In our app we use WPF and Caliburn Micro. We use a custom WindowManager:
public class OurWindowManager : Caliburn.Micro.WindowManager
{
protected override Window EnsureWindow(object model, object view, bool isDialog)
{
var window = base.EnsureWindow(model, view, isDialog);
if (isDialog) window.ResizeMode = ResizeMode.NoResize;
window.Icon = new BitmapImage(new Uri("pack://application:,,,/NWB.ico"));
// TODO: Change to dynamic minWidth/minHeight based on window
window.MinWidth = 600;
new WindowSettingsBehavior().Attach(window);
return window;
}
}
In our code we mostly use this WindowManager like so:
public void SomeMethod()
{
var result = _windowManager.ShowDialog(new ConfirmDialogViewModel("some title",
"some text"));
if(result == true){ // if OK is pressed
// do something on OK
}
// do nothing
}
In one of my recent methods I want to do the following (in semi pseudo-code):
public void SomeOtherMethod()
{
_windowManager.ShowDialog(new ConfirmDialogViewModel("some title", "some text"));
//if window is closed without pressing any of the buttons
return; // do nothing
//if OK is pressed {
// do something on OK
}
// if Cancel is pressed: do something else
}
Unfortunately, ShowDialog also returns false if the Window is closed (even though the ShowDialog returns a Nullable bool (bool?)).
So, what I did so far is just completely remove the Close Button by making a new Window-Behavior, and I've added it to the OurWindowManager class inside the if(isDialog):
if (isDialog)
{
window.ResizeMode = ResizeMode.NoResize;
new WindowHideBarBehavior().Attach(window);
}
This works, and I now got a Window with just a title, and without a Close (X) button. Unfortunately, the window can still be closed with Alt+F4 and such. I thought about catching Alt+F4 and cancel the closing, but since Alt+F4 is standard Window behavior, I don't think users will appreciate it a lot and I find it a bit unintuitive for the users to disable it..
So, my question: How can I accomplish the pseudo-code in SomeOtherMethod mentioned above. Is there a way to get the difference between closing a Dialog or canceling a Dialog. (NOTE: As mentioned above, keep in mind we use Caliburn.Micro.WindowManager, not the default C# WPF one. Don't know if there are a lot of differences, but I guess there are at least some.)
EDIT:
I also know I can catch the closing event and cancel the closing:
window.Closing -= DisableDialogClosing;
if (isDialog)
{
window.ResizeMode = ResizeMode.NoResize;
new WindowHideBarBehavior().Attach(window);
window.Closing += DisableDialogClosing;
}
...
private static void DisableDialogClosing(object sender, CancelEventArgs e)
{
e.Cancel = true;
}
But then it also cancels the closing when I want it to close (for example when the Cancel/OK button is pressed). Maybe I can add some kind of Property-flag to this overridden Closing-EventHandler, but perhaps you guys/girls have other suggestions to accomplish the same results.
You can fulfil your requirements if you just implement your own dialog Window by extending the Window class. From inside your custom Window, you can handle the Closed event and set the Window.DialogResult property to null in that case. For the normal Ok and Cancel states, you can simply attach Click handlers to those Buttons and set the Window.DialogResult property to true and false accordingly.
private void CustomDialogWindow_Close(object sender, RoutedEventArgs e)
{
DialogResult = null;
}
private void OkButton_Click(object sender, RoutedEventArgs e)
{
DialogResult = true;
}
private void CancelButton_Click(object sender, RoutedEventArgs e)
{
DialogResult = false;
}
You could then check for the Window closed state like this:
if (CustomDialogWindow.DialogResult == null) DoSomethingUponDialogWindowClose();
You can find further helpful information in the following pages on MSDN:
Dialog Boxes Overview
Window.DialogResult Property
After #Sinatr's suggestion I've added a ClosedBy property to my ConfirmDialogViewModel:
(before):
public sealed class ConfirmDialogViewModel : Screen
{
public ConfirmDialogViewModel(string title, string message)
{
DisplayName = title;
Message = message;
}
public string Message { get; set; }
public void Ok()
{
TryClose(true);
}
public void Cancel()
{
TryClose(false);
}
}
(after):
public sealed class ConfirmDialogViewModel : Screen
{
public ClosedBy CloseReason { get; private set; }
public ConfirmDialogViewModel(string title, string message)
{
DisplayName = title;
Message = message;
CloseReason = ClosedBy.Other;
}
public string Message { get; set; }
public void Ok()
{
CloseReason = ClosedBy.Ok;
TryClose(true);
}
public void Cancel()
{
CloseReason = ClosedBy.Cancel;
TryClose(false);
}
}
public enum ClosedBy
{
Other,
Ok,
Cancel
}
And I now use it like so:
public void SomeOtherMethod()
{
var confirmDialog = new ConfirmDialogViewModel("some title", "some text");
var result = _windowManager.ShowDialog(confirmDialog);
if(result == null || confirmDialog.CloseReason == ClosedBy.Other) return;
if(result == true && confirmDialog.CloseReason == ClosedBy.Ok){
// Do something on OK
}
// Do something on cancel
}
I still kept the behavior to remove the close button, and also added window.ShowInTaskbar = false; to the OurWindowManager inside the if(isDialog).
