I have a question about doing the custom painting operations in WPF MVVM View. My case is:
External manipulation of model data happens, and the observable collection of data to be shown is modified (storing some data to be shown in a diagram). I have to react to that change in my view, and custom layout the diagram elements (remove the ones not used, place new ones, calculate positions on diagram canvas). How can I do that, and what would be the best way to do it conform to MVVM pattern? I cant subclass the diagram class, as it is sealed. The diagraming framework used is MindFusion.
Edit: A solution was proposed on MindFusion Support forum, and it works.
http://mindfusion.eu/Forum/YaBB.pl?board=wpfdg_disc;action=display;num=1306412889;start=0
Last I checked MindFusion diagraming component for WPF, it supported MVVM through data binding. If you bind the diagram to a ObservableCollection you can then write custom Node Templates which are basically DataTemplate that will render YourDiagramModel items on the diagram panel.
Unlike WinForms you usually don't need to manually refresh or paint control surface in WPF custom controls.
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I currently develop a WPF control which is simply canvas with some additional properties like grid lines, children drag and drop etc.
I need a mechanism to call some of my canvas functional from view model binded to view that contains my canvas.
For example, view can contain my canvas and a button "Show grid". When user clicks the button canvas should paint grid on itself.
The problem is to do this according to MVVM pattern without direct reference to canvas in view's view model.
What is the best practice to do this?
UI related stuff can be still written in view behind cs file. It does not mean that you violated MVVM. If view models are for business logic, view behind is for view logic. To achieve more encapsulation and re-usability, you can use Behaviors.
You can write a behavior which do all painting logic and attach it to the button. Even you can add dependency properties to your behavior to have more control on it.
I have an app with MVVM which works fine. Now I want to replace one of my controls with a dynamic control. By dynamic I mean that I have no idea what control this is, only that it is a GUI control. It could be something as simple as a image, or a custom third party user control that will be created by someone else after this app is done.
Can someone shed some light on how this can be achieved in MVVM? I've done it before a long time ago using ListBox or similar (iirc) to generate GUI elements (don't remember details). But I'd like to learn the theory behind it this time.
Edit:
Lets say the View contains a list of instances of for example System.Windows.UIElement. I want to display all of these UI controls on a surface (for instance in a stacked control).
You could create a View that exposes a Content property as a placeholder (so a ContentControl might be all that is needed) The content property could then be set to the dynamic control.
You would have to add a little reflection to dynamically load the assembly and instantiate the required control.
The dynamically loaded control would have to access the data by using the DataContext property. If the dynamic control is MVVM too it might have its own ViewModel so you would have to find a way to load that too (reflexction again?) and point the DataContext of the control to the loaded ViewModel.
Does this make sense, is this what you are looking for?
Well I'm designing a Custom WPF control - fore the sake of learning - that display logs message in a similar way Visual Studio does. I want to allow the user add messages by adding message istances to an Items collection, or by binding to an ItemSource. I think this is a well established pattern in many wpf controls, but I have no Idea on how achieve it. I know I can obtain the same result by adding a listview as a part of my control, but the project goal is learning, so I prefer avoid that solution. Any idea ?
Have a read around the ItemsControl, your custom control can inherit from an ItemsControl, or a derivative of it. If you create an ObservableCollection containing your items and bind that to your ItemsSource, then your list will be automatically updated. You can style the ItemTemplate and Template to give the list a different look and feel.
There's loads of info here
I created a rough, non MVVM demo in Silverlight that drew various lines and other 2d objects on an Canvas, based on an object model.
I'm now porting the application over to MVVM (Caliburn Micro) and am now at the point where I have my objects in my ViewModel and need to draw them on the canvas in the View.
Is MVVM in this case the wrong tool for the job?
Where should I stick the 2d drawing code?
In code-behind of the View?
Let me know if you need any more info about my situation to help. Thanks!
In a situation like this, I would personally treat your Canvas as a custom, independent control.
Ideally, you'd want to make it a control (perhaps a UserControl) with a dependency property for the "objects". The user of this control would bind the objects to a collection inside their (parented control's) ViewModel, and just treat this as part of the View.
As such, it's 100% View - so the code can be implemented any way you choose. It kind of falls outside of MVVM, since it's entirely "view."
