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The what3words Free API plan will no longer include convert-to-coordinate requests. To continue using this feature, please upgrade to one of our paid plans starting from £7.99/month. Learn more about our API plans here.

As a reminder, emergency services can make use of the what3words API for free, and we have a dedicated plan for NGOs and registered charities. If your organisation falls within these categories, please get in touch. For any questions or assistance, feel free to reach out to support@what3words.com.

The Dart API wrapper (now null safe) is useful for Dart or Flutter developers who wish to seamlessly integrate the what3words API into their Dart or Flutter applications, without the hassle of having to manage the low level API calls themselves.

A full example of how to integrate the what3words Dart wrapper is available in our
github icon whiteDart Github repository

1
2Installation

The artifact is available through pub.dev. Update your pubspec.yaml file with

dependencies:
 what3words: 3.1.0
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3Setup

Import the what3words library

import 'package:what3words/what3words.dart';
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4Initialise

Instantiate an instance of What3WordsV3, from which all API requests can be made

var api = What3WordsV3('what3words-api-key');
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5Usage

Convert to what3words address

This function converts coordinates (expressed as latitude and longitude) to a what3words address.

More information about ConvertTo3wa, including returned results is available in the what3words REST API documentation.

Find the words for (51.508344,0.12549900):

var words = await api
  .convertTo3wa(Coordinates(51.508344, -0.12549900))
  .language('en')
  .execute();
print('Words: ${words.data()?.toJson()}');
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Convert to coordinates

This function converts a what3words address to a position, expressed as coordinates of latitude and longitude.

It takes the words parameter as a string of a what3words 'table.book.chair'

More information about ConvertToCoordinates, including returned results is available in the what3words REST API documentation.

Find the words for ///filled.count.soap:

var coordinates = await api
	.convertToCoordinates('table.book.chair')
	.execute();
print('Coordinates ${coordinates.data()?.toJson()}');
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AutoSuggest

When presented with a what3words address which may be incorrectly entered, AutoSuggest returns a list of potential correct 3 word addresses. It needs the first two words plus at least the first character of the third word to produce suggestions.

This method provides corrections for mis-typed words (including plural VS singular), and words being in the wrong order.

Optionally, clipping can narrow down the possibilities, and limit results to:

  • One or more countries
  • A geographic area (a circle, box or polygon)

This dramatically improves results, so we recommend that you use clipping if possible.

To improve results even further, set the Focus to user’s current location. This will make AutoSuggest return results which are closer to the user.

More information about AutoSuggest, including returned results is available in the what3words REST API documentation.

Code example Simple basic call:

var autosuggest = await api
	.autosuggest('fun.with.code')
	.nResults(3)
	.execute();
print('Autosuggest: ${autosuggest.data()?.toJson()}');
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Code example AutoSuggest, clipping the results returned to the United Kingdom and Belgium:

var autosuggest = await api
	.autosuggest('fun.with.code')
	.clipToCountry(['gb', 'be'])
	.execute();
print('Autosuggest: ${autosuggest.data()?.toJson()}');
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Code example AutoSuggest, Focus on (51.4243877,-0.34745).

var autosuggest = await api
  .autosuggest('fun.with.code')
  .focus(Coordinates(51.4243877, -0.34745))
  .execute();
print('Autosuggest: ${autosuggest.data()?.toJson()}');
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Code example AutoSuggest, with Generic Voice input type.

var autosuggest = await api
  .autosuggest('fun with code')
  .input-type('generic-voice')
  .language('en')
  .execute();
print('Autosuggest: ${autosuggest.data()?.toJson()}');
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Grid section

Grid section returns a section of the what3words 3m x 3m grid as a set of horizontal and vertical lines covering the requested area, which can then be drawn onto a map.

The requested box must not exceed 4km from corner to corner, or a BadBoundingBoxTooBig error will be returned.

More information about GridSection, including returned results is available in the what3words REST API documentation.

