B4X

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.

B4X

'  One way to create JSON is to do it in a straightforward manner:
Dim json As ChilkatJsonObject
json.Initialize
json.EmitCompact = False
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)
Log(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:

Dim jsonTemplate As ChilkatJsonObject
jsonTemplate.Initialize
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:
Dim jsonDonut As ChilkatJsonObject
jsonDonut.Initialize
jsonDonut.EmitCompact = False
jsonDonut.LoadPredefined("donut")
Log(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:
Dim donutValues As ChilkatHashtable
donutValues.Initialize
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:
Dim omitEmpty As Boolean = True
Log(jsonDonut.EmitWithSubs(donutValues, 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")

Log(jsonDonut.EmitWithSubs(donutValues, 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
'  	  }
'  	}