My control has a property that returns an ICommand object. Using XAML, how to I bind a button to it?
Without knowing anything about the relation of the two I would use element binding. E.g.
<YourControl x:Name="CmdSrc" />
<Button Command={Binding ElementName=CmdSrc, Path=CmdProperty} />
You should think about the approach that a control provides a command. It's seems to me some kind of weird. ;)
Regards
EDIT
Ah ok, it was just a hint. Just in case you didn't think about it.
Here is another way to bind your command. I've to admit that I didn't test it. But I think the following should work too.
When the Button is in the control you could also use relative binding.
<YourControl>
<Button Command={Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type YourControl}}, Path=CmdProperty} />
</YourControl>
Then you don't need a name for the control. I'm avoiding names when ever I can to prevent dirty workarounds in code behind.
Yes, I know it some kind of paranoid. ;)
Related
Just this. I want that when the databound property Text of a TextBlock for example changes, an animation is performed to give some feedback to the user. How can this be done?? thanks!
I found a way to do it using a PropertyChangedTrigger
<Interactivity:Interaction.Triggers>
<ec:PropertyChangedTrigger Binding="{Binding KnownMeaning}" >
<eim:ControlStoryboardAction Storyboard="StaticResource Storyboard2}"/>
</ec:PropertyChangedTrigger>
</Interactivity:Interaction.Triggers>
There may be a more elegant solution, but I think this is pretty straightforward
You can simply add event to ViewModel and start animation (Storyboard.Begin) in code-behind. Or even do it without extra event by adding handler of ViewModel.PropertyChanged in code-behind.
More advanced options are listed here:
Re: How to Annimate (Storyboard.Begin() ) in MVVM.
first of all I would like to thank you for the many good posts that i read in this forum. Unluckily I could not find anything of help for my current problem (either here or anywhere else).
What I'm trying to do sounds quite simple, but I have no clue how to get it to work ... perhaps I'm still to new to wpf or I don't thing wpfy enough :)
I'm designing a front end for a part in an automated manufacturing:
I have a quantity of places where pallets can be put (but it can be empty as well).
Each pallet has up to 3 places where parts can be mounted
Everything is created dynamically of a database and is reacting to changes.
The position of the parts on the pallet comes from the database as well and should be visualized
What I would like to have is:
An overview over the pallet-places with a preview of the pallet
When I select a place I want to see a detail view of the place
When I click on a part on the pallet of the detailed pallet I want to see details to the part
The first two points are quite simple and work nicely:
I have got a DataTemplate for every component (part, pallet, pallet-place). Actually those are UserControls that are imported as Datatemplates
the overview is a ListBox with the places as DataContext
for the detail-place-view I use the UserControl and bound it to the SelectedItem of the Listbox
I tried to bind the Text of a Textblock to the ID of the selected Part ... and fail.
Probably I could use some global variables in the code behind - but that sound very ugly.
Can anybody help?
I have got a solution ... it is not nice but works.
I created an event in the pallet, that triggers, when the selected part-place changes
I handle the event in the pallet-place and create a new one
And finally I handle it in the overview and change the detailview accordingly
Most likely there are much nicer solutions, but it will suffice.
Perhaps try an ElementName binding?
<TextBlock Text="{Binding ElementName=Name_of_your_Listbox, Path=SelectedItem.ID" />
Can you post a bit more code of your TextBlock and your Binding?
Context is important, if i use a ContentControl and bind its content to the SelectedItem like this:
<ContentControl Content="{Binding SelectedItem, ElementName=mylistbox}">
I can bind to the ID of the selected item in the DataTemplate like this:
<ContentControl.ContentTemplate>
<DataTemplate>
<TextBlock Text="{Binding ID}" />
</DataTemplate>
</ContentControl.ContentTemplate>
That is because setting the Content of the ContentControl automatically sets the DataContext as well, and this binding is relative to the DataContext since no source (ElementName, RelativeSource, Source) has been specified.
I do not know how your UserControl handles the context, if the DataContext is not affected such bindings will not work. You would need to bind directly then:
<uc:MyDetailsView Data="{Binding SelectedItem, ElementName=mylistbox}">
<!-- ... -->
<TextBlock Text="{Binding SelectedItem.ID, ElementName=mylistbox}" />
This of course defeats the purpose of having the binding on the UserControl itself in the first place. But unless you post some relevant code it's quite hard to tell what is wrong.
Also check the Output window in VisualStudio, binding errors will show up there and might provide valuable information as to what went wrong.
I have several MenuItems whose Commands are bound to my ViewModel. Until today, all of them execute properly.
Now I have added a MenuItem whose ItemsSource is bound to an ObservableCollection. The point of this MenuItem is to enumerate a list of plugins so that the name of all plugins show up. Then when the user clicks on a plugin name, it should call a function to display properties for audio filters.
In my current implementation, which doesn't work, I tried to databind like this:
<MenuItem Header="Filters" ItemsSource="{Binding FilterPluginNames}">
<MenuItem.ItemContainerStyle>
<Style>
<Setter Property="MenuItem.Command" Value="{Binding ShowFilterDialogCommand}" />
</Style>
</MenuItem.ItemContainerStyle>
</MenuItem>
The problem is that I get a BindingExpression path error because it's trying to use a String as the MenuItem's DataContext.
This leads me to believe that the DataContext for a MenuItem's MenuItems is automatically set to type of objects in the ItemsSource. Is this true?
