Approach for doing animations in drawRect:(CGRect)

I am putting together a feed in a UITableView. I am adding a custom UIView to my UITableViewCells an开发者_如何学Pythond is drawing all the content of the cell in drawRect:(CGRect).

This works well, when a user taps a cell I expand the cell and drawRect:(CGRect) is called again by the UITableViewCell on the subview and everything is drawn to reflect this. This is great for performance, the UITableViewCell only consists of a single subview, with all content drawn directly into the CGContext.

Now that I am polishing the functionality of the feed I would like to add a few animations to make it more clear to the user what is happening.

I would like to do animations before, during and after the cell expands. the drawRect approach is a "one shot" way of doing it and I understand that the trade off is the same as the advantage, that you don't have a bunch of subview references that you can animate etc. How could I go about implementing animations?

Is there any delegate methods called on the subview when the cellHeight is changed that I can hook into. If I do so will I have to make subview "copies" of all the elements I need to animate, then animate them, remove them and redraw them in the context afterwards?

I am a bit afraid of going down a very wrong path and end up loosing performance and readability of the drawRect if I try to make conditional blocks for every thinkable event/animation that can be displayed.

Hope someone can point in the right direction. Thanks in advance.

When resizing your cell, do this to animate the cell resize process:

[tableView beginUpdates];
[tableView reloadRowsAtIndexPaths:... withRowAnimation:YES];
[tableView endUpdates];

Now your cell's drawRect: will be called for the duration of the animation, which you can measure and implement.

A problem might arise if a consistent framerate is not always achieved and you don't finish the animation.

I think a better solution is to use CALayers and animate your drawing there.