Related
I am building a simple text editor program. When the text has been edited a window shows up and asking if you want to save the file. This has been implemented using forms and booleans stored in the popup window.
If i press yes, no or cancel the first time the setters doesn't work. But if i press the second the setters work perfectly. Why doesn't it work the first time?
Code for the popup window.
public bool Exit { set; get; }
public bool Save { set; get; }
public bool _Open { set; get; }
case ("Yes"):
{
if (form1.Operation() == "Exit")
{
Exit = true; //Bool that tells the program to exit.
MessageBox.Show(Exit.ToString()); //This prints the correct value
}
Save = true; //Bool that states if file should be saved.
return;
}
Code for main textedit window. Example with a user pressed the exit button.
public partial class Form1 : Form
{
Form3 form3 = new Form3(); //the popup class.
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
if (e.CloseReason == CloseReason.UserClosing)
{
if (_edited)
{
_operation = "Exit";
form3.ShowDialog();
MessageBox.Show(form3.Exit.ToString()); //Always false on first entry?
if (form3.Exit)
{
if (form3.Save)
{
Save();
}
}
else
{
e.Cancel = true;
}
}
}
}
}
In your question you say "yes, no or cancel" but in the second block of code it seems to only set Exit = true for the "Yes" case. Could this be the issue?
You could try setting breakpoints and debugging the code to be able to figure what is going on. If you remove auto properties and add backing field manually, you could also set breakpoints to see when the setters are called. You could write your Exit like this:
private bool _exit;
public bool Exit
{
get => _exit;
set
{
_exit = value;
}
}
This would allow you to set a breakpoint and see exactly when the setter is called.
If you need help with debugging, please provide some information about which code editor you are using.
I needed functionality that doesn't exist in the standard ComboBox, so I wrote my own from a TextBox and a form. When the user types in the TextBox, it shows a dropdown as a separate form.
Here's some of the relevant code:
internal class FilteredDropDown : Form
{
public Control OwnerControl { get; set; }
public bool CloseOnLostFocus { get; set; }
protected override OnLostFocus(EventArgs e)
{
if (CloseOnLostFocus && !OwnerControl.IsFocused)
this.Close();
}
protected override OnMouseMove(MouseEventArgs e)
{
base.OnMouseMove(e)
// highlight the moused over item in the list
}
...
}
public class FilteredCombo : TextBox
{
private FilteredDropDown dropDown;
public FilteredCombo()
{
dropDown = new FilteredDropDown();
dropDown.OwnerControl = this;
}
public void ShowDropDown()
{
if (dropDown.Visible)
return;
dropDown.RefreshFilter();
var loc = PointToScreen(new Point(0, this.Height));
dropDown.Location = loc;
dropDown.CloseOnLostFocus = false;
int selectionStart = this.SelectionStart;
int selectionLength = this.SelectionLength;
dropDown.Show(this);
this.Focus();
this.SelectionStart = selectionStart;
this.SelectionLength = selectionLength;
dropDown.CloseOnLostFocus = false;
}
protected override OnLostFocus(EventArgs e)
{
if (dropDown.Visible && !dropDown.ContainsFocus())
dropDown.Close();
}
protected override OnTextChanged(EventArgs e)
{
base.OnTextChanged(e);
ShowDropDown();
}
...
}
There's obviously a whole lot more code than that to deal with all kinds of stuff irrelevent to my question.
The problem is when I put the FilteredCombo on a modal dialog. Somehow the FilteredDropDown form doesn't receive mouse events at all when it is parented by a modal dialog.
