ImageListPopup, a C# class which pops up a window to select an image from an image list

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Introduction

The ImageListPopup is a quite easy to use Class that inherits from System.Windows.Forms.Form and allows to show a popup displaying the content of a specified Image List. When you click over an image, an event is fired and you get the index of the clicked image in the imagelist.

Features

The ImageListPopup class supports:

• Custom colors for the grid, background color and selection color
• Adjustable horizontal and vertical spaces between images

Compatibility

This class is stand alone and doesn't need any particular Libraries except .NET default ones. It runs in managed code and hence should be portable.

How to use the Class

• First of all, copy ImageListPopup.cs in your project directory.
• Add on the top of your source code the directive using CustomUIControls;
• add a member variable in your class:

  ImageListPopup imageListPopup;

• In your constructor add the following lines:

  imageListPopup = new ImageListPopup();
  
  // facultative properties
  
  imageListPopup.BackgroundColor = Color.FromArgb(241,241,241);
  imageListPopup.BackgroundOverColor = Color.FromArgb(102,154,204);
  imageListPopup.HLinesColor = Color.FromArgb(182,189,210);
  imageListPopup.VLinesColor = Color.FromArgb(182,189,210);
  imageListPopup.BorderColor = Color.FromArgb(0,0,0);
  imageListPopup.EnableDragDrop = true;
  
  imageListPopup.Init(imageList,8,8,5,4);
  imageListPopup.ItemClick += new ImageListPopupEventHandler(OnItemClicked);
  

Details

imageListPopup.BackgroundColor = Color.FromArgb(241,241,241);
imageListPopup.BackgroundOverColor = Color.FromArgb(102,154,204);
imageListPopup.HLinesColor = Color.FromArgb(182,189,210);
imageListPopup.VLinesColor = Color.FromArgb(182,189,210);
imageListPopup.BorderColor = Color.FromArgb(0,0,0);

These properties allow us to customize the different colors of the ImageList Popup (see the picture below for details):

The properties must be set before calling Init(), otherwise they won't be taken into account.

imageListPopup.EnableDragDrop = true;

This property allows to Enable Drag'n'Drop support (default is false). You can drag a bitmap from the popup to any Drop target. A Bitmap object and a string containing the Id of the dropped image in the imagelist are available to the target.

imageListPopup.Init(imageList,8,8,5,4);

This line sets the image list, the horizontal and vertical pixel spaces between 2 images, and the rows and columns number (must be present).

imageListPopup.ItemClick += new ImageListPopupEventHandler(OnItemClicked);

This is the Event that is fired when an image is selected. The delegate should look like this:

private void OnItemClicked(object sender, ImageListPopupEventArgs e)
{
 label1.Text = "Selected Image: " + e.SelectedItem;
}

When you want to show the ImageListPopup, you just have to call:

imageListPopup.Show(x,y);

Technical issues

When Init is called, a pre-calculated bitmap is generated with all the static drawing (the background Color, the grid, and all the images)

public bool Init(ImageList imageList, int nHSpace, int nVSpace,
                 int nColumns, int nRows)
{
    _imageList = imageList;
    _nColumns = nColumns;
    _nRows = nRows;
    _nHSpace = nHSpace;
    _nVSpace = nVSpace;
    _nItemWidth = _imageList.ImageSize.Width + nHSpace;
    _nItemHeight = _imageList.ImageSize.Height + nVSpace;
    _nBitmapWidth = _nColumns * _nItemWidth + 1;
    _nBitmapHeight = _nRows * _nItemHeight + 1;
    this.Width = _nBitmapWidth;
    this.Height = _nBitmapHeight;


    _Bitmap = new Bitmap(_nBitmapWidth,_nBitmapHeight);
    Graphics grfx = Graphics.FromImage(_Bitmap);
    grfx.FillRectangle(new SolidBrush(BackgroundColor), 0, 0,
                                      _nBitmapWidth, _nBitmapHeight);
    for (int i=0;i<_nColumns;i++)
        grfx.DrawLine(new Pen(VLinesColor), i*_nItemWidth, 0,
                              i*_nItemWidth, _nBitmapHeight-1);
    for (int i=0;i<_nRows;i++)
        grfx.DrawLine(new Pen(HLinesColor), 0, 
                        i*_nItemHeight, _nBitmapWidth-1, i*_nItemHeight);
    
    grfx.DrawRectangle(new Pen(BorderColor), 0 ,0 , 
                               _nBitmapWidth-1, _nBitmapHeight-1);

    for (int i=0;i<_nColumns;i++)
        for (int j=0;j<_nRows ;j++)
            if ((j*_nColumns+i) < imageList.Images.Count)
                imageList.Draw(grfx,
                        i*_nItemWidth+_nHSpace/2,
                        j*_nItemHeight+nVSpace/2,
                        imageList.ImageSize.Width,
                        imageList.ImageSize.Height,
                        j*_nColumns+i);

    return true;
}

In the PaintBackground method, we blit the previously generated bitmap onto a hidden bitmap, then we draw the selection rectangle, and finally we blit everything to the screen with a basic double buffering technique.

protected override void OnPaintBackground(PaintEventArgs pea)
{
    Graphics grfx = pea.Graphics;
    grfx.PageUnit = GraphicsUnit.Pixel;
    
    // Basic double buffering technique

    Bitmap offscreenBitmap = new Bitmap(_nBitmapWidth, _nBitmapHeight);
    Graphics offscreenGrfx = Graphics.FromImage(offscreenBitmap);
    // We blit the precalculated bitmap on the offscreen Graphics

    offscreenGrfx.DrawImage(_Bitmap, 0, 0);

    if (_nCoordX!=-1 && _nCoordY!=-1 && 
       (_nCoordY*_nColumns+_nCoordX)<_imageList.Images.Count)
    {
        // We draw the selection rectangle

        offscreenGrfx.FillRectangle(new SolidBrush(BackgroundOverColor),
                                    _nCoordX*_nItemWidth + 1,
                                    _nCoordY*_nItemHeight + 1,
                                    _nItemWidth-1, _nItemHeight-1);
        if (_bIsMouseDown)
        {
            // Mouse Down aspect for the image

            _imageList.Draw(offscreenGrfx,
                _nCoordX*_nItemWidth + _nHSpace/2 + 1,
                _nCoordY*_nItemHeight + _nVSpace/2 + 1,
                _imageList.ImageSize.Width,
                _imageList.ImageSize.Height,
                _nCoordY*_nColumns + _nCoordX);
        }
        else
        {
            // Normal aspect for the image

            _imageList.Draw(offscreenGrfx,
                _nCoordX*_nItemWidth + _nHSpace/2,
                _nCoordY*_nItemHeight + _nVSpace/2,
                _imageList.ImageSize.Width,
                _imageList.ImageSize.Height,
                _nCoordY*_nColumns + _nCoordX);
        }
        // Border selection Rectangle

        offscreenGrfx.DrawRectangle(new Pen(BorderColor),
                                    _nCoordX*_nItemWidth, 
                                    _nCoordY*_nItemHeight,
                                    _nItemWidth, _nItemHeight);
    }

    // We blit the offscreen image on the screen

    grfx.DrawImage(offscreenBitmap, 0, 0);
}

Conclusion

I hope this code will be useful to you. If you have suggestions to enhance this class functionalities, please post a comment.

Updates

• 24/02/2003 : Initial Release
• 25/02/2003 : Added Keyboard support, Added Drag'n'Drop Support (disabled by default) - The selected Image and its Id are available to the drop target