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Image Viewer Single Item Mode

Summary

ImageViewer supports any number of items with multiple view layouts. However, some applications simply want to use the viewer with a single image and do not want to deal with setting up the layouts or dealing with the item collection. For these types of applications, ImageViewer offers the single item mode.

As described in Image Viewer Items, if there are items in the viewer, one of them is donated as the active item and from Image Viewer Layouts, the viewer supports the ImageViewerSingleViewLayout that displays a single item at the item - the active item. Therefore it is easy to setup the viewer to display a single item all the time:

// Get the div element for the viewer 
var div = document.getElementById("imageViewer"); 
// Create a single view layout 
var layout =  new lt.Controls.ImageViewerSingleViewLayout(); 
// Create the viewer, passing this layout 
var createOptions = new lt.Controls.ImageViewerCreateOptions(div); 
createOptions.viewLayout = layout; 
var imageViewer = new lt.Controls.ImageViewer(createOptions); 
// Add an empty item 
var item = new lt.Controls.ImageViewerItem(); 
imageViewer.items.add(item); 
// Now, ImageViewer.activeItem is item

This is exactly what happens when we pass null for ImageViewerCreateOptions.ViewLayout:

var createOptions = new lt.Controls.ImageViewerCreateOptions(div); 
createOptions.viewLayout = null; 
var imageViewer = new lt.Controls.ImageViewer(createOptions);

After the viewer is set up like this, it is easy to forget about the view layout and the items collection and just use the ActiveItem property to view images. Set an image into the viewer:

imageViewer.activeItem.image = myImage;

Or to remove the image:

imageViewer.activeItem.image = null;

To get its transform:

var transform = imageViewer.getItemImageTransform(imageViewer.activeItem);

Or to convert a point from image to control coordinate and back:

controlPoint = imageViewer.convertPoint(imageViewer.activeItem, lt.Controls.ImageViewerCoordinateType.image, lt.Controls.ImageViewerCoordinateType.control, imagePoint); 
imagePoint = imageViewer.convertPoint(imageViewer.activeItem, lt.Controls.ImageViewerCoordinateType.control, lt.Controls.ImageViewerCoordinateType.image, controlPoint);

In addition to using the ActiveItem property, the viewer also contains shortcut methods and properties that can be used in single item mode. The following is the same code as above using these shortcuts. Set an image into the viewer:

imageViewer.image = myImage;

Or to remove the image:

imageViewer.image = null;

To get its transform:

var transform = imageViewer.imageTransform;

Or to convert a point from image to control coordinate and back:

controlPoint = imageViewer.convertPoint(null, lt.Controls.ImageViewerCoordinateType.image, lt.Controls.ImageViewerCoordinateType.control, imagePoint); 
imagePoint = imageViewer.convertPoint(null, lt.Controls.ImageViewerCoordinateType.control, lt.Controls.ImageViewerCoordinateType.image, controlPoint);

With these properties/methods, you can use the ImageViewer control without touching any of the "view" or "item" property or methods. These shortcuts perform all the necessary check to make sure an active item is added to the viewer. For example, ImageViewer.Image get method is implemented like this:

if (this.activeItem != null) // Do we have an active item? 
   return this.activeItem.image; // Yes, return its image 
else 
   return null; // No, return null

And the set method:

if (this.activeItem != null) // Do we have an active item? 
   this.activeItem.image = value; // Yes, set its image 
// Else, nothing to do

The following table lists all the single item mode shortcuts and the equivalent internal code:

Shortcut	Equivalent
ImageViewer.Image	ImageViewer.ActiveItem.Image
ImageViewer.Canvas	ImageViewer.ActiveItem.Canvas
ImageViewer.ImageSize	ImageViewer.ActiveItem.Size
ImageViewer.ImageResolution	ImageViewer.ActiveItem.Resolution
ImageViewer.ImageUrl	ImageViewer.ActiveItem.Url
ImageViewer.BackImageUrl	ImageViewer.ActiveItem.BackImageUrl
ImageViewer.LoadImageUrlMode	ImageViewer.ActiveItem.LoadUrlMode
ImageViewer.BackImageLoadImageUrlMode	ImageViewer.ActiveItem.BackImageLoadUrlMode
ImageViewer.HasImage	ImageViewer.ActiveItem.Image or ImageViewer.ActiveItem.Canvas is not null
ImageViewer.ImageTransform	ImageViewer.GetItemImageTransform(ImageViewer.ActiveItem)
ImageViewer.GetImageTransformWithDpi	ImageViewer.GetItemImageTransformWithDpi(ImageViewer.ActiveItem, useDpi)
ImageViewer.Floater	ImageViewer.ActiveItem.Floater
ImageViewer.FloaterTransform	ImageViewer.ActiveItem.FloaterTransform
ImageViewer.ImageBounds	ImageViewer.GetItemViewBounds(ImageViewer.ActiveItem, ImageViewerItemPart.View, false)
ImageViewer.ConvertPoint, ImageViewer.ConvertPoints and ImageViewer.ConvertRect	Accept null as the item parameter to donate the active item

In addition to these shortcuts, the following are members used only when ImageViewer is used in single item mode:

Member	Description
ImageViewer.AutoResetOptions	Determines which transformation values to reset when a new image is set into the viewer.
ImageViewer.Reset	Reset the transformation values