asked on

How can I detect if a modal dialog is currently open in my application?

A while back I needed to add scroll wheel functionality to a panel. I am using this bit of code to capture and process the wheel messages and it works fine.

		public bool PreFilterMessage(ref Message m)
		{
			if (m.Msg == MSG.WM_MOUSEWHEEL)
			{
				if (recipientControl.Parent.ClientRectangle.Contains(recipientControl.PointToClient(System.Windows.Forms.Control.MousePosition)))
				{
					NativeMethods.SendMessage(recipientControl.Handle, m.Msg, m.WParam, m.LParam);
					return true;
				}
			}
			return false;
		}

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There's just one problem, it processes the message even if another window is open on top of the main window. If I open another window using the ShowDialog() method it should block mousewheel handling for the panel in the underlying form. I just don't know how to detect whether or not a dialog is currently open. Can anyone help with this?

Obadiah Christopher

Window.ShowModalDialog() ?

Russ Suter

ASKER

Was that just a guess? Because that isn't even a method defined in the .NET library. If you mean Window.ShowModal() then that's used to display a form as a modal dialog. That won't tell me if a dialog is currently being displayed at the time of message capture.

it_saige

You could pass an instance of the parent form to your filter and then check for the TopMost or ContainsFocus property, e.g. -

Form1.cs -

using System;
using System.Windows.Forms;

namespace EE_Q29148449
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            Application.AddMessageFilter(new ScrollingFilter(this, richTextBox1));
        }

        private void OnClick(object sender, EventArgs e)
        {
            var frm2 = new Form2();
            frm2.ShowDialog();
        }
    }
}

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Form1.Designer.cs -

namespace EE_Q29148449
{
    partial class Form1
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.richTextBox1 = new System.Windows.Forms.RichTextBox();
            this.splitContainer1 = new System.Windows.Forms.SplitContainer();
            this.button1 = new System.Windows.Forms.Button();
            ((System.ComponentModel.ISupportInitialize)(this.splitContainer1)).BeginInit();
            this.splitContainer1.Panel1.SuspendLayout();
            this.splitContainer1.Panel2.SuspendLayout();
            this.splitContainer1.SuspendLayout();
            this.SuspendLayout();
            // 
            // richTextBox1
            // 
            this.richTextBox1.Dock = System.Windows.Forms.DockStyle.Fill;
            this.richTextBox1.Location = new System.Drawing.Point(0, 0);
            this.richTextBox1.Name = "richTextBox1";
            this.richTextBox1.Size = new System.Drawing.Size(800, 402);
            this.richTextBox1.TabIndex = 0;
            this.richTextBox1.Text = "";
            // 
            // splitContainer1
            // 
            this.splitContainer1.Dock = System.Windows.Forms.DockStyle.Fill;
            this.splitContainer1.Location = new System.Drawing.Point(0, 0);
            this.splitContainer1.Name = "splitContainer1";
            this.splitContainer1.Orientation = System.Windows.Forms.Orientation.Horizontal;
            // 
            // splitContainer1.Panel1
            // 
            this.splitContainer1.Panel1.Controls.Add(this.richTextBox1);
            // 
            // splitContainer1.Panel2
            // 
            this.splitContainer1.Panel2.Controls.Add(this.button1);
            this.splitContainer1.Size = new System.Drawing.Size(800, 450);
            this.splitContainer1.SplitterDistance = 402;
            this.splitContainer1.TabIndex = 1;
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(339, 11);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(122, 23);
            this.button1.TabIndex = 3;
            this.button1.Text = "Open Modal";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.OnClick);
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(8F, 16F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(800, 450);
            this.Controls.Add(this.splitContainer1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.splitContainer1.Panel1.ResumeLayout(false);
            this.splitContainer1.Panel2.ResumeLayout(false);
            ((System.ComponentModel.ISupportInitialize)(this.splitContainer1)).EndInit();
            this.splitContainer1.ResumeLayout(false);
            this.ResumeLayout(false);

        }

        #endregion

        private System.Windows.Forms.RichTextBox richTextBox1;
        private System.Windows.Forms.SplitContainer splitContainer1;
        private System.Windows.Forms.Button button1;
    }
}

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Form2.cs -

using System;
using System.Windows.Forms;

namespace EE_Q29148449
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }

        private void OnClick(object sender, EventArgs e)
        {
            Close();
        }
    }
}

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Form2.Designer.cs -

namespace EE_Q29148449
{
    partial class Form2
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.button1 = new System.Windows.Forms.Button();
            this.SuspendLayout();
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(54, 27);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 23);
            this.button1.TabIndex = 2;
            this.button1.Text = "Close Modal";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.OnClick);
            // 
            // Form2
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(8F, 16F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(182, 77);
            this.Controls.Add(this.button1);
            this.Name = "Form2";
            this.Text = "Form2";
            this.ResumeLayout(false);

        }

        #endregion

        private System.Windows.Forms.Button button1;
    }
}

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ScrollingFilter.cs -

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace EE_Q29148449
{
    class ScrollingFilter : IMessageFilter
    {
        const int WM_MOUSEWHEEL = 0x020A;

        private Form instance;
        private Control control;

        [DllImport("user32.dll")]
        static extern int SendMessage(IntPtr handle, int msg, int wParam, int lParam);

        public ScrollingFilter(Form instance, Control control)
        {
            this.instance = instance;
            this.control = control;
        }

        bool IMessageFilter.PreFilterMessage(ref Message m)
        {
            if (m.Msg == 0x020A && (instance.TopMost || instance.ContainsFocus))
            {
                MessageBox.Show($"{{ Handle: {m.HWnd}, LParam: {m.LParam}, Message: {m.Msg}, WParam: {m.WParam}, Result: {m.Result} }}{Environment.NewLine}");
                return true;
            }
            return false;
        }
    }
}

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Which produces the following results -

With Form1 focused and moving the mouse wheel -

Opening the modal and moving the mouse wheel produces nothing -

Bear in mind that this means your form must be focused and be top most in order to process mouse wheel messages.

-saige-

Russ Suter

ASKER

I've just stumbled upon an answer and it turns out it's ridiculously simple.

I can just use System.Windows.Forms.Application.OpenForms and look for the last one. If the last one in the collection isn't my main window then I know a dialog is showing.

it_saige

Glad you got it sorted...

-saige-

ASKER CERTIFIED SOLUTION

Russ Suter

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it_saige

You could also use LINQ -

!Application.OpenForms.Cast<Form>().Any(f => f is MyForm)

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-saige-