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Why does VS2017 keep losing my derived controls?

In my app namespace = DRT, I'm creating control classes (e.g., button, textbox) that derive fron their corresponding Windows control classes, e.g.,
internal abstract class DRT_Button_Abstract : Button
{
....
}
internal class DRT_Button_CancelSearch : DRT_Button_Abstract
{
....
}
internal class DRT_Button_StartSearch : DRT_Button_Abstract
{
....
}
All together I currently have 13 derived classes that derive either from one of my abstracts or from a Windows control class. After a successful build, I see my control classes (e.g., DRT_Button_CancelSearch and DRT_Button_StartSearch) on the Toolbox and I successfully drop them onto my main form. All is fine for a while, but ultimately, I'll go to open the main form.cs [Design] (i.e., the UI designer) and it will show the error The variable '{control property name}' is either undeclared or was never assigned. for some combination of my controls.
When I examine the main form Designer.cs file, the expected code for all the controls is present EXCEPT for the expected new statement. They are not present in the main form Designer.cs file. For example, I expect to see this.drt_Button_CancelSearch = new DRT.DRT_Button_CancelSearch(); but its missing
I've tried ignoring the error, proceeding to the UI designer windows to re-apply the lost controls, but the problem just repeats with the newly applied control
What the heck is going on? Is there a way to recover from this situation?

This is most likely a problem of the Designer not being able to clear/reload its cache. There is not much you can do. In the past I:
closed and reopened all designers that have user controls
put all the controls in a separate project (in the same solution)
put all the controls in a separate solution/Visual Studio instance and set a proper reference to the controls' dll (or even nuget package)
With the first two options I have had varying success. Reopening the designer is not very convenient and doesn't work.
That last option is the best but also the most annoying because every adjustment requires a rebuild of the project and update of the reference/package.
Also make sure that all controls that you create have public default constructors and function well when this constructor is used.

Winforms User Control MissingMethodException

So essentially, I have a custom user control called ExcelDisplay. I try to drag it over in visual studio from the toolbox into my webform in the same project and I get a missing method exception. At one time the constructor was parameterized, but I changed it after deciding it was a bad design idea.
It looks like it is saying the constructor is missing, but its obviously there.
My winform to house the control is empty with the exception of the autogenerated code visual studio puts there.
The code for my ExcelDisplay's constructor looks like this.
namespace STS_Console.UserControls
{
public partial class ExcelDisplay : UserControl
{
public ExcelDisplay()
{
InitializeComponent();
DataDisplay.Columns[0].HeaderText = "Data";
//debug
string x = DataDisplay.Columns[0].GetType().ToString();
x.ToString();
}
The error message is this.
So that error occurs when do I drag and drop in the designer like this
Anyway so that is my problem. I am not sure what is causing it or how to fix it. I would be glad to post additional code upon request.

You should put your user controls in a class library of their own. For the designer to work, it needs a compiled version of your user control. If you cannot compile your user control before you compile your form, you will get into all kinds of trouble.

Rebuild Solution fixed it for me, although if your making regular changes to your user control, you should put them into a separate project.
My particular problem, was a user control, within a user control.

How to put an extended WinForms Control on ToolBox

I plan to add functionalities to TextBox with the following:
public class TextBoxExt : TextBox
{
protected override void OnKeyPress(KeyPressEventArgs e)
{
base.OnKeyPress(e);
}
}
The question is how can we use this TextBoxExt? Is there anyway to get this class onto the ToolBox so that we can just drag and drop it onto the form? If not, what is the best way to use the TextBoxExt?

