ListView Background Image in .NETCF

In this short entry I’d like to demonstrate how to display a background image in the ListView control. For this we will send the LVM_SETBKIMAGE or the LVM_GETBKIMAGE message to the ListView control with the LVBKIMAGE struct as the LPARAM. Unfortunately, the Windows CE version of LVBKIMAGE does not support LVBKIF_SOURCE_URL flag which allows using an image file on the file system for the background image of the ListView.

The layout of the background image can be either tiled or specified by an offset percentage. The background image is not affected by custom drawing, unless of course you decide to fill each sub item rectangle. For setting the background image we use the LVBKIF_SOURCE_HBITMAP flag together with the layout which is either LVBKIF_STYLE_TILE or LVBKIF_STYLE_NORMAL. If we set the layout to LVBKIF_STYLE_NORMAL, then we have the option of setting where the image will be drawn by setting the value of xOffsetPercentage and yOffsetPercentage.

In this example I’d like to make use of extension methods to add the SetBackgroundImage() and GetBackgroundImage() methods to ListView. This can of course be easily used to in a property to an inherited ListView.

public static class ListViewExtensions
{
    [DllImport("coredll")]
    static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, ref LVBKIMAGE lParam);
 
    const int LVM_FIRST = 0x1000;
    const int LVM_SETBKIMAGE = (LVM_FIRST + 138);
    const int LVM_GETBKIMAGE = (LVM_FIRST + 139);
    const int LVBKIF_SOURCE_NONE = 0x00000000;
    const int LVBKIF_SOURCE_HBITMAP = 0x00000001;
    const int LVBKIF_STYLE_TILE = 0x00000010;
    const int LVBKIF_STYLE_NORMAL = 0x00000000;
 
    struct LVBKIMAGE
    {
        public int ulFlags;
        public IntPtr hbm;
        public IntPtr pszImage; // not supported
        public int cchImageMax;
        public int xOffsetPercent;
        public int yOffsetPercent;
    }
 
    public static void SetBackgroundImage(this ListView listView, Bitmap bitmap)
    {
        SetBackgroundImage(listView, bitmap, false);
    }
 
    public static void SetBackgroundImage(this ListView listView, Bitmap bitmap, bool tileLayout)
    {
        SetBackgroundImage(listView, bitmap, tileLayout, 0, 0);
    }
 
    public static void SetBackgroundImage(
        this ListView listView,
        Bitmap bitmap,
        bool tileLayout,
        int xOffsetPercent,
        int yOffsetPercent)
    {
        LVBKIMAGE lvBkImage = new LVBKIMAGE();
        if (bitmap == null)
            lvBkImage.ulFlags = LVBKIF_SOURCE_NONE;
        else
        {
            lvBkImage.ulFlags = LVBKIF_SOURCE_HBITMAP | (tileLayout ? LVBKIF_STYLE_TILE : LVBKIF_STYLE_NORMAL);
            lvBkImage.hbm = bitmap.GetHbitmap();
            lvBkImage.xOffsetPercent = xOffsetPercent;
            lvBkImage.yOffsetPercent = yOffsetPercent;
        }
 
        SendMessage(listView.Handle, LVM_SETBKIMAGE, 0, ref lvBkImage);
    }
 
    public static Bitmap GetBackgroundImage(this ListView listView)
    {
        LVBKIMAGE lvBkImage = new LVBKIMAGE();
        lvBkImage.ulFlags = LVBKIF_SOURCE_HBITMAP;
 
        SendMessage(listView.Handle, LVM_GETBKIMAGE, 0, ref lvBkImage);
 
        if (lvBkImage.hbm == IntPtr.Zero)
            return null;
        else
            return Bitmap.FromHbitmap(lvBkImage.hbm);
    }
}

Here’s an example of exposing the background image as a property in an inherited ListView by using the extension methods above.

class ListViewEx : ListView
{
    public Bitmap BackgroundImage
    {
        get { return this.GetBackgroundImage(); }
        set { this.SetBackgroundImage(value, BackgroundLayout == BackgroundImageLayout.Tile); }
    }
 
    public BackgroundImageLayout BackgroundLayout { get; set; }
 
    public enum BackgroundImageLayout
    {
        Tile,
        Center
    }
}

A small catch with the ListView background image is that it is only supported in Windows CE 5.0 and later. Hope you found this information useful.

ListView Custom Drawing in .NETCF

In this article I would like to demonstrate how to do custom drawing in the ListView control that the .NET Compact Framework provides. I’ll be extending the code I published last year in the article entitled ListView Extended Styles in .NETCF

This is normally a very tedious and frustrating task to do and to accomplish this task we’ll have to take advantage of the custom drawing service Windows CE provides for certain controls. A very good reference for custom drawing is an MSDN article called Customizing a Control’s Appearance using Custom Draw. Before going any further, I may have to warn you about the extensive interop code involved in this task.

