Have UITableViewCell resize itself with autolayout

问题:

I have 3 labels in a UITableViewCell and have the labels set so they will wordwrap. If they word wrap the text goes into the next cell. How do I get AutoLayout to expand the cell based on the content without having to write code in the heightForRowAtIndex method? Isn't there a constraint I can use to automatically adjust the cell based on the contentView?

The cell looks fine if the text doesn't wrap in the label. Once it wraps that is when the problem occurs and I would like to have the cell resize to fit the content and have the same spacing between the bottom label and the bottom as there is between the top and top label.

回答1:

Unfortunately no, you can't do this. A table view calculates its own total height first and has a fixed idea of the size of each cell as they load, it won't determine it's height from the outside in and it won't let layout constraints change the height of a cell.

If you think about how tables work, with cell reuse, then you couldn't really size the table from its cells without loading in every cell and adding it to the scrollview, and performing a layout pass on the whole thing. That would probably lead to quite poor performance.

You could experiment with populating a "free" cell (i.e a cell you've just instantiated, not added to a table) and laying it out for each row in your datasource when calculating heightForRow.

回答2:

As you are loading the individual cells, after you fill the labels, but before you load the instance of the cell, check the label height.

 Something like:
     cell.frame.size.height

If the height is large enough that you know the label has wrapped to two lines, then increase the height of the cell you are about to load.