forked from bblanchon/ArduinoJson
89 lines
2.3 KiB
Markdown
89 lines
2.3 KiB
Markdown
Migrating code written for Arduino JSON v3 to v4
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Arduino JSON v4 was a major rewrite of the library, and the API change significantly.
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## Includes
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Arduino JSON v3 had two include files:
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#include <JsonParser.h>
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#include <JsonGenerator.h>
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Arduino JSON v4 only has one:
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#include <ArduinoJson.h>
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Node: the header `src/ArduinoJson.h` is intended to be used within the Arduino IDE, if you're in another environment, you may need to include the following headers:
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#include <ArduinoJson/StaticJsonBuffer.hpp>
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#include <ArduinoJson/JsonObject.hpp>
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#include <ArduinoJson/JsonArray.hpp>
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## Namespaces
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Arduino JSON v3 had two namespaces:
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using namespace ArduinoJson::Parser;
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using namespace ArduinoJson::Generator;
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Arduino JSON v4 only has one:
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using namespace ArduinoJson;
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If you include the header `ArduinoJson.h` (recommended if in Arduino IDE), the `using` directivei is already done for you, so you don't have to write it.
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## StaticJsonBuffer
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Arduino JSON v3 had different memory allocation models for parser:
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JsonParser<16> parser; // 16 being the capacity in "tokens"
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and for the generator:
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JsonArray<4> array; // 4 being the number of element
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JsonObject<4> object;
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Arduino JSON v4 only has one memory allocation mode:
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StaticJsonBuffer<128> buffer; // 128 being the capacity in bytes
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## Return values for the parser
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Arduino JSON v3 returned `JsonArray` and `JsonObject`:
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JsonArray array = parser.parseArray(json);
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JsonObject object = parser.parseObject(json);
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Arduino JSON v4 returns references:
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JsonArray& array = buffer.parseArray(json);
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JsonObject& object = buffer.parseObject(json);
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Everything else is compatible
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## Creating arrays and objects
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Arduino JSON v3 allowed to create `JsonArray` and `JsonObject` directly:
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JsonArray<4> array;
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JsonObject<4> object;
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Arduino JSON v4 requires that you use a `StaticJsonBuffer` for that:
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JsonArray& array = buffer.createArray();
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JsonObject& object = buffer.createObject();
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Note: you don't have to specify the capacity anymore.
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## Printable interface
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Arduino JSON v3 used to implement the Printable interface, that allowed that kind of statement:
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Serial.print(array);
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Arduino JSON v4 doesn't, so you need to write this:
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array.printTo(Serial);
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Note: there is a good reason for that: reducing the size of `JsonArray` and `JsonObject`. |