We’ll have to handle the ListView windows messages ourselves, and we accomplish this by subclassing this ListView. Subclassing a window means that we assign a new window procedure for messages that are meant for the ListView. This can be done through the SetWindowLong() method with the GWL_WNDPROC parameter. When subclassing, the developer is responsible for choosing which messages they want to handle, which to ignore, and which they let operating system handle. To have the operating system handle the message, a call to CallWindowProc() is done using a pointer to original window procedure.

Before setting the new window procedure its important to get a pointer to the original one in case the developer wishes to let the operating system handle the message. This is done through GetWindowLong()

Let’s get started…

First we need to define the interop structures for custom drawing

    struct RECT
    {
        public int left;
        public int top;
        public int right;
        public int bottom;
    }
 
    struct NMHDR
    {
        public IntPtr hwndFrom;
        public IntPtr idFrom;
        public int code;
    }
 
    struct NMCUSTOMDRAW
    {
        public NMHDR nmcd;
        public int dwDrawStage;
        public IntPtr hdc;
        public RECT rc;
        public int dwItemSpec;
        public int uItemState;
        public IntPtr lItemlParam;
    }
 
    struct NMLVCUSTOMDRAW
    {
        public NMCUSTOMDRAW nmcd;
        public int clrText;
        public int clrTextBk;
        public int iSubItem;
        public int dwItemType;
        public int clrFace;
        public int iIconEffect;
        public int iIconPhase;
        public int iPartId;
        public int iStateId;
        public RECT rcText;
        public uint uAlign;
    }

Note: In C# (and VB and C++), the StructLayout is Sequencial by default, hence I didn’t state it

The P/Invoke declarations we need are the following:

    [DllImport("coredll.dll")]
    static extern IntPtr CallWindowProc(IntPtr lpPrevWndFunc, IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
 
    [DllImport("coredll")]
    static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, ref RECT lParam);
 
    [DllImport("coredll.dll")]
    static extern uint SendMessage(IntPtr hwnd, uint msg, uint wparam, uint lparam);
 
    [DllImport("coredll.dll", SetLastError = true)]
    static extern int SetWindowLong(IntPtr hWnd, int nIndex, WndProcDelegate newProc);
 
    [DllImport("coredll.dll", SetLastError = true)]
    static extern IntPtr GetWindowLong(IntPtr hWnd, int nIndex);

And to make life a bit easier, I created some extension methods to the RECT struct we just defined.

    static class RectangleExtensions
    {
        public static Rectangle ToRectangle(this RECT rectangle)
        {
            return Rectangle.FromLTRB(rectangle.left, rectangle.top, rectangle.right, rectangle.bottom);
        }
 
        public static RectangleF ToRectangleF(this RECT rectangle)
        {
            return new RectangleF(rectangle.left, rectangle.top, rectangle.right, rectangle.bottom);
        }
    }

We’ll need the following constants defined in the windows platform SDK

    const int GWL_WNDPROC = -4;
    const int WM_NOTIFY = 0x4E;
    const int NM_CUSTOMDRAW = (-12);
    const int CDRF_NOTIFYITEMDRAW = 0x00000020;
    const int CDRF_NOTIFYSUBITEMDRAW = CDRF_NOTIFYITEMDRAW;
    const int CDRF_NOTIFYPOSTPAINT = 0x00000010;
    const int CDRF_SKIPDEFAULT = 0x00000004;
    const int CDRF_DODEFAULT = 0x00000000;
    const int CDDS_PREPAINT = 0x00000001;
    const int CDDS_POSTPAINT = 0x00000002;
    const int CDDS_ITEM = 0x00010000;
    const int CDDS_ITEMPREPAINT = (CDDS_ITEM | CDDS_PREPAINT);
    const int CDDS_SUBITEM = 0x00020000;
    const int CDIS_SELECTED = 0x0001;
    const int LVM_GETSUBITEMRECT = (0x1000 + 56);

Custom drawing in the ListView will only work in the Details view mode. To ensure this, I set the View to View.Details in the constructor method. Since I’m extending my old ListViewEx (Enables ListView Extended Styles) I’m gonna enable Double buffering, Grid lines, and the Gradient background. I’m gonna enable subclassing on the ListView only when the parent is changed, this is because I need to receive messages sent to the parent control of the ListView. We also need a delegate for the new window procedure and a pointer to the original window procedure. And last but not the least we need the actual window procedure method.

    delegate IntPtr WndProcDelegate(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);
    IntPtr lpPrevWndFunc;
 
    public ListViewCustomDraw()
    {
        View = View.Details;
        DoubleBuffering = true;
        GridLines = true;
        Gradient = true;
 
