I have buttons in a listbox and for each of them, I want
to provide a different name. This is how I setup the binding in XAML:
<Button Content="{Binding count}"
x:Name="{Binding buttonName}"
Width="55"
Height="55"
BorderThickness="3"
FontSize="18.667"
Padding="-1,-2,0,0"
Margin="-400,0,0,0"
FontWeight="Bold"
Click="servingButtonClicked" />
buttonName is a string, which is stored in an object in a LinkedList<string> as an itemSource for this listBox.
Why won't this work?
Error:
Object reference not set to an instance of an object.
x:Name must not bet via DataBinding - this is a name for the instance of the object, not something dynamic.
Related
This is my XAML that is trying to have my ListView pass a parameter to the ViewModel command.
xmlns:mvvm="http://www.galasoft.ch/mvvmlight"
<ListBox x:Name="MyListView" ItemsSource="{Binding Objects}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<mvvm:EventToCommand Command="{Binding MyCommand}"
PassEventArgsToCommand="True"
EventArgsConverter="{StaticResource ParamConverter }"
EventArgsConverterParameter ="{Binding Name}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
And this is my converter:
public class ParamConverter : IEventArgsConverter
{
public object Convert(object value, object parameter)
{
var args = (SelectionChangedEventArgs)value;
var name = parameter as string;
return (string)name.ToString();
}
}
But I got the following error:
The resource "ParamConverter" could not be resolved
Your converter is not declared in XAML, you should add something like
<ListBox.Resources>
<yournamespace:ParamConverter x:Key="ParamConverter"/>
</ListBox.Resources>
inside your listbox tags.
EDIT: I'm not an expert at all, so bear with my "imprecise" terms if any. I think you're missing something: there is no magic that allows your XAML to be aware of your C#. You need to tell XAML that somewhere in your code (in yournamespace) there will be a ParamConverter object, that can be referenced inside xaml with ParamConverter key.
You can declare your resource locally inside ListBox tags as suggested, or at outer scope if needed.
Once resource is declared inside XAML, you can access it via StaticResource.
I have a UserControl with a button inside it. The UserControl its DataContext is one of my models so I can bind to it. However, for the button I want to be able to call a method from my viewmodel. The DataContext of the ListBox is this ViewModel.
Because my ContextMenu also needs the same DataContext I've bound them like this:
Command="{Binding Path=DataContext.AttendEventCommand, ElementName=EventListBox}"
Calling the EventListBox element and using its DataContext to call the AttendEventCommand. However I would like to call the AttendEventCommand from a button on the UserControl. I tried doing it the same way but sadly it doesn't work.
My data context is set like this:
DataContext="{Binding Path=EventList, Source={StaticResource Locator}}
My listbox code:
<ListBox x:Name="EventListBox" ItemsSource="{Binding Occurrences}" Margin="0,50,0,0" >
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<uctl:EventListItem HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="auto" Height="auto">
<toolkit:ContextMenuService.ContextMenu>
<toolkit:ContextMenu IsZoomEnabled="True" x:Name="ContextMenu">
<toolkit:MenuItem x:Name="Going" Header="{Binding AttendingText}" Command="{Binding Path=DataContext.AttendEventCommand, ElementName=EventListBox}" CommandParameter="{Binding}"/>
</toolkit:ContextMenu>
</toolkit:ContextMenuService.ContextMenu>
</uctl:EventListItem>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
And my UserControl's button:
<Button Grid.RowSpan="3" Grid.Column="5" Opacity="0" Command="{Binding Path=DataContext.AttendEventCommand, ElementName=EventListBox}" CommandParameter="{Binding}"/>
I believe your problem is not that what you want to do is not working; instead, your design appears to be wrong.
What you have now is like this:
You have a Window that has a DataContext and a ListBox. The ListBox has an ItemsSource, which we'll assume is some IEnumerable<Occurrence>.
The appearance of each item in your ListBox is an EventListItem, which is a UserControl that contains at least one Button.
You want this Button's Command to call a method on your Window's DataContext.
