iOS/Swift - Accessing shared DB using App Groups

Question

I use App Groups Capability to share a SQLite DB between two Apps.

Now i want to migrate to Swift from Objective-C.

To obtain the path of DB, in Objective-C i've

NSFileManager *fileMgr = [NSFileManager defaultManager];

NSURL *groupContainerURL = [fileMgr containerURLForSecurityApplicationGroupIdentifier:@"<APP_GROUPS_ID>"];

NSString *groupContainerString = [groupContainerURL path];

NSString *sharedDB = [groupContainerString stringByAppendingPathComponent:dbFilename];

const char *dbPath = [sharedDB UTF8String];

and it works.

In Swift i've tried this way

let groupContainerURL = fileMgr!.containerURL(forSecurityApplicationGroupIdentifier: "<APP_GROUPS_ID>")

let groupContainerString = groupContainerURL.path

pathToDatabase = groupContainerString.appending(databaseFileName)

and i've declared also

let databaseFileName = "<DB_NAME>"

var pathToDatabase: String!

var fileMgr : FileManager!

But i've this error, about Optional Value

fatal error: unexpectedly found nil while unwrapping an Optional value
2017-07-24 11:25:09.086974 CatchTheData[7941:4022839] fatal error: unexpectedly found nil while unwrapping an Optional value

at the start.

Where i wrong?

Answer 1

Runtime exception: unexpectedly found nil while unwrapping an Optional value, occurs:

1. when you unwrap an optional that contains nil OR
2. when you use an implicitly unwrapped optional without assigning a value to it.

In the following lines:

var pathToDatabase: String!
var fileMgr : FileManager!

make sure you have assigned value to pathToDatabase and fileMgr before using them. Since these 2 variables are implicitly unwrapped optionals, so in case you use them without assigning values, it will result in runtime exception similar to unexpectedly found nil while unwrapping an Optional value.

let groupContainerURL = fileMgr!.containerURL(forSecurityApplicationGroupIdentifier: "<APP_GROUPS_ID>")

In the above line of code, you are using fileMgr!. First of all no need to unwrap it. It is implicitly unwrapped. Just make sure fileMgr has value so that the app won't crash.