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Posted 2 Jul 2011

Smooth Resize and Reposition

, 2 Jul 2011
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A demo on how to smoothly change the size or position of a Windows Form while holding down a button.

In the image above, the cursor is held down on the top button, and the windows width enlarges smoothly to the right.


This is a simple demonstration of how to smoothly resize or reposition a Windows Form by holding down a button. When the form is resized, the button and cursor remain in a constant position while the edge smoothly expands or contracts. When the form is repositioned, the cursor floats along on top of the button as it smoothly moves with the form.


I was distracted by flashy advertising on a web site, and initially hid it under "Sticky Notes"; but that was unsatisfactory. Then I made a simple empty form with option "Top Most" set. That was awkward. What I wanted was something to slide just a bit right or grow just a bit taller. I came up with "Obscure", and worked on moving a window smoothly about while holding down one of several buttons. I thought it is worth sharing.

Using the Code

The key is one does not "Click" a button. The action is in a combination of MouseDown, MouseUp and a timer event. There is a MouseDown/Up event for each button. The MouseDown centers the cursor on an active control (button) in followButton(), sets a class enum buttonPick and enables a timer. The button might move the window or change its size.
If moving: in the timer, a switch branches on buttonPick, and there changes the client and cursor origins by an incremental step.
If resizing: the switch increments/decrements the current side of the window. Then, resets the client size via doResze().

In the little project "SlideDemo", shown here and which you can download, one can only expand or contract the right side of the window. Or slide the window to the right. The project "Obscure" is more complex. It allows one to move in 4 directions and expand and contract all 4 edges of the window. Plus, some other features.

MouseDown/Up events are very simple:

private void button_RightOut_MouseDown(object sender, MouseEventArgs e)
    timer1.Enabled = true;
    buttonPick = ButtonPick.RightOut;

private void button_RightOut_MouseUp(object sender, MouseEventArgs e)
    buttonPick = ButtonPick.none;
    timer1.Enabled = false;

The timer handles the switch on buttonPick. You can see that SlideRight changes the location of both the client and the cursor. While RightOut only increments the width of the client passing that onto doResize(width, height);

switch (buttonPick)
    case ButtonPick.RightOut:
        width += step;

        // Keep the window from growing to wide
        if (width > defaultWidthMax)
            width = defaultWidthMax;
    case ButtonPick.SlideRight:
        topX += step;
        clientOrigin.Y = topY;
        clientOrigin.X = topX;
        this.Location = clientOrigin;

        buttonsOrigin.X += step;
        Cursor.Position = buttonsOrigin;

    doResize(width, height);

doResize() is common code called at the end of the switch to change the client's size.

private void doResize(int width, int height)
    ignoreEvent = true;
    this.ClientSize = new System.Drawing.Size(width, height);
    ignoreEvent = false;

One must also handle two other Form events, else the window may jump when you mouse down on a button.

private void Form1_LocationChanged(object sender, EventArgs e)
    topX = Location.X;
    topY = Location.Y;

private void Form1_ClientSizeChanged(object sender, EventArgs e)
    if (ignoreEvent) return;

    width = this.ClientSize.Width;
    height = this.ClientSize.Height;

Points of Interest

Figuring out how to handle the mouse events in coordination with a timer was fairly easy. The handling of the LocationChanges and ClientSizeChanged events was not so obvious. And the window kept jumping on me. In "Obscure", I save form settings and allow the user to change the granularity of increments.


  • Version 1.0


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

United States United States
Retired C programmer and Unix Sys Admin, then VC6 C++ MFC programmer. I moved to VC7 C++ 2003 in Oct of 04, and VC8 C++/CLI early in 06. I resisted C# for a long time. But now C# is my preferred language. I'm through with upgrading. I'll stay at VC2008 and C# as I only program for fun anymore.

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Comments and Discussions

QuestionMy vote of 5 Pin
professionalAYDIN EBRAHIMI HOMAY6-Dec-13 23:13 
QuestionTanks!! Pin
Bruno Sousa10-Dec-12 2:16
memberBruno Sousa10-Dec-12 2:16 

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