Develop Reference

Taskbar Issue for My App

When I click on my Winforms app then its forms are opened in separate section in Taskbar with default C# icon. How can I solve this issue?
Update:
At first I open my login form as bellow:
Application.Run(new frmLogin());
Then I open my main form from the login form as bellow:
this.Hide();
frmMain frmMain = new frmMain();
frmMain.Show();

This sounds like a system problem. Here are 3 solutions:
Restart your computer.
Restart explorer.exe or File Explorer. How to do it.
Unpin then re-pin your program on the taskbar.

first solution: you can set this property of the form
and another solution :
Did you try parent form and child form?
Set Parent of the forms, So they will be open as child of your main form
For Example(In the main form when You want to open another form) :
FrmChild frmChild= new FrmChild ();
frmChild.Parent = this;
FrmChild.Show();

Owner of Form which is not inside Application.Run

I'm trying to show a Form before an application's start and get its DialogResult, so I'm just creating it and using ShowDialog (because Application.Run's return value is void).
What I'm worried about is that it might get 'hijacked' by mistake by some other Form that might be shown at the time. Not by this application, obviously. See What is the meaning of Form.Show(null)? that it's not advisable to use the parameterless overload of ShowDialog.
I have tested and seen that the Form's Owner property was null. But will it always be so? Or should I create a Form and use that as the Owner without showing it? That seems a strange solution but logically it should avoid any problem. Or will that introduce new ones?

Not by this application, obviously
This is already taken care of by Windows, it enforces a strong separation between processes and windows owned by threads. A typical choice for the owner of a dialog for example is the window returned by GetActiveWindow(). The active window is a property of a thread. Which explains for example why a MessageBox.Show() call made from a worker thread is never modal to the rest of the windows.
Making a window modal against the windows of another process is technically possible but requires lots of effort. The app would have to call AttachThreadInput(), a very unsubtle winapi function that nobody ever calls by accident. Also a great source of deadlock.
Unless you are programming in a boat near the Somali coast, there is no good reason to fear your window getting hijacked.

[STAThread]
static void Main()
{
Form1 form1 = new Form1();
//here I suppose the form you want to show
Form1 form2 = new Form2();
form2.ShowDialog(form1);
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(form1);
}

Basically you use ShowDialog() when there are no parents for this window. Usually this happens for the main window. If you are opening one window after another, while closing previous, then there will be multiple ShowDialog()s.
If you are showing dialog (which is also a window), then you can specify it's parent to achieve a certain behavior. To example, when alt-tabbing to that window, it's dialog will be shown in front. Think about this as making child-parent relations.
I don't know about the case, when multiple forms are the claiming same parent. But it sounds like a clear mistake, to example:
public Form1 FormMain = new Form1();
...
// show main form
FormMain.ShowDialog();
...
// somewhere in the main form - show dialog
Form2 form2 = new Form2();
form2.ShowDialog(FormMain);
...
// somewhere in form2 - show dialog
Form3 form3 = new Form3();
form3.ShowDialog(FormMain); // wrong, should be form2!

This is not tested because I couldn't recreate a case where the parent is ever anything but null (i.e. a reference to a third-party un-managed parent), but maybe you could do something like this on your form to set the parent to null if it changes:
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
this.ParentChanged += MyParentChanged;
}
public void MyParentChanged(Object sender, EventArgs e)
{
this.Parent = null;
}
}

Form losing focus in c#

I have a main form, which opens form A, where from form A I can open form B, where from form B I can open form C. The problem is that if I open till form B, everything works fine, but if I open form C as well, and then close Form C and B, form A goes behind the main form. For the forms I m just creating an instance of the form and then use .Show()
cNewForm form = new cNewForm();
form.Show();
I m doing this for every form

You have not set the window ownership properly because you are using the no parameter version of Show(). You need to set the owner by calling the Show() overload that receives an owner parameter. Alternatively you can set the Owner property directly, but it's much better to do so when you call Show().
The window owner is an important Win32 concept. I recommend reading the MSDN documentation on the subject.
An owned window is always above its owner in the z-order.
The system automatically destroys an owned window when its owner is destroyed.
An owned window is hidden when its owner is minimized.
In your case I think you want form A to be owned by your main form, and form B to be owned by form A, and form C to be owned by form B.

