How to set a Winform window to only open one instance.

To ensure only one instance of a Winform window can be opened, you can implement the singleton pattern.

1. Firstly, add a private static member variable in the class of the form to store the unique instance.

private static Form1 instance;

1. Then, set the constructor of the window to private to prevent instances from being created directly using the new keyword.

private Form1()
{
    InitializeComponent();
}

1. Next, create a public static method to obtain the unique instance of the form. Within this method, firstly check if an instance already exists; if it doesn’t, create an instance and store it in a static variable, then return the instance.

public static Form1 GetInstance()
{
    if (instance == null || instance.IsDisposed)
    {
        instance = new Form1();
    }
    return instance;
}

1. Finally, call the GetInstance method to obtain the instance of the form and display it where needed.

Form1 form = Form1.GetInstance();
form.Show();

This way, no matter how many times the GetInstance method is called, it will only return the same window instance, ensuring that only one window can be opened.