This last sentence is wrong. The fact that the item has the button implies that it does something that is related to the item, not the window contents. If this is not true, then the visual design of the window and listbox items should probably be reconsidered.
If the button is in fact affecting the item, then you should not call a method on your Window's DataContext, but instead call a method on your item's DataContext.
The solution is to wrap your model object Occurrence in a view model class of its own. Let's call it OccurrenceViewModel. Your ListBox's ItemsSource would be some form of IEnumerable<OccurrenceViewModel>. Because it's a view model, it's allowed to implement Command methods, which can then in one way or another manipulate the Occurrence, either directly or preferably by passing it to some class that implements the use case.
The DataContext of your EventListItem will be a Model of your ItemsSource because it is part of the DataTemplate. So you have to set it explicitly.
Refer to How to implement a navigation button for some of the code I'll be using as a solution.
Lets assume your custom UserControlis very basic like so:
<UserControl>
<Grid x:Name="LayoutRoot" Background="{StaticResource PhoneChromeBrush}">
<Button Command="{Binding DataContext.SimpleCommand}" CommandParameter="1"></Button>
</Grid>
</UserControl>
Where SimpleCommand is the Command you want to call in the Top View Model.
Then you have to change your DataTemplate to
<DataTemplate>
<Grid>
<uctl:EventListItem
DataContext="{Binding ElementName=myListBox}"/>
<!-- more xaml -->
</Grid>
</DataTemplate>
Your <toolkit:ContextMenu> should work as is.
Put a break point at the Execute function of the ICommand and you will see it will get
hit there everytime.
public void Execute(object parameter)
{
// logic to execute when user hits the command
int debug_var = 0; // put a break point here
}
I am styling the ListPicker with a DataTemplate. All the examples I have read assume that the ListItems are bound complex objects and so can refer to properties on the objects using the usual Binding Property syntax. e.g.
this.myListPicker.Items.Add(new Profile() { Name = "Joe",
Occupation="Button pusher" });
and in the XAML,
<DataTemplate>
<StackPanel>
<TextBox Text="{Binding Name}" />
<TextBox Text="{Binding Occupation}" />
</StackPanel>
</DataTemplate>
However my ListPickers are bound to a List of simple strings and there does not seem to be a property on the string that actually refers to the string.
How do I get a handle to the string inside the DataTemplate so that I can assign them to a e.g. TextBox in the template?
In the example code you show, you do actually have a "complex" object, a Profile, and the binding you specify should work.
If you really just have strings as the items, then the binding in your ItemTemplate would look like:
<TextBox Text="{Binding }" />
The relevant detail is that all ItemsControls (and ListPicker seems to be one) set the DataContext of the view of each item to the item. The binding syntax, above, means "bind to the source itself", and, unless otherwise specified (like with Source or RelativeSource, etc.), the source of any binding is the DataContext.
MSDN has more details here.
I Have a ListBox and I am defining its ItemsTemplate using a custom control. I want the control to be displayed in different ways depending on the state of cetain properties of the object. How can I access the item that the ListBox.ItemTemplate is bound to?
<ListBox>
<ListBox.ItemTemplate>
<DataTemplate>
<custom:MyControl />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
With in the code of the custom control how would I do something like:
if((this.DataContext as SomeObject).CollectionProperty.Count() > 0)
DoAction();
I was accessing dataContext in the constructor and it was null. I accessed it in the this.Loaded event and it worked fine.
Say I have a listbox, whose itemsource is bound to a Collection of classes Foo
How can I xaml bind a property directly to the instance of Foo?
The property I want to bind is the source of an Image, and the Foo class has several properties that influence the source, so in my Converter class. I want Foo
If you mean that you have the ItemsSource property of an ListBox bound to the collection (you don't bind to controls, but to their properties), and you want to show an image for each Foo in the collection, you can do it like this:
<ListBox ItemsSource="{Binding whatever}">
<ListBox.ItemTemplate>
<DataTemplate>
<Image Source="{Binding Converter={StaticResource converter}}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Just by leaving the binding's path empty, it is set to the current item.