Flutter SDK 3

import 'package:amplitude_flutter/amplitude.dart';
import 'package:amplitude_flutter/identify.dart';
class YourClass {
  Future<void> exampleForAmplitude() async {
    // Create the instance
    final Amplitude analytics = Amplitude.getInstance(instanceName: "project");
    // Initialize SDK
    analytics.init(widget.apiKey);
    // Log an event
    analytics.logEvent('MyApp startup', eventProperties: {
      'friend_num': 10,
      'is_heavy_user': true
    });
  }
}

// Events queued in memory will flush when number of events exceed upload threshold
// Default value is 30
Amplitude.getInstance().setEventUploadThreshold(1);
// Events queue will flush every certain milliseconds based on setting
// Default value is 30,000 milliseconds
Amplitude.getInstance().setEventUploadPeriodMillis(10000);

// For versions starting from 3.6.0
// No need to call setServerUrl for sending data to Amplitude's EU servers
Amplitude.getInstance().setServerZone("EU");
// For earlier versions
Amplitude.getInstance().setServerUrl("https://api.eu.amplitude.com")

Amplitude.getInstance().logEvent('BUTTON_CLICKED');

Amplitude.getInstance().logEvent('BUTTON_CLICKED', {"Hover Time": "100ms"});

Amplitude.getInstance().uploadEvents();

import 'package:amplitude_flutter/identify.dart';

final Identify identify = Identify()
                          ..set('gender','female')
                          ..set('age',20);
Amplitude.getInstance().identify(identify);

final Identify identify1 = Identify();
identify1.setOnce('sign_up_date', '2015-08-24');
Amplitude.getInstance().identify(identify1);
final Identify identify2 = Identify();
identify2.setOnce('sign_up_date', '2015-08-24');
Amplitude.getInstance().identify(identify2);// is ignored

final Identify identify = Identify().add('karma', 0.123);
Amplitude.getInstance().identify(identify);

final Identify identify = Identify()
                          ..preInsert('existing_list', 'some_property')
Amplitude.getInstance().identify(identify);

final Identify identify = Identify()
                          ..postInsert('existing_list','some_property')
Amplitude.getInstance().identify(identify);

Map<String, dynamic> userProps = {
  'KEY': 'VALUE',
  'OTHER_KEY': 'OTHER_VALUE'
};
Amplitude.getInstance().setUserProperties(userProperties);

const colors = ["rose", "gold"];
const numbers = [4, 5];
final Identify identify = Identify()
                          ..set("colors", colors)
                          ..append("ab-tests", "campaign_a")
                          ..prepend("existing_list", numbers);
Amplitude.getInstance().identify(identify);

const array = ["some_string", 56];
final Identify identify = Identify()
                          ..append("ab-tests", "new-user-test")
                          ..prepend("some_list", array)
Amplitude.getInstance().identify(identify);

Amplitude.getInstance().clearUserProperties();

const array = ["some_string", 56];
final Identify identify = Identify()
                          ..remove("ab-tests", "new-user-test")
                          ..remove("some_list",array);
Amplitude.getInstance().identify(identify);

final Identify identify = Identify()
                          ..unset("ab-tests", "new-user-test")
                          ..unset("some_list",array);
Amplitude.getInstance().identify(identify)

String productId = "product001";
int quantity = 2;
double price = 20;
double amount = 35;
Amplitude.getInstance().logRevenue(productId, quantity, price);
Amplitude.getInstance().logRevenueAmount(amount);

final Identify identify = Identify()
                          ..set("gender", "female")
                          ..set("age", 20);
Amplitude.getInstance().groupIdentify("groupType", "groupValue", identify);

//Enable automatically log start and end session events
Amplitude.getInstance().trackingSessionEvents(true);
//Disable automatically log start and end session events
Amplitude.getInstance().trackingSessionEvents(false);

Amplitude.getInstance().setUserId("test_user_id");

Amplitude.getInstance().setDeviceId('test_device_id');

// Enable COPPA Control
Amplitude.getInstance().enableCoppaControl();
// Disable COPPA Control
Amplitude.getInstance().disableCoppaControl();

//Disables instrumentation
Amplitude.getInstance().setOptOut(true);
//Enables instrumentation
Amplitude.getInstance().setOptOut(false);

Amplitude.getInstance().setUseDynamicConfig(true);

<script type="text/javascript" defer>
  (function (e, t) {
    var n = e.amplitude || { _q: [], _iq: {} };
    var r = t.createElement("script");
    r.type = "text/javascript";
    r.integrity =
      "sha384-UcvEbHmT0LE2ZB30Y3FmY3Nfw6puAKXz/LpCFuoywywYikMOr/519Uu1yNq2nL9w";
    r.crossOrigin = "anonymous";
    r.async = true;
    r.src = "https://cdn.amplitude.com/libs/amplitude-8.12.0-min.gz.js";
    r.onload = function () {
      if (!e.amplitude.runQueuedFunctions) {
        console.log("[Amplitude] Error: could not load SDK");
      }
    };
    var s = t.getElementsByTagName("script")[0];
    s.parentNode.insertBefore(r, s);
    function i(e, t) {
      e.prototype[t] = function () {
        this._q.push([t].concat(Array.prototype.slice.call(arguments, 0)));
        return this;
      };
    }
    var o = function () {
      this._q = [];
      return this;
    };
    var a = [
      "add",
      "append",
      "clearAll",
      "prepend",
      "set",
      "setOnce",
      "unset",
      "preInsert",
      "postInsert",
      "remove",
    ];
    for (var c = 0; c < a.length; c++) {
      i(o, a[c]);
    }
    n.Identify = o;
    var u = function () {
      this._q = [];
      return this;
    };
    var l = [
      "setProductId",
      "setQuantity",
      "setPrice",
      "setRevenueType",
      "setEventProperties",
    ];
    for (var p = 0; p < l.length; p++) {
      i(u, l[p]);
    }
    n.Revenue = u;
    var d = [
      "init",
      "logEvent",
      "logRevenue",
      "setUserId",
      "setUserProperties",
      "setOptOut",
      "setVersionName",
      "setDomain",
      "setDeviceId",
      "enableTracking",
      "setGlobalUserProperties",
      "identify",
      "clearUserProperties",
      "setGroup",
      "logRevenueV2",
      "regenerateDeviceId",
      "groupIdentify",
      "onInit",
      "logEventWithTimestamp",
      "logEventWithGroups",
      "setSessionId",
      "resetSessionId",
      "getDeviceId",
      "getUserId",
      "setMinTimeBetweenSessionsMillis",
      "setEventUploadThreshold",
      "setUseDynamicConfig",
      "setServerZone",
      "setServerUrl",
      "sendEvents",
      "setLibrary",
      "setTransport",
    ];
    function v(e) {
      function t(t) {
        e[t] = function () {
          e._q.push([t].concat(Array.prototype.slice.call(arguments, 0)));
        };
      }
      for (var n = 0; n < d.length; n++) {
        t(d[n]);
      }
    }
    v(n);
    n.getInstance = function (e) {
      e = (!e || e.length === 0 ? "$default_instance" : e).toLowerCase();
      if (!Object.prototype.hasOwnProperty.call(n._iq, e)) {
        n._iq[e] = { _q: [] };
        v(n._iq[e]);
      }
      return n._iq[e];
    };
    e.amplitude = n;
  })(window, document);
</script>