In my Silverlight app I have a view containing a tab control and a view model of this view.
When the selected tab is changed, I need to refresh its data. In order to do that in the view model I'm using a command triggered by EventTrigger in the view and passing the appropriate event args to it (as described here http://weblogs.asp.net/alexeyzakharov/archive/2010/03/24/silverlight-commands-hacks-passing-eventargs-as-commandparameter-to-delegatecommand-triggered-by-eventtrigger.aspx).
Each tab item has its own view model and, therefore, to distinguish which view model I have to use to refresh the data, I'm watching the header in the tab item which I can get from the event args, e.g:
_tabSelectionChangedCommand = new DelegateCommand<SelectionChangedEventArgs>(TabSelectionChanged);
public ICommand TabSelectionChangedCommand
{
get { return _tabSelectionChangedCommand; }
}
private void TabSelectionChanged(SelectionChangedEventArgs e)
{
var tabItem = (TabItem)e.e.AddedItems[0];
if (tabItem.Header == "Header1" )
{
TabItem1ViewModel.Refresh();
}
.....
}
So, my question is :
Is good that I'm using in the view model the types related to the UI(TabItem, SelectionChangedEventArgs) and are there better ways to do what I've described above?
Maybe you can bind the SelectedIndex of the TabControl to a property defined in your viewmodel and attach an InvokeActionCommand to the TabControl and subscrible to its SelectionChanged event.
Then when the command gets called, check which index it is then load the data accordingly?
Related
I have a List bound to a (Telerik) GridView. The selected item is a separate variable of type T which is assigned the object of the selected row in the GridView when the user clicks on a row. T is derived from ObservableObject. This means I am using MVVM Light Toolkit.
I need to deselect the row from my ViewModel in certain situations. On the GridView control this works, if the selected item is set to NULL in the ViewModel. Whenever I do this, MVVM reports a crash (NPE). I debugged it and saw that it is failing in ObservableObject.cs. It calls a method
protected bool Set<T>(
Expression<Func<T>> propertyExpression,
ref T field,
T newValue)
and crashes one line before return when calling RaisePropertyChanged(propertyExpression)
I don't know if this is working as designed or not. My problem is, that I need to set the selected Object to NULL in the ViewModel to deselect a row of my GridView in the View. I CANNOT use CodeBehind for the deselection!
Code I have:
public ObservableCollection<ContractTypeDto> ContractTypes { get; private set; }
public ContractTypeDto SelectedContractType
{
get { return _selectedContractType; }
set
{
Set(() => SelectedContractType, ref _selectedContractType, value);
RaisePropertyChanged(() => SelectedContractType);
}
}
When you click on a row in the grid it opens a new UserControl containing lots of details of this record. This control has its own ViewModel. I store the calling view Model (where the selected item is stored). When the page (control) is closed (destroyed) I have to deselect the row in the grid. I call a method like so:
protected void DeselectCallersSelectedItem()
{
if (CallingObject == typeof(ContractTypeListViewModel))
{
var vm = SimpleIoc.Default.GetInstance<ContractTypeListViewModel>();
vm.SelectedContractType = null;
}
}
Any ideas?
To remove the collection you can either set the SelectedItem property to null or clear the SelectedItems.
gridViewName.SelectedItem = null;
gridViewName.SelectedItems.Clear();
Without showing the code, we cannot precisely help you. A solution I think you can do is to implement the INotifyPropertyChanged interface in your view model and bind the selected item to a property of that type. Also check the output window if there is any binding failure.
I have a wpf Treeview which has a dynamic itemssource. The User can add and remove items at runtime.
I'm missing an event which gives me the currently added UIElement that was added to the treeviews itemsSource. So I guess I need to switch to OnCollectionChanged.
This is what I have:
// MyItemViewModel is a viewmodel for a TreeViewItem
// MyCollection is bound to hte Treeview's ItemsSource
public class MyCollection : ObservableCollection<MyItemViewModel>
{
protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
// i like to have the UIelement which was added to the collection
// (e.NewItems contains the FrameworkElement's DataContext)
break;
}
}
}
Im following MVVM, as good as I can, and don't want to hold any view elements in the viewmodel.
