Salesforce API global variable in a visualforce page

In salesforce custom links, a user can reference the salesforce session ID by using the API global variable, like so: {!Api.Session_ID}

I have a visualforce page that needs this variable, but it doesn't seem to recognize it. The error message says to create the 开发者_开发问答apex property 'api' in the page's custom controller.

This is my desired use of it: My link

How can I achieve this?

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Your issue is easily sorted, global variables are prefixed by $ so what you actually want is

{!$Api.Session_ID}

What you are asking for current is the controller to call a getApi method which would return an object containing a field called Session_ID. It's the $ that lets SFDC recognise a global variable and not a controller method.

Paul