Autosize the last column in a ListView control using WndProc

Introduction

It has always been a pet-peeve of mine, that I prefer grid or list controls to auto size their columns to fit the control canvas. Some of you may remember the early OCX and ActiveX controls that implemented auto-size last column properties to resolve this problem. Essentially, the last column in the grid or list view is automatically expanded to take up any available space. As the form is resized, or column widths are resized by the user at runtime, the last column size is automatically increased or decreased to keep the column aligned with the control right edge.

I love the Windows Explorer look, and I love the ListView control features and appearance - we just have to do something with that last column! Having scoured the internet trying to find examples or clues, the end result that, finding a solution proved to be difficult, but implementing the solution was actually very simple.

Setting the Column Size

In fact, the ListView class does provide a ColumnHeader.Width property. The MSDN documentation describes two special values related to auto-sizing the column, as follows: "To adjust the width of the longest item in the column, set the Width property to -1. To auto size to the width of the column heading, set the Width property to -2".

A special feature of setting the Width to -2, is that it ALSO automatically expands the last column to the right-edge of the control. This would seem to solve the problem, except that it does it a one-time auto-size that is not preserved if the user resizes any of the column widths at runtime, or the ListView control is set to resize with the form.

Responding to Change

When I first approached this problem, I figured the answer would lie in responding to some event when the user resized a column or the control was resized, or sub-classing the ListView to gain access to some protected interfaces. In fact, the ColumnHeaderCollection and ColumnHeader classes used to provide the implementation of the ListView.Columns member are completely buried inside the parent control.

My next approach was to look to the Win32 API, but faced the same obstacles. I could find no examples of how to access the ListView column headers directly.

The final step to any tricky problem like this was to look to the Window message loop. A handy feature of .NET controls is they expose the WndProc method for handling messages received by the control. By analyzing the messages that were pumped through the ListView control while columns widths were resized, or the control was resized, I discovered that the hidden ColumnHeader class sends a WM_PAINT message to the parent control to notify it during a column resize, and as a final step when the user finishes resizing the column. The WM_PAINT method is also the last message processed when the user resizes the ListView control.

The Solution

To implement the the auto-size of the last column, subclass the ListView control, and override the WndProc method.

protected override void WndProc( ref Message message )
{
    const int WM_PAINT = 0xf ;

    // if the control is in details view mode and columns
    // have been added, then intercept the WM_PAINT message
    // and reset the last column width to fill the list view
    switch ( message.Msg )
    {
    case WM_PAINT:
        if ( this.View == View.Details && this.Columns.Count > 0 )
            this.Columns[this.Columns.Count - 1].Width = -2 ;
        break ;
    }

    // pass messages on to the base control for processing
    base.WndProc( ref message ) ;
}