coded string as the command parameter, but now I'm wanting to pass the x:Name so i can reuse this command etc for more than one View-ViewModel.
Main Window's XAML snippets:
<Window.Resources>
<!--User Controls and Accompanying View Models-->
<DataTemplate DataType="{x:Type EmployerSetupVM:EmployerSetupVM}" x:Key="EmployerSetup" x:Name="EmployerSetup">
<EmployerSetupView:EmployerSetupView />
</DataTemplate>
<DataTemplate DataType="{x:Type VendorSetupVM:VendorSetupVM}">
<VendorSetupView:VendorSetupView />
</DataTemplate>
</Window.Resources>
<Button Style="{StaticResource LinkButton}" Command="{Binding ShowCommand}" CommandParameter="{StaticResource EmployerSetup}">
...
In the Main Window's ViewModel, here relevant code so far:
public RelayCommand<DataTemplate> ShowCommand
{
get;
private set;
}
ShowCommand = new RelayCommand<string>((s) => ShowExecuted(s));
private void ShowExecuted(DataTemplate s)
{
var fred = (s.DataType); //how do i get the actual name here, i see it when i hover with intellisense, but i can't access it!
if (!PageViewModels.Contains(EmployerSetupVM))
{
EmployerSetupVM = new EmployerSetupVM();
PageViewModels.Add(EmployerSetupVM);
}
int i = PageViewModels.IndexOf(EmployerSetupVM);
ChangeViewModel(PageViewModels[i]);
}
...
in other words, how do i get the name of the my DataTemplate w/ x:Key="EmployerSetup" in the XAML? If it matters, I'm using MVVMLight too
Try using the Name property of the class Type:
private void ShowExecuted(DataTemplate s) {
var typeName = s.DataType as Type;
if (typeName == null)
return;
var className = typeName.Name; // className will be EmployerSetupVM or VendorSetupVM
...
}
I'd still say passing the DataTemplate to the VM just seems strange. I'd just have two commands and switch the command used in the Button.Style according to the conditions you got.
If you "have" to use a single RelayCommand or the world might end, I'd tend to use a static enum that you can reference from xaml for CommandParameter than pass the whole DataTemplate object.
The application I'm currently writing is using MVVM with the ViewModel-first pattern. I have XAML similar to the following:
<ContentControl Content="{Binding FooViewModel.BarViewModel.View, Mode=OneWay}"/>
Every VM is a DependencyObject. Every property is a DependencyProperty. Depending upon the state of the application, the value of the BarViewModel property of the FooViewModel can change, thus changing the value of the View property. Unfortunately when this happens, the new view is not displayed, and the old one remains.
This is extremely frustrating. I thought that if any part of a path expression changed, the binding would update, but that doesn't appear to be the case. When I've used shallower path expressions, such as FooViewModel.View and I've changed the value of the FooViewModel property, that has updated the ContentControl to which it's bound, but not in this case.
If your solution is that I abandon ViewModel-first, that is not an option, though I appreciate your advice. I must get this working as is.
CLARIFICATION
This is a question about data binding, and not about MVVM or how to implement it. You can safely ignore the MVVM aspects of this if it helps you to think about the problem, or if you have a different idea about how MVVM should be implemented. This is a large, existing project in which the MVVM design pattern cannot be changed. (It is far too late for that.)
So, with that said, the correct question to be answering is the following:
Given a binding path expression in which every element is a DependencyProperty and the final property is a view bound to a ContentControl, why does a change in a property in the middle of the path not cause the binding to update?
Although I would expect this to work, there are several problems with your approach.
Firstly, your view models should not use DependencyObject or DependencyProperty, this ties them in to WPF. They should instead implement INotifyPropertyChanged. This makes your view models reusable in other presentation technologies such as Silverlight.
Secondly, your view models shouldn't have references to your views, so you shouldn't require a View property on your view models.
I would seriously consider using an MVVM framework for view composition - Caliburn.Micro, for example, makes view model first development extremely straightforward, and already provides a view model base class which implements INotifyPropertyChanged, and a mechanism for building view compositions with conventions.
I.e. you can have a conductor view model which has an ActiveItem property, and you simply place a ContentControl on your view with the same name as the property:
<ContentControl x:Name="ActiveItem" />
You can use the ActivateItem() method to change the current active item.
