The owner window of a modal dialog can get activated when taskbar buttons are created for both windows

Symptoms

Consider the following scenario:

• A .NET desktop application is created by using Windows Forms or Windows Presentation Foundation (WPF).

• The application uses the ShowDialog() method to display a modal dialog that is owned by another window.

• The application creates taskbar buttons for both windows by setting the ShowInTaskbar property value to true.

  Napomena

  The window has a taskbar button if the property value is true. The default value is true.

In this scenario, the owner window can be activated by selecting its associated taskbar button. However, activating the owner window of a modal dialog can cause unexpected behavior or crashes in some applications, as the owner window should remain inactive and disabled until the modal dialog is dismissed.

Resolution

Use the following method corresponding to your situation to create a single taskbar button for windows in a window ownership group, which includes the top-level window and any owned windows:

• If you use a System.Windows.Forms.Form object to display a modal dialog with an owner window, set the Form object's ShowInTaskbar property value to false prior to calling the ShowDialog method.

• If you use a System.Windows.Window object to display a modal dialog with an owner window, set the Window object's ShowInTaskbar property value to false prior to calling the ShowDialog method.

Then, when the taskbar button is selected, the system will activate the correct window in the ownership group.

More information

The following example demonstrates this resolution in a .NET 6 desktop application using Windows Forms:

C#

namespace WinFormsApp1
{
    internal static class Program
    {
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.SetHighDpiMode(HighDpiMode.SystemAware);
            Application.Run(new Form1());
        }
    }

    public class Form1 : Form
    {
        public Form1()
        {
            this.button1 = new System.Windows.Forms.Button();
            this.SuspendLayout();
            this.button1.Location = new System.Drawing.Point(20, 20);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(200, 34);
            this.button1.TabIndex = 0;
            this.button1.Text = "Form2.ShowDialog";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.Button1_Click);
            this.AutoScaleDimensions = new System.Drawing.SizeF(10F, 25F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(800, 450);
            this.Controls.Add(this.button1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);
        }

        private void Button1_Click(object? sender, EventArgs e)
        {
            Form2 form = new Form2();
            form.Owner = this;
            form.ShowInTaskbar = false;
            form.ShowDialog();
        }
        private Button button1;
    }

    public class Form2 : Form
    {
        public Form2()
        {
            this.button1 = new System.Windows.Forms.Button();
            this.SuspendLayout();
            this.button1.Location = new System.Drawing.Point(20, 20);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(200, 34);
            this.button1.TabIndex = 0;
            this.button1.Text = "Form3.ShowDialog";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.Button1_Click);
            this.AutoScaleDimensions = new System.Drawing.SizeF(10F, 25F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(800, 450);
            this.Controls.Add(this.button1);
            this.Name = "Form2";
            this.Text = "Form2";
            this.BackColor = System.Drawing.Color.Aqua;
            this.ResumeLayout(false);
        }

        private void Button1_Click(object? sender, EventArgs e)
        {
            Form3 form = new Form3();
            form.Owner = this;
            form.ShowInTaskbar = false;
            form.ShowDialog();
        }
        private Button button1;
    }

    public class Form3 : Form
    {
        public Form3()
        {
            this.SuspendLayout();
            this.AutoScaleDimensions = new System.Drawing.SizeF(10F, 25F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(800, 450);
            this.Name = "Form3";
            this.Text = "Form3";
            this.BackColor = System.Drawing.Color.Olive;
            this.ResumeLayout(false);
        }
    }
}