no result by using SDK 1.3.13 and swift

Hi,
I completed some tests with success by writing code in a view controller but when I moved my code in a class (to be used in background) I have no result and no error.
Could you please help ? any suggestion ?
Many thanks
Sébastien

---

My previous code:

class ViewController: UIViewController, DBRestClientDelegate, NSXMLParserDelegate {
    private var dbRestClient: DBRestClient?     // dropbox rest client
     @IBAction func btconnect(sender: AnyObject) {
        if !DBSession.sharedSession().isLinked() {
            // should let use know why you are asking for dropbox permissions
            // now ask for permission
            DBSession.sharedSession().linkFromController(self)
            txtLogs.insertText("linked \n")
        }
        if dbRestClient == nil {
            dbRestClient = DBRestClient(session: DBSession.sharedSession())
            dbRestClient!.delegate = self
            txtLogs.insertText("dbRestClient \n")
        }
    }

    @IBAction func btList(sender: AnyObject) {
        txtLogs.insertText("Start List \n")
        dbRestClient?.loadMetadata("/myFolder/")
        txtLogs.insertText("End List \n")
    }

    func restClient(client: DBRestClient!, loadedMetadata metadata: DBMetadata!){
        if (metadata.isDirectory) {
            println("Folder \(metadata.path) contains: \n")
            txtLogs.insertText("Folder \(metadata.path) contains: \n")
            for FILE in metadata.contents {
                println(" \(FILE.filename) \n")
                txtLogs.insertText(" \(FILE.filename) \n")
            }
        }
    }
    func restClient(client: DBRestClient!, loadMetadataFailedWithError error: NSError!){
        println("loadedMetadata failed with error: \(error)")
        activityIndicatorView.stopAnimating()
    }

....

My new code:

import Foundation

class Cloud : NSObject, DBRestClientDelegate{
    private var dbRestClient: DBRestClient?     // dropbox rest client

    func DownloadMain() -> Bool{
        var myResult : Bool = false
        ConnectToDropBox()
        dbRestClient?.loadMetadata("/myfolder/")
return myResult
    }

    func ConnectToDropBox() {
        if !DBSession.sharedSession().isLinked() {
            // should let use know why you are asking for dropbox permissions
            // now ask for permission
            DBSession.sharedSession()//.linkFromController(self)
        }
        if dbRestClient == nil {
            dbRestClient = DBRestClient(session: DBSession.sharedSession())
            dbRestClient!.delegate = self
        }
    }

    func restClient(client: DBRestClient!, loadedMetadata metadata: DBMetadata!){
        if (metadata.isDirectory) {
            println("Folder \(metadata.path) contains: \n")
            for FILE in metadata.contents {
                println(" \(FILE.filename) \n")
            }
        }
    }

    func restClient(client: DBRestClient!, loadMetadataFailedWithError error: NSError!){
        println("loadedMetadata failed with error: \(error)")
    }