如果子（图形）控件已经在滚动，则防止父容器通过鼠标滚轮滚动

Question

How to prevent the parent container from scrolling by the mouse wheel if the child (graphic) control is already focused and is scrolling?

I have a GMap.NET WinForms control embedded in a WinForms. Whenever that control is focused and scrolled via the mouse wheel, the parent form will also be scrolled. I just want the parent form to stay put while I'm scrolling the GMap.NET control via the mouse wheel. And when I want to scroll the parent form, I can always make GMap.NET control lose focus. How to do what I want?

Here's my code:

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.gMapControl = new GMap.NET.WindowsForms.GMapControl();
        this.flowLayoutPanel1 = new System.Windows.Forms.FlowLayoutPanel();
        this.SuspendLayout();
        // 
        // gMapControl
        // 
        this.gMapControl.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Right)));
        this.gMapControl.Bearing = 0F;
        this.gMapControl.CanDragMap = true;
        this.gMapControl.EmptyTileColor = System.Drawing.Color.Navy;
        this.gMapControl.GrayScaleMode = false;
        this.gMapControl.HelperLineOption = GMap.NET.WindowsForms.HelperLineOptions.DontShow;
        this.gMapControl.LevelsKeepInMemmory = 5;
        this.gMapControl.Location = new System.Drawing.Point(525, 1);
        this.gMapControl.MarkersEnabled = true;
        this.gMapControl.MaxZoom = 2;
        this.gMapControl.MinZoom = 2;
        this.gMapControl.MouseWheelZoomEnabled = true;
        this.gMapControl.MouseWheelZoomType = GMap.NET.MouseWheelZoomType.MousePositionAndCenter;
        this.gMapControl.Name = "gMapControl";
        this.gMapControl.NegativeMode = false;
        this.gMapControl.PolygonsEnabled = true;
        this.gMapControl.RetryLoadTile = 0;
        this.gMapControl.RoutesEnabled = true;
        this.gMapControl.ScaleMode = GMap.NET.WindowsForms.ScaleModes.Integer;
        this.gMapControl.SelectedAreaFillColor = System.Drawing.Color.FromArgb(((int)(((byte)(33)))), ((int)(((byte)(65)))), ((int)(((byte)(105)))), ((int)(((byte)(225)))));
        this.gMapControl.ShowTileGridLines = false;
        this.gMapControl.Size = new System.Drawing.Size(198, 378);
        this.gMapControl.TabIndex = 0;
        this.gMapControl.Zoom = 0D;
        // 
        // flowLayoutPanel1
        // 
        this.flowLayoutPanel1.BackColor = System.Drawing.Color.Black;
        this.flowLayoutPanel1.Location = new System.Drawing.Point(1, 1);
        this.flowLayoutPanel1.Name = "flowLayoutPanel1";
        this.flowLayoutPanel1.Size = new System.Drawing.Size(489, 885);
        this.flowLayoutPanel1.TabIndex = 6;
        // 
        // Form1
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(8F, 16F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.AutoScroll = true;
        this.ClientSize = new System.Drawing.Size(745, 533);
        this.Controls.Add(this.flowLayoutPanel1);
        this.Controls.Add(this.gMapControl);
        this.Name = "Form1";
        this.Text = "Form1";
        this.Load += new System.EventHandler(this.Form1_Load);
        this.ResumeLayout(false);

    }

    #endregion

    private GMap.NET.WindowsForms.GMapControl gMapControl;
    private System.Windows.Forms.FlowLayoutPanel flowLayoutPanel1;
}

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        gMapControl.MapProvider = GMapProviders.GoogleTerrainMap;
        gMapControl.MinZoom = 5;
        gMapControl.MaxZoom = 12;
        gMapControl.Zoom = 7.5;
        gMapControl.ShowCenter = true;
        gMapControl.DragButton = MouseButtons.Middle;
    }
}

This is not just a problem of the GMap.NET for sure, I've tested with other (proprietary) graphic control and it behaves all the same.

Answer 1

I'm not sure if there's a better way around this but here's a hacky workaround to stop the WM_MOUSEWHEEL message from reaching the control and still execute the zooming logic.

Add the following class to your project:

public class MyGMapControl : GMapControl, IMessageFilter
{
    public MyGMapControl()
    {
        Application.AddMessageFilter(this);
    }
    protected override void Dispose(bool disposing)
    {
        if (disposing) Application.RemoveMessageFilter(this);
        base.Dispose(disposing);
    }
    public bool PreFilterMessage(ref Message m)
    {
        const int WM_MOUSEWHEEL = 0x020A;
        if (m.HWnd == this.Handle && m.Msg == WM_MOUSEWHEEL)
        {
            Point posOnScreen = new Point(m.LParam.ToInt32());
            Point pos = PointToClient(posOnScreen);
            int delta = m.WParam.ToInt32();

            var args = new MouseEventArgs(MouseButtons.None, 0, pos.X, pos.Y, delta);
            this.OnMouseWheel(args);
            return true;
        }
        return false;
    }
}

Then, use MyGMapControl instead of GMapControl .

Here, we're creating a MessageFilter to intercept the WM_MOUSEWHEEL message and return true in PreFilterMessage to stop the message from reaching the control. Now, the scrolling won't occur but neither will the zooming logic because it's implemented inside OnMouseWheel() which is triggered by the WM_MOUSEWHEEL message. So, we manually call the OnMouseWheel() method before returning true to ensure that the zooming occurs.

---

As Jimi suggested in the comments, you could override WndProc() of the control's parent container , check for WM_MOUSEWHEEL , and return if the mouse cursor is over the GMapControl :

protected override void WndProc(ref Message m)
{
    const int WM_MOUSEWHEEL = 0x020A;
    if (m.Msg == WM_MOUSEWHEEL)
    {
        if (gMapControl.Bounds.Contains(PointToClient(MousePosition))) return;
    }
    base.WndProc(ref m);
}