I currently need to create a visual representation of a ferry system that displays the actual ferries their position on the sea and the state of their cargo. The ferries contain trucks and the trucks contain cars. I need to display the actual trucks and their xy postion on the deck. When the ferries are loaded the postions of the trucks are updated frequently so the look animated. Also I need to display the actual cars on the trucks. Trucks, cars and ferries have some states that need to be displayed too. So I have a hierarchical structure of data that I need to visualize in a rather realistic manner.
What would be a good way to implement this kind of stuff in WPF? Should I use MVVM with one TreeView control and create a HierarchicalDataTemplates for sea, ferry, truck and car and a ControlTemplate for the TreeView? Or should I better use UserControls and compose and update them in code instead of databinding to observable collections of the ViewModel. Do you have any experience with this? How would you do this? Could you sketch out class/control setup?
I'd recommend making a "lookless" control as opposed to making user controls. Generally I use user controls as glue/container for my lookless controls. An example of a lookless control is the Button class. It contains a default style and in Blend, you can modify the style all you like. It also supports the visual state manager so you can change how the presentation looks when states change. You can think of the codebehind of a lookless control as a mini ViewModel. Here it is ok to mix some presentation stuff and your domain classes.
If you follow this same design, you could create a Ferry lookless control. This control would have a set of it's own dependency properties (possibly listening to the OnChange of the DP).
Your Ferry control may have an ObservableCollection DP called "Trucks".
Then in your Themes\generic.xaml, create a default style for your Ferry control. Your default style may have an ItemsControl with an ItemsSource={TemplateBinding Trucks}. The ItemsControl panel template, could be your own custom panel for arranging the Trucks, or maybe you use a Canvas. For the ItemsControl items template, you would have something like this:
<DataTemplate>
<mynamespace:TruckControl/>
</DataTemplate>
You Truck control, would also be a lookless control with it's own default style, and it's data context will already be set, so you can directly do the {Binding Path=xyz}. Your Truck control could also set it's Canvas.Left/Top (if you chose to use a canvas in the pervious items control..or maybe it doesn't set its position at all if you made a custom panel for it) or a render transform as to put it at the correct X,Y. You could also use the items control in the truck's template to render out the cars in the same fashion you rendered out the trucks in the ferry control. Also its possible to create states for the VisualStateManager as to make it fully Blend supportable. So if a truck goes into a "problem state" you could easily style that state in blend to make it blink red, for instance.
I know it sounds like a lot to digest, but in the end having stylable controls all supporting an MVVM model will make your life 1000000x easier.
I'd suggest studying Microsoft's silverlight toolkit to get a good idea how to do lookless controls and such. Try looking at a simple control, like the DatePicker ( http://silverlight.codeplex.com/SourceControl/changeset/view/25992# ) One caveat is ignore DatePicker.xaml file (it's just a mirror of what gets put in generic.xaml and nothing bad would happen if you just deleted it).
The things you should pay close attention to are:
1.) The attributes on the class. These help Blend know how to deal with your control.
2.) The OnApplyTemplate override. This is where you can pull out specific elements from your template. These are known as "parts" and you will see the parts tab in Blend. The attributes in #1 can define what "parts" are in the template and what type they are expected to be.
3.) The DefaultStyleKey = typeof(...) in the constructor. This tells Silverlight what default template to use in the generic.xaml
4.) Look at Themes\generic.xaml. This is a special hardcoded file location that stores all your default templates. Search for the DatePicker style and you will get the idea :)
Good luck!
I just wanted to let you know, how I actually implemented it. It turned out that it was not necessary at all, to write custom controls or UserControls for this. All I did, was writing datatemplates for the car, ship, ferry, truck etc ViewModels. For example the datatemplate for the FerryViewModel contained an ItemsControl with a ItemsPanel of type Canvas (to be able to position the trucks) and an ItemTemplate that was a DataTemplate for TruckViewModel. A very simple and fast approach.
I'd suggest having one user control handle all the drawing. Otherwise you can get lost the the hierarchy of objects. Also it makes it easier if another item was added, say people in cars, trucks and ferries.
If your model is hierarchical then you can just pass in the top level into the control, and let the control sort itself out.
MVVM works well for existing controls, but existing WPF controls only work if there's a control that's close to what you need, and with a few tweaks would work. I can't think of a standard control in WPF that's close to what you need, so it's time to write a new control.
WPF works really really well with view models. If you can keep code behind away until specifically needed then you can separate ui from data so much more easily. It will allow your ui's to be some much more upgradeable if the data model doesn't change between different display.