wordpress - how to get php variable in page from sidebar

I wrote my own custom page template for my Wordpress page, now I want to change sidebar.php to insert a sm开发者_开发知识库all menu whenever that page template is loaded.

// sidebar.php
if ( isset($event_name) ) {
  // do something
}

But apparently sidebar.php doesn't recognize variable $event_name.

How do I come about solving this?

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While I'm not familiar with the way WordPress implements templates, have you tried declaring the variable global in the sidebar page?

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See: Function Reference/is page template « WordPress Codex to be able to detect page template in use.