{"id":182,"date":"2012-03-13T22:24:06","date_gmt":"2012-03-13T14:24:06","guid":{"rendered":"https:\/\/www.techcoil.com\/blog\/?p=182"},"modified":"2018-09-03T21:34:30","modified_gmt":"2018-09-03T13:34:30","slug":"how-to-save-and-load-objects-to-and-from-file-in-c","status":"publish","type":"post","link":"https:\/\/www.techcoil.com\/blog\/how-to-save-and-load-objects-to-and-from-file-in-c\/","title":{"rendered":"How to save and load objects to and from file in C#"},"content":{"rendered":"

Persistency is almost always a requirement for applications that are meant for serious usage. Perhaps we want the data that our C# program had harvested or generated to be available everytime it runs. Or for that load of data that we are unable to send to a server to be remembered, so that we can try sending at a later time.<\/p>\n

Because most of the data that is held by a C# application at runtime is in the form of objects, it is convenient to be able to save and load objects to file directly. Such capability is dubbed object serialization<\/strong>, and like many other programming languages, C# has the facilities to perform object serialization for developers.<\/p>\n

Remembering our friends<\/h3>\n

Suppose we want to write a C# program that can remember our friends' email addresses. Instead of using System.Data.SQLite<\/a>, let's use object serialization to achieve the data persistence aspect of our program. <\/p>\n

The serializable Friend class<\/h3>\n

In order to be able to save and load objects, the class has to be indicated as being serializable. We mark a class with the Serializable<\/code> attribute to indicate that we want to be able to save its objects:<\/p>\n

