Develop Reference

Keep Control always on top

Is it possible to keep a control (Panel) always over all other controls even if they also use Control.BringToFront()?
I tired to use BringToFront itself, but it seems that this loose its effectiveness if another control under this control also uses this command.

It would help if you try to explain what are you trying to achieve. We might be then able to better convince you, that you are doing something very wrong :)
Anyway, no matter what trick you do, the other control may use the same trick to override you.
You can get step ahead for example by handling parent control's Layout event to force your control back to front. The Layout event is trigerred (among other) when child controls' Z-order is changed.
private void Form1_Layout(object sender, LayoutEventArgs e)
{
panel1.BringToFront();
}

A dirty way of dealing with this is setting a timer and everytime it ticks use the .BringToFront() method on the control, you can also add multiple controls you wish to perform this on and can arrange them however you like.

Drag and drop the user control won't work in .net windows project

I created a user control and it shows up on the tool box as form components. Then when I try to drag and drop the user control on to a form , I get this visual studio error.
" The specified named connection is either not found in the configuration ,not intended to be used with the entity client provider or not valid."
Why am I getting this error?
But some other user controls I can drag and drop which are under the same project. I don't know what I missed in creating this user control.

Beware that code in the UserControl class runs at design time. The constructor, the OnLoad method and Load event. But also methods like OnPaint(). If this code does anything that depends on the environment being setup properly, that code is liable to throw an exception and cause the designer to change its mind about adding the control to the form. That certainly seems to be the case when you get a "not found in the configuration" error, there is no configuration file yet.
Use the DesignMode properly to skip such code. Like this:
protected override void OnLoad(EventArgs e) {
if (!this.DesignMode) {
// Do stuff...
}
base.OnLoad(e);
}

As Hans says, you might need to use the DesignMode property in the Constructor or OnLoad. Also, make sure any public properties that use the connection have this attribute:
[DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
public string Foo
{
get;
set;
}
That way, the designer won't attempt to set them when you add the control to a form. This is always a good habit to get into anyway for properties that you won't be setting at design time.

this error show if you put the code of loading data from database into the constructor of userControl.
"loading data or initialize entity framework"
so the solution is to move the code of loading data from constructor to a method. you can call it "loadData".
and call this method "loadData" in the constructor of the parent form

Form.Load event triggered every time

I was wondering if I am doing correctly.
I instantiate a Form (let's call this Form_B) within my class (also a form) and handle Form_B's Load event. Within this event I do some initialization.
Form_B can be displayed by the user multiple times, and I call ShowDialog on my instance variable.
The problem is that the Load is called each time I show the form. I tried debugging and also tried with Show() instead of ShowDialog(). Show() fails as I closed the window but ShowDialog() does not fail, but calls Load every time it is displayed.
Is it incorrect to continue using the instance once the form is closed?
Thanks,
Stefan

Using the Load event to initialize a form is an anachronism from the VB6 days. It was really important back then, that unfortunately carried over in the design of the Winforms designer. It made Load the default event for a form.
That is however not the .NET way, you initialize a class object with the constructor. The only time you need to override OnLoad() (another .NET way, events are for code in other classes) is when you care about the size and position of the form. It won't be the design Size and Location when the user changed the Windows theme or runs the video adapter at a higher DPI setting. So you might want to use OnLoad to move the window or rearrange the controls. Not actually a very common thing to do.
So, fix your problem first by using the constructor instead. If you still need OnLoad then just use a bool flag that keeps track of whether or not it already ran.
private bool initialized = false;
protected override void OnLoad(EventArgs e) {
if (!initialized) {
initialized = true;
// etc...
}
base.OnLoad(e);
}
And yes, this only works if you use ShowDialog(). A form that's displayed with Show() automatically disposes itself when it is closed. That doesn't happen with ShowDialog() to avoid problems retrieving the dialog results. Re-creating the dialog instance is the better way, unless you really care about keeping the last entered values. That's however a really expensive way to do so, form objects take a lot of .NET and Windows resources.

That is the correct behaviour of the Load event, each time it is loaded it is called. If you want to reuse the form and avoid the the Load event, rather than close the form you should hide it and use the show method to bring it out when needed.

The load event is called once all the components of the form are loaded. If you redisplay the form, its components load again and therefore the Load event is triggered once more.
You could trigger a custom event that would only be triggered in your form's constructor if that's what you're looking for but I think it's bad practice to use a form after it's been closed.

I'm having the same problem. After searching awhile, I think the "ShowDialog" is an exception.
Since it's 2018 right now, MS has opened .Net. I've checked the source and found this.
this.CalledOnLoad = false;
this.CalledMakeVisible = false;
in the ShowDialog() function.
https://referencesource.microsoft.com/#System.Windows.Forms/winforms/Managed/System/WinForms/Form.cs,ab288b84e00f8282

How bad is the following snippet?

