<TextBlock Text="{Binding Name}"/>
Binding works fine when I first navigate to a page containing the code above. Then I navigate forward to a page that that makes changes to the model (the Name property) and navigate back (with back key). The Text property, however, is still displaying the old value. How can I force the bound value to update on back navigation.
Make sure that your model implements INotifyPropertyChanged and that the PropertyChanged event is firing within the setter of Name
Related
I have an Entry and a Button. I want the command "CallWebServiceCommand" to be called when I press the button. The call to that command needs to include the url of the web service as a CommandParameter. The BindingContext is set to the ViewModel of the page.
The CommandParameter property of the button needs to reference the Text property of the entry. In WPF, I could do something like this:
<Button Text="Call web service" Command="{Binding CallWebServiceCommand}" CommandParameter="{Binding ElementName=url, Path=Text}" />
I know that it's not possible to have multiple binding contexts per view, but what would be a good workaround for this particular situation?
This is a bit of a hack, but it's worked for us in the past:
Use the ViewModel as a "relay" for the view. To do this, create a String property on your ViewModel that the text field binds its Text property to, and bind the CommandParameter of the button to this property. If you raise the PropertyChanged event for this "parameter" property, the command will supply the updated value to the method specified as the command's Action. It's certainly non-ideal, but it does work as a poor man's replacement for RelativeSource binding.
I have a ViewCharacter page that has a View Model (CharacterViewModel) as its DataContext, in that CharacterViewModel I have an ObservableCollection of WeaponViewModel that a ListBox is using as an ItemSource. The ListBox's DataTemplate contains a UserControl that is designed for the WeaponViewModels in the parent page's View Model's ObservableCollection. I need to bind a CommandParameter of a button in the UserControl to a property on the Parent page's view model (CharacterViewModel). I've tried using {Binding DataContext.TargetProperty, RelativeSource={RelativeSource TemplatedParent}} with no success and am at a loss of what to do without outright breaking all MVVM patterns.
Windows Phone 7 lacks a relative source binding. I have created a Silverlight implementation here:
http://www.scottlogic.co.uk/blog/colin/2009/02/relativesource-binding-in-silverlight/
But for WP7, where performance is critical, I would avoid using it!
I would instead recommend making the relationship between CharacterViewModel and WeaponViewModel bi-directional. In other words, add a Parent property to WeaponViewModel which will be a reference to the owning CharacterViewModel. You can then bind to properties on CharacterViewModel via this property.
Using MVVM Light I have a listbox databound to a collection of several items.
One of the items is the selected one.
With this code it works perfectly and ViewModel structures are updated correctly:
<Name="listBox1"
ItemsSource="{Binding Path=Models}"
SelectedItem="{Binding Path=csProfile.Model, Mode=TwoWay}">
My problem is that when I enter the page if the selected Item is not in the first items it is not visible and the user does not know what was the previous selection.
How could I force the Listbox to always show the Selected Item?
Possibly via properties or Binding.
M
There's no property you can bind to to set what's visible. Instead call ScrollToVerticalOffset() on the ScrollViewer inside the ListBox.
I think you are looking for the ScrollIntoView method. A similar topic was discussed here:
Automatic Scrolling in a Silverlight List Box
The API reference is here: http://msdn.microsoft.com/en-us/library/system.windows.controls.listbox.scrollintoview(VS.95).aspx
Calling UpdateLayout() before calling ScrollIntoView on the selected item seems to be necessary.
I have a view with a list box, bound to am obvervable collection of DisplayItems, which has 'Label', 'DisplayValue' and 'IconUri' properties.
I have a View Model which exposes this observable collection. The List Box is correctly populated first time around.
I then have a button which takes action on the selected item. I need to indicate that action has been taken by changing the image.
I am changing the IconUri of the selected item, and can see the new value present when debugging, but the image doesn't change. I can also change the 'Label' and 'DisplayValue' properties and see the new values correctly there when debugging, but the list doesn't change.
My ViewModel implements INotifyPropertyChanged. My DisplayItem class implements INotifyPropertyChanged. I'm calling RaisePropertyChanged I'm sure in too many places rather than too few.
None of the changes are ever reflected on screen.
I'm using a DataItemTemplate for the generated rows. If I could access the image of the selected row I could change it manually, but I can't even do that.
Any help greatly appreciated. I could actually do with a example of a list box displaying items from a bound observable collection, where one property of the selected item is changed and that change is reflected in the list box.
Thanks in advance
A
You didn't implement INotifyPropertyChanged correctly, or you're using it wrong.
I have a Listbox with Button and Textblock as ItemTemplate. Button has an onClick event.
All i want is to get the index of the clicked item, but SelectedIndex property in my ListBox is always -1!
How can I get the index of the clicked item?
The problem is that the Button control is swallowing the mouse events to provide the Click behavior, so the ListBox never receives any events to tell it that the selection has changed.
As #Alexander suggests, you could use an MVVM-style approach with commands to handle the action in a view model and pass the data context as the parameter.
Alternatively, you could replace the Button with any other layout control and either use the gesture service from the Silverlight Toolkit or use the regular MouseLeftButtonUp event. In either instance, the mouse events will bubble up and enable the ListBox to handle selection.
You might want to actually select something in your listbox then :p
If you want to get data object associated with current ListItem use RouteCommand. Here is example
<ListView.ItemTemplate>
<DataTemplate>
<Button Margin="5,0" Command="{StaticResource ButtonCommand}"
CommandParameter="{Binding}">
</DataTemplate>
<ListView.ItemTemplate>
You need also define Command at least in ListView.Resources
<RoutedCommand x:Key="ButtonCommand"/>
And then setup CommandBinding like this
<ListView.CommandBindings>
<CommandBinding Command="{StaticResource ButtonCommand}" Executed="Button_Click"/>
</ListView.CommandBindings>
In the end write handler
Button_Click(object sender, ExecutedRoutedEventArgs e)
{
e.Parameter// object that you Specified in CommandParameter
}
In advance you can use any MVVM framework, define all command and commands logic in model and then just bind this commands to corresponding elements.