Multiple Image Sizes for ToolStrip Items

IconToolStrip_demo
IconToolStrip_src

Introduction

Tool strips are a fantastic asset because they provide a tidy and user-friendly interface for the user. It is possible to add images to many of the different tool strip items. It is even possible to force such items to appear larger by adjusting the property ImageScalingSize, however at the cost of pixelisation.
Usually it is desirable to make our applications as accessible as possible. Larger tool strip items are fantastic for those with poorer sight, or even those who just simply enjoy the quality of larger icons. Unfortunately, the standard ToolStrip class does not provide Icon support. When an icon is specified, it is converted into an Image instance. Thus the benefits of using an icon are lost.
So I decided that it would be a nice idea to add multi-image support to the ToolStrip control. Whilst my primary focus was on adding some support for Icon, I thought it more desirable to generalize this by using the two interfaces IImageProvider and IMultipleImageProvider.

Design

When MultipleImageToolStrip is being updated, it calls upon available IImageProvider‘s to acquire images of the required size.
An IImageProvider exposes the two methods IsImageSupported and GetImage. When multiple icon providers are available, it is possible to access the required icon using a key. In the code supplied with this article, the key represents a ToolStripItem. The following illustration provides an overview of the design using a UML class diagram.

When no IImageProvider is available, the original ToolStripItem is maintained and stretched where necessary to match the overall tool strip size.
For my extension, I decided that four discreet sizes would ease the implementation of custom image providers. The available sizes are: Small (16 x 16), Medium (24 x 24), Large (32 x 32), and ExtraLarge (48 x 48). When the requested image size is not available, a default icon can be automatically substituted if the MultipleImageToolStrip.UseUnknownImageSizeIcon is set to true.
Images are selected as follows:

• If an image provider is available from within the tool strip:
  • If the required image size is supported, that image is acquired.
  • If the required image size was not supported and UseUnknownImageSizeIcon is set, the default image provider is utilized.
  • When no image can be acquired using those criteria, the original image is simply stretched to match that of the scaled buttons.
• If the above fails and the item is itself an IImageProvider then it is used to acquire the required image.
• Finally if the items ToolStripItem.Tag is an IImageProvider then it is used to acquire the required image.

Using the Code

It is always a good idea to backup your project before trying something new!
To use the attached code simply:

• Add the source files to your project.
• Recompile your project.
• Drag MultipleImageToolStrip onto your Form or UserControl from the tool box.
• Add some buttons.
• You should now have a ToolStrip which behaves much the same as before.

If you want to convert an existing ToolStrip into a MultipleImageToolStrip:

• Find the “.designer.cs” file which is associated with your form or control.
• Open it up and replace instances of ToolStrip with MultipleImageToolStrip.

To make items automatically resizable, add a handler for your form’s (or control’s) Load event. Take a look below for an example of how to do this:

private void Form1_Load(object sender, EventArgs e)
{
    // Begin updating tool strip images. This is important because it prevents
    // the tool strip from refreshing after each image assignment.
    this.iconToolStrip.BeginUpdateImages();
    // Here it is possible to provide an 'IImageProvider' instance.
    this.iconToolStrip.AssignImage(toolStripBack, new IconImageProvider(
        Resources.arrow_left));
    // Or just provide icons themselves.
    this.iconToolStrip.AssignImage(toolStripForward, Resources.arrow_right);
    this.iconToolStrip.AssignImage(toolStripHome, Resources.home);
    this.iconToolStrip.AssignImage(toolStripStop, Resources.stop);
    // Finalize updating.
    this.iconToolStrip.EndUpdateImages();
    // Then to select an initial icon size.
    this.iconToolStrip.ImageSize = ImageSize.Medium;
}

When a tool strip item is permanently removed, the associated IImageProvider must also be manually removed. This decision was made because often an item is only removed temporarily and then reinserted.
If you always want to remove an associated IImageProvider when a tool item is removed, add a handler for the MultipleImageToolStrip.ItemRemove event:

private void iconToolStrip_ItemRemoved(object sender, ToolStripItemEventArgs e)
{
    // Automatically remove associated image provider.
    this.iconToolStrip.RemoveImage(e.Item);
}

Alternatively the associated provider can be removed along with the item:

public void RemoveToolStripItem(ToolStripItem item)
{
    // Remove item itself.
    this.iconToolStrip.Items.Remove(item);
    // Remove any associated provider.
    this.iconToolStrip.RemoveImage(item);
}