My question is simple: how bad is the following snippet of code? How would you do it?
CancelEventHandler _windowClosing;
private CancelEventHandler WindowClosing
{
set
{
clearEventHandlerList();
this.Closing += value;
_windowClosing = value;
/*
* if calling the method with null parameters,
* it will set up itself as the primary control on the Window
*/
_windowClosing(null,null);
}
get
{
return _windowClosing;
}
}
private readonly CancelEventHandler[] CONTROLS = null;
private int current = 0;
public InitializerForm()
{
InitializeComponent();
/*
* these are the handlers for the different controls,
* in the order of appereance to the user
*/
STATES = new CancelEventHandler[] { handler1, handler2, etc. };
WindowClosing = CONTROLS[0];
}
private void clearEventHandlerList()
{
foreach (CancelEventHandler c in CONTROLS)
{
this.Closing -= c;
}
}
private void handler1(object obj, CancelEventArgs e)
{
if (obj == null)
{
//hide every other control, but this one, also set up if necessary
}
else
{
//do something
WindowClosing = CONTROLS[++current]; // set the next control to show
e.Cancel = true;
}
}
The point would be that the code wouldn't close a form, but instead show another component on it, and the set the way to handle that (this is mobile platform, so clicking OK button on the top generates a closing event). This is because showing several forms (4 or 5) one after another to the user makes the app blink, and also very annoying, while replacing just components is much smoother. This model works, but seems very nasty, and I would like a cleaner way to handle this.
Update:
I updated the code sample so that variable names are somewhat speaky. Still, I'm convinced this is awful, (a) but not sure how much, and more importantly, (b) how to do it better.
Update 2:
So, it seems that the code is still a bit mysterious.
Now here's what the problem is:
I show the user a form, which instructs him what to do in several languages. He proceeds by clicking OK on the window. Next, I ask for his language, and then a few questions (where his/her GPS is, etc.) like this. After he could answer the questions (this shouldn't take more than a few seconds each), I show him a splash screen (I load stuff in a separate thread meanwhile), which has a picture. Showing these forms one after another makes the whole application start slow, and filled with UI lags.
Here's what I do to work around the lags: I put the content of the windows into panels, and put those panels one on another, and hide every one of them but the one that should be visible to the user. (current variable) Each of the windows does different things, so I need to change handler of the window closing event in addition. In this code the part which enables the panel is in the same function (handler1, handler2, etc.) with the part which handles the window closing event. If the arguments are null, it does the former, if it isn't (that means it was triggered by the user) it does the latter.
I need an extensible solution to this so that I can insert and remove dialogs anytime I want (the order and the pointers to the functions are stored in the CONTROLS field, and this seems to be very convenient, if you actually understand it. Although it is never easy to change the entire content of a form, there ought to be a simpler way to do this, as well a nicer one, that is what I'm looking for.
I hope this time I could explain how the model works.

I think it might be theoretically possible to make that code more delightfully diverting, perilously puckish, jovially jeopardous, cheerily chancy and unwarily whimsical but it would require some serious thought.

somehow your code makes me want to cry, i´m sorry. i read it twice and all i know about it is that it "doesStuff" with "STATES".
if you really want some help on this one you will have to work on it yourself first...

Use, XML! It's human-readable!
More seriously-
It seems like you're trying to create some sort of configuration wizard, so I'd start by researching that. Regarding your particular solution, I generally advocate very strongly against the "layered panel" approach. I do so because I maintain apps written by people who found this approach, or the related "hidden tabs on a tab control" approach, to be a good idea. It's not, and maintainers will curse your name for years to come.
That being said, what alternatives are there? Well, one alternative is what you've already dismissed because of its "flicker". I'd say that, in general, the flicker isn't that big of a deal for a quick and dirty application. It might be a good idea to make sure that your new window is called up before closing the old one, for example. (I'm assuming this is possible, I haven't developed on a mobile device.)
Another possibility might be a less-evil version of your layered panels. Instead of throwing a half-dozen panels into one form, create a separate user control for each wizard page and then add/remove the user controls to a containing form. This can avoid your flicker and will prove to be much easier to maintain because each page is in a different control. This might also ease any subsequent "Back" button functionality and make your data structures more naturally defined because those user controls will be associated with a specific logical bit of data. It's still not ideal, but it's probably good enough for a one-off solution.
A third technique, if you foresee extensive wizard modification as the product matures, might be to generalize the creation of your user controls by defining them in a more logical/declarative manner (e.g. via XML). If you dynamically generate sensible controls based on XML, then modifying the panels might be as easy as diving into your XML and doing something like:
<Questions>
<Question type="Text"> <!-- generate a textbox for the answer field -->
Favorite Color:
</Question>
<Question type="Number" range="0-255"> <!-- Maybe this is a spinner -->
The answer to life, the universe, and everything:
</Question>
</Questions>
That's just off the top of my head, and completely overkill for any one-off application, but it's a possibility.