\r\nusing System;\r\nusing System.Text;\r\n\r\n[Serializable]\r\npublic class Friend\r\n{\r\n    private string name;\r\n    private string email;\r\n\r\n    public Friend (string name, string email) {\r\n        this.name = name;\r\n        this.email = email;\r\n    }\r\n\r\n    public string Name\r\n    {\r\n        get\r\n        {\r\n            return this.name;\r\n        }\r\n\r\n        set\r\n        {\r\n            this.name = value;\r\n        }\r\n    } \/\/ end public string Name\r\n\r\n    public string Email\r\n    {\r\n        get\r\n        {\r\n            return this.email;\r\n        }\r\n        set\r\n        {\r\n            this.email = value;\r\n        }\r\n    } \/\/ end public string Email\r\n} \/\/ end public class Friend\r\n<\/pre>\n
Here, the Friend<\/code> class is a data wrapper class that we will use to hold the name and email address of a particular friend. As we add more friends to our program, more Friend<\/code> instances will be created. Such instances will be maintained by the FriendsInformation<\/code> class.<\/p>\n
The FriendsInformation class<\/h3>\n
Let's create a singleton class<\/a>, FriendInformation<\/code>, that will be responsible for the saving and loading of information of our friends.<\/p>\n
\r\nusing System;\r\nusing System.Collections.Generic;\r\nusing System.IO;\r\nusing System.Runtime.Serialization;\r\nusing System.Runtime.Serialization.Formatters.Binary;\r\nusing System.Text;\r\n\r\npublic class FriendsInformation\r\n{\r\n\r\n    private static FriendsInformation friendsInformation;\r\n\r\n    private Dictionary<string, Friend> friendsDictionary;\r\n    private BinaryFormatter formatter;\r\n\r\n    private const string DATA_FILENAME = "friendsinformation.dat";\r\n\r\n    public static FriendsInformation Instance()\r\n    {\r\n        if (friendsInformation == null) {\r\n            friendsInformation = new FriendsInformation();\r\n        } \/\/ end if\r\n\r\n        return friendsInformation;\r\n    } \/\/ end public static FriendsInformation Instance()\r\n\r\n    private FriendsInformation()\r\n    {\r\n        \/\/ Create a Dictionary to store friends at runtime\r\n        this.friendsDictionary = new Dictionary<string, Friend>();\r\n        this.formatter = new BinaryFormatter();\r\n    } \/\/ end private FriendsInformation()\r\n\r\n    public void AddFriend(string name, string email)\r\n    {\r\n        \/\/ If we already had added a friend with this name\r\n        if (this.friendsDictionary.ContainsKey(name))\r\n        {\r\n            Console.WriteLine("You had already added " + name + " before.");\r\n        }\r\n        \/\/ Else if we do not have this friend details \r\n        \/\/ in our dictionary\r\n        else\r\n        {\r\n            \/\/ Add him in the dictionary\r\n            this.friendsDictionary.Add(name, new Friend(name, email));\r\n            Console.WriteLine("Friend added successfully.");\r\n        } \/\/ end if\r\n    } \/\/ end public bool AddFriend(string name, string email)\r\n\r\n    public void RemoveFriend(string name)\r\n    {\r\n        \/\/ If we do not have a friend with this name\r\n        if (!this.friendsDictionary.ContainsKey(name))\r\n        {\r\n            Console.WriteLine(name + " had not been added before.");\r\n        }\r\n        \/\/ Else if we have a friend with this name\r\n        else\r\n        {\r\n            if (this.friendsDictionary.Remove(name))\r\n            {\r\n                Console.WriteLine(name + " had been removed successfully.");\r\n            }\r\n            else\r\n            {\r\n                Console.WriteLine("Unable to remove " + name);\r\n            } \/\/ end if\r\n        } \/\/ end if\r\n    } \/\/ end public bool RemoveFriend(string name)\r\n\r\n    public void Save()\r\n    {\r\n        \/\/ Gain code access to the file that we are going\r\n        \/\/ to write to\r\n        try\r\n        {\r\n            \/\/ Create a FileStream that will write data to file.\r\n            FileStream writerFileStream = \r\n                new FileStream(DATA_FILENAME, FileMode.Create, FileAccess.Write);\r\n            \/\/ Save our dictionary of friends to file\r\n            this.formatter.Serialize(writerFileStream, this.friendsDictionary);\r\n\r\n            \/\/ Close the writerFileStream when we are done.\r\n            writerFileStream.Close();\r\n        }\r\n        catch (Exception) {\r\n            Console.WriteLine("Unable to save our friends' information");\r\n        } \/\/ end try-catch\r\n    } \/\/ end public bool Load()\r\n             \r\n    public void Load() \r\n    {\r\n     \r\n        \/\/ Check if we had previously Save information of our friends\r\n        \/\/ previously\r\n        if (File.Exists(DATA_FILENAME))\r\n        {\r\n\r\n            try\r\n            {\r\n                \/\/ Create a FileStream will gain read access to the \r\n                \/\/ data file.\r\n                FileStream readerFileStream = new FileStream(DATA_FILENAME, \r\n                    FileMode.Open, FileAccess.Read);\r\n                \/\/ Reconstruct information of our friends from file.\r\n                this.friendsDictionary = (Dictionary<String, Friend>)\r\n                    this.formatter.Deserialize(readerFileStream);\r\n                \/\/ Close the readerFileStream when we are done\r\n                readerFileStream.Close();\r\n\r\n            } \r\n            catch (Exception)\r\n            {\r\n                Console.WriteLine("There seems to be a file that contains " +\r\n                    "friends information but somehow there is a problem " +\r\n                    "with reading it.");\r\n            } \/\/ end try-catch\r\n\r\n        } \/\/ end if\r\n        \r\n    } \/\/ end public bool Load()\r\n\r\n    public void Print()\r\n    {\r\n        \/\/ If we have saved information about friends\r\n        if (this.friendsDictionary.Count > 0)\r\n        {\r\n            Console.WriteLine("Name, Email");\r\n            foreach (Friend friend in this.friendsDictionary.Values)\r\n            {\r\n                Console.WriteLine(friend.Name + ", " + friend.Email);\r\n            } \/\/ end foreach\r\n        }\r\n        else\r\n        {\r\n            Console.WriteLine("There are no saved information about your friends");\r\n        } \/\/ end if\r\n    } \/\/ end public void Print()\r\n\r\n} \/\/ end public class FriendsInformation\r\n\r\n<\/pre>\n
