I have a user control with 2 grids on it. Now I want to be able to retrieve the grid that has the focus and expose it to my view model. How can I do this in WPF?
I want to fill a property in my view model with the name of the Grid that has focus. It seems not to be easy.
Can anyone help?
Thx!
You really should reconsider your design if you are exposing UI elements or specific parts to your viewmodel. Usually your viewmodel should not know of any specific ui element. What exactly do you want to do with the name of the ui element? You could listen to a GotFocus event on your two grids
like
<Grid x:Name="Grid1" GotFocus="OnGridGotFocus"/>
<Grid x:Name="Grid2" GotFocus="OnGridGotFocus"/>
and add this method to your UserControl, in this method you could retrieve it via
private static void OnGridGotFocus(object aSender, RoutedEventArgs aE)
{
string name = (string)(aSender as DependencyObject).GetValue(NameProperty);
}
the name could now be written into a DependencyProperty which you bind to your view model. But again, i still think you should not do this.
If you explain what exactly you are trying to achieve, maybe we can help you better.
Related
Let's say I have a Customer Window showing information about a customer, like Name, address and phone number. On the bottom there is a DataGrid of their orders. Of course the Customer has an Orders property, so if you're using MVVM, you would just set:
ItemsSource = "{Binding Customer.Orders}"
However, now let's say that the data grid is now part of a user control, which also includes controls for editing/adding/removing Orders. I want to use this same set of controls in multiple places, and I would like all the logic for editing/adding/removing Order objects to be encapsulated in the user control. And because I want to use commands, rather than event handlers, I would like the user control to have its own view model.
So now the question is: how do I pass the orders from the Customer view model to the Orders user control's view model? Because the Orders user control will be bound to a view model, I can't say:
<local:OrdersUserControl DataContext="{Binding Customer.Orders}" />
because the user control has it's own view model. It would expect to see Customer.Orders there, and of course it's not.
I guess this is kind of a chicken or the egg situation.
Your help is always appreciated.
Aaron
And now for my weekly "don't do that" answer...
I can't say ... because the user control has it's own view model.
To which I say
Creating a ViewModel for your UserControl is a code smell.
You're experiencing this issue because of that smell, and it should be an indication that you're doing something wrong.
The solution is to ditch the VM built for the UserControl. If it contains business logic, it should be moved to an appropriate location in another ViewModel.
You should think of a UserControl as nothing more than a more complex control. Does the TextBox have its own ViewModel? No. You bind your VM's property to the Text property of the control, and the control shows your text in its UI.
MVVM doesn't mean no codebehind. Put your UI logic for your user control in the codebehind. If it is so complex that you need business logic inside the user control, that suggests it is too encompassing. Break it down into two or more.
Think of UserControls in MVVM like this--For each model, you have a UserControl, and it is designed to present the data in that model to the user. You can use it anywhere you want to show the user that model. Does it need a button? Expose an ICommand property on your UserControl and let your business logic bind to it. Does your business logic need to know something going on inside? Add a routed event.
Normally, in WPF, if you find yourself asking why it hurts to do something, it's because you shouldn't do it.
There are many ways to skin a cat. The way I've been doing this is by having my CustomerViewModel have a property of type OrdersViewModel. Then in the constructor (or wherever you are setting the customer) have it set the "OrdersContext" with a new OrdersViewModel passing in the customer.orders.
XAML:
<local:OrdersUserControl DataContext="{Binding OrdersContext}" />
ViewModel:
public CustomerViewModel(Customer customer)
{
Customer = customer;
OrdersContext = new OrdersViewModel(customer.Orders);
}
I currently have one view with 3 fairly simplistic view models. For the sake of this discussion, we will focus on 2 of the three view models.
The View is a User Management user control. It contains a DataGrid that has its ItemsSource binding set to a UserListViewModel. This view model simply displays user information in the data grid.
The User Management View also contains some other controls, such as buttons for adding new users and removing users. Those buttons are currently bound to a second view model called UserManagementViewModel. For example, the Remove button will successfully call the RemoveUser method on the UserManagementViewModel.
My question is, via XAML (as I hate code-behind), how can I pass the SelectedItem property of the DataGrid (bound to UserListViewModel) into the RemoveUser method call on the UserManagementViewModel? I realize that, in the MVVM design pattern, my view model can't look into the view to retrieve the information necessary, so there must be a way via binding to pass that information into the method.
XAML code examples (or links that show how) to perform similar functionality would be appreciated. Thanks for any help!
you can simply use a commandparameter
<Button Command="{Binding RemoveCommand} CommandParameter="{Binding Elementname=gridUser, Path=SelectedItem}" />
or your UserManagementViewModel have access to the UserListViewModel then you need a command without commandparameter and simply use the SelectedUser property of your UserListViewModel instance
public void ExecuteRemove()
{
var userToRemove = this._myUserListViewModelinstance.SelectedUser;
...
}
I believe what you seek is commanding with a command target bound to the datagrid's selecteditem where one can route such information from the datagrid; say when a button is pressed.