        ParentChanged += delegate
        {
            lpPrevWndFunc = GetWindowLong(Parent.Handle, GWL_WNDPROC);
            SetWindowLong(Parent.Handle, GWL_WNDPROC, WndProc);
        };
    }
 
    private IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
    {
        if (msg == WM_NOTIFY)
        {
            var nmhdr = (NMHDR)Marshal.PtrToStructure(lParam, typeof(NMHDR));
            if (nmhdr.hwndFrom == Handle && nmhdr.code == NM_CUSTOMDRAW)
                return CustomDraw(hWnd, msg, wParam, lParam);
 
        }
 
        return CallWindowProc(lpPrevWndFunc, hWnd, msg, wParam, lParam);
    }

In the new window procedure, we are only really interested in the WM_NOTIFY message, because this is what the NM_CUSTOMDRAW message is sent through. The LPARAM parameter of the message will contain the NMHDR which then contains the NM_CUSTOMDRAW message. The LPARAM also contains the NMLVCUSTOMDRAW which provide state and information about the ListView.

The trickiest part in performing custom drawing in the ListView is handling the drawing stage. We create a method called CustomDraw to handle the different drawing stages of the ListView

    private IntPtr CustomDraw(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
    {
        int result;
        var nmlvcd = (NMLVCUSTOMDRAW)Marshal.PtrToStructure(lParam, typeof(NMLVCUSTOMDRAW));
        switch (nmlvcd.nmcd.dwDrawStage)
        {
            case CDDS_PREPAINT:
                result = CDRF_NOTIFYITEMDRAW;
                break;
 
            case CDDS_ITEMPREPAINT:
                var itemBounds = nmlvcd.nmcd.rc.ToRectangle();
                if ((nmlvcd.nmcd.uItemState & CDIS_SELECTED) != 0)
                {
                    using (var brush = new SolidBrush(SystemColors.Highlight))
                    using (var graphics = Graphics.FromHdc(nmlvcd.nmcd.hdc))
                        graphics.FillRectangle(brush, itemBounds);
                }
 
                result = CDRF_NOTIFYSUBITEMDRAW;
                break;
 
            case CDDS_SUBITEM | CDDS_ITEMPREPAINT:
                var index = nmlvcd.nmcd.dwItemSpec;
                var rect = new RECT();
                rect.top = nmlvcd.iSubItem;
                SendMessage(Handle, LVM_GETSUBITEMRECT, index, ref rect);
                rect.left += 2;
 
                Color textColor;
                if ((nmlvcd.nmcd.uItemState & CDIS_SELECTED) != 0)
                    textColor = SystemColors.HighlightText;
                else
                    textColor = SystemColors.ControlText;
 
                using (var brush = new SolidBrush(textColor))
                using (var graphics = Graphics.FromHdc(nmlvcd.nmcd.hdc))
                    graphics.DrawString(Items[index].SubItems[nmlvcd.iSubItem].Text,
                                        Font,
                                        brush,
                                        rect.ToRectangleF());
 
                result = CDRF_SKIPDEFAULT | CDRF_NOTIFYSUBITEMDRAW;
                break;
 
            default:
                result = CDRF_DODEFAULT;
                break;
        }
 
        return (IntPtr)result;
    }

In the first stage we handle is the CDDS_PREPAINT. Here we return CDRF_NOTIFYITEMDRAW to tell that we want to handle drawing of the row ourselves. After this we receive the CDDS_ITEMPREPAINT where we can draw the entire row.

We check if the row is selected through the uItemState field of NMCUSTOMDRAW, if this field has the CDIS_SELECTED flag then it means the item is selected, hence we draw a fill rectangle. After handling the CDDS_ITEMPREPAINT, we return CDRF_NOTIFYSUBITEMDRAW to tell that we want to draw the sub items ourselves.

For drawing the sub items we need to handle CDDS_SUBITEM | CDDS_ITEMPREPAINT. We can get the position index of the item through the dwItemSpec field of NMCUSTOMDRAW. To get the bounds of the current sub item we send the LVM_GETSUBITEMRECT message to the ListView and pass a pointer to RECT as the LPARAM. Before sending this message, set the “top” field of the RECT to the index of the sub item (retrieved from iSubItem field of NMLVCUSTOMDRAW. After drawing the sub item we return CDRF_SKIPDEFAULT | CDRF_NOTIFYSUBITEMDRAW to tell that we only care about handling the next sub item.

Well I hope you guys find this interesting and helpful. To keep things simple, I only demonstrated displaying plan text and a plain rectangle for the selection.

If you’re interested in the full source code then you can grab it here.

ListView Extended Styles in .NETCF

In this article I would like to demonstrate how to extend the ListView control in the .NET Compact Framework. We will focus on enabling some of the ListView Extended Styles. If we take a look at the Windows Mobile 5.0 Pocket PC SDK we will see that there are certain features of ListView that aren’t provided by the .NET Compact Framework.

