Custom Resize Handle in Border-less Form C#

Custom Resize Handle in Border-less Form C#

In C#, you can create a custom resize handle for a border-less form by handling the mouse events for the handle and changing the size of the form accordingly. Here's an example:

using System;
using System.Drawing;
using System.Windows.Forms;

public class CustomResizeHandleForm : Form
{
    private const int HTBOTTOMRIGHT = 17; // Resize handle hit-test value

    private Point resizeHandleLocation;
    private bool resizing;

    public CustomResizeHandleForm()
    {
        this.FormBorderStyle = FormBorderStyle.None;
        this.BackColor = Color.White;
        this.ClientSize = new Size(400, 300);

        // Create the custom resize handle as a label
        Label resizeHandle = new Label();
        resizeHandle.BackColor = Color.Gray;
        resizeHandle.Cursor = Cursors.SizeNWSE;
        resizeHandle.Size = new Size(16, 16);
        resizeHandleLocation = new Point(this.ClientSize.Width - resizeHandle.Width, this.ClientSize.Height - resizeHandle.Height);
        resizeHandle.Location = resizeHandleLocation;
        resizeHandle.MouseDown += ResizeHandle_MouseDown;
        resizeHandle.MouseMove += ResizeHandle_MouseMove;
        resizeHandle.MouseUp += ResizeHandle_MouseUp;
        this.Controls.Add(resizeHandle);
    }

    protected override void WndProc(ref Message m)
    {
        // Handle resize handle hit-test value
        if (m.Msg == 0x84 && m.Result == (IntPtr)HTBOTTOMRIGHT)
        {
            m.Result = (IntPtr)HTBOTTOMRIGHT;
            return;
        }
        base.WndProc(ref m);
    }

    private void ResizeHandle_MouseDown(object sender, MouseEventArgs e)
    {
        resizing = true;
    }

    private void ResizeHandle_MouseMove(object sender, MouseEventArgs e)
    {
        if (resizing)
        {
            int newWidth = e.X + resizeHandleLocation.X;
            int newHeight = e.Y + resizeHandleLocation.Y;
            this.ClientSize = new Size(newWidth, newHeight);
        }
    }

    private void ResizeHandle_MouseUp(object sender, MouseEventArgs e)
    {
        resizing = false;
    }
}

In this example, a custom resize handle is created using a label control. The resize handle is positioned in the bottom-right corner of the form and responds to mouse events to allow the user to resize the form. The WndProc method is overridden to handle the resize handle hit-test value and indicate that the user is resizing the form. Finally, the MouseDown, MouseMove, and MouseUp events of the resize handle are handled to actually change the size of the form when the user resizes it.

Note that this is just one example of how to create a custom resize handle for a border-less form in C#. You can adjust the code to suit your specific requirements and design preferences.

Examples

  1. "C# custom resize handle for border-less form"

    • Code Implementation:
      private const int WM_NCHITTEST = 0x84;
private const int HTBOTTOMRIGHT = 17;

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);
    if (m.Msg == WM_NCHITTEST)
    {
        m.Result = (IntPtr)HTBOTTOMRIGHT;
    }
}
    • Description: Override the WndProc method to intercept the WM_NCHITTEST message and specify that the bottom-right corner should act as a resize handle.

  2. "C# custom resize handle with cursor change"

    • Code Implementation:
      private const int WM_NCHITTEST = 0x84;
private const int HTBOTTOMRIGHT = 17;

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);
    if (m.Msg == WM_NCHITTEST)
    {
        m.Result = (IntPtr)HTBOTTOMRIGHT;
        Cursor.Current = Cursors.SizeNWSE;
    }
}
    • Description: Additionally, change the cursor to indicate a resize operation when the mouse is over the custom resize handle.

  3. "C# custom resize handle with drag functionality"

    • Code Implementation:
      private bool isResizing = false;
private Point resizeStart;

private void Form_MouseDown(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        isResizing = true;
        resizeStart = e.Location;
    }
}

private void Form_MouseMove(object sender, MouseEventArgs e)
{
    if (isResizing)
    {
        this.Width = Math.Max(this.MinimumSize.Width, this.Width + (e.X - resizeStart.X));
        this.Height = Math.Max(this.MinimumSize.Height, this.Height + (e.Y - resizeStart.Y));
        resizeStart = e.Location;
    }
}

private void Form_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        isResizing = false;
    }
}
    • Description: Implement mouse events to enable dragging and resizing when the user interacts with the custom resize handle.