Build you project with TextBoxExt, make sure it compiles ok.
With the form that you want TextBoxExt on, open the toolbox, right click and select "choose items"
Browse to you .exe or dll that you compiled in 1)
make sure that TextBoxExt has a tick next to it, press ok
TextBoxExt should appear in the toolbox, drag it onto your form
(There is another way of doing this, opening the designer file and renaming the instances of TextBox to TextBoxExt but manual editing of designer files can be considered hazardous by some)

I know this is super old question, but maybe still useful for someone else that has same problem like me - as it's still on the top Google :)
You might interest to use ToolboxItemAttribute (http://msdn.microsoft.com/en-us/library/system.componentmodel.toolboxitemattribute(v=vs.110).aspx).
I did this at my end to resolve the problem.
[ToolboxItem(true)]
public class PanelTitle : LabelControl {
// Whatever code to override LabelControl here...
}
Rebuild the solution and the extended control should be shown in the toolbox.

Any custom control in your project should show up in the Toolbox automatically. I have found that sometimes the controls won't show until you close a re-open Visual Studio. I assume the issue has something to do with caching of the contents of the Toolbox.

You need to add a constructor to your derived class.
public class TextBoxExt : TextBox
{
public TextBoxExt()
{
}
protected override void OnKeyPress(KeyPressEventArgs e)
{
base.OnKeyPress(e);
}
}

Your control should appear in the toolbox for your solution automatically. To have it appear for other projects, you have to do Choose Toolbox items, as others have said.
If you want to provide special design-time functionality, then you will also need to provide some additional designer related attributes and probably your own class derived from ControlDesigner.

I fell into this trap just a couple of hours ago.
I've got a .NET 2.0 Windows Application project with some custom UserControls; it worked fine.
So I decided to order my files in subfolders, to make my project a little bit cleaner.
After that, Visual Studio 2010 designer stopped loading my forms, and ToolBox won't show my controls anymore.
I freaked out, moving back source files in project root, resetting ToolBox, but nothing seemed to work.
After that, I remembered I used ReSharper "Remove Unused References", so I tried to put back unused reference, in particular System.Data: problem solved! :O
I can't say you why, but this worked for me.
Hope my experience can help someone else. :)
Bye,
Nando

I created an empty constructor for my custom implementation of UltraGridBagLayoutPanel. Although david.healed is right it isn't necessary, it is quite useful to put a breakpoint in to check that when the form initialises it is using your class to implement your custom control.
It would have been a lot easier to edit the designer file, but I tried it and changed both the field type for the control and also changed the assignment of the field to a new instance of my custom control.
private Infragistics.Win.Misc.UltraGridBagLayoutPanel ultraGridBagLayoutPanel1;
this.ultraGridBagLayoutPanel1 = new Infragistics.Win.Misc.UltraGridBagLayoutPanel();
to
private Athia.Reports.ultraGridBagLayoutPanel1 ultraGridBagLayoutPanel1;
this.ultraGridBagLayoutPanel1 = new Athia.Reports.ultraGridBagLayoutPanel1();
Doing this destroys Visual Studio every time, and to fix it requires using a text editor to put it back again. Therefore unless anyone can describe what is wrong with my implementation of this approach, perhaps calling the class the same as the control name isn't a great idea, I think the only safe and reliable way to achieve this is as Calanus describes in steps 1 to 5 or as an small deviation from that as Rob Windsor rightly points out restarting VS will bring the control into the Toolbox automatically. Unfortunately for me I then have to change all of the child controls over from the original class to my customised class :-(.

Within the same Solution this should work automatically. However, I have found that if the Target Framework aren't matching the Toolbox does not populate. ( I'm assuming really Reference needs to be of version same or lower than target of Reference. ) ( I did get a warning about non-matching Frameworks )
By making these the same Target Framework, Recompile, Restart VS. the control populated correctly. ( I also added the ToolboxItem(true) Attribute)

How to create a derived ComboBox with pre-bound datasource that is designer friendly?