An example of the ListView extended styles is displaying gridlines around items and subitems, double buffering, and drawing a gradient background. These extended styles can be enabled in native code by using the ListView_SetExtendedListViewStyle macro or by sending LVM_SETEXTENDEDLISTVIEWSTYLE messages to the ListView.

Send Message

We will be using a lot of P/Invoking so let’s start with creating an internal static class called NativeMethods. We need a P/Invoke declaration for SendMessage(HWND, UINT, UINT, UINT).

internal static class NativeMethods
{
  [DllImport(“coredll.dll”)]
  public static extern uint SendMessage(IntPtr hwnd, uint msg, uint wparam, uint lparam);
}

Enabling and Disabling Extended Styles

Now that we have our SendMessage P/Invoke declaration in place, we can begin extending the ListView control. Let’s start off with creating a class called ListViewEx that inherits from ListView. We need to look into the native header files of the Pocket PC SDK to get the ListView Messages. For now we will only need LVM_[GET/SET]EXTENDEDLISTVIEWSTYLE message which will be the main focus of all the examples. I will declare my class as a partial class and create all the pieces one by one for each example. Let’s create a private method called SetStyle(), this method will enable/disable extended styles for the ListView

public partial class ListViewEx : ListView
{
  private const uint LVM_FIRST = 0x1000;
  private const uint LVM_SETEXTENDEDLISTVIEWSTYLE = LVM_FIRST + 54;
  private const uint LVM_GETEXTENDEDLISTVIEWSTYLE = LVM_FIRST + 55;

  private void SetStyle(uint style, bool enable)
  {
    uint currentStyle = NativeMethods.SendMessage(
      Handle,
      LVM_GETEXTENDEDLISTVIEWSTYLE,
      0,
      0);

    if (enable)
      NativeMethods.SendMessage(
        Handle,
        LVM_SETEXTENDEDLISTVIEWSTYLE,
        0,
        currentStyle | style);
    else
      NativeMethods.SendMessage(
        Handle,
        LVM_SETEXTENDEDLISTVIEWSTYLE,
        0,
        currentStyle & ~style);
  }
}

Grid Lines

For my first example, let’s enable GridLines in the ListView control. We can do this by using LVS_EX_GRIDLINES. This displays gridlines around items and sub-items and is available only in conjunction with the Details mode.

public partial class ListViewEx : ListView
{
  private const uint LVS_EX_GRIDLINES = 0x00000001;

  private bool gridLines = false;
  public bool GridLines
  {
    get { return gridLines; }
    set
    {
      gridLines = value;
      SetStyle(LVS_EX_GRIDLINES, gridLines);
    }
  }
}

What the code above did was add the LVS_EX_GRIDLINES style to the existing extended styles by using the SetStyle() helper method we first created.

An interesting discovery to this is that the Design Time attributes of the Compact Framework ListView control includes the GridLines property. Now that we created the property in the code, when we open the Visual Studio Properties Window for our ListViewEx we will notice that GridLines property we created falls immediately under the “Appearance” category and even includes a description 🙂

Double Buffering

Do you notice that when you populate a ListView control with a lot of items, the drawing flickers a lot when you scroll up and down the list? Although it is not in the Pocket PC documentation for Windows Mobile 5.0, the ListView actually has an extended style called LVS_EX_DOUBLEBUFFER. Enabling the LVS_EX_DOUBLEBUFFER solves the flickering issue and gives the user a more smooth scrolling experience.

public partial class ListViewEx : ListView
{
  private const uint LVS_EX_DOUBLEBUFFER = 0x00010000;

  private bool doubleBuffering = false;
  public bool DoubleBuffering
  {
    get { return doubleBuffering; }
    set
    {
      doubleBuffering = value;
      SetStyle(LVS_EX_DOUBLEBUFFER, doubleBuffering);
    }
  }
}

Gradient Background

Another cool extended style is the LVS_EX_GRADIENT. This extended style draws a gradient background similar to the one found in Pocket Outlook. It uses the system colors and fades from right to left. But what is really cool about this is that this is done by the OS. All we had to do was enable the style.

public partial class ListViewEx : ListView
{
  private const uint LVS_EX_GRADIENT = 0x20000000;

  private bool gradient = false;
  public bool Gradient
  {
    get { return gradient; }
    set
    {
      gradient = value;
      SetStyle(LVS_EX_GRADIENT, gradient);
    }
  }
}

If you want to look more into extended styles then I suggest you check out the Pocket PC Platform SDK documentation. There a few other extended styles that I did not discuss that might be useful for you. You can get the definitions in a file called commctrl.h in your Windows Mobile SDK “INCLUDE” directory.