I've read something about WinForms filtering out events on all except the current modal dialog, I suspect that is what's going on, but I have no ideas of how to fix it. Is there some way to get the mouse up/down/move/click/etc. events to work when parented by a model dialog?
I had to go digging through the ShowDialog source code, and I found that it calls user32.dll EnableWindow(Handle, false) on all the windows except the shown one. The problem was that the FilteredDropDown already existed by the time the ShowDialog() method got called. I discovered two different ways to fix this:
Don't allow the DropDown to be shown until the parent form is shown. This is a bit trickier to guarantee, so I also implemented the second way.
Re-enable the DropDown window when it is made visible:
[DllImport("user32.dll")]
private static extern bool EnableWindow(IntPtr hWnd, bool enable);
protected override void OnVisibleChanged(EventArg e)
{
base.OnVisibleChanged(e);
if (this.Visible)
{
EnableWindow(this.Handle, true);
}
}
I'm writing a simple input form using Model-View-Presenter, and I've encountered difficulty with handling the FormClosing event.
When dealing with a normal Form, it has an event that fires on closing called FormClosing that I can use to cancel the close if I deem it necessary. In this case, I'd like to cancel the form close if the input is bad. For instance:
public interface IView
{
event EventHandler<CancelEventArgs> Closing;
string Input { get; set; }
string ErrorMessage { set; }
}
public class Presenter
{
private IView view;
public Presenter(IView view)
{
this.view = view;
// bind to events
view.Closing += view_Closing;
}
private void view_Closing(object sender, CancelEventArgs e)
{
e.Cancel = !ValidateInput();
}
private bool ValidateInput()
{
bool validationSuccessful = true;
// perform validation on input, set false if validation fails
return validationSuccessful;
}
}
I created my own event handler (Closing) because my understanding of MVP states that utilizing anything in System.Windows.Forms is not a good idea (e.g. if someday I update my view to WPF). Thus, in the WinForms implementation, I pass the event forward, as such:
public partial class View : IView
{
public event EventHandler<CancelEventArgs> Closing;
public string Input { get { return textBoxInput.Text; } set { textBoxInput.Text = value; } }
public string ErrorMessage { set { errorProvider.SetError(textBoxInput, value) ; } }
public View()
{
InitializeComponent();
}
private void View_FormClosing(object sender, FormClosingEventArgs e)
{
if (Closing != null)
Closing(this, new CancelEventArgs(e.Cancel));
}
}
I've found that even though in my Presenter I tell e.Cancel to set to true when validation fails, it does not cause the form to cancel the close. I'm clearly doing something wrong here, but I'm not sure what the proper solution is.
I figured it out after experimenting with the solution in another StackOverflow question. I needed to create a new CancelEventArgs in the View as follows:
private void View_FormClosing(object sender, FormClosingEventArgs e)
{
CancelEventArgs args = new CancelEventArgs();
if (Closing != null)
Closing(this, args);
e.Cancel = args.Cancel;
}
args.Cancel properly updated after the Closing event was called, and successfully mapped the resultant boolean to e.Cancel.
I'd like to know what's the best way (read most elegant) to have a single instance of a given Window per application in WPF.
I'm a newcomer to .NET and WPF and what I came up with looks pretty lame.
private static readonly Object MUTEX = new Object();
private static AboutWindow INSTANCE;
public static AboutWindow GetOrCreate() {
lock (MUTEX) {
if (INSTANCE == null) {
INSTANCE = new AboutWindow();
}
INSTANCE.Show();
return INSTANCE;
}
}
private AboutWindow() {
InitializeComponent();
}
private void AboutWindow_Closed(object sender, EventArgs e) {
// the Closed events are handy for me to update values across
// different windows.
lock (MUTEX) {
INSTANCE = null;
}
}
Thing is... this looks like utter crap. There must be some way to achieve the same goal in a much more elegant way, right?
PS: I'm often using the Closed event to change values in other open windows. For instance I have the SettingsWindow with the "Account" button. When I push that button, the AccountWindow pops up. When I close AcountWindow, I want something in the SettingsWindow to change (a label). Hence the constant creation of windows.
Besides, Close is something you always have to deal with because of the X button on the window frame...
there are probably better ways to do this, but here is a relatively simple way....
put a static bool on your window class to flag if its open or not. then, in the load() event set it to true, and on the close event set it to false. Then, in the code that opens the window, check the flag.
here is some pseudo-code to give you an idea...
public class AboutWindow
{
public static bool IsOpen {get;private set;}
onLoadEvent(....)
