FBSOpenApplicationErrorDomain code =4 error

This worked for me:

iOS Simulator -> Reset Contents and Settings... -> Reset

https://i.stack.imgur.com/dFoKf.png

https://i.stack.imgur.com/OhjPb.png

referenced from Qiita: Unable to run app in Simulator エラーの対応方法.

Just closing the iOS Simulator worked for me.

There is not always the need to reset the iOS Simulator. I did not even had to close Xcode.

This happened to me once when I added some assets as symbolic links (through ln -sf). Even installing to devices was failing.

After I removed the links and made a hard copy, it worked and error was gone.

No need to quit the simulator or reset all content every time .

Just close the app on which you are working if running on background .

it works for me .

As mentioned in the Xcode release notes, this error (along with a couple others) results from a timing bug. The workaround is to just retry.

See https://developer.apple.com/library/prerelease/mac/releasenotes/DeveloperTools/RN-Xcode/Chapters/xc6_release_notes.html#//apple_ref/doc/uid/TP40001051-CH4-SW1

Testing on iOS simulator may produce an error indicating that the application could not be installed or launched. Re-run testing or start another integration.

Also see:

https://devforums.apple.com/thread/248879?tstart=0

I just quit the simulator , cleaned up the project and ran again it worked.

Just quit the xcode6.0 beta or else and run project again, it worked for me.

Reseting the Xcode will delete some bad junk which simulator has cached, so reseting is good option to resolve this issue.

iOS Simulator -> Reset Contents and Settings.

Be careful if you skip installs. I accidentally changed Skip Install on the main target, when i meant to change it on a dependency . When changing it back I had to do a clean.

This problem probably started after we enabled background mode in our app.My solution :

1) Go to simulator 2) Hold cmd + shift 3) Tap 'H' key two times 4) Slide the application off to stop it running in the background. 5) Run again.

(Very tiring to have to repeat the above step each time I build and run)

Open your app scheme setting and edit it as shown in attached screenshot, Actually you have to disable the "Launch Due to background fetch". Worked for me. Steps, 1. Select your target and select "edit scheme" 2. Select "Options" tab on right side of detail window 3. Uncheck "Launch Due to background fetch" checkbox.

Disconnect hardware keyboard. In ios simulator main menu Hardware -> Keyboard -> Disconnect Hardware keyboard.