If I need to change the DataContext, then I'd like to change it to the ViewModel that handles all of my other Commands. But if I do that, how in the world am I able to tell which plugin I want to display filter properties for? I'd need to pass in a CommandParameter at the very least, but binding this value to the filter name isn't my most favorite option. Are there any other ways to do this?
If the DataContext is indeed automatically set to the object type in the ObservableCollection, then I'd rather just call my interface method ShowFilterProperties() directly. I bet that I can't do this without Command binding. If that is the case, how do you all deal with this sort of application? Do you make all of the plugins expose a command handler, which will then show the dialog?
EDIT -- I modified my code to change the ObservableCollection type, and sure enough, WPF wants to databind to the type T. So I guess one option is to have the plugin expose the ICommand, but I don't know if this is a weird approach or not?
EDIT -- ok, I just learned something new. Interfaces can't have fields, so is it not possible to databind with plugins, period?
You are likely not quite binding like you think you are. You might want to just put some diagnostics on your bindings and see what object they are binding to. Here is a good link for debugging bindings:
http://www.beacosta.com/blog/?p=52
Here's a sample:
<Window …
xmlns:diagnostics="clr-namespace:System.Diagnostics;assembly=WindowsBase"
/>
<TextBlock Text="{Binding Path=Caption, diagnostics:PresentationTraceSources.TraceLevel=High}" … />
I think your approach is correct... it probably just needs to be debugged a little.
One of the things I really like with WPF is the extent to which my views can be built declaratively, ie. using XAML rather than code-behind.
Now I'm really stumped by InputBindings, because their CommandParameters don't accept bindings. I imagine my case is pretty generic and straightforward, but I cannot see how I can do it without resorting to code-behind. Consider:
<ListBox Name="casingsListBox" ItemsSource="{Binding Path=Casings}" SelectedValuePath="Id">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=Title}"/>
</DataTemplate>
</ListBox.ItemTemplate>
<ListBox.InputBindings>
<!-- Doesn't work: -->
<MouseBinding Gesture="LeftDoubleClick"
Command="ApplicationCommands.Open"
CommandParameter="{Binding RelativeSource={RelativeSource Self} Path=SelectedValue}"/>
</ListBox.InputBindings>
</ListBox>
This will not work, since the binding expression for the MouseBinding's CommandParameter is illegal.
I ask myself: what's the point of adding a mouse-click gesture to a listbox if I cannot get to the selected value?
This can be easily solved using a code-behind event handler, of course, or by having the command consumer extract the id from the command source, but there are several reasons why this is undesirable. Apart from the fact that droves of code-behind code defeats (some of) the purpose of WPF in the first place, it makes the UI designers working in Expression Blend less empowered. And dammit, my command parameter shall be an id, not some UI element!!
Subjective: Having browsed SO for a while, I'm struck by the amount of code I see in the WPF-related questions. I get the feeling we developers stick to our old habits and happily hack away in the code-behind file rather than trying to utilize the fresh take on UI building that WPF is supposed to represent. What do you think?
But most importantly: can anyone show me a code-free workaround for this seemingly trivial problem? Preferably without terrible hacks like this one.
I wrote a markup extension that allows an InputBinding's Command to be databound :
<KeyBinding Modifiers="Control" Key="E" Command="{input:CommandBinding EditCommand}"/>
Your situation is slightly different since you want to bind the CommandParameter, but you can probably adapt my code to fit your case. Note that this code uses private reflection, which only works in full-trust, and can be broken in later versions of WPF (actually it is broken in WPF 4.0... I can post a modified version if you need it).
Another option is to use the CommandReference class that can be found in the MVVM toolkit :
<Window.Resources>
<c:CommandReference x:Key="EditCommandReference" Command="{Binding EditCommand}"/>
</Window.Resources>
...
<KeyBinding Modifiers="Control" Key="E" Command="{StaticResource EditCommandReference}"/>
Again, this is for binding the Command property, but can probably be adapted to bind the CommandParameter...
The new way to solve this problem is by using Expression Triggers / Actions which allow you to set up keyboard shortcuts on arbitrary controls that do custom actions (like firing a Command).
I am trying to use the MVVM pattern to write a WPF application. I am using WPF data grid (from the toolkit) which lacks the autofiltering feature. So I want to implement it. I've added a context menu to the column header template, it has MenuItem called "Filter" which should actually call the filtering method.
So I've set a MenuItem's command to be the appropriate DelegateCommand which goes to the ViewModel. The problem is that I need to pass the information about the actual column that has been right-clicked! If I wasn't using MVVM, I would implement an event handler which would receive a "sender" argument (the MenuItem), then I would find its parent (the ContextMenu), then its parent would give me the column. But how can I achieve the same thing here? How can I pass the sender to my command? Can this be done using ComandParameter?
I really don't want to use additional complicated patterns to achieve such a simple task. After all, MVVM should simplify the development and not vice versa...
Can you pass the Column header value as a Command Parameter and use that to get the Column details at the ViewModel?
You could try some relative source magic, but it might be easier on you if you can have a different ViewModel that you bind to for each header, like HeaderViewModelItem. From there you'd just be firing a DelegateCommand in your HeaderViewModelItem, rather on your larger viewmodel.
I've used this model with pretty good success. Gets around a little bit of databinding dance.
If you want to pass something into the command parameter it is important to note that a context menu is on its own visual tree. Luckily it still inherits the DataContext from its parent, so something like
<MenuItem CommandParameter="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContextMenu}}, Path=DataContext}" />
should get you the GridViewColumnHeader, or at least something in the visual tree of it.