Developer's Guide - MapGuide Open Source - OSGeo

page, then emit a function containing the correct parameters. Use this
technique when you want the Viewer to change when the page loads.
■ Execute the JavaScript inside the script frame. Use this technique when
you want the Viewer to change as a result of an action in the MapGuide
page, without reloading the page.
■ Call the Viewer API during client-side interaction with the page or using
the Invoke Script command type in the web layout. Use this technique
when you want to call the API directly from the tool bar.
NOTE It is important to know the relationships between the frames. Pages in the
task area must refer to parent.parent.mapFrame in order to traverse the frame
hierarchy properly. However, if the same function executes from the script frame
or the task bar, it only needs to refer to parent.mapFrame, because the script
frame and the map frame are part of the same frame set.
Many Viewer API calls will generate requests to the site server, either to refresh
data in the Viewer or to notify the site server of a change in Viewer state.
These requests are generated automatically.
Calling the Viewer API from the Task Pane
Use this technique when you want the Viewer API calls to be made when the
page loads. For example, if you have a task in the task list that zooms the map
to a pre-defined location, then you do not need any user input. The Viewer
should zoom as soon as the page loads.
The map frame contains a JavaScript function to center the map to a given
coordinate at a given map scale. To call this function from a page loading in
the task pane, create a function that will be executed when the onLoad event
occurs. The following is a simple example. If you add this to the task list and
select the task, the displayed map will reposition to the given location.
14 | Chapter 1 Introduction