NSTextAttachment is somehow caching the image. Any ideas about how?

Question

When creating a NSAttributedString from an HTML string which contains an image link (https), somehow the downloaded image is cached. How did I came up with this fact?

Install app.
Open the app. Image is there.
Close the app (terminate). Go for Airplane mode.
Open the app. Image is still there.
Delete the app completely, and reinstall.
Open app while still in airplane mode. No image.

Caching the image is actually what I want. But I want to know deeper, how and where the image is cached. Since my app should work offline, I have to be sure that the image is cached or not. I dig into the docs and couldn't find anything. Can someone enlighten me? Thank you.

EDIT to clarify:

I am not using NSTextAttachment directly. I'm initializing NSAttributedString from a String, using UTF8 encoded data. Why I am talking about NSTextAttachment is I guess its automatically creating an NSTextAttachment for "img" tags in the HTML String.

No. I'm using an NSAttributedString, a String which contains HTML and an UITextView. But I guess its automatically creating an NSTextAttachment from "img" tag to display the image. Am I wrong? — Arda Oğul Üçpınar, Jan 14 '18 at 00:16

score 0 · Answer 1 · answered Jan 14 '18 at 00:20

0

As the docs don't state that the images will be cached, it's best to assume that there is no caching. Therefore, the best solution to your situation is to download the file with URLSession and store the file on disk, so when the device is offline, the image can be displayed.

answered Jan 14 '18 at 00:20

Papershine

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Actually while NSAttributedString doing all the job in a single line (e.g. parsing HTML, getting image link from HTML, downloading it and somehow caching it (I believe it does! Maybe I want to believe :) )) doing all of these manually is not wise :( – Arda Oğul Üçpınar Jan 14 '18 at 00:26
please see the below answer. Image is really cached. – Arda Oğul Üçpınar Jan 14 '18 at 00:52

score 0 · Answer 2 · answered Jan 14 '18 at 00:51

Some digging into the simulator data proved that my image is really cached.

/Users/<username>/Library/Developer/CoreSimulator/Devices/<simulator-id>/data/Containers/Data/Application/<app-id>/Library/Caches/<app-bunle-identifier>/Cache.db file is a SQLite file holding the cache info. And there is my image, with its link and its data.

Its odd that Apple didn't documented this, and I still don't know how / when it caches.

NSTextAttachment is somehow caching the image. Any ideas about how?

2 Answers2