My Swift strings cheatsheet

The Swift strings support representing Unicode strings natively. As such it is no longer possible to have random access inside the string because some characters might be represented on more than one byte.

I always forget how to do basic things so I put together a cheatsheet that might be useful to others too.

Counting characters



Iterating through the string characters


Indexes inside the string


Is string contained in another string


Split a string by separator, iteratively



Split a string by separator, recursively


Fix UITabBar icon images as alpha-channel

Apple asks that your UITabBar icons be pure alpha-channel images with added anti-alias. That means that usual RGB channel images will just show as a blue square.

So how to go from a normal RGB channel image to a pure alpha-channel. I use Photoshop and there is probably┬ámore than one way, but what works best for me is creating a “Gradient map” adjustment layer.

To create a gradient map adjustment layer go to the “Layers” tab and click “Create fill or adjustment layer…” like below.

Screen Shot 2016-01-31 at 18.50.15

Afterwards save your image and all should be fine.

Fix putty garbled text after window resize

So you resized your putty window. When going through history, if there are lines which are longer than 80 chars, the default putty window, then just going through the will show the text garbled.

The fix is simple: tell the terminal the new window size. Arguably this should be automatically done by putty, but hey, there’s a workaround. Checkout the stty command.

Pass the cols parameter to specify the new width of the window in columns.

Find your home directory in the iPhone simulator

This is huge.

Start your application, then “Debug/Pause” it.

Then type this magic into your lldb console (the debugging pane should be at the bottom of the Xcode window).

Your debugger console should now show the local directory where your application has its home.

WatchKit simulator displays spinner, willActivate is not called

So you developed your first WatchKit app, except when you’re testing it in the simulator all it does is display the spinner.

iOS Simulator Screen Shot - Apple Watch 06 Apr 2015 11.19.35

More over, method willActivate from WKInterfaceController is never called. That means the app is never displayed on the watch for the user to see. It’s as if the display was locked.

In my experience there is nothing wrong with the app, might be just small bugs that will be fixed in the later versions of XCode/simulator. You can force display on the watch. With the Simulator in focus go to menu “Hardware” and choose “Lock”. At this time your phone/watch is locked. Now, do the same thing “Hardware” then “Lock” and unlock the phone by dragging on the screen. Method “willActivate” should no be called and your app screen will be displayed on the watch display.

Push segue from button doesn’t work

First of make sure your source controller is embedded inside a navigation controller, otherwise push segues don’t work.

But, in my case, even after that clicking the button wouldn’t change the view. What I discovered is that messed up auto layout constraints can do that. If in doubt remove all your constraints and try your segue like that.

Navigation bar pushes view down

I came across recently a problem where I had a UITableView just below the navigation bar of a UINavigationController. Even though they aligned perfectly in the storyboard, the simulator showed the table view as if pushed down with the exact size of the UINavigationBar.

The solution was to uncheck “Translucent” checkbox in the “Navigation bar”

Screen Shot 2014-11-01 at 19.29.52 copy