Book Image

Delphi Cookbook - Second Edition

By : Daniele Teti
Book Image

Delphi Cookbook - Second Edition

By: Daniele Teti

Overview of this book

Delphi is a cross-platform Integrated Development Environment (IDE) that supports rapid application development for Microsoft Windows, Apple Mac OS X, Google Android, and Apple iOS. It helps you to concentrate on the real business and save yourself the pain of wandering amid GUI widget details, or having to tackle inter-platform incompatibilities. It also has a wide range of drag-and-drop controls, helping you code your business logic into your business model, and it compiles natively for desktop and mobile platforms. This book will teach you how to design and develop applications, deploy them on the cloud platform, and distribute them within an organization via Google Play and other similar platforms. You will begin with the basics of Delphi and get acquainted with JSON format strings, XSLT transformations, unicode encodings and various types of streams. We then move on to more advanced topics such as developing higher-order functions and using enumerators and RTTI. You will get an understanding of how Delphi RTL functions and how to use FireMonkey in a VCL application. We will then cover topics such as multithreading, using the parallel programming library and putting Delphi on a server. We will also take a look at the new feature of WebBroker Apache modules and then ride the mobile revolution with FireMonkey. By the end of the book, you will be able to develop and deploy cross-platform applications using Delphi .
Table of Contents (10 chapters)
9
Index

Manipulating JSON

JSON (JavaScript Object Notation) is a lightweight data-interchange format. As the reference site says, "It is easy for humans to read and write. It is easy for machines to parse and generate." It is based on a subset of the JavaScript programming language, but it is not limited to JavaScript in any way. Indeed, JSON is a text format that is completely language agnostic. These properties make JSON an ideal data-interchange language for many uses. In recent years, JSON has become on a par with XML in many applications, especially when the data size matters, because of its intrinsic conciseness and simplicity.

Getting ready

JSON provides the following five datatypes: String, Number, Object, Array, Boolean, and Null.

This simplicity is an advantage when you have to read a JSON string into some kind of language-specific structure, because every modern language supports the JSON datatypes as simple types or as HashMap (in the case of JSON objects) or List (in the case of JSON arrays). So, it makes sense that a data format that is interchangeable with programming languages is also based on these types and structures.

Since version 2009, Delphi provides built-in support for JSON. The System.JSON.pas unit contains all the JSON types with a nice object oriented interface. In this recipe, you'll see how to generate, modify, and parse a JSON string.

How to do it…

  1. Create a new VCL application and drop three TButton and a TMemo. Align all the buttons as a toolbar at the top of the form and the memo to all the remaining form client area.
  2. From left to right, name the buttons as btnGenerateJSON, btnModifyJSON, and btnParseJSON.
  3. We'll use static data as our data source. A simple matrix is enough for this recipe. Just after the start of the implementation section of the unit, write the following code:
    type
      TCarInfo = (
        Manufacturer = 1,
        Name = 2,
        Currency = 3,
        Price = 4);
    
    var
      Cars: array [1 .. 4] of array [Manufacturer .. Price] of string = (
        ('Ferrari','360 Modena','EUR', '250000'),
        ('Ford', 'Mustang', 'USD', '80000'),
        ('Lamborghini', 'Countach', 'EUR','300000'),
        ('Chevrolet', 'Corvette', 'USD', '100000')
      );
  4. TMemo is used to show our JSON files and our data. To keep things clear, create a public property called JSON on the form and map its setter and getter to the Memo1.Lines.Text property. Use the following code:
    //…other form methods declaration 
    private
      procedure SetJSON(const Value: String);
      function GetJSON: String;
    public
      property JSON: String read GetJSON write SetJSON;
    end;
    