{
IsOpen = true;
}
onUnloadEvent(...)
{
IsOpen = false;
}
}
public void OpenAbout()
{
if ( AboutWindow.IsOpen ) return;
AboutWindow win = new AboutWindow();
win.Show();
}
If you truly need to enforce a single instance of a window, then a static instance (some flavor of what you have) with a factory creation method is certainly a viable option, much like a single DataContext instance when working with a database.
You could also write your own WindowManager class, although that seems like overkill, and will essentially be the same thing (except the Factory methods would be in a single class).
However, re-reading your post, I wonder if this is a case of missing the forest for the trees. Your mentioning of your SettingsWindow, which in turn calls AccountWindow, makes me think that you should simply be using ShowDialog(). This opens a window modally, meaning that there can be no interaction with the calling window (or any other window in your application). You simply set a property in that dialog, set the DialogResult to true when the OK button is pressed, and read that property in the parent window.
Basically, you just use the ShowDialog like this. I am leaving out a lot of the implementation details, as far as binding vs. hard-coding to controls. Those details aren't as important as just seeing how ShowDialog works.
For simplicity, assume that you have a class called MyAppOptions that, well, reflect the options of your application. I will leave off most of the implementation details of this for simplicity, but it would likely implement INotifyPropertyChanged, have methods and fields and properties, etc.
public class MyAppOptions
{
public MyAppOptions()
{
}
public Boolean MyBooleanOption
{
get;
set;
}
public String MyStringOption
{
get;
set;
}
}
Then, let's make this simple, and assume that you want to show an Options dialog when you press a button on some window. Furthermore, I will assume that there are variables that have been set with your options, which were loaded at startup.
void btnOptions_Click(object sender, RoutedEventArgs e)
{
MyAppOptions options = new MyAppOptions();
options.MyBooleanOption = mSomeBoolean;
options.MyStringOption = mSomeString;
OptionsDialog optionsDialog = new optionsDialog(options);
if (optionsDialog.ShowDialog() == true)
{
// Assume this function saves the options to storage
// and updates the application (binding) appropriately
SetAndSaveOptions(optionsDialog.AppOptions);
}
}
Now assume that the OptionsDialog is a window you've created in your project, and it has a CheckBox on it related to MyBooleanOption and a TextBox for MyStringOption. It also has an Ok button and a Cancel button. The code-behind will likely use Binding, but for now we'll hard code the values.
public class OptionsDialog : Window
{
public OptionsDialog(MyAppOptions options)
{
chkBooleanOption.IsChecked = options.SomeBooleanOption;
txtStringOption.Text = options.SomeStringOption;
btnOK.Click += new RoutedEventHandler(btnOK_Click);
btnCancel.Click += new RoutedEventHandler(btnCancel_Click);
}
public MyAppOptions AppOptions
{
get;
set;
}
void btnOK_Click(object sender, RoutedEventArgs e)
{
this.AppOptions.SomeBooleanOption = (Boolean) chkBooleanOption.IsChecked;
this.AppOptions.SomeStringOption = txtStringOption.Text;
// this is the key step - it will close the dialog and return
// true to ShowDialog
this.DialogResult = true;
}
void btnClose_Click(object sender, RoutedEventArgs e)
{
// this will close the dialog and return false to ShowDialog
// Note that pressing the X button will also return false to ShowDialog
this.DialogResult = false;
}
}
This is a pretty basic example as far as implementation details. Search online for ShowDialog for more details. The important keys to remember are:
ShowDialog opens a window modally,
meaning it is the only window in your
application that can be interacted
with.
Setting DialogResult to true
will close the dialog, which can be
checked for from the calling parent.
Setting DialogResult to false will
also close the dialog, in which case
you skip updating the values in the
calling window.
Pressing the X button
on the window automatically sets the
DialogResult to false
You can have public properties in the dialog window that can be set before doing the ShowDialog, and can get values from after the dialog disappears. It will be available while the dialog is still in scope.
The following extends on the above solution to reshow the window if it is already open. In this case it is a help window.