Encapsulating some facilitators<\/h4>\n
To facilitate the representation, addition and removal of friends information, we maintain an instance of the System.Collections.Generic.Dictionary<\/code><\/a> class as an instance variable.<\/p>\n
On the other hand, to be able to serialize (save) and deserialize (load), we maintain an instance of the System.Runtime.Serialization.Formatters.Binary.BinaryFormatter<\/code><\/a> class.<\/p>\n
Adding new friend<\/h4>\n
The AddFriend<\/code> method allows callers to add the name and email of a friend to the underlying Dictionary<\/code> instance, via its Add<\/code><\/a> method. If we had already added a friend with the same name, the friend will not be added. <\/p>\n
Removing a friend<\/h4>\n
The RemoveFriend<\/code> method allows callers to remove a friend, based on his name, from our underlying Dictionary<\/code> instance, via its Remove<\/code><\/a> method. If there is no friend with the supplied name, no removal will take place.<\/p>\n
Saving Friend objects to file<\/h4>\n
The Save<\/code> method is all about writing to file<\/a>. We first obtain an instance of System.IO.FileStream<\/code><\/a> which has write access to friendsinformation.dat<\/code>. <\/p>\n
If we are successful in doing so, we use the Serialize<\/a> method of our BinaryFormatter<\/code> instance to save the entire friendsDictionary<\/code> to friendsinformation.dat<\/code>.<\/p>\n
Loading Friend objects from file<\/h4>\n
On the contrary, the Load method is all about reading from file<\/a>. We first check whether there are previous calls to the Save<\/code> method by checking the existence of friendsinformation.dat<\/code>. <\/p>\n
If friendsinformation.dat<\/code> exists, we first obtain an instance of FileStream<\/code> that has read access to friendsInformation.dat<\/code>. We then use the Deserialize<\/a> to read from the FileStream<\/code> instance.  <\/p>\n
When the Deserialize<\/code> method is called successfully, a Dictionary<\/code> instance, which contains Friend<\/code> objects that were previously saved to file, will be created. This Dictionary<\/code> instance is then set to the friendsDictionary<\/code> variable.<\/p>\n
Printing of friends' information<\/h4>\n
The Print<\/code> method allows us to inspect the Friend<\/code> objects that are maintained by our program at runtime. It iterates the list of Friend<\/code> objects and outputs the name and email. <\/p>\n
A simple command line application<\/h3>\n
To sum up this post, let's create a command line application that we can use to remember the names and email addresses of our friends.<\/p>\n
\r\n\r\nusing System;\r\nusing System.Collections.Generic;\r\nusing System.IO;\r\nusing System.Text;\r\n\r\npublic class Program\r\n{\r\n    private static string programName = \r\n        Path.GetFileNameWithoutExtension(System.AppDomain.CurrentDomain.FriendlyName);\r\n\r\n    public static void Main(string[] args)\r\n    {\r\n\r\n        if (args.Length < 1)\r\n        {\r\n            PrintUsage();\r\n        }\r\n        else\r\n        {\r\n\r\n            FriendsInformation fi = FriendsInformation.Instance();\r\n            fi.Load();\r\n\r\n            String command = args[0].ToLower();\r\n\r\n            if (command == "list") \r\n            {\r\n                fi.Print();\r\n            }\r\n            else if (command == "add") {\r\n\r\n                if (args.Length >= 3)\r\n                {\r\n                    String name = args[1];\r\n                    String email = args[2];\r\n                    fi.AddFriend(name, email);\r\n                    fi.Save();\r\n                }\r\n                else\r\n                {\r\n                    PrintUsage();\r\n                    return;\r\n                } \/\/ end if\r\n                \r\n            }\r\n            else if (command == "remove")\r\n            {\r\n\r\n                if (args.Length >= 2)\r\n                {\r\n                    String name = args[1];\r\n                    fi.RemoveFriend(name);\r\n                    fi.Save();\r\n                }\r\n                else\r\n                {\r\n                    PrintUsage();\r\n                    return;\r\n                } \/\/ end if\r\n\r\n            }\r\n            else\r\n            {\r\n                Console.WriteLine("Command not found: " + command);\r\n                PrintUsage();\r\n            } \/\/ end if\r\n\r\n                \r\n        } \/\/ end if\r\n\r\n    } \/\/ end public static void Main(string[] args)\r\n\r\n    public static void PrintUsage() \r\n    {\r\n        Console.WriteLine("Usage: ");\r\n        Console.WriteLine(programName + " list");\r\n        Console.WriteLine(programName + " add <name> <email>");\r\n        Console.WriteLine(programName + " remove <name>");\r\n    } \/\/ end public static void Main(string[] args)\r\n} \/\/ end public class Program\r\n<\/pre>\n
The application accepts three commands via the command line:<\/p>\n
    \n
  1. list<\/strong> displays the names and email addresses of all our friends which we have added to our program.<\/li>\n
  2. add<\/strong> allows us to add a new friend to our program. <\/li>\n
  3. remove<\/strong> allows us to remove a friend from our program.<\/li>\n<\/ol>\n
    For each of the 3 commands, the FriendsInformation<\/code> singleton is created and called upon to attempt to load previously saved Friend objects into runtime. <\/p>\n
    Except for the list<\/strong> command, the Save<\/code> method of the FriendsInformation<\/code> is called to save any changes made to the collection of Friend objects back into friendsInformation.dat<\/code>.<\/p>\n
    After several execution of the add<\/strong> and remove<\/strong> commands, friendsInformation.dat<\/code> should appear in the same folder as our command line application. To check whether our command line application can remember (or forget) our friends, we can execute the list<\/code> command.<\/p>\n
    Related posts<\/h3>\n