I'd like to create a derived control from System.Windows.Forms.ComboBox that is bound to a list of objects that I retrieve from the database. Idea is other developers can just drop this control on their form without having to worry about the datasource, binding, unless they want to.
I have tried to extend combobox and then set the DataSource, DisplayMember, and ValueMember in the constructor.
public class CustomComboBox : ComboBox
{
public CustomComboBox()
{
this.DataSource = MyDAL.GetItems(); // Returns List<MyItem>
this.DisplayMember = "Name";
this.ValueMember = "ItemID";
}
}
Works when I run, but throws a lot of errors in Visual Studio's once it's added to any form. The error I get is:
"Code generation for property 'Items' failed. Error was: 'Object reference not set to an instance of an object"
What's the correct way to accomplish this (C#, Winforms, .NET 2.0+)?

The problem is that the designer actually does some compilation and execution in a slightly different context than normally running the program does.
In the constructor, you can wrap your code in:
if (!DesignMode)
{
//Do this stuff
}
That will tell the designer to not run any of your initialization code while it is being designed.

DesignMode property doesn't work in a constructor. From googling for a while, found this LicenseManager thing.
if (LicenseManager.UsageMode != LicenseUsageMode.Designtime)
{
// Do your database/IO/remote call
}
However LicenseManager only works in constructors. For eventhandlers use DesignMode.
Source: http://dotnetfacts.blogspot.com/2009/01/identifying-run-time-and-design-mode.html
Another reference: http://weblogs.asp.net/fmarguerie/archive/2005/03/23/395658.aspx

My usual comment here - DesignMode is not reliable in any situation other than if the control is placed directly on a design surface - i.e. if the control is placed on another control, DesignMode is not true even if you are in design mode. I have found NO reliable way to tell if you are in design mode - especially with inherited controls. Even variants using Site are not reliable if the control is inherited from a non-visual control (e.g. Common Dialog).
See http://keyofdflat.livejournal.com/5407.html (make sure to read the last comment).

.Net C# Design View errors

I have subclassed a Treeview and on instantiation it loads a new ImageList (and the associated Images).
Whenever I switch to the designer view, it's also trying to run this code, however the images aren't in the designer's path, so it crashes. I ended up putting in a hack to see if the current directory is "Visual Studio", then do nothing... but that's so ugly.
I find this happening for other things. If a control is trying to use objects during load/initalization that are only available while the program is running, then the Design View cannot bring up the control.
But is there a way to get around this?
I guess what I'm hoping for is having a try/catch for the Designer (only) with the ability to ignore a few errors I know will be happening (like FileNotFoundException, etc.).
Thanks

Everything that inherits from System.Windows.Forms.Control has a DesignMode property that returns a boolean indicating if you are in design mode or not. You could use this to determine when to/when not to load external resources.

Usually it is better to move the loading of these resources to an override of OnLoad as they are rarely required directly at construction. This fixes the issue you are seeing and means that only trees which get displayed at least once will perform these additional resource loading steps.
Otherwise, you can just exclude these steps during design time by checking the DesignMode property and acting accordingly.

This is a fine pattern to use if you're making a control library with a sample of images when shown in the designer or hook ins to other designer features but as a pattern for development I'm not sure it's very effective.
I would suggest shifting your "business logic" (in this case your loading of certain images into a treeview) outside of the bounds of your treeview control. In your case I would place the logic within the Load event of the form that the control is inside:
public void Load(object sender, EventArgs e)
{
string path = "c:\somePath\toAwesome\Images";
myFunkyTreeView.AddImages(path);
}
For larger apps I personally think you want to shift the logic even out of the forms themselves, but this is debatable measure as it requires additional plumbing as a trade-off for the flexibility this provides.

Thanks for pointing me in the right directioon guys.
I had tried registering to the OnLoad event, but that event is triggered when the Design View comes up, so that didn't quite work for me (am I doing something wrong?).
Anyway, I looked a bit more into the DesignMode property. It can only work for Controls, and sometimes your object may not even be a control.
So here's the answer I prefer:
if (LicenseManager.UsageMode == LicenseUsageMode.Designtime) {
// design-time stuff
} else {
// run-time stuff
}
Found it here.