Can I get the position of scrollbar in ui module?

In js https://stackoverflow.com/questions/2481350/how-to-get-scrollbar-position-with-javascript

mikael

@lpl, yes, check ui.ScrollView.content_offset.

@mikael And I need to set an action for it. Like preloading a book on web, when I scroll down, I check the position of scrollbar. And if I almost finish one page, I would preload the next page. Can I make that?

mikael

@lpl, ScrollView has a content_size attribute that you should set to the size of the content already displayed.

Then there’s ScrollView.delegate where you can define a scrollview_did_scroll method to react every time there’s scrolling. In that method you should compare scroll_offset y value + ScrollView.height to see if you are close to the content_size height value. If yes, add more content below existing content, and increase the content_size accordingly.

@mikael It is so strange since I can't change the content just like ScrollView.text. Must I use subview to show texts in ScrollView?

mikael

@lpl, yes. You can either use one that you grow by adding more text, or add separate pages as more views.

If your content is all text, you could of course use a TextView (with editable=False), but then you would need to use objc to access the scrolling logic.

@mikael I think maybe I can set Textviews as subviews of a Scrollview. But there is another problem. I shouldn't allow the scrollbars in Textviews to show out. So I need to adjust the size of Textview to different length of the text. Can I make it? It sounds so difficult.....

mikael

@lpl, how about you use Labels with number_of_lines set to 0?

There is another problem. We should pre-set some labels and then we find one label is out of the screen(can't be seen by users), we move the label to the end of the lable lists or to the beginning of them. But we need to know whether the scrollbar is coming up or coming down. How to get this attribute?

I found a way to check that. By using a value to record the old position and compare the old with the new one.

@mikael But another problem. The text could be very very long. But the content size of the Scrollview is limited (max=9999). What can I do to make it unlimited?

mikael

@lpl, maybe use reverse logic to adding new content. If you are down far enough, remove content from the beginning, move the remaining labels up and adjust scroll_offset so that this is not visible to user.

Then you need to implement the ”add content to top” logic as well.

Might be a performance problem there, but worth trying.

@mikael said:

@lpl, maybe use reverse logic to adding new content. If you are down far enough, remove content from the beginning, move the remaining labels up and adjust scroll_offset so that this is not visible to user.

Then you need to implement the ”add content to top” logic as well.

Might be a performance problem there, but worth trying.

I have made this. But the content size of a scrollview is limited. So if I have a long text, then I can't finish the text by using one scrollview.

mikael

@lpl, I think I understood. The idea was to not let the content grow beyond a specific limit, by removing content from the start and shifting the scroll position back up again, equal to the height of the removed content, thus creating the illusion of an infinite scroll with a constant amount of content.

You said you had implemented this. What went wrong?

@mikael Sorry, my English is not good. I mean I have made like 8 labels move up or down when I scrolled the scrollbar. But content size of the scrollview( http://omz-software.com/pythonista/docs/ios/ui.html#ui.ScrollView.content_size) is limited. This means the Scrollview is not infinite.

mikael

@lpl, please re-read my previous post. Note how we would NOT keep scrolling down, just making it look like it, thus no problem with a finite ScrollView.

@mikael I just find a way to make an unlimited content_size. By changing the size in the code.

JonB

I wonder if you'd rather use TableView instead of scrollview?

i dont think scrollview has a contentsize limit -- but if you are adding labels with text you might certainly reach a memory limit if you have 1000's of subviews!

TableView lets you be much more memory efficient, because the tableview cells are only created on demand.

@JonB We can break down the limitation in the code. And we can use several subviews. When we scroll, if one subview is hidden(can't be seen by users), then we can move the subview from the top side to the other side. So we don't need many subviews.

JonB

That is what tableview does for you already, plus you don't have to manage where the subviews go, just the order and number.