See Commanding Overview on MSDN
I'm writting a form in WPF/c# with the MVVM pattern and trying to share data with a user control. (Well, the User Controls View Model)
I either need to:
Create a View model in the parents and bind it to the User Control
Bind certain classes with the View Model in the Xaml
Be told that User Controls arn't the way to go with MVVM and be pushed in the correct direction. (I've seen data templates but they didn't seem ideal)
The usercontrol is only being used to make large forms more manageable so I'm not sure if this is the way to go with MVVM, it's just how I would of done it in the past.
I would like to pass a class the VM contruct in the Xaml.
<TabItem Header="Applicants">
<Views:ApplicantTabView>
<UserControl.DataContext>
<ViewModels:ApplicantTabViewModel Client="{Binding Client} />
</UserControl.DataContext>
</Views:ApplicantTabView>
</TabItem>
public ClientComp Client
{
get { return (ClientComp)GetValue(ClientProperty); }
set { SetValue(ClientProperty, value); }
}
public static readonly DependencyProperty ClientProperty = DependencyProperty.Register("Client", typeof(ClientComp),
typeof(ApplicantTabViewModel),
new FrameworkPropertyMetadata
(null));
But I can't seem to get a dependancy property to accept non static content.
This has been an issue for me for a while but assumed I'd find out but have failed so here I am here.
Thanks in advance,
Oli
Oli - it is OK (actually - recommended) to split portions of the View into UserControl, if UI became too big - and independently you can split the view models to sub view models, if VM became too big.
It appears though that you are doing double-instantiations of your sub VM. There is also no need to create Dependency Property in your VM (actually, I think it is wrong).
In your outer VM, just have the ClientComp a regular property. If you don't intend to change it - the setter doesn't even have to fire a property changed event, although it is recommended.
public class OuterVm
{
public ClientComp Client { get; private set; }
// instantiate ClientComp in constructor:
public OuterVm( ) {
Client = new ClientComp( );
}
}
Then, in the XAML, put the ApplicantTabView, and bind its data context:
...
<TabItem Header="Applicants">
<Views:ApplicantTabView DataContext="{Binding Client}" />
</TabItem>
I answered a similar question as yours recently: passing a gridview selected item value to a different ViewModel of different Usercontrol
Essentially setting up a dependency property which allows data from your parent view to persist to your child user control. Abstracting your view into specific user controls and hooking them using dependency properties along with the MVVM pattern is actually quite powerful and recommended for Silverlight/WPF development, especially when unit testing comes into play. Let me know if you'd like any more clarification, hope this helps.
My first question here on the Stack. Forgive me for the bad explanation in advance.
I am working on my first MVVM application (Silverlight). I have a custom user control that contains a ListBox to show navigation items. This control is placed in my main xaml page. I don't know if I need to create a composite view model (my main page view model) with a view model especially for the custom control in it or if there is some way to elevate the ListBox properties that I need to bind to.
Through XAML I don't know how to bind, let's say, the ItemsSource property of the ListBox inside the custom control to my main page viewmodel. Basically, I'm at the point that I am questioning my design decision for trying to bind the custom control through my main page view model.
What I have done so far is create dependency properties for the custom control and try to tunnel those dependency properties down to the ListBox properties. I've achieved success with this method for ItemsSource but am having issues with SelectedItem.
Even if I do get SelectedItem to work, it still feels Wrong. Thanks for any advice in advance.
The UserControl should inherit the DataContext from its parent control, unless you are setting it directly. You can then bind to the properties on your view model from your UserControl.
If you would like to create a ViewModel specifically for the UserControl, you can also do that. You would then expose it as a property on your main ViewModel, and bind to it in the MainPage. Example:
public class MainViewModel
{
public ChildViewModel ChildInfo { get; private set; }
}
And then in the view:
<Grid>
...
<lcl:ChildView DataContext="{Binding ChildInfo}" />
...
</Grid>
Your ChildViewModel would then contain properties like SelectedItem to bind your ListBox to.
I'm just getting started with silverlight.
Basically I have a silverlight user control that has various dataGrids and a combobox, their item sources set to the properties of a custom plain c# object.
My problem is that I have a dropdown list that when a user selects an item from the list a new row should appear in one of the grids.
All I'm doing is handling the SelectionChanged event and adding a new item to to a list in my custom object and setting the itemsource for the grid again. This doesnt seem to work; no row is added to the dataGrid
I have no idea how to force my grid to "rebind" to this property.
I've been reading about dependency properties, are these what I need?
Any pointers would be really appreciated.
The list you are binding against should be of the type ObservableCollection. Then the datagrid should display the new item automatically .
The problem is that when you assign the same List to the ItemsSource the DataGrid knows its the same List so it does nothing.
As Henrik points out you should expose an Observable<T> not a List<T> for properties that are to be bound to ItemsSource properties of multi-item controls such as DataGrid, ListBox etc.
In addition your "plain c# objects" should implement the INotifyPropertyChanged interface if you want changes made by code to these properties to automatically appear in the UI.
What you probably want to do is update the binding source - which is relatively easily done.
private void ComboBox_SelectionChanged(object sender, RoutedEventArgs e)
{
this.dataGrid.GetBindingExpression(DataGrid.ItemsSource).UpdateSource();
}
This is a tad hack-y but will do what you need it to do. Implementing INotifyPropertyChanged is another great suggestion.
Silverlight show have some great info on INotifyPropertyChanged here