I like to have an event that is fired when an item is added, which provides the new added UIElement in its sender or EventArgs.
I already tried ItemContainerGenerator class, but it's not useful inside a viewmodel since it requires already a UIElement Control.
You seem to be looking at this problem from the wrong direction... in MVVM, you can pretty much forget about the UI for the most part. So, instead of thinking how to get hold of the item that the user added into the collection control in the UI, think about accessing the data object that you added to the data collection in the view model that is data bound to the UI collection control in response to an ICommand that was initiated by the user.
So to me, it sounds like you need to implement an ICommand that is connected to a Button in the UI, where you add the new item into the data bound collection rather than any event. In this way, you'll always know the state of all of your data items.
I have this WPF/MVVM Application that a TabControl with a bunch of tabs. When the app loads, data for all tabs are loaded. There are some calculations that are made on Tab1 that's dependent on values from Tab2. what's happening is, when I enter / change data on tab2, it simply doesn't reflect on Tab1 when I click on Tab1. under the hood, the calculations are made properly but it doesn't reflect on tab1. I have to go to the main tab to re-load all the data to reflect changes. Any ideas how to implement this?
You need to implement INotifyPropertyChanged on your view model data properties. Then, have your view model subscribe to the event (the Initialize() method is called by the view model constructor):
private void Initialize()
{
// Subscribe to events
this.PropertyChanging += OnPropertyChanging;
this.PropertyChanged += OnPropertyChanged;
this.Books.CollectionChanging += OnBooksCollectionChanging;
}
The view model handler for the event can then update any properties that need to be updated:
void OnPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
switch(e.PropertyName)
{
case "FirstProperty":
this.SomeOtheProperty = whatever;
break;
case "Another property":
this.YetAnotherProperty = somethingElse;
break;
}
}
That should get the job done.
If two different ViewModels need to show the same data/value they should bind to the same ViewModel.
I think that adding a binding between ViewModels is bad because it introduces a lot of dependencies.
If a property of a single ViewModel is dependent on an other property of the same ViewModel you could use property changed notification as mentioned in David's answer.
This is my first attempt at MVVM. My application's core is loosely based Josh Smith's msdn article. And I am also using the mvvm light framework.
I have a main window containing a command list area and a workspace area which shows usercontrols/views as tabitems, each usercontrol has a corresponding viewmodel. The mainWindow also has a viewmodel containing my command list, and the workspace viewmodels have a base workspace viewmodel.
My default view has a master datagrid, of MappingSets, that can have one selected item. The commands launch new tabitems with views that handle MappingSet detail based on that selected item. I have a View/ViewModel that, depending on the command used should return either a tabitem for creating a new MappingSet with no existing data, or a tabitem containing the detail of the selected item for editing, or a tabitem containing detail the selected item as the base for a new MappingSet.
Having Set the scene, what I have not managed to work out is command dependent way to pass parameters, such as the identifier of the selected MappingSet object, to instantiate my viewmodel in one of the three states mentioned above? For instance would the mvvmlight messenger be appropriate for this task?
This is a perfect scenario for the messenger/eventaggregator. However, your message chain might be a bit convoluted. From what I'm understanding, your Main window holds a list of commands (like a menu or a ribbon). Here is how I see the chain of events.
You select a MappingSet from the datagrid, this causes a MappingSetSelected message to be fired (with a payload of the selected MappingSet)
The main window listens for that message and stores the currently selected MappingSet
When the user clicks the button a "EditMappingSet" or "CreateNewMappingSet" message is fired (or if the Window is responsible for creating the new views, it creates them itself).
If there are only three options, you could have them binding to three different commands and within the commands do the passing of your self-defined variable.
private RelayCommand _openMappingSetCommand;
//Command that one of your options is bound to
public ICommand ViewMappingSetOption1
{
get
{
if (_openMappingSetCommand == null)
{
_openMappingSetCommand = new RelayCommand(param => this.DoTabRequest("your parameter");
}
return _openMappingSetCommand ;
}
}
// Method that creates your viewmodel
private void DoTabRequest(parameterType parameter)
{
WorkspaceViewModel viewModel = null;
if (viewModel == null)
{
viewModel = (WorkspaceViewModel)Activator.CreateInstance(typeof (viewModelType), parameter);
this.Workspaces.Add(viewModel);
}
this.ActiveWorkspace = viewModel;
}
Then allow for that parameter on the constructor of your viewmodel and do whatever else you need based on that.
