[android-developers] How to implement a multi-direction scrollable view for potentially large content
Hello,
I'm working on a document viewer which would display all the pages of the document laid out vertically - allowing the user to scroll within the document. If the user zooms in using pinch, the pages would zoom - now the user would be able to scroll in all directions.
I am considering a couple of options for the implementation:
1. Implement a custom View
- Handle scrolling in all directions by a) setting the scroll bounds (override the computeHorizontal/VerticalScrollRange) and b) calling the View's scrollBy(x, y) API to scroll in all directions.
- Handle drawing by overriding onDraw and drawing the page content in this callback.
The drawback is this approach doesn't take advantage of View Layout to handle the pages - laid out vertically with some gaps between them. That would be need to be handled manually by actually drawing gaps too along with page content in the onDraw callback.
2. Add Views to a multi-direction scrollable View
- Implement a custom View which allows multi-direction scrolling (similar to ScrollView, but allows horizontal and diagonal scrolling too)
- Add children (representing pages) to this scrollable View.
- How should I manage the memory taken up by these Views? Since the number of pages could potentially be very large and the size of each View could be large (after zoom), the backing Bitmap memory could be extremely large.
3. Similar to 2, but doesn't use a drawable View for pages
- Use the multi-directional scrolling View as above.
- Instead of adding Views capable of drawing to this scrollable view, use a non-drawing View like a RelativeLayout for each page instead. To each Layout, add smaller Views (could be ImageViews). Handle these manually by removing Views that are not visible. Since the backing Bitmaps would be created for the smaller ImageViews, the memory requirements should be manageable.
If folks have any suggestions/feedback regarding the approaches mentioned above, or any other solutions, that would be very helpful.
Thanks in advance.
-- I'm working on a document viewer which would display all the pages of the document laid out vertically - allowing the user to scroll within the document. If the user zooms in using pinch, the pages would zoom - now the user would be able to scroll in all directions.
I am considering a couple of options for the implementation:
1. Implement a custom View
- Handle scrolling in all directions by a) setting the scroll bounds (override the computeHorizontal/VerticalScrollRange) and b) calling the View's scrollBy(x, y) API to scroll in all directions.
- Handle drawing by overriding onDraw and drawing the page content in this callback.
The drawback is this approach doesn't take advantage of View Layout to handle the pages - laid out vertically with some gaps between them. That would be need to be handled manually by actually drawing gaps too along with page content in the onDraw callback.
2. Add Views to a multi-direction scrollable View
- Implement a custom View which allows multi-direction scrolling (similar to ScrollView, but allows horizontal and diagonal scrolling too)
- Add children (representing pages) to this scrollable View.
- How should I manage the memory taken up by these Views? Since the number of pages could potentially be very large and the size of each View could be large (after zoom), the backing Bitmap memory could be extremely large.
3. Similar to 2, but doesn't use a drawable View for pages
- Use the multi-directional scrolling View as above.
- Instead of adding Views capable of drawing to this scrollable view, use a non-drawing View like a RelativeLayout for each page instead. To each Layout, add smaller Views (could be ImageViews). Handle these manually by removing Views that are not visible. Since the backing Bitmaps would be created for the smaller ImageViews, the memory requirements should be manageable.
If folks have any suggestions/feedback regarding the approaches mentioned above, or any other solutions, that would be very helpful.
Thanks in advance.
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