iPhone Simulator suddenly started running very slow

Question

I have been working on an app in iphone simulator for a number of weeks and it has been running well up until now, but all of a sudden has begun running very slow both when

Answer 1

Select Simulator,

Select Debug and uncheck slow animation.
shortcut command + t

That's work for me.

Answer 2

Go to the simulator's Debug menu and select "Toggle Slow Animations".

Update: In Xcode 10, it's just "Slow Animations":

Answer 3

You accidentally pressed the slow animation on debug when using simulator. So Run Simulator -> Debug -> Uncheck Slow Animation.

Answer 4

I think you pressed command + T instead of command + R by mistake.

Answer 5

Another potential fix for React-Native users:

Chrome de-prioritizes Javascript running in any tabs not in the foreground. So if you have enabled remote debugging, be sure to put the debugger in its own window.

Answer 6

If the Cmd-T (slow animations) option doesn't work for you and Debug -> Slow Animations is off but you still have slow animations try Simulator -> Reset Contents and Settings (or possibly Hardware -> Erase All Content and Settings). That worked for me when none of the other answers in here did. Anyone have a suggestion as to why?

Also having a debugger attached (at all) may make the animations very slow.