Now, let me caveat this by saying this might work, but it may not be the answer to your real problem - that of a slow and unresponsive UI when you have a lot of forms. The real answer may be to just go ahead and do all separate forms, but have each form load its child forms in a background thread while the user is staring at the first form.
But assuming you're still set on this, I'd start off by making a separate class just to handle the Panel stacking/hierarchy. Call it PanelManager. You would instantiate the PanelManager and associate it with the main form, then add Panels to it (perhaps keyed to a String) and set the order. In the main form, have the closing handler call PanelManager.CloseCurrentPanel() and if there are no more Panels to show then it's time to close the main form.
Time for pseudo-code! Here's a quick idea for the class, i'll leave it to you to implement it:
public class PanelManager {
// constructor
public PanelManager (Form ownerForm);
// short-cut properties
public Panel this[int idx]
{ get; set; }
public int Index
{ get; set; }
// main functionality
public int AddPanel (Panel p);
public void SetPanelOrder (Panel p, int idx);
public void RemovePanel (Panel p);
public void RemovePanelAt (int idx);
// shows the first Panel
public void Show ();
// shows Panel[idx]
public void Show (int idx);
// adds the panel to the top of the stack and displays it
// returns the index of the panel
public int AddPanelAndShow (Panel p);
// hides the current panel, displays the one underneath it
// returns false if there are no more panels
public bool HideCurrentPanel ();
}
in the constructor for the main form, instantiate it by new PanelManager (this), then in the closing event handler, call panelManager.HideCurrentPanel () and then figure out whether or not you need to close it after that.

Winform & user control - C#

I have a Form and a UserControl. The UserControl has a menu, and the form has a tabstrip (General, Food, Vitamins etc).
In the UserControl, I have the following code: (Form name is frmForm, the tab names in the form are tabGeneral,tabFood, tabVitamins)
frmForm fm=new frmForm();
fm.tabMain.Selected=tabVitamins;
I call these line from the UserControl to capture the tab to get selected on the form, but it does not select the vitamins tab.
Where am I going wrong? I have access specifier as Protected Internal for tabs in the form.
Please advice.
Thanks,
Karthick

When you write new frmForm(), you're creating a completely new instance of frmForm, which is then discarded.
To get the frmForm instance that holds your control, call the FindForm() method and cast to frmForm.
For example:
frmForm myForm = FindForm() as frmForm;
if(myForm != null)
myForm.tabMain.SelectedTab = myForm.tabVitamins;
If the control is on some other form, this code won't do anything.
By the way, Hungarian notation is frowned upon in .Net.
Your form should probably be named something like MainForm.

SLaks has correctly pointed out your fundamental error, and given you a valid example of a way, via a call to the method 'FindForm, to get the Form the UserControl is sited on.
It may be valuable to you to keep in mind that a UserControl (and all Controls) also has a 'Parent property, but, of course, a UserControl could be placed inside another Control on a Form (like your UserControl could be inside a Panel on the Form) : in that case the UserControl's Parent would be the control it's inside on the Form (like, a Panel), not the Form itself, but 'FindForm will do the right thing to get you the Form it's on.
However you are calling a Method every time you use 'FindForm, and "best practice" suggests that what you want to do is to "inject" a reference to the Form into the UserControl at run-time so that it can always access its Form property easily, without calling a 'Method.
In your example, on a practical level, this (calling the Method) may make almost no difference in performance, but, imho, as you get to a place with WinForms and .NET where you might have a UserControl that will need access to its Parent Form very frequently, this will pay off, and it's a better way to structure your code in the long run, for maintenance.
Wes showed you one way you can "embed" (inject) the UserControl's hosting Form : using an overloaded constructor for the UserControl. But that requires you to modify the Designer.cs file in standard WinForms, and I strongly advise you against that, even though it will work. Particularly if you are just "getting your feet on the ground" in .NET, I strongly advise you against modifying it, or anything having to do with the Form's constructor and its internal call to : InitializeComponent();
Also, as you progress with WinForms you are going to meet many situations where you are going to want instances of "objects" (a Control, a Form, an instance of a Class) to contain references to other instances of "objects.
If you can understand and use one simple use of "injection" here, you are going to make progress to make yourself ready to handle more complex .Net programming in the future.
Another way is to put a Public Property in the UserControl that can be set in code from the MainForm. In the UserControl something like :
private frmForm ParentForm;
public frmForm UCParentForm
{
set { ParentForm = value; }
}
So then in your main form's code, perhaps in the Load event like this :
private void frmForm_Load(object sender, EventArgs e)
{
TheUserControl.UCParentForm = this;
}
or when you need to, you set the UserControl's 'ParentForm property once. So you have eliminated using the method 'FindForm().
In this case, if you only want access to a specific control on the UserControl's Parent Form, like a TabControl, you might consider that you want to make the Property you set of type TabControl, rather than Form : the same coding technique shown above can be used in the UserControl :
private TabControl mainFormTabControl;
public TabControl MainFormTabControl
{
set { mainFormTabControl = value; }
}
imho, it is when you are creating UserControls dynamically at run-time, using an overloaded constructor, as Wes suggests, is the best strategy. And using overloaded constructors has many, many others uses in .NET that you'll get into.
good luck !

You should not be creating a new frmForm() inside the user control. You could pass a reference to the frmForm to the user control.
In your user control constructor try something like this.
private frmForm fm;
public YourUserControl(frmForm fm)
{
this.fm = fm;
}
Then you could use.
fm.tabMain.Selected=tabVitamins;
Does that help?