Force the display of scroll bars in a ListView?

问题

• The background: Most of us know the SysListView32 common control and the equivalent wrapper ListView class provided by the .NET Framework. A little depth into its internals show that the scroll bars it provides for scrolling its contents are NOT controls themselves, but are managed by the SysListView32 control.

• The goal: Always draw scroll bars even if it has no ListViewItems to display or has very few such that no scroll bars are needed anyway; sort of like mimicking the RichTextBox class with its ScrollBars property set to ForcedBoth. Or kinda like this ListBox:

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• The problem(s):

  1. .NET has NO sugar at all for scroll bars within a ListView.
  2. Win32 documentation does not state when to show/hide and/or enable/disable scrollbars.

• My workaround(s):

  1. override the WndProc in a derived class and handle its WM_HSCROLL and WM_VSCROLL messages as per steps 2 and 3.
  2. Call base.WndProc to do the actually required processing of the scroll functionality.
  3. Create a method like WmScroll and do my processing on it immediately after base.WndProc has returned.
  4. This consists of a p/invoke call to GetScrollInfo. Determine if a scroll bar is actually needed. If it's not then call ShowScrollBar and EnableScrollBar with required values to draw visibly disabled scroll bars.

• Problems with the workaround:

  1. It barely works. The scroll bars are displayed and disabled but are like the ones under Windows Classic Theme.
  2. It hides the collapse buttons of each ListViewGroup, rendering them useless!

The descriptive image:

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The long awaited actual question:

How do I force scroll bars to always be Visible within a ListView irrespective of the number of ListViewItems and disable them if they are unnecessary, at the same time avoiding size miscalculation (to display collapse buttons of the ListViewGroups) and theme deterioration?

Answers without code, and answers with code in C#, VB.NET and C++/CLR are welcome. If you post code in any other language supported by .NET, please also leave a link to a code conversion website I may use if the code seems, uh, incomprehensible.

回答1:

• Information:

  • Firstly, I have to admit this is an okay answer and not the best/most efficient one. If you have a different answer from mine, please post it.
  • Secondly, this answer owes some credit to Plutonix's answer, experimenting with which I learned that by default ListView does not have WS_HSCROLL | WS_VSCROLL flags set in its styles.
    • This is why my previous workaround had problem with themes.
    • These Classic scroll bars are ones Windows provides to Controls that do not have these flags set.
    • Changing the CreateParams does not work either. You have to set it manually in the OnHandleCreated method using SetWindowLong.
    • The solution I am posting does not use the above technique. Apparently, calling ShowScrollBar for each window message forces these flags to be set.

• The Solution:

  • Define your WndProc like the following:

    protected override void WndPoc(ref Message m)
    {
    //custom code before calling base.WndProc
    base.WndProc(ref m);
    //custom after base.WndProc returns
    WmScroll(); //VERY INEFFICIENT, called for each message :(
    }
    

  • Define WmScroll() as follows:

    protected virtual void WmScroll()
    {
    NativeMethods.ShowScrollBar(Handle, SB_BOTH, true);
    	
    //si.fMask = SIF_PAGE | SIF_RANGE <- initialized in .ctor
    	
    NativeMethods.GetScrollInfo(Handle, SB_HORZ, ref si);
    if(si.nMax < si.nPage)
    	NativeMethods.EnableScrollBar(Handle, SB_HORZ, ESB_DISABLE_BOTH);
    else
    	NativeMethods.EnableScrollBar(Handle, SB_HORZ, ESB_ENABLE_BOTH);
    NativeMethods.GetScrollInfo(Handle, SB_VERT, ref si);
    if(si.nMax < si.nPage)
    	NativeMethods.EnableScrollBar(Handle, SB_VERT, ESB_DISABLE_BOTH);
    else
    	NativeMethods.EnableScrollBar(Handle, SB_VERT, ESB_ENABLE_BOTH);
    }
    

  • Output:

It now, looks like:

These are with another item added featuring the horizontal scroll and working ListViewGroup collapse button:

• Imperfection, yes there is:
  • A call to AutoResizeColumns is required if group collapse changes effective text width, otherwise the vertical scroll bar hides the collapse buttons.

来源：https://stackoverflow.com/questions/39057774/force-the-display-of-scroll-bars-in-a-listview