表格视图单元格可选-快速

Question

I have researched this question to no end but continue to struggle. I have seen the following code written as : cell.textLabel?.text when creating cells. Why is there a question mark only on textLabel and not text?

According to apple docs, textLabel is an optional property of type UILabel and text is an optional string, yet we only use one question mark? Why not two questions marks, one for each optional?

Answer 1

The textLabel of UITableViewCell is optional because the label can be missing when using a custom cell.

If you are using the standard cell with one of the 4 predefined styles textLabel is guaranteed to exist and you can safely unwrap the optional: cell.textLabel!.text

To answer the question the first question mark is required for Optional Chaining , any optional except the last item in a chain ( foo.bar.baz ) must be marked as optional or unwrapped. In case of the last item the compiler can "negotiate" a type match directly with the item across the equal sign.