I wonder how you do such thing. Assume, we have MVVM CRUD app which modifies a tree (menu structure, for example). We have a view model with the menu items and two views: the first with a TreeView and the second with a DataForm. Main problems are:
DataForm can not handle
hierarchical data.
Depending on the menu item selected
in the TreeView the DataForm
should display different set of
fields (for example for menu items
with children or without).
I've ended up with the following. View model has 3 fields:
Items — the collection of
MenuItem objects which have their
own Children collection for
building hierarchical data source.
SelectedItem — currently selected
MenuItem in the TreeView.
EditedItem — EditViewModel
object which basically has two
descendants: MenuItemEditViewModel
and LeafMenuItemEditViewModel.
This property is set automatically
when SelectedItem is changed. Its
actual type is inferred from the
SelectedItem.Children emptiness.
TreeView is bound to Items and SelectedItem. DataForm is not required to maintain currency in this case (instead current item is set by the TreeView) nor it is responsible for creating and deleting items. That's why I decided to bind only its CurrentItem to view model's EditedItem (ItemsSource is unbound). Its AutoCommit is set to False (when it is True and ItemsSource is unbound all current item changes get copied to newly selected item when you select different item in the TreeView, which is not so nice). DataForm fields are autogenerated.
Obviously, that now if we select an item in the TreeView, then make some changes in the DataForm and try to select different item in the TreeView we'll get well-known
Cannot change currency when an item
has validation errors or it is being
edited and AutoCommit is false. Set
ItemsSource to a ICollectionView to
manage currency instead
In this case I want DataForm to discard all changes implicitly. There is a workaround to call DataForm.CancelEdit() before TreeView selected item is changed (usually an event like PreviewSelectionChanged or BeforeSelectionChanged). But it is not the MVVM way since the TreeView and the DataForm are defined in completely different views (read: is not acceptable).
Is there something like AutoCancel which forces DataForm to cancel changes when its CurrentItem is changed? Maybe someone from dev team can answer? Or how would you deal with such problem?
I was surprised to find the Silverlight is severly lacking in this functionality, considering all the business oriented RIA functionality. AutoCommit is not acceptable to me because I want the user to explicitly acknowledge pending changes, rather than just commit something to the database that they may not want.
You can reliably track the edit mode of the DataForm using a private member variable and trapping the BeginningEdit and EditEnded events of the DataForm (naming inconsistency! Why one is called xxxEdit and the others are Editxxx is beyond me. Should it not be EditBeginning and EditEnded??). Inside the event handler for BeginningEdit, set the flag to true and set it to false in EditEnded.
In your SelectionChanged event, you can then check the flag. If it is true, you can call the CancelEdit on the DataForm.
private bool _editing = false;
public MainPage() {
DataForm1.BeinningEdit +=
new EventHandler<CancelEventArgs>(DataForm1_BeginningEdit);
DataForm1.EditEnded +=
new EventHandler<DataFormEditEndedEventArgs>(DataForm1_EditEnded);
}
protected void DataForm1_BeginningEdit(object sender,
System.ComponentModel.CancelEventArgs e) {
_editing = true;
}
protected void DataForm1_EditEnded(object sender,
DataFormEditEndedEventArgs e) {
_editing = false;
}
void TreeView1_SelectedItemChanged(object sender,
RoutedPropertyChangedEventArgs<object> e)
{
if (_editing) {
object previous = DataForm1.SelectedItem;
object current = TreeView1.SelectedItem;
if (MessageBox.Show("Are you sure you want to cancel the changes?",
"Confirm", MessageBoxbutton.OKCancel) == MessageBoxResult.OK) {
DataForm1.CancelEdit();
}
else {
TreeView1.SelectedItem = previous;
}
}
}
Have you tried to set AutoCommit at True ?