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Is there any way to check whether an app explicitly supports Lion's new Resume feature or not? For example, as of right now, Safari supports Resume, meaning all the tabs are reopened, however in Google Chrome, this is not the case.

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Most "Lion-Ready" apps will also support the new full-screen mode, so if you see the little full screen button, it is likely the application will also support Resume. However, there is no definitive list that I am aware of yet, nor is there a way (beyond a mention in the app's documentation) of knowing whether it will support Resume.

However, there is now a list of "Enhanced for Lion" apps on the appstore which might be a good place to start.

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Activity monitor has a column with yes/no for apps that support sudden termination which should be a good proxy for resume functionality.

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Sudden termination and resume is quite different, but yes, it could be an indication of whether Resume is supported. – JFW Sep 11 '11 at 19:42
You are totally correct @JFW - they are separate and have distinct implementation steps to exist in software. If a developer is inclined and able to do one just makes it more likely the other could be there even though it doesn't have to be so. – bmike Sep 11 '11 at 20:45
It's worth mentioning that an app that supports sudden termination may show a "no" in Activity Monitor if the app is actively doing something or possibly even if it has a document open. – joelseph Sep 13 '11 at 2:21

The combination of bmike & lemonginger's answers may be better than either one alone.

bmike is referring to a developer API that was added in Mac OS 10.6 (and therefore may not be a perfect proxy for the full resume support).

From Apple's developer documentation:

Mac OS X v10.6 includes a new mechanism that allows the system to log out or shut down more quickly by, whenever possible, killing applications instead of requesting that they quit themselves.

(You may need a developer account to view this document. I'm not sure.)

He suggests it because support for "sudden termination" is a prerequisite for Lion resume support. As bmike suggests this makes it a reasonable proxy for support even if it is not a guarantee of support.

leonginger's is basically suggesting that an application that has been updated in any way for Lion is more likely to include resume support. This is a faulty assumption on its own but becomes more powerful when combined with bmike's suggestion.

Logic: if an application has obvious signs of having been updated for Lion (such as fullscreen support) AND the application has support for sudden termination the chances are quite high that that application supports resume.

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Perhaps the presence of Quit and Discard Windows... in the file menu when holding the Option key down is the only canonical way to determine which running apps support resume. – bmike Sep 11 '11 at 20:49

The new (in 10.7) NSWindowRestoration protocol is the entry point for restoring windows. Due to Objective-C's dynamic nature, it won't be a perfect test, but there's probably a very good correlation between an application containing a reference to this symbol, and that application supporting Resume.

$ grep NSWindowRestoration "/Applications/QuickTime Player"
Binary file /Applications/QuickTime Player matches
$ grep NSWindowRestoration "/Applications/Photo Booth" 

If this symbol is present, it means the programmer at some point in the program at least mentioned the name of the new API which is only used for Lion Resume. This isn't a guarantee of anything (it could even be a string that says "I don't support NSWindowRestoration yet, sorry"!), but it's good circumstantial evidence.

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open the app, open a generic new file and hit command+Q. then relaunch the app. does it re-open the previous file? then if it's been updated in the last 2 months it supports lion's resume.

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In short, it appears that most document-based apps will work with Resume, and non-document-based apps (such as web browsers and terminals) probably (or at least possibly) will not work with Resume.

Even old apps such as Photoshop CS4 and Word 2008 will have their documents reopened with Resume in Lion. Apps such as Safari and Terminal indicate that non-document-based apps can be developed to explicitly use features of Resume.

I've tried a variety of document-based apps, old and new, and they've all worked with Resume to have their documents reopened. I've also tried Chrome, Firefox, Opera and iTerm2, and none of them work with Resume.

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