Caliburn.Micro also has a host of other features, such as being able to place a Button control with x:Name="Save" on your view, and your Save method on your view model will automatically be invoked when the button is clicked.
Every VM is a DependencyObject. Every property is a
DependencyProperty.
why? a viewmodel should be a simple class with INotifyPropertyChanged and the Properties should be simple properties.
and if you want your different viewmodel be rendered in a different way - you should use DataTemplate.
<Window>
<Window.Resources>
<DataTemplate DataType="{x:Type local:MyViewModelA}>
<MyViewA/>
</DataTemplate>
<DataTemplate DataType="{x:Type local:MyViewModelB}>
<MyViewB/>
</DataTemplate>
</Windows.Resources>
<Grid>
<ContentControl Content="{Binding MyActualVM}"/>
</Grid>
</Window>
EDIT: btw you always bind to the last Property: FooViewModel.BarViewModel.View --> so the INotifyPropertyChanged (if raised) just work for the .View
EDIT2: another approach could be to get the BindingExpression of your content control and call.
System.Windows.Data.BindingExpression expr = //get it from your contentcontrol
expr.UpdateTarget();
EDIT3: and a simple mvvm way - just use INotifyPropertyChanged
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.MyFooVM = new FooVM();
this.MyFooVM.MyBarVM = new BarVM(){View = "erster"};
this.DataContext = this;
}
public FooVM MyFooVM { get; set; }
private void Button_Click(object sender, RoutedEventArgs e)
{
this.MyFooVM.MyBarVM = new BarVM(){View = "zweiter"};
}
}
public class INPC : INotifyPropertyChanged
{
#region Implementation of INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropChanged(string property)
{
var handler = PropertyChanged;
if(handler != null)
handler(this, new PropertyChangedEventArgs(property));
}
#endregion
}
public class FooVM:INPC
{
private BarVM _myBarVm;
public BarVM MyBarVM
{
get { return _myBarVm; }
set { _myBarVm = value;OnPropChanged("MyBarVM"); }
}
}
public class BarVM : INPC
{
private string _view;
public string View
{
get { return _view; }
set { _view = value;OnPropChanged("View"); }
}
}
Sorry - my question is almost identical to this one but since it didn't receive a viable answer, I am hoping that someone else has some fresh ideas.
I have a WPF TreeView that is bound to a hierarchy of a single type:
public class Entity
{
public string Title { get; set; }
public ObservableCollection<Entity> Children { get; set; }
}
The Entity class implements INotifyPropertyChanged, but I have omitted this code for clarity.
The TreeView is bound to an ObservableCollection<Entity> and each Entity instance exposes a set of contained Entity instances via its Children property:
<TreeView ItemsSource="{Binding Path=Entities}">
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:Entity}" ItemsSource="{Binding Path=Children}">
<TextBlock Text="{Binding Path=Title}" />
</HierarchicalDataTemplate>
</TreeView.Resources>
</TreeView>
Initially the TreeView binds as expected and correctly displays a multi-level hierarchy. Also, when the membership of one of the Children collections is programmatically modified, the changes are correctly reflected in the TreeView.
However, changes to the membership of the root member level ObservableCollection<Entity> are not reflected in the TreeView.
Any suggestions would be appreciated.
Thanks,
Tim
My initial guess is that you have something like the following for the root node:
public ObservableCollection<Entity> Entities
{
get;
set;
}
Then, instead of doing something [good] like the following:
Entities.Clear();
foreach (var item in someSetOfItems)
Entities.Add(item);
You are doing something [bad] like this:
Entities = new ObservableCollection<Entity>(someSetOfItems);
You should be able to track down the issue by making the backing field of the Entities property readonly:
private readonly ObservableCollection<Entity> _entities
= new ObservableCollection<Entity>();
public ObservableCollection<Entity> Entities
{
get
{
return _entities;
}
}
Further explanation, long time for answer to come, but I believe that if you do the binding in XAML, and then in code assign a new object to the property you break the binding, so you would have to redo the binding in code for it to work. Hence the solution with the readonly backing field. If doing like that you will not be able to assign a new ObservableCollection and you won't break the binding by assigning a new object to the backing field.