Library tutorials & articles
Hosting Windows Forms Designers
- Introduction
- The Service Hierarchy
- The Designer Container & Host
- Starting Off
- Implementing ISite and more
- Extender Services
- Making it Work
The Designer Container & Host
The Design Container
No matter what you're designing, be it Windows Forms or Web Forms, everything in design mode is said to be on the Design Surface . What this means is that it's in the design container. Forms and controls are hierarchical in nature, but everything is also in the design container, which is a one-level collection. This container has the code to discover and instantiate designers for objects, and also dispose of them when they're done.
As you probably already know, all designers implement the IDesigner interface. However, there is always one special designer in a document which has to implement IRootDesigner. This is the one that acts as a parent to all the rest, and is responsible for providing the interface you use to view the object you're designing. This is always the first object to be added to the design container. The framework provides three root designers - for Forms, UserControls and Components. You've probably seen all these if you've used the various designable types in Visual Studio. The framework doesn't contain any Web Forms root designers.
The root designer is a great idea, it means you don't have to write any special hosting code no matter what you're designing. Once your hosting framework is in place you can design anything that offers one.
The Designer Host
This is where you start when hosting designers (obviously). It all begins with the IDesignerHost interface, which you might well have already used from designers you've written. It exposes the design container, the root component, and methods for creating components and getting their designers. It also provides the support for designer transactions and acts as a service container.
Although we'll be implementing quite a few interfaces apart from this one, the most important two are ISelectionService and IComponentChangeService, because every designer uses them. Thankfully most of the .NET controls behave gracefully when they fail to find a service implemented, if they didn't we would have a much harder time getting started.
The core designer hosting architecture is split in to several interfaces, but since they are tightly bound together we will be implementing the most important ones all in one class:
-
IDesignerHost- The core interface. -
IContainer- The container that holds all components on the design surface. -
IComponentChangeService- Used to broadcast events when components change. -
IExtenderProvider- Used to give components a configurable name.
Design Sites
In order to be on the design surface, a class has to implement IComponent. This means it has a Site property, which is how its name is kept track of at design time. For every object that is placed on the design surface an object implementing ISite needs to be assigned to it. It's through this that the components are able to request services, establish that they are in design mode and get their name.
We will create a class, DesignSite, that implements ISite and provides this necessary information. Anyway, enough with the theory, let's get down to business.
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How would I go about saving a form that I have designed?
I have (am still) modifying this code to create a stand-alone Xaml generator for forms. The Xaml is structured for direct consumption by Windows Presentation Foundation. This was a great starting place.
In the course of my modifications and testing, I found a couple of bugs in the code which you may wish to correct in your source.
The Name property is listed twice in the property grid.
If you add a control (i.e. a Button), then change the name from the default (Button1) to anything else, then add another button, you get an unhandled exception. This does not occur if all like controls are added first then the names are modified. The cause is when the control is first added to the designer, it is added to the DesignerHost components collection using the default (Button1) control name as a key. When the Name property is updated, the components collection is not. When adding a second like control, the DesignerHost attempts to add it using the default name as well. However, since the first control was renamed, the default name of the second control is the same as it was for the first (Button1). An unhandled exception is thrown when the second control is added because the components collection already contains a control with the same key value.
I corrected this by attaching a handler to the PropertyValueChanged event of the PropertyGrid which removes the original entry for the control and readds it with the new name as the key whenever the Name property value is changed.
how to change Designer for design PocketPC components?
htx
v!tek
Hi Tim, great article. I am currently creating a designer in a similar manner to your article, used to create pdf files. I am using it to add only textboxes and pictures, and can save the data to a database. However I need to bring back the objects and add them to the form programmatically so the user can edit the objects (change the positions etc) Do you know how (or explain how) to add items to the designer surface programmatcally without using the drag and drop from the toolbox
Thanks
John Harry
Tim:
Thanks for your nice article.
How can I get the location of a control in the design surface. I want to show the coordinates when the user moves the control, but I can't figure how!
Did you figure it out how to persist the designer content? I would appreciate any help on this
Thanks
Sgirase
Hi!
That article is really great. It gave me useful hints to start my application in perfectmanner , which looks like an .Net IDE . but can you please tell me how to remove a control from the designer form ....
Hello Tim,
Thank you very much for this excellent article.
We have developed a graphical macro language in C# for our customers and one of the remaining hurdles that we have is the ability to edit the location of controls on a runtime form.
When the customer wants to edit our form, we scan our macro and generate controls on the form based upon the macro content.
We would then like to display that form with the controls where the customer can position and size those controls like you can in this Designer example. We would then iterate through the list of controls and remember their locations and sizes within the macro.
Can you please lead us in the right direction? We have been searching, trying, and reading many examples to no avail. It appears that you possess this knowledge and could help us. We are not inexperienced developers, I personally have been a software developer for 22 years in many languages.
For example, how would you modify this example so that controls can be placed on the form with out the user clicking on the designer surface?
Thank you very much for your reply,
Rick Wirch
Good question ... I am actually tasked with building a Web Forms Designer. I can load ASP.NET controls into my toolbox but of course can't drop those controls onto a Windows forms. Can somebody help me!!
Much appreciated -
Jon
Is it possible to use a treeview for that?
That article is really great.
It gave me the needed hints to step into this subject as deep as I wanted to. As i'm currently trying tom write a lightweight IDE for customumizing my own applications, i need to know, how the content auf the designer could be persisted and reloaded.
Is there any standard-mechanism for that, or will I have to implement my own handlers?
Any help would be appreciated!
Its possible to do something similar to your example using web forms designer?
This article is simply great. I wish to see more like this one.
Arthur
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