///<summary>
/// Show help from the resources for a particular control by contextGUID
///</summary>
///<param name="contextGUID"></param>
private void ShowApplicationHelp(string contextGUID = "1")
{
if (HelpWin != null)
{
if (HelpWin.IsOpen)
{
HelpWin.BringToFront();
return;
}
}
HelpWin = new MigratorHelpWindow();
HelpWin.Owner = Application.Current.MainWindow;
HelpWin.ResizeMode = ResizeMode.CanResizeWithGrip;
HelpWin.Icon = new Image()
{
Source =
new BitmapImage(
new Uri(
"pack://application:,,,/ResourceLibrary;component/Resources/Images/Menu/Help.png",
UriKind.RelativeOrAbsolute))
};
HelpWin.Show();
HelpWin.BringToFront();
}
This code is all in a viewmodel (MVVM) associated with the window. It is called by an ICommand hooked to a button on the window (naturally, it shows a question mark!!)
The following property is involved (in this case it is a Telerik RadWindow but it can be any window object, and you can probably also just store the window handle but using this property permits manipulation of the object more smoothly e.g. HelpWin.BringToFront() as in the above example...
...
...
private Telerik.Windows.Controls.RadWindow **HelpWin**
{
get;
set;
}
...
...
In the window itself (WPF window)
///<summary>
/// Flag to indicate the window is open - use to prevent opening this particular help window multiple times...
///</summary>
public static bool IsOpen { get; private set; }
...
...
...
private void HelpWindowLoaded(object sender, RoutedEventArgs e)
{
IsOpen = true;
}
private void HelpWindowUnloaded(object sender, RoutedEventArgs e)
{
IsOpen = false;
}
and in the view Xaml
...
...
DataContext="{Binding Path=OnlineHelpViewModelStatic,Source={StaticResource Locator}}"
RestoreMinimizedLocation="True"
**Loaded="HelpWindowLoaded" Unloaded="HelpWindowUnloaded"** >
Here's an alternative approach that doesn't require a static property to set and update in each of your window:
public static bool IsWindowInstantiated<T>() where T : Window
{
var windows = Application.Current.Windows.Cast<Window>();
var any = windows.Any(s => s is T);
return any;
}
Usage:
private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
if (IsWindowInstantiated<SettingsWindow>())
return;
var window = new SettingsWindow();
window.Show();
}
How about using a Singleton?
public class MyWindow : Window {
private static MyWindow instance;
public static MyWindow Instance
{
get
{
if (instance == null)
{
instance = new MyWindow();
}
return instance;
}
}
}
Then just use
MyWindow.Instance.Show() and MyWindow.Instance.Hide()
I found this because I am trying to ensure my users do not open multiple instances of an rtsp stream window. I like Aybe's answer, it works well and is easy to understand.
I have built on it a bit as I wanted to bring the window into focus if it is open.
Here is my code:
public static void OpenWindow<T>() where T: Window
{
var windows = System.Windows.Application.Current.Windows.Cast<Window>();
var any = windows.Any(s => s is T);
if (any)
{
var win = windows.Where(s => s is T).ToList()[0];
if (win.WindowState == WindowState.Minimized)
win.WindowState = WindowState.Normal;
win.Focus();
}
else
{
var win = (Window)Activator.CreateInstance(typeof(T));
win.Show();
}
}
I am also quite new to C# and WPF so I am sure this can be improved even more.
Call it using
OpenWindow<SettingsWindow>();
public static void ShowWindow<T>() where T : Window, new()
{
var existingWindow = Application.Current.Windows.OfType<T>()
.SingleOrDefault();
if (existingWindow == null)
{
new T().Show();
return;
}
existingWindow.WindowState = WindowState.Normal;
existingWindow.Activate();
}
Usage:
ShowWindow<AboutWindow>();
When windows is created then Window.IsLoaded == true. My implementation of singleton windows is:
public partial class MySingletonWindow : Window
{
private static MySingletonWindow _instance = null;
private MySingletonWindow()
{
InitializeComponent();
}
public static MySingletonWindow Show(System.Windows.Window owner = null)
{
// On First call _instance will be null, on subsequent calls _instance will not be null but IsLoaded is false if windows was closed.
if (_instance == null || !_instance.IsLoaded)
_instance = new MySingletonWindow();
_instance.Owner = owner; // Optional owner
_instance.Show(); // Display the window
_instance.Focus(); // Bring it to front
return _instance; // Return instance if user needs it
}
}
Simply show windows using this call:
MySingletonWindow.Show(ParentWindow);
OR
MySingletonWindow.Show();
In my C# application I have an option dialog that can be opened from a menu command.
