Flat Button Style - Hide border and Focus Cue when the Button is active

Question

I created a flat Button with a transparent border, also setting FlatAppearance.BorderSize = 0.
The border is hidden on a mouse click and the Button background uses a custom Color when the Mouse button is pressed.

My problem is that cannot remove the border that is drawn when the Button becomes active, for example pressing the Tab key.
I can't use the TabStop property (set it to false) because I want the functionalities I've designed.

I just want to paint the background color and hide the border (the same as mouse click colors).

The Button properties in the Form Designer:

this.importBtn.BackgroundImage = global::CompetitionManager.Properties.Resources.Open;
this.importBtn.BackgroundImageLayout = System.Windows.Forms.ImageLayout.Center;
this.importBtn.Cursor = System.Windows.Forms.Cursors.Hand;
this.importBtn.Delta = 5;
this.importBtn.Dock = System.Windows.Forms.DockStyle.Fill;
this.importBtn.FlatAppearance.BorderSize = 0;
this.importBtn.FlatAppearance.MouseDownBackColor = System.Drawing.Color.SteelBlue;
this.importBtn.FlatAppearance.MouseOverBackColor = System.Drawing.Color.Transparent;
this.importBtn.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
this.importBtn.ForeColor = System.Drawing.Color.Transparent;
this.importBtn.Location = new System.Drawing.Point(3, 50);
this.importBtn.MoveXDirection = false;
this.importBtn.MoveYDirection = true;
this.importBtn.Name = "importBtn";
this.importBtn.Size = new System.Drawing.Size(183, 162);
this.importBtn.TabIndex = 0;
this.ToolTip.SetToolTip(this.importBtn, "Import Competitors (Excel/XML)");
this.importBtn.UseMargin = true;
this.importBtn.UseVisualStyleBackColor = true;
this.importBtn.Click += new System.EventHandler(this.ImportFile_Click);

 

Answer 1

As described in the question, the custom control - a Button, here - is showing its standard Focus Cues when it becomes the ActiveControl. The default rendering doesn't appears to fit in, because the Background color is rendered transparent in a specific context, causing the standard Focus Cue to become obnoxious.

▶ The standard Focus Cue rendering is disabled overriding Control.ShowFocusCues to always return false (except when the handle is not yet created).

▶ The NotifyDefault method is also overridden, to avoid a similar effect when the Button is used to open a Windows that becomes active: in this case, the Button is rendered with a border meant as a visual clue that it's the ActiveControl of that Window.

▶ Some properties that define the Button specialization are removed from the PropertyGrid using a custom ControlDesigner, to avoid unwanted tampering with specific defining properties.

Finally, a custom Focus Cue is drawn at the bottom of the Custom Control's ClientRectangle, to give some feedback, otherwise a User would have no clue what the current Button/Control is.
The custom cue is not shown when the Mouse is hovering or the Button is being clicked.

It's an example of a possible custom rendering. Of course you can now paint whatever you want: a different border, background, translucent overlay etc.

using System;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Drawing.Design;
using System.Windows.Forms;
using System.Windows.Forms.Design;

[ToolboxItem(true)]
[DesignerCategory("code")]
[Designer(typeof(CustomDesigner))]
public class ImportButton : Button
{
    private Color m_FocusColor = Color.LightBlue;
    private bool m_DrawFocusCue = false;

    public ImportButton() {
        Cursor = Cursors.Hand;
        Image = new Bitmap(Properties.Resources.[SomeImage]);
        FlatAppearance.BorderSize = 0;
        FlatAppearance.MouseDownBackColor = Color.SteelBlue;
        FlatAppearance.MouseOverBackColor = Color.Transparent;
        FlatStyle = FlatStyle.Flat;
    }

    protected override bool ShowFocusCues {
        get {
            m_DrawFocusCue = !ClientRectangle.Contains(PointToClient(MousePosition));
            return !IsHandleCreated;
        }
    }

    public override void NotifyDefault(bool value) => base.NotifyDefault(false);

    // Make it public if this value should be customizable
    private int FocusBorderSize { get; set; } = 2;

    protected override void OnPaint(PaintEventArgs e) {
        base.OnPaint(e);
        
        if (Focused && m_DrawFocusCue) {
            var rect = ClientRectangle;
            rect.Inflate(-FocusBorderSize, -FocusBorderSize);
            using (var pen = new Pen(FlatAppearance.MouseDownBackColor, FocusBorderSize)) {
                e.Graphics.DrawLine(pen, 0, rect.Bottom, rect.Right, rect.Bottom);
            }
        }
    }

    protected override void Dispose(bool disposing) {
        if (disposing) {
            Image?.Dispose();
        }
        base.Dispose(disposing);
    }

    public class CustomDesigner : ControlDesigner
    {
        private static string[] RemovedProperties = new[] {
            "AutoEllipsis", "AutoSize", "AutoSizeMode",
            "BackColor", "Cursor", "FlatAppearance", "FlatStyle",
            "ForeColor", "Text", "TextAlign", "TextImageRelation"
        };

        public CustomDesigner() { }

        protected override void PreFilterProperties(IDictionary properties) {
            foreach (string prop in RemovedProperties) {
                properties.Remove(prop);
            }
            base.PreFilterProperties(properties);
        }
    }
}