When Xcode is debugging, the value of the variable is not displayed and the PO is not out.

First check whether the scheme of operation is release or Debug. Check the optimization level in the targets build settings of the project where debug is usually none, so that all the information can be output. Finally, check a more easily overlooked place, in the scheme of the run in the location of the debug diagnostics to see all the options, should not select all. It is usually easy to make mistakes in the Enable Zombie Objects. The selection of this item will result in some variables being lost.