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Figure 10.8 This figure shows the various measurements used to calculate a list item s width and height.
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The following steps implement the code required for the MeasureItem event. Figure 10.8 illustrates the various measurements used to determine the width and height of the item.
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CALCULATE THE LIST ITEM SIZE DYNAMICALLY Action 1 In the MainForm.cs window, add a static Rectangle to the MainForm class to hold the drawing rectangle for the image. Add a MeasureItem event handler for the lstPhotos list box. Calculate the size of the image when scaled into the drawing rectangle. Calculate the item s height. Calculate the item s width.
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Result
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private static Rectangle _drawRect = new Rectangle(0,0,45,45);
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private void lstPhotos_MeasureItem (object sender, Windows.Forms.MeasureItemEventArgs e) { Photograph p = _album[e.Index]; Rectangle scaledRect = p.ScaleToFit(_drawRect); e.ItemHeight = Math.Max(scaledRect.Height, lstPhotos.Font.Height) + 2; e.ItemWidth = scaledRect.Width + 2 + (int) e.Graphics.MeasureString( p.Caption, lstPhotos.Font).Width;
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For the item s height, this code uses the larger of the scaled item s height and the ListBox control s font height, plus 2 pixels as padding between subsequent items in the list.
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e.ItemHeight = Math.Max(scaledRect.Height, lstPhotos.Font.Height) + 2;
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For the item s width, the width of the scaled image plus the width of the drawn string is used, plus 2 pixels as padding between the image and the text. To do this, the OWNER-DRAWN LISTS 347
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Graphics.MeasureString method is used to calculate the size of the string when drawn with the Font object used by the ListBox control.
e.ItemWidth = scaledRect.Width + 2 + e.Graphics.MeasureString(p.Caption, lstPhotos.Font);
Our final task is to draw the actual items using the DrawItem event. 10.5.3 DRAWING THE LIST ITEMS As you may recall, the DrawItem event and related DrawItemEventArgs class were discussed in chapter 4. See .NET Table 4.4 on page 119 for an overview of the DrawItemEventArgs class. Before we look at how to draw the list items in our application, let s make a small change to the Photograph class to improve the performance of our drawing. Since we may have to draw an item multiple times, it would be nice to avoid drawing the thumbnail from the entire image each time. To avoid this, let s create a Thumbnail property in our Photograph class to obtain a more appropriately sized image.
Set the version number of the MyPhotoAlbum library to 10.5. STORE A THUMBNAIL IMAGE IN THE PHOTOGRAPH OBJECT Action 1 In the Photograph.cs file, create an internal _thumbnail field to store the new thumbnail image. Update the Dispose method to properly dispose of the new object. Result
. . . private Bitmap _thumbnail = null;
public void Dispose() { if (_bitmap != null && _bitmap != InvalidPhotoImage) _bitmap.Dispose(); if (_thumbnail != null) _thumbnail.Dispose(); _bitmap = null; _thumbnail = null; }
Add a static constant to store the default width and height for a thumbnail.
private const int ThumbSize = 90;
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STORE A THUMBNAIL IMAGE IN THE PHOTOGRAPH OBJECT Action 4 Add a property to retrieve the thumbnail. Note: While we draw our list items into a 45-pixel box, we draw our thumbnail into a 90-pixel box. Aside from the fact that we might want to use the Thumbnail property in other code, it is beneficial, when downsizing an image, to have an original image with a higher resolution than the final size. Result
public Bitmap Thumbnail { get { if (_thumbnail == null) { // Create the "thumbnail" bitmap Rectangle sr = this.ScaleToFit( new Rectangle(0,0, ThumbSize,ThumbSize)); Bitmap bm = new Bitmap(sr.Width, sr.Height); Graphics g = Graphics.FromImage(bm); GraphicsUnit u = g.PageUnit; g.DrawImage(this.Image, bm.GetBounds(ref u)); _thumbnail = bm; } return _thumbnail; } }
This ensures that we will not have to load up and scale the full-size image every time we draw an item. With this property in place, we have everything we need to draw our list items.
HANDLE THE DRAWITEM EVENT TO DRAW A LIST ITEM Action 5 Add a static Brush field to the MainForm.cs file. Result
private static SolidBrush _textBrush = new SolidBrush(SystemColors.WindowText);
Note: This will improve the performance of our handler by eliminating the need to recreate a brush each time an item is drawn. 6 Add a DrawItem event handler for the ListBox control. To implement this method, get the Graphics and Photograph objects required for this handler.
private void lstPhotos_DrawItem (object sender, System.Windows.Forms.DrawItemEventArgs e) { Graphics g = e.Graphics; Photograph p = _album[e.Index];
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