Instruments - iOS Programming: The Big Nerd Ranch Guide - page 594

You've seen this information before, but after turning on Record reference counts , there is
much more of it. Each time the selected Line instance gained an owner, a Retain event
was added to this table. Each time the line lost an owner, a Release event was added to the
table. The RefCt column tells you the number of owners a Line has after that event. You
can click on a row to see the stack trace that caused that event.
Heapshot analysis
The last item we'll examine in the Allocations instrument is Heapshot Analysis . First,
clear the search box so that you aren't filtering results anymore. Then, find the Heapshot
Analysis category on the left side of the Instruments window and click Mark Heap . A cat-
egory named Baseline will appear in the table. You can click the disclosure button next to
this category to see all of the allocations that took place before you marked the heapshot.
Now draw more lines in TouchTracker and click Mark Heap again. Another category will
appear named Heapshot 1 . Click the disclosure button next to Heapshot 1 ( Figure 21.15 ).
Figure 21.15 Heapshot
Every allocation that took place after the first heapshot is in this category. You can see the
Line instances that you just created as well as a few objects that were used to handle oth-
er code during this time. You can take as many heapshots as you like; they are very useful
for seeing what objects get allocated for a specific event. Double-tap the screen in
TouchTracker to clear the lines and notice that the objects in this heapshot disappear.
To return to the full object list where we started, select the pop-up button in the bread-
crumb bar that currently says Heapshots and change it to Statistics .