解决Alamofire上传图片绑定参数问题

项目的上传图片协议，包含多种参数，其中图片必须放入指定参数，以下是使用Alamofire解决此问题方法：

Alamofire.upload(.POST, urlStr, headers: headers,
  multipartFormData: { (multipartFormData) in
            
    // 图片绑定参数
    let imageName = String(NSDate()) + ".png"
    multipartFormData.appendBodyPart(data: fileData, name: "file_data", fileName: imageName, mimeType: "image/png")
                
    // 其余参数绑定
    for (key, value) in parameters! {
      assert(value is String)
      multipartFormData.appendBodyPart(data: value.dataUsingEncoding(NSUTF8StringEncoding)!, name: key)
    }
  },
  encodingCompletion: { encodingResult in
                
    switch encodingResult {
    case .Success(let upload, _, _):
      upload.responseString(completionHandler: { (response) in
        //
      })
      break
    case .Failure(let error):
        //
      break
      }
    }
  )