04 - JSON

JSON - JavaScript Object Notation

Final standard..

DataTypes:

• String
• Number
• Object – {….}
• Array (one dimensional only. Jagged is ok) – [….]
• True
• False
• Null

Example of JSON

{
  "FirstName": "Andres",
  "LastName": "Käver",
  "Subjects": ["C#", "Android"]
}

Serialization & Deserialization

Serialization - Converting objects to bytestream

Deserialization - Converting bytestream to objects

JSON in .NET since .NET Core 3

New serialization library

!!! warning Does not support multidimensional arrays

using System;
using System.Text.Json;
using System.Text.Json.Serialization;

class WeatherForecast {
    public DateTime Date { get; set; }
    public double TempC { get; set; }
    public string Summary { get; set; }
}

Serialization

var jsonOptions = new JsonSerializerOptions()
{
    WriteIndented = true,
    AllowTrailingCommas = true,
};

var w = new WeatherForecast()
{
    Date = DateTime.Now,
    TempC = 31.45,
    Summary = "Very hot!"
};

Console.WriteLine(JsonSerializer.Serialize(w, jsonOptions));

{
  "Date": "2020-10-08T23:06:54.197136+03:00",
  "TempC": 31.45,
  "Summary": "Very hot!"
}

Deserialization

var jsonOptions = new JsonSerializerOptions()
{
    WriteIndented = true,
    AllowTrailingCommas = true,
};

var jsonStr = @"
{
    ""Date"": ""2020-10-08T23:06:54.197136+03:00"",
    ""TempC"": 31.45,
    ""Summary"": ""Very hot!""
}";

var ww = JsonSerializer.Deserialize<WeatherForecast>(jsonStr, jsonOptions);

Console.WriteLine(ww.Date);
Console.WriteLine(ww.TempC);
Console.WriteLine(ww.Summary);

Newtonsoft library

If you need/want to use json with multidimensional arrays – Newtonsoft library supports it.
Newtonsoft is very mature, slightly slower 3rd party library.

Newtonsoft is not allowed in this course (or next). Stick to the standards!
Circular reference serialization is also forbidden!

Directory and File IO

System.IO namespace.

Directory

Use the Directory class for typical operations such as copying, moving, renaming, creating, and deleting directories.

• To create a directory, use one of the CreateDirectory methods.
• To delete a directory, use one of the Delete methods.
• To get or set the current directory for an app, use the GetCurrentDirectory or SetCurrentDirectory method.
• To manipulate DateTime information related to the creation, access, and writing of a directory, use methods such as SetLastAccessTime and SetCreationTime.

User's Home directory

string homeDirectory = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
Console.WriteLine($"User's Home Directory: {homeDirectory}");

File

Use the File class for typical operations such as copying, moving, renaming, creating, opening, deleting, and appending to a single file at a time. You can also use the File class to get and set file attributes or DateTime information related to the creation, access, and writing of a file.

System.IO.File namespace
AppendText
CreateText

using (StreamWriter writer = System.IO.File.AppendText("logfile.txt")) {
    writer.WriteLine("log message");
}

Path

A path is a string that provides the location of a file or directory. A path does not necessarily point to a location on disk; for example, a path might map to a location in memory or on a device.

• ChangeExtension(String, String) - Changes the extension of a path string.
• Combine(String[]) - Combines an array of strings into a path.
• Exists(String) - Determines whether the specified file or directory exists.
• GetTempPath() - Returns the path of the current user's temporary folder.
• DirectorySeparatorChar - Provides a platform-specific character used to separate directory levels in a path string that reflects a hierarchical file system organization.