Microsoft KB Article 320687 has a detailed answer to this question.
Basically, you override the WndProc method to return HTCAPTION to the WM_NCHITTEST message when the point being tested is in the client area of the form -- which is, in effect, telling Windows to treat the click exactly the same as if it had occured on the caption of the form.
private const int WM_NCHITTEST = 0x84;
private const int HTCLIENT = 0x1;
private const int HTCAPTION = 0x2;
protected override void WndProc(ref Message m)
{
switch(m.Msg)
{
case WM_NCHITTEST:
base.WndProc(ref m);
if ((int)m.Result == HTCLIENT)
m.Result = (IntPtr)HTCAPTION;
return;
}
base.WndProc(ref m);
}
Here is a way to do it using a P/Invoke.
public const int WM_NCLBUTTONDOWN = 0xA1;
public const int HTCAPTION = 0x2;
[DllImport("User32.dll")]
public static extern bool ReleaseCapture();
[DllImport("User32.dll")]
public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);
void Form_Load(object sender, EventArgs e)
{
this.MouseDown += new MouseEventHandler(Form_MouseDown);
}
void Form_MouseDown(object sender, MouseEventArgs e)
{
if (e.Button == MouseButtons.Left)
{
ReleaseCapture();
SendMessage(Handle, WM_NCLBUTTONDOWN, HTCAPTION, 0);
}
}
The following code assumes that the ProgressBarForm form has a ProgressBar control with Dock property set to Fill
public partial class ProgressBarForm : Form
{
private bool mouseDown;
private Point lastPos;
public ProgressBarForm()
{
InitializeComponent();
}
private void progressBar1_MouseMove(object sender, MouseEventArgs e)
{
if (mouseDown)
{
int xoffset = MousePosition.X - lastPos.X;
int yoffset = MousePosition.Y - lastPos.Y;
Left += xoffset;
Top += yoffset;
lastPos = MousePosition;
}
}
private void progressBar1_MouseDown(object sender, MouseEventArgs e)
{
mouseDown = true;
lastPos = MousePosition;
}
private void progressBar1_MouseUp(object sender, MouseEventArgs e)
{
mouseDown = false;
}
}
The accepted answer is a cool trick, but it doesn't always work if the Form is covered by a Fill-docked child control like a Panel (or derivates) for example, because this control will eat all most Windows messages.
Here is a simple approach that works also in this case: derive the control in question (use this class instead of the standard one) an handle mouse messages like this:
private class MyTableLayoutPanel : Panel // or TableLayoutPanel, etc.
{
private Point _mouseDown;
private Point _formLocation;
private bool _capture;
// NOTE: we cannot use the WM_NCHITTEST / HTCAPTION trick because the table is in control, not the owning form...
protected override void OnMouseDown(MouseEventArgs e)
{
_capture = true;
_mouseDown = e.Location;
_formLocation = ((Form)TopLevelControl).Location;
}
protected override void OnMouseUp(MouseEventArgs e)
{
_capture = false;
}
protected override void OnMouseMove(MouseEventArgs e)
{
if (_capture)
{
int dx = e.Location.X - _mouseDown.X;
int dy = e.Location.Y - _mouseDown.Y;
Point newLocation = new Point(_formLocation.X + dx, _formLocation.Y + dy);
((Form)TopLevelControl).Location = newLocation;
_formLocation = newLocation;
}
}
}
VC++ 2010 Version (of FlySwat's):
#include <Windows.h>
namespace DragWithoutTitleBar {
using namespace System;
using namespace System::Windows::Forms;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Data;
using namespace System::Drawing;
public ref class Form1 : public System::Windows::Forms::Form
{
public:
Form1(void) { InitializeComponent(); }
protected:
~Form1() { if (components) { delete components; } }
private:
System::ComponentModel::Container ^components;
HWND hWnd;
#pragma region Windows Form Designer generated code
void InitializeComponent(void)
{
this->SuspendLayout();
this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
this->ClientSize = System::Drawing::Size(640, 480);
this->FormBorderStyle = System::Windows::Forms::FormBorderStyle::None;
this->Name = L"Form1";
this->Text = L"Form1";
this->Load += gcnew EventHandler(this, &Form1::Form1_Load);
this->MouseDown += gcnew System::Windows::Forms::MouseEventHandler(this, &Form1::Form1_MouseDown);
this->ResumeLayout(false);
}
#pragma endregion
private: System::Void Form1_Load(Object^ sender, EventArgs^ e) {
hWnd = static_cast<HWND>(Handle.ToPointer());
}
private: System::Void Form1_MouseDown(Object^ sender, System::Windows::Forms::MouseEventArgs^ e) {
if (e->Button == System::Windows::Forms::MouseButtons::Left) {
::ReleaseCapture();
::SendMessage(hWnd, /*WM_NCLBUTTONDOWN*/ 0xA1, /*HT_CAPTION*/ 0x2, 0);
}
}
};
}
