以后绝对回用得着的东西：
swift2.1 类型转换String->Int, Float, Double

class CommonManager: NSObject {
    
    static let sharedManager = CommonManager() //singleton 
    
    static func toStringValue(someValue: String?) -> String {
        return someValue ?? ""
    }
    
    static func toIntValue(someValue: String?) -> Int {
        return Int(CommonManager.toStringValue(someValue)) ?? 0
    }
    
    static func toDoubleValue(someValue: String?) -> Double {
        return Double(CommonManager.toStringValue(someValue)) ?? 0.0
    }
    
    static func toFloatValue(someValue: String?) -> Float {
        return Float(CommonManager.toStringValue(someValue)) ?? 0.0
    }
}