Internet Explorer 5.5 Demos : Edit Host (IE 5.5)

Description:IHTMLEdit Host provides a way to control how elements are resized and moved when the user grabs and drags the handles on a control element. For instance, you could cause an element to resize or move by specific increments (a snap-to-grid feature), limit resizing to a minimum or maximum size, or constrain the area to which an element can be moved. The use of IHTMLEditHost is limited to applications hosting MSHTML or the WebBrowser control. IHTMLEditHost cannot be used with binary behaviors or rendering behaviors.

More Details
Whenever the MSHTML Editor is activated, it looks to see if an IHTMLEditHost is available. The Editor first asks the host application for an IServiceProvider interface. If it finds IServiceProvider, it will query for an IHTMLEditHost interface pointer.
IHTMLEditHost acts like a callback routine. The MSHTML Editor holds a pointer to an IHTMLEditHost interface (with which you provide it) and calls IHTMLEditHost's one method, IHTMLEditHost::SnapRect, whenever the user resizes or moves a resizable/moveable element in the editing environment. When the MSHTML Editor calls IHTMLEditHost::SnapRect, the method's arguments will tell you which element is being resized, the original size and position of the element, and which handle the user has grabbed. You have the ability to control the size and position of the element when the user releases the handle.

The IHTMLEditHost interface will remain active until the Editor is turned off or the WebBrowser navigates to a new page. At this point, the Editor releases its pointer to any IHTMLEditHost interface it holds.

The sample for this tutorial implements a snap-to-grid feature using IHTMLEditHost. It demonstrates the important features that IHTMLEditHost provides, and offers implementation details to consider:

How you can tell which element is being resized and moved, determine the selected element's current position and size, and know which handle the user has grabbed.
How you can change the element's current position and size.
How and when MSHTML calls IHTMLEditHost's SnapRect method.
How to implement the IServiceProvider interface needed to give the MSHTML Editor a pointer to your IHTMLEditHost interface implementaton.
How you can deactivate and reactivate the IHTMLEditHost interface. This sample is a simple browser implementation with an address bar, five buttons, and a combo box. The specifications are as follows:

The first button turns the MSHTML Editor on and off.
The second button turns the snap-to-grid feature on and off.
The third button turns a red dashed grid on and off, so you can see how element resizing and movement is constrained to a specific increment when the snap-to-grid feature is turned on.
The combo box holds the snap and grid increment, which can be changed.
The fourth button turns two-dimensional positioning on and off. The fifth button turns live resizing on and off.
Browser/Platform Compatibility
The EditHost sample requires Microsoft Internet Explorer 5.5 or later on the Win32 platform. For developers, header and library files for Internet Explorer 5.5 or later are needed for use in your development environment; in particular, Mshtml.h is necessary.

Note You must download the sample to your own computer to run it. The source code for this sample is included in a Microsoft Visual C++ 6 workspace. It uses ATL to provide COM support, standard implementations of some of the standard interfaces, and "smart" interface pointers that handle their own reference counting. You can use this sample as a structure for building your own implementations of IHTMLEditHost.

Note: You will need to include the Windows 2000 Headers and Libraries from the Platform SDK in your development path when building this sample.

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