How to enable and disable dragging a button? - winforms

Question

I have a form. On this form there is a button and a panel. Both have the same parent: the form. I want to be able to enable or disable the dragging operation of the button. The code I am using is:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace DraggableControls
{
public partial class Form2 : Form
{
private bool isDragged;
private Point pointOffset;
public Form2()
{
InitializeComponent();
this.Size = new System.Drawing.Size(800, 800);
this.AllowDrop = false;
Button button1 = new Button();
button1.Location = new Point(50, 50);
button1.BackColor = Color.Red;
button1.Size = new System.Drawing.Size(80, 80);
button1.Parent = this;
button1.AllowDrop = false;
button1.Draggable(false);
this.Controls.Add(button1);
isDragged = false;
// For the object that will be dragged:
button1.MouseDown += new MouseEventHandler(button1_MouseDown);
button1.MouseMove += new MouseEventHandler(button1_MouseMove);
button1.MouseUp += new MouseEventHandler(button1_MouseUp);
Panel panel1 = new Panel();
panel1.SuspendLayout();
panel1.Location = new System.Drawing.Point(100, 100);
panel1.Name = "panel1";
panel1.TabIndex = 0;
panel1.Size = new Size(500, 500);
panel1.BackColor = Color.Green;
panel1.AllowDrop = true;
panel1.Parent = this;
this.Controls.Add(panel1);
panel1.ResumeLayout(false);
// For the receiving object:
panel1.DragEnter += new
System.Windows.Forms.DragEventHandler(control_DragEnter);
this.DragEnter += new
System.Windows.Forms.DragEventHandler(control_DragEnter);
this.ResumeLayout(false);
}
private void button1_MouseDown(object sender, MouseEventArgs e)
{
if (sender is Button)
{
Button senderButton = (Button)sender;
if (e.Button == MouseButtons.Left)
{
isDragged = true;
Point ptStartPosition = senderButton.PointToScreen(new
Point(e.X, e.Y));
pointOffset = new Point();
pointOffset.X = senderButton.Location.X - ptStartPosition.X;
pointOffset.Y = senderButton.Location.Y - ptStartPosition.Y;
}
else
{
isDragged = false;
}
}
}
private void button1_MouseMove(object sender, MouseEventArgs e)
{
if (sender is Button)
{
Button senderButton = (Button)sender;
if (isDragged)
{
Point newPoint = senderButton.PointToScreen(new Point(e.X,
e.Y));
newPoint.Offset(pointOffset);
senderButton.Location = newPoint;
}
}
}
private void button1_MouseUp(object sender, MouseEventArgs e)
{
if (sender is Button)
{
Button senderButton = (Button)sender;
Point newPoint = senderButton.PointToScreen(new Point(e.X,
e.Y));
isDragged = false;
}
}
private void control_DragEnter(object sender, DragEventArgs e)
{
e.Effect = DragDropEffects.None;
}
/// <summary>
/// Prevents Window and any of the controls from being dragged by means
of the mouse.
/// </summary>
/// <param name="message"></param>
protected override void WndProc(ref Message message)
{
int WM_NCLBUTTONDOWN = 0xA1;
int WM_SYSCOMMAND = 0x112;
int HTCAPTION = 0x02;
int SC_MOVE = 0xF010;
if (message.Msg == WM_SYSCOMMAND && message.WParam.ToInt32() ==
SC_MOVE)
{
return;
}
if (message.Msg == WM_NCLBUTTONDOWN && message.WParam.ToInt32() ==
HTCAPTION)
{
return;
}
base.WndProc(ref message);
}
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace DraggableControls
{
public static class ControlDragExtension
{
private static Dictionary<Control, bool>
controlDraggabilityByControl = new Dictionary<Control, bool>(); // TKey
is
control to drag, TValue is a Boolean
flag used to determine the dragging state.
private static System.Drawing.Size mouseOffset;
/// <summary>
/// Enable/Disable control dragging.
/// </summary>
public static void Draggable(this Control control, bool enable)
{
if (enable) // Enable control drag feature.
{
if (controlDraggabilityByControl.ContainsKey(control))
{
return; // Return if control is already draggable.
}
controlDraggabilityByControl.Add(control, false); // 'false' -
Initial state is 'control not draggable'.
// Assign required event handlers.
control.MouseDown += new MouseEventHandler(Control_MouseDown);
control.MouseUp += new MouseEventHandler(Control_MouseUp);
control.MouseMove += new MouseEventHandler(Control_MouseMove);
}
else // Disable control drag feature.
{
if (!controlDraggabilityByControl.ContainsKey(control))
{
return; // Return if control is not draggable.
}
// Remove event handlers.
control.MouseDown -= Control_MouseDown;
control.MouseUp -= Control_MouseUp;
control.MouseMove -= Control_MouseMove;
controlDraggabilityByControl.Remove(control);
}
}
static void Control_MouseDown(object sender, MouseEventArgs e)
{
mouseOffset = new System.Drawing.Size(e.Location);
controlDraggabilityByControl[(Control)sender] = true; // Turn
control dragging feature on.
}
static void Control_MouseUp(object sender, MouseEventArgs e)
{
controlDraggabilityByControl[(Control)sender] = false; // Turn
control dragging feature off.
}
static void Control_MouseMove(object sender, MouseEventArgs e)
{
if (controlDraggabilityByControl[(Control)sender] == true) // Only
if dragging is turned on.
{
// Calculation of control's new position.
System.Drawing.Point newLocationOffset = e.Location -
mouseOffset;
((Control)sender).Left += newLocationOffset.X;
((Control)sender).Top += newLocationOffset.Y;
}
}
}
}
Even though I have the statements: this.AllowDrop = false; , panel1.AllowDrop = false; and button1.Draggable(false); and also the override void WndProc method that should disable dragging,
the button1 is always draggable.

Answer 1

I changed the event handlers thus:
private void button1_MouseDown(object sender, MouseEventArgs e)
{
if (sender is Button)
{
Button senderButton = (Button)sender;
if (enableDragOperations)
{
if (e.Button == MouseButtons.Left)
{
isDragged = true;
Point ptStartPosition = senderButton.PointToScreen(new Point(e.X, e.Y));
pointOffset = new Point();
pointOffset.X = senderButton.Location.X - ptStartPosition.X;
pointOffset.Y = senderButton.Location.Y - ptStartPosition.Y;
}
else
{
isDragged = false;
}
}
}
}
private void button1_MouseMove(object sender, MouseEventArgs e)
{
if (sender is Button)
{
Button senderButton = (Button)sender;
if (enableDragOperations)
{
if (isDragged)
{
Point newPoint = senderButton.PointToScreen(new Point(e.X, e.Y));
newPoint.Offset(pointOffset);
senderButton.Location = newPoint;
}
}
}
}
private void button1_MouseUp(object sender, MouseEventArgs e)
{
if (sender is Button)
{
Button senderButton = (Button)sender;
if (enableDragOperations)
{
Point newPoint = senderButton.PointToScreen(new Point(e.X, e.Y));
isDragged = false;
}
}
}
I defined a global field: bool enableDragOperations and set it to false.