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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
Dart Github repository

1Get API key

2Installation

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

dependencies:
 what3words: 3.2.0

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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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In the case that you run our Enterprise Suite API Server yourself, you may specify the URL to your server like so:

var api = What3WordsV3.withEndpoint( 'what3words-api-key', 'https://api.yourserver.com');

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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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6RegEx Functions

This section introduces RegEx functions that can assist with checking and finding possible what3words addresses in strings. The three main functions covered are:

isPossible3wa – Match what3words address format;
findPossible3wa – Find what3words address in Text;
isValid3wa – Verify a what3words address with the API;

isPossible3wa

Our API wrapper RegEx function “isPossible3wa” can be used to detect if a text string (like “filled.count.soap“) in the format of a what3words address without having to ask the API. This functionality checks if a given string could be a what3words address. It returns true if it could be, otherwise false.

Note: This function checks the text format but not the validity of a what3words address. Use isValid3wa to verify validity.

void main() async {
  // Replace 'what3words-api-key' with your actual API key
  var api = What3WordsV3('what3words-api-key');

  List<String> addresses = ["filled.count.soap", "not a 3wa", "not.3wa address"];

  // Check if the addresses are possible what3words addresses
  for (String address in addresses) {
    bool isPossible = api.isPossible3wa(address);
    print("Is '$address' a possible what3words address? $isPossible");
  }
}

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Expected Output

isPossible3wa(“filled.count.soap”) returns true
isPossible3wa(“not a 3wa”) returns false
isPossible3wa(“not.3wa address”)returns false

findPossible3wa

Our API wrapper RegEx function “findPossible3wa” can be used to detect a what3words address within a block of text, useful for finding a what3words address in fields like Delivery Notes. For example, it can locate a what3words address in a note like “Leave at my front door ///filled.count.soap”. The function will match if there is a what3words address within the text. If no possible addresses are found, it returns an empty list.

Note:

This function checks the text format but not the validity of a what3words address. Use isValid3wa to verify validity.
This function is designed to work across languages but does not work for Vietnamese (VI) due to spaces within words.

void main() async {
  // Replace 'what3words-api-key' with your actual API key
  var api = What3WordsV3('what3words-api-key');

  List<String> texts = [
    "Please leave by my porch at filled.count.soap",
    "Please leave by my porch at filled.count.soap or deed.tulip.judge",
    "Please leave by my porch at"
  ];

  // Check each text for possible what3words addresses
  for (String text in texts) {
    List<String> possibleAddresses = api.findPossible3wa(text);
    print("Possible what3words addresses in '$text': $possibleAddresses");
  }
}

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Expected Output

findPossible3wa(“Please leave by my porch at filled.count.soap”) returns ['filled.count.soap']
findPossible3wa(“Please leave by my porch at filled.count.soap or deed.tulip.judge”) returns ['filled.count.soap', 'deed.tulip.judge']
findPossible3wa(“Please leave by my porch at”) returns []

isValid3wa

Our API wrapper RegEx function “isValid3wa” can be used to determine if a string is a valid what3words address by checking it against the what3words RegEx filter and verifying it with the what3words API.

void main() async {
  // Replace 'what3words-api-key' with your actual API key
  var api = What3WordsV3('what3words-api-key');

  List<String> w3w_addresses = [
    "filled.count.soap",
    "filled.count.",
    "coding.is.cool"
  ];

  // Iterate over the list and check if each address is valid
  for (String w3w_address in w3w_addresses) {
    var response = await api.isValid3wa(w3w_address);

    if (response.isSuccessful() && response.isValid == true) {
      print("$w3w_address is a valid what3words address");
    } else if (response.isSuccessful() && response.isValid == false) {
      print("$w3w_address is an invalid what3words address");
    } else {
      print("isValid3wa error: ${response.error?.code} - ${response.error?.message}");
    }
  }
}

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Expected Outputs

isValid3wa(“filled.count.soap”) returns True
isValid3wa(“filled.count.”) returns False
isValid3wa(“coding.is.cool”) returns False

Also make sure to replace <YOUR_API_KEY> with your actual API key. These functionalities provide different levels of validation for what3words addresses, from simply identifying potential addresses to verifying their existence on Earth.

7Troubleshooting

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.

8Full 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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Mobile App Server and Scripting Add 3 word addresses to a voice assistant Add a 3 word address input field Batch convert 3 word addresses or co-ordinates Use 3 word addresses with a map Use 3 word addresses with voice input Use 3 word addresses within a GIS Use 3 word addresses within an address search Dart

Developer

All tutorials

Dart

Convert to what3words address

Convert to coordinates

AutoSuggest

Grid section

Available languages

Handling errors

isPossible3wa

Expected Output

findPossible3wa

Expected Output

isValid3wa

Expected Outputs

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