    //…then in the implementation section
    function TMainForm.GetJSON: String;
    begin
      Result := Memo1.Lines.Text;
    end;
    
    procedure TMainForm.SetJSON(const Value: String);
    begin
      Memo1.Lines.Text := Value;
    end;
  5. Now, create event handlers for each button and write the code that follows. Pay attention to the event names:
    procedure TMainForm.btnGenerateJSONClick(Sender: TObject);
    var
      i: Integer;
      JSONCars: TJSONArray;
      Car, Price: TJSONObject;
    begin
      JSONCars := TJSONArray.Create;
      try
        for i := Low(Cars) to High(Cars) do
        begin
          Car := TJSONObject.Create;
          JSONCars.AddElement(Car);
          Car.AddPair('manufacturer', Cars[i][TCarInfo.Manufacturer]);
          Car.AddPair('name', Cars[i][TCarInfo.Name]);
          Price := TJSONObject.Create;
          Car.AddPair('price', Price);
          Price.AddPair('value', TJSONNumber.Create(Cars[i][TCarInfo.Price].ToInteger));
          Price.AddPair('currency',Cars[i][TCarInfo.Currency]);
        end;
        JSON := JSONCars.ToJSON;
      finally
        JSONCars.Free;
      end;
    end;
    
    procedure TMainForm.btnModifyJSONClick(Sender: TObject);
    var
      JSONCars: TJSONArray;
      Car, Price: TJSONObject;
    begin
      JSONCars := TJSONObject.ParseJSONValue(JSON) 
    as TJSONArray;
      try
        Car := TJSONObject.Create;
        JSONCars.AddElement(Car);
        Car.AddPair('manufacturer', 'Hennessey');
        Car.AddPair('name', 'Venom GT');
        Price := TJSONObject.Create;
        Car.AddPair('price', Price);
        Price.AddPair('value', TJSONNumber.Create(600000));
        Price.AddPair('currency', 'USD');
        JSON := JSONCars.ToJSON;
      finally
        JSONCars.Free;
      end;
    end;
    
    procedure TMainForm.btnParseJSONClick(Sender: TObject);
    var
      JSONCars: TJSONArray;
      i: Integer;
      Car, JSONPrice: TJSONObject;
      CarPrice: Double;
      s, CarName, CarManufacturer, CarCurrencyType: string;
    begin
      s := '';
      JSONCars := TJSONObject.ParseJSONValue(JSON) 
                                             as TJSONArray;
      if not Assigned(JSONCars) then
        raise Exception.Create('Not a valid JSON');
      try
        for i := 0 to JSONCars.Count - 1 do
        begin
          Car := JSONCars.Items[i] as TJSONObject;
          CarName := Car.GetValue('name').Value;
          CarManufacturer := Car.GetValue('manufacturer').Value;
          JSONPrice := Car.GetValue('price') as TJSONObject;
          CarPrice := (JSONPrice.GetValue('value') as TJSONNumber).AsDouble;
          CarCurrencyType := JSONPrice.GetValue('currency')
          .Value
          s := s + Format(
            'Name = %s' + sLineBreak +
            'Manufacturer = %s' + sLineBreak +
            'Price = %.0n%s' + sLineBreak +
            '-----' + sLineBreak,
            [CarName, CarManufacturer,
            CarPrice, CarCurrencyType]);
        end;
        JSON := s;
      finally
        JSONCars.Free;
      end;
    end;
  6. Run the application by hitting F9 (or by going to Run | Run).
  7. Click on the btnGenerateJSON button, and you should see a JSON array and some JSON objects in the memo.
  8. Click on the btnModifyJSON button, and you should see one more JSON object inside the outer JSON array in the memo.
  9. Click on the last button, and you should see the same data as before, but in a normal text representation.
  10. After the third click, you should see something similar to the following screenshot:
    How to do it…

    Figure 6.1: Text representation of the JSON data generated and modified

There's more…

Although not the fastest or the most standard compliant on the market, JSON usability is important because other Delphi technologies, such as DataSnap, use it. Luckily, there are a lot of alternative JSON parsers for Delphi, if you find you have trouble with the standard one.

Other notable JSON parsers are:

If your main concern is speed, then check out these alternative JSON parsers.

There are also a lot of serialization libraries that use JSON as a serialization format. In general, every parser has its own way to serialize an object to JSON. Find your favorite. Just as an example, in Chapter 5, The Thousand Faces of Multithreading, in the Using tasks to make your customer happier recipe you will see an open source library containing a set of serialization helpers using the default Delphi JSON parser.

However, JSON is not the right tool for every interchange or data-representation job. XML has been creating other technologies that can help if you need to search, transform, and validate your data in a declarative way. In JSON land, there is no such level of standardization, apart from the format itself. However, over the years, there is an effort to include at least the XML Schema counterpart in JSON, and you can find more details at http://json-schema.org/.