C ++ Viewport缓存目录中的文件

Question

In my C++ app, I have a table widget used to display a list of files in a directory. There is enough screen real estate to display ~20 files at a time. It is wrapped around a viewport so the user can scroll up and down to navigate to other files in the list.

Each file in the list contains metadata of arbitrary size which is cached in a background thread. Attempting to cache all files in a directory containing lots of metadata rich files quickly hoovers up available memory on the heap, with severe consequences.

Of course, I don't need to cache all the files at once; only those that are visible. It would also be nice if those files containing metadata immediately above/below the viewport bounds were cached, so that scrolling up and down wouldn't incur too much of a delay.

I guess this is related to a problem that many UI applications containing viewports (web browsers, text/ hex editors) have to solve. Are there any patterns, algorithms or containers ( deque springs to mind) that would help in solving this problem?

Thanks!

Answer 1

If your data is in eg a std::vector , then you can have a first_visible and last_visible variables that are indexes into the vector. The items in the vector between those two (inclusive) will be the ones you need to cache (plus X extra on each side).

Whenever the user changes the UI element to display new items, those indexes are updated, and new data is loaded if needed.

Answer 2

您可以查看Flyweight和Proxy设计模式。