Open Url with UIImage

In Swift you can validate with isEmpty and show a UIAlertView ():

if (textField.text.isEmpty) {
                let alert = UIAlertView()
                alert.title = "Error"
                alert.message = "No existe url definida"
                alert.addButtonWithTitle("Ok")
                alert.show()
}

Using Swift 2.0, if:

if let urlImagen = textField.text where textField.text.isEmpty {
    // crea UIAlertView()
}

Swift 2.0, guard:

guard let urlImagen = textField.text where textField.text.isEmpty else {
    // crea UIAlertView()
    return
}

To load an image url into a UIImage , this is a example:

if let url = NSURL(string: "http://www.mydominio.com/myimagen.jpg") {
  if let data = NSData(contentsOfURL: url) {
     imageURL.image = UIImage(data: data)
  }        
}

Very simple ... check if the url field of your data is empty and if so use a UIAlertView, if you want with a delegate = nil, something like this:

if miUrl.isEmpty {
    let alert = UIAlertView("Aviso!!!", message: "Mmmm, no tengo url!", delegate: nil,
                            cancelButtonTitle: "OK")
    alert.show()
}else{
    //hacer algo
}