Miscellaneous issues

Last Updated: 9/12/2007

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Custom Component Development
Developing components in Delphi
Miscellaneous issues
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Templates

When a form has a template, then it is valid to not have a tag for one or more controls of the form. The missing controls just won't get rendered.

An IWForm renders all its controls by calling RenderHTML(), before the HTML template is processed and applied. The problem is now, that if a control issues JavaScript (in RenderHTML via AddToInitProc() for example), which relies on the fact that the control exists, this code will of course fail (throw an exception) under the condition described above.

To avoid these exceptions we recommend to do something like this:

example from IWTreeview.RenderHTML():

...
//This add every item via JavaScript to the TreeView
LScript := iif(FContext.WebApplication.IsPartialUpdate, 'window.parent.')
+ HTMLName + 'IWCL.Items = ' + EOL + BuildAddition(nil) + ';' 
+ EOL
+ iif(FContext.WebApplication.IsPartialUpdate, 'window.parent.')
+ 'InitTreeView('+ 
iif(FContext.WebApplication.IsPartialUpdate, 'window.parent.') + 
HTMLName + 'IWCL, "' + HTMLName + 'Container");' + EOL;

//if used with HTML template, the control might not be created at all
LScript := 'if (' + HTMLName + 'IWCL){' + LScript + '}';
...
FContext.AddToInitProc(LScript)
...

The line in blue basically wraps the whole JavaScript in an if-block, which checks the existence of the control first. At this point (RenderHTML) there is no way to tell if the control would be handled by a possibly attached template - unfortunately.