xcode - ioS Swift: Unexpectedly found nil while unwrapping optional value -

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while trying read contents of file var:

var mytext = "" ... println(downloadfilepath) mytext = string(contentsoffile: downloadfilepath, encoding: nsutf8stringencoding, error: nil)!

i error: unexpectedly found nil while unwrapping optional value

the file present, , generated earlier. size , contents of file may vary @ each run. same code works sometimes.

could size of file (21k) or contents - cause this?

trust me, compiler. know i'm doing. i'm taking off seatbelt , helmet.

that's tell compiler when use force-unwrap operator, !, or deal "implicitly unwrapped optional" type such string!. avoid @ costs. try restructuring code this:

assert(nil != (downloadfilepath string?)) var error: nserror? = nil if let mytext = string(contentsoffile: downloadfilepath, encoding: nsutf8stringencoding, error: &error) {     println("contentsoffile called successfully!")     println("mytext: \(mytext)") } else {     println("i should implement error handling. happened? \(error)")     assertionfailure("until have ui telling user fail, let's visit debugger.") }

there 2 techniques in here use keep code happy:

  • use assertions , preconditions. crash @ earliest sign of unrecoverable failure. dead program lot less damage crippled one, quoth pragprog tips. assertions serve executable documentation: if assert state, next programmer reading code can reason possible states in method.

  • until world entirely safe nil (which isn't if you're using foundation or introduce ! force-unwrap code), may find nil in non-optional types error shows. if suspect this, turn non-optional optional , check it. threw few examples of how can deal these sneaky nils. combine these assertions around method calls don't express contracts in signatures.


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