I have often found that these kinds of issues are resolved by assigning owners to windows. When you show the window:
FormA formA = new FormA();
formA.Show(this); // assuming this code is in the main form

try to use the ShowDialog(); methode instead of show() in order to show it as a modal form. see the documentation

Saving Data on Parent Window from a Child Window?

I have a Windows application.
The windows application has our XML Library on it.
public NetspotXMLLibV1 XMLLib;
public Form1()
{
InitializeComponent();
XMLLib = new XmlLibrary.NetspotXMLLibV1();
}
It also has a custom control.
That custom control has a button on it that has
SelectWidgitWindow widgit = new SelectWidgitWindow();
widgit.ShowDialog();
when clicking a button, it opens up the new window. I do some stuff on this new window. When I click a button on the new window I want to save stuff on the Form1 Window
How do I access this on my new Window (SelectWidgitWindow ) ?
Ie
form1.XMLLib.Add(ItemForProcessing);
or
Windows(1).XMLLib.Add(ItemForProcessing);
Please help

Use the ShowDialog overload to which you can pass an owner for the new form:
Form2 f = new Form2();
f.ShowDialog(this.Parent);
and in Form2:
((Form1)Owner).MyProperty = 11;

Couple of ways:
1) Expose the items you want the parent form to extract as properties of the child form. In the parent form's code, when ShowDialog returns you can get the values you want to save from the properties.
2) Pass a reference to the parent form to the form (perhaps when it's constructed). Then the child form can call some method or set some properties on the parent form. Note that this is not preferred as it couples the child for to the parent form, meaning it couldn't be called from any other form.

How to know if the Form App open or not c#

Does anyone know how can I know if the Windows Form Application (C#) is open or that the client closed it?
(In my App I have a Windows Form Application (Form1) that allow the user to open another Forms (Form2). I want to know if the Form2 is open or close.)
I need to know that because I run the Form2 from a thread, and I want to make the thread runnig until the user close Form2.
Many thanks!

You can check if a form of a given type is open in your application like this (using LINQ):
if (Application.OpenForms.OfType<Form2>().Count() > 0)
{
// there is an instance of Form2 loaded
}

You need to elaborate on your question a bit more. Are you talking about monitoring the application from another application? Or that one form needs to know if another one is open? Or a form needs to know when another form closes?
There are a couple of ways to monitor forms closing within the same application.
Calling ShowDialog() on your form instead of Show() will ensure that code following the ShowDialog() call doesn't get executed until the user closes the form.
The Form class has a Visible property, which returns true/false depending on whether the form is visible or not.
As for the application itself, there is an ApplicationExit event on the static Application class which gets called just before the application closes so you could listen to that event if, for example, you need to perform some clean-up on exit.

If you want to run only single instance of application, check this link.
There you will also see how to check whether a process is still active.

If you mean MDI application with its child forms:
private Dictionary<Type, Form> SingleInstanceForms = new Dictionary<Type, Form>();
public Form ActivateForm<T>() where T : Form, new()
{
Cursor.Current = Cursors.WaitCursor;
if (!this.SingleInstanceForms.ContainsKey(typeof(T)))
{
T newForm = new T();
//setup child
newForm.MdiParent = this;
newForm.WindowState = FormWindowState.Maximized;
//newForm.Icon = Icon;
newForm.FormClosed += new FormClosedEventHandler(delegate(object sender, FormClosedEventArgs e)
{
this.SingleInstanceForms.Remove(sender.GetType());
});
this.SingleInstanceForms.Add(typeof(T), newForm);
newForm.Show();
this.Refresh();
}
Form formToActivate = this.SingleInstanceForms[typeof(T)];
formToActivate.Activate();
Cursor.Current = Cursors.Default;
return formToActivate;
}
this will create the form child if hasn't been created yet and activate it if it has been created.
sample: ActivateForm<dlgChildOne>();