Delphi ActiveX

Using Pre-defined JSON Templates

See more JSON Examples

Demonstrates how to predefine a JSON template, and then use it to emit JSON with variable substitutions.

Note: This example requires Chilkat v9.5.0.67 or greater.

Delphi ActiveX

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Chilkat_TLB;

...

procedure TForm1.Button1Click(Sender: TObject);
var
json: TChilkatJsonObject;
jsonTemplate: TChilkatJsonObject;
jsonDonut: TChilkatJsonObject;
donutValues: TChilkatHashtable;
omitEmpty: Integer;

begin
// One way to create JSON is to do it in a straightforward manner:
json := TChilkatJsonObject.Create(Self);
json.EmitCompact := 0;
json.UpdateString('id','0001');
json.UpdateString('type','donut');
json.UpdateString('name','Cake');
json.UpdateString('image.url','images/0001.jpg');
json.UpdateInt('image.width',200);
json.UpdateInt('image.height',200);
json.UpdateString('thumbnail.url','images/thumbnails/0001.jpg');
json.UpdateInt('thumbnail.width',32);
json.UpdateInt('thumbnail.height',32);
Memo1.Lines.Add(json.Emit());

// The JSON created by the above code:

// 	{ 
// 	  "id": "0001",
// 	  "type": "donut",
// 	  "name": "Cake",
// 	  "image": { 
// 	    "url": "images/0001.jpg",
// 	    "width": 200,
// 	    "height": 200
// 	  },
// 	  "thumbnail": { 
// 	    "url": "images/thumbnails/0001.jpg",
// 	    "width": 32,
// 	    "height": 32
// 	  }
// 	}

// An alternative is to predefine a template, and then use it to emit with variable substitutions.
// For example:

jsonTemplate := TChilkatJsonObject.Create(Self);
jsonTemplate.UpdateString('id','{$id}');
jsonTemplate.UpdateString('type','donut');
jsonTemplate.UpdateString('name','{$name}');
jsonTemplate.UpdateString('image.url','{$imageUrl}');
// The "i." indicates that it's an integer variable.
jsonTemplate.UpdateString('image.width','{$i.imageWidth}');
jsonTemplate.UpdateString('image.height','{$i.imageHeight}');
jsonTemplate.UpdateString('thumbnail.url','{$thumbUrl}');
jsonTemplate.UpdateString('thumbnail.width','{$i.thumbWidth}');
jsonTemplate.UpdateString('thumbnail.height','{$i.thumbHeight}');
// Give this template a name.
jsonTemplate.Predefine('donut');

// --------------------------------------------------------------------------
// OK, the template is defined.  Defining a template can be done once
// at the start of your program, and you can discard the jsonTemplate object (it
// doesn't need to stick around..)

// Now we can create instances of the JSON object by name:
jsonDonut := TChilkatJsonObject.Create(Self);
jsonDonut.EmitCompact := 0;
jsonDonut.LoadPredefined('donut');
Memo1.Lines.Add(jsonDonut.Emit());

// The output is this:

// 	{ 
// 	  "id": "{$id}",
// 	  "type": "donut",
// 	  "name": "{$name}",
// 	  "image": { 
// 	    "url": "{$imageUrl}",
// 	    "width": "{$i.imageWidth}",
// 	    "height": "{$i.imageHeight}"
// 	  },
// 	  "thumbnail": { 
// 	    "url": "{$thumbUrl}",
// 	    "width": "{$i.thumbWidth}",
// 	    "height": "{$i.thumbHeight}"
// 	  }
// 	}

// Finally, we can substitute variables like this:
donutValues := TChilkatHashtable.Create(Self);
donutValues.AddStr('id','0001');
donutValues.AddStr('name','Cake');
donutValues.AddStr('imageUrl','images/0001.jpg');
donutValues.AddInt('imageWidth',200);
donutValues.AddInt('imageHeight',200);
donutValues.AddStr('thumbUrl','images/thumbnails/0001.jpg');
donutValues.AddInt('thumbWidth',32);
donutValues.AddInt('thumbHeight',32);

// Emit with variable substitutions:
omitEmpty := 1;
Memo1.Lines.Add(jsonDonut.EmitWithSubs(donutValues.ControlInterface,omitEmpty));

// Output:

// 	{ 
// 	  "id": "0001",
// 	  "type": "donut",
// 	  "name": "Cake",
// 	  "image": { 
// 	    "url": "images/0001.jpg",
// 	    "width": 200,
// 	    "height": 200
// 	  },
// 	  "thumbnail": { 
// 	    "url": "images/thumbnails/0001.jpg",
// 	    "width": 32,
// 	    "height": 32
// 	  }
// 	}

// Change some of the values:
donutValues.AddStr('id','0002');
donutValues.AddStr('imageUrl','images/0002.jpg');
donutValues.AddStr('thumbUrl','images/thumbnails/0002.jpg');

Memo1.Lines.Add(jsonDonut.EmitWithSubs(donutValues.ControlInterface,omitEmpty));

// Output:

// 	{ 
// 	  "id": "0002",
// 	  "type": "donut",
// 	  "name": "Cake",
// 	  "image": { 
// 	    "url": "images/0002.jpg",
// 	    "width": 200,
// 	    "height": 200
// 	  },
// 	  "thumbnail": { 
// 	    "url": "images/thumbnails/0002.jpg",
// 	    "width": 32,
// 	    "height": 32
// 	  }
// 	}
end;