Get a grid for 52.207988,0.116126) in the south west, and 52.208867,0.117540 in the north east:

// Obtain a grid section within the provided bounding box
var gridSection = await api
      .gridSection(Coordinates(51.515900, -0.212517), Coordinates(51.527649, -0.191746))
      .execute();
print(gridSection.data()?.toJson());
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Available languages

This function returns the currently supported languages. It will return the two letter code, and the name of the language both in that language and in English.

More information about AvailableLanguages, including returned results is available in the what3words REST API documentation.

var languages = await api
	.availableLanguages()
	.execute();
print('Languages: ${languages.data()?.toJson()}');
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Handling errors

Success of failure of an API call can be determined through the use of the isSuccessful() function.

If it’s been determined that an API call was not successful, code and message values which represent the error, are accessible from through the getError() function.

var autosuggest = await api
  .autosuggest('freshen.overlook.clo')
  .clipToCountry(['fr', 'de'])	
  .execute();

if (autosuggest.isSuccessful()) {
  ...
} else {
  var error = autosuggest.getError();

  if (error == What3WordsError.BAD_CLIP_TO_COUNTRY) {
    // Invalid country clip is provided
    print('BadClipToCountry: ${error.message}');
  }
}
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6Troubleshooting

If you encounter errors or issues related to convert-to-coordinate requests while using the Free plan, please check the network panel for the following error message Error 402 payment required and its response, indicating the need to upgrade to a higher plan:

{
    "error": {
        "code": "QuotaExceeded",
        "message": "Quota Exceeded. Please upgrade your usage plan, or contact support@what3words.com"
    }
}
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For more information, visit our API plans page. If you need further assistance, contact support@what3words.com.

7Full example

The example below takes the concepts described above, and turns some of them into a complete example. Here we take a partial 3 word address and pass it into AutoSuggest – clipping the results to consider only addresses in France, setting a focus of Paris, and returning a single result

We then take the result and convert the 3 word address to coordinates, and find the nearest place.

import 'package:what3words/what3words.dart';

void main() async {
  // For all requests a what3words API key is needed
  var api = What3WordsV3('what3words-api-key');

  var autosuggest = await api
      .autosuggest('freshen.overlook.clo')
      .clipToCountry(['fr'])
      .focus(Coordinates(48.856618, 2.3522411))
      .nResults(1)
      .execute();

  if (autosuggest.isSuccessful()) {
    var words = autosuggest.suggestions[0].words;
    print(
      'Top 3 word address match: ${words}',
    );

    var convertToCoordinates = await api.convertToCoordinates(words).execute();
    if (convertToCoordinates.isSuccessful()) {
      print(
          'WGS84 Coordinates: ${convertToCoordinates.coordinates.lat}, ${convertToCoordinates.coordinates.lng}');
      print(
        'Nearest Place: ${convertToCoordinates.nearestPlace}',
      );
    } else {
      var error = autosuggest.getError();
      if (error == What3WordsError.INTERNAL_SERVER_ERROR) {
        // Server Error
        print('InternalServerError: ');
      } else if (error == What3WordsError.NETWORK_ERROR) {
        // Network Error
        print('NetworkError: ${error.message}');
      }
    }
  } else {
    var error = autosuggest.getError();

    if (error == What3WordsError.BAD_CLIP_TO_COUNTRY) {
      // Invalid country clip is provided
      print('BadClipToCountry: ${error.message}');
    } else if (error == What3WordsError.BAD_FOCUS) {
      // Invalid focus
      print('BadFocus: ${error.message}');
    } else if (error == What3WordsError.BAD_N_RESULTS) {
      // Invalid number of results
      print('BadNResults: ${error.message}');
    } else if (error == What3WordsError.INTERNAL_SERVER_ERROR) {
      // Server Error
      print('InternalServerError: ${error.message}');
    } else if (error == What3WordsError.NETWORK_ERROR) {
      // Network Error
      print('NetworkError: ${error.message}');
    } else {
      print('error: ${error.message}');
    }
  }
}
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