I want to ensure that the option dialog have only one instance (user cannot open more than one option window at a given time) without making it modal.
Also if the user already have this window opened, and he clicks in the menu item to open it again, the app just makes the already visible form became the top most window.
Can anyone point me directions on how accomplish these tasks?
Thank you very much.
Well, the simplest way is to have a static field which stores a reference to the single instance or null, and then a method to retrieve it or create a new one.
Note that this isn't the same as making it a singleton - because I assume if the form is closed, you'd want to create a new instance next time. (The alternative - hiding it and reusing it - is shown in STO's answer.) You may want something like this:
public class OptionsDialog : Form
{
private static OptionsDialog openForm = null;
// No need for locking - you'll be doing all this on the UI thread...
public static OptionsDialog GetInstance()
{
if (openForm == null)
{
openForm = new OptionsDialog();
openForm.FormClosed += delegate { openForm = null; };
}
return openForm;
}
}
You may want to make the method perform the "bring it to the front" steps as well, of course.
You need to prevent the form from closing. If you don't, the form will be disposed and becomes unusable. You can do this by implementing the FormClosing event:
protected override void OnFormClosing(FormClosingEventArgs e) {
if (e.CloseReason == CloseReason.UserClosing) {
this.Hide();
e.Cancel = true;
}
}
To make it a singleton, just keep track of the life time of the form in your main form class:
frmOptions options;
private void btnShowOptions_Click(object sender, EventArgs e) {
if (options == null) {
options = new frmOptions();
// To make absolutely sure:
options.FormClosed += (o, ea) => options = null;
}
else {
options.WindowState = FormWindowState.Normal;
}
options.Show();
}
You will need this form as property
Form1 myForm = null;
private void Form1_FormClosed(object sender, FormClosedEventArgs e)
{
myForm = null;
}
private void ShowForm()
{
if (myForm != null)
{
myForm.BringToFront();
}
else
{
myForm = new Form1;
myForm.Show();
}
}
you may use code like this:
private MyDialogForm _FormInstance;
public void ShowOptions()
{
if (_FormInstance == null)
{
_FormInstance = new MyDialogForm();
_FormInstance.FormClosing += (s,e) =>
{
e.Cancel = true;
_FormInstance.Hide();
}
}
_FormInstance.Show();
}
I assume you have at least two forms. One form, call it frmMain, allows you to open frmOptions. In frmMain, add a variable of type frmOptions like this:
public partial class frmMain : Form
{
private frmOptions optionsInstance = null;
...
In the routine that opens the Options dialog, add this:
if (optionsInstance == null || !optionsInstance.Visible)
{
optionsInstance = new frmOptions();
optionsInstance.Show();
}
When frmOptions closes, optionsInstance will not be null, so that's why you check if it's visible before instantiating a frmOptions instance.
If this doesn't work for you, you could try a mutex, but that's probably overkill.
Based on Jon Skeet's answer, I'm using the following code for showing a form as a modal dialog box.
if (this.aboutForm == null)
{
this.aboutForm = new AboutForm();
this.aboutForm.FormClosed += (sender2, e2) => { this.aboutForm = null; };
this.aboutForm.ShowDialog(this);
}
else
{
this.aboutForm.Focus();
}
I have to do this because I have a menu item to display the About form in the menu of the main form, and in the context menu of the notify icon. If I open the About form using the menu of the main form, I still can open another instance by using the context menu item of the notify icon.
Main_Frm _main_Frm = null;
private void Show_bt_Click(object sender, EventArgs e)
{
if (_main_Frm != null)
{
_main_Frm .BringToFront();
}
else
{
_main_Frm = new Comission_Frm();
_main_Frm .Show();
}
//This condition used when you closed the form the form will disposed and when you reopen.
if (_main_Frm .IsDisposed)
{
_main_Frm = new _Main_Frm ();
_main_Frm .Show();
}
}
This May Help!
Note: The following code was taken from the article Below:
https://www.dotnetcurry.com/ShowArticle.aspx?ID=150
static class Program
{
///<summary>
/// The main entry point for the application.
///</summary>
[STAThread]
static void Main()
{
bool instanceCountOne = false;
using (Mutex mtex = new Mutex(true, "MyRunningApp", out instanceCountOne))
{
if (instanceCountOne)
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
mtex.ReleaseMutex();
}
else
{
MessageBox.Show("An application instance is already running");
}
}
}
}