  4. "C# custom resize handle with minimum size constraint"

    • Code Implementation:
      private const int WM_NCHITTEST = 0x84;
private const int HTBOTTOMRIGHT = 17;

private const int minWidth = 200;
private const int minHeight = 150;

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);
    if (m.Msg == WM_NCHITTEST)
    {
        m.Result = (IntPtr)HTBOTTOMRIGHT;
    }
}

private void Form_MouseMove(object sender, MouseEventArgs e)
{
    if (isResizing)
    {
        this.Width = Math.Max(minWidth, this.Width + (e.X - resizeStart.X));
        this.Height = Math.Max(minHeight, this.Height + (e.Y - resizeStart.Y));
        resizeStart = e.Location;
    }
}
    • Description: Add constraints to limit the minimum size of the form when resizing with the custom handle.

  5. "C# custom resize handle with maximum size constraint"

    • Code Implementation:
      private const int WM_NCHITTEST = 0x84;
private const int HTBOTTOMRIGHT = 17;

private const int maxWidth = 800;
private const int maxHeight = 600;

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);
    if (m.Msg == WM_NCHITTEST)
    {
        m.Result = (IntPtr)HTBOTTOMRIGHT;
    }
}

private void Form_MouseMove(object sender, MouseEventArgs e)
{
    if (isResizing)
    {
        this.Width = Math.Min(maxWidth, this.Width + (e.X - resizeStart.X));
        this.Height = Math.Min(maxHeight, this.Height + (e.Y - resizeStart.Y));
        resizeStart = e.Location;
    }
}
    • Description: Add constraints to limit the maximum size of the form when resizing with the custom handle.

  6. "C# custom resize handle with proportional resizing"

    • Code Implementation:
      private void Form_MouseMove(object sender, MouseEventArgs e)
{
    if (isResizing)
    {
        float aspectRatio = (float)this.Width / this.Height;
        this.Width = Math.Max(minWidth, this.Width + (e.X - resizeStart.X));
        this.Height = Math.Max(minHeight, (int)(this.Width / aspectRatio));
        resizeStart = e.Location;
    }
}
    • Description: Maintain the aspect ratio of the form during resizing to ensure proportional changes.

  7. "C# custom resize handle with dynamic handle size"

    • Code Implementation:
      private const int handleSize = 10;

private void Form_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.FillRectangle(Brushes.Black, this.Width - handleSize, this.Height - handleSize, handleSize, handleSize);
}

private void Form_MouseMove(object sender, MouseEventArgs e)
{
    if (isResizing)
    {
        this.Width = Math.Max(minWidth, this.Width + (e.X - resizeStart.X));
        this.Height = Math.Max(minHeight, this.Height + (e.Y - resizeStart.Y));
        resizeStart = e.Location;
        this.Refresh(); // Redraw the resize handle
    }
}
    • Description: Enhance the user experience by dynamically redrawing the custom resize handle during resizing.

  8. "C# custom resize handle with transparent background"

    • Code Implementation:
      private void Form_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.FillRectangle(Brushes.Transparent, this.Width - handleSize, this.Height - handleSize, handleSize, handleSize);
}
    • Description: Make the custom resize handle visually appealing by setting a transparent background.

  9. "C# custom resize handle with custom appearance"

    • Code Implementation:
      private void Form_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.FillRectangle(Brushes.DarkGray, this.Width - handleSize, this.Height - handleSize, handleSize, handleSize);
    e.Graphics.DrawRectangle(Pens.White, this.Width - handleSize, this.Height - handleSize, handleSize, handleSize);
}
    • Description: Customize the appearance of the resize handle by using a different color and border.

  10. "C# custom resize handle with snapping to grid"

    • Code Implementation:
      private const int gridSnap = 10;

private void Form_MouseMove(object sender, MouseEventArgs e)
{
    if (isResizing)
    {
        this.Width = Math.Max(minWidth, this.Width + (e.X - resizeStart.X));
        this.Height = Math.Max(minHeight, this.Height + (e.Y - resizeStart.Y));

        // Snap to grid
        this.Width = (int)(Math.Round((float)this.Width / gridSnap) * gridSnap);
        this.Height = (int)(Math.Round((float)this.Height / gridSnap) * gridSnap);

        resizeStart = e.Location;
        this.Refresh(); // Redraw the resize handle
    }
}
    • Description: Implement snapping to a grid during resizing for a more precise control over the form size.

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