Dart Cheat Sheet

By Syncfusion®, Inc. · Last updated November 11, 2026

A lookup page for the whole course: one table per topic, from data types and null safety to classes, patterns, async code, files and JSON.

What Is This Page?

Reference page = a page you look things up in, not one you read from top to bottom.

Nobody remembers every method name. Programmers remember that a tool exists, then look up how to spell it.

This page gives you:

• one table per topic, in course order
• a Run box wherever seeing beats reading
• the traps worth keeping in your head

Simple lesson: remember that a tool exists, and look up the details here.

A Real-World Example

A developer building a school app forgets whether it is trim() or strip(). They do not reread a whole tutorial. They open a reference, find the strings table, and get the answer in seconds. This page is that reference for everything in the course.

types and null safety

if, switch, loops

functions, libraries

lists, sets, maps

classes and patterns

async, files, JSON

Dart

Every topic of the course, on one page.

Here is most of the course working together in one program:

The whole course in one program

class Result {
  final String name;
  final String subject;
  final int mark;

  Result(this.name, this.subject, this.mark);

  String get grade => mark >= 35 ? 'pass' : 'fail';
}

void main() {
  var results = [
    Result('Asha', 'Maths', 78),
    Result('Ravi', 'Science', 85),
    Result('Meera', 'English', 30),
  ];

  results.sort((a, b) => b.mark.compareTo(a.mark));
  for (var r in results) {
    print('${r.name.padRight(8)}${r.subject.padRight(10)}${r.mark.toString().padLeft(4)}  ${r.grade}');
  }

  var passed = results.where((r) => r.grade == 'pass').length;
  var average = results.map((r) => r.mark).reduce((a, b) => a + b) / results.length;
  print('$passed of ${results.length} passed, average ${average.toStringAsFixed(1)}');
}

What You Will Learn

On this page, you will find:

1. The syntax for every topic in the course.
2. Run boxes for the trickiest parts.
3. The traps worth remembering, in one table.

Data Types

Every basic type from the course, side by side:

The ways to make a variable:

Checking and converting

void main() {
  var text = '78';
  print(text.runtimeType);
  print(int.parse(text) + 2);
  print(int.tryParse('abc'));
  print(double.parse('78.5').round());
  print(78.toString().length);
  print((2 / 3).toStringAsFixed(2));
}

int.parse crashes on bad text. int.tryParse gives null instead.

Keywords

Keyword = a word Dart keeps for itself. You cannot use most of them as names.

Contextual keyword = a word like on, show or async that is special only in one place. You can still use it as a variable name.

Operators

The operator groups:

The ones that surprise people

void main() {
  print(7 / 2);
  print(7 ~/ 2);
  print(-7 ~/ 2);
  print(7 % 2);
  int? bonus;
  print(88 + (bonus ?? 5));
  var list = [3, 1, 2]..sort();
  print(list);
}

/ always gives a double. ~/ gives an int and drops the part after the point.

Null Safety

Conditional Statements

Loops

Functions

Control flow and functions

String grade(int m) => switch (m) {
  >= 90 => 'A',
  >= 75 => 'B',
  _ => 'C',
};

void greet({required String name, String title = 'Student'}) {
  print('Hello, $title $name');
}

void main() {
  for (var m in [95, 80, 60]) {
    print('$m: ${grade(m)}');
  }
  greet(name: 'Asha');
}

Libraries and Packages

The core libraries you will use most: dart:core (automatic), dart:math, dart:convert, dart:io, dart:async, dart:isolate.

Collections

The iterable methods:

Collections in one go

void main() {
  var marks = {'Asha': 92, 'Ravi': 75, 'Priya': 85};
  var good = marks.entries.where((e) => e.value >= 80).map((e) => e.key).toList();
  print(good);
  print(marks.values.fold(0, (a, b) => a + b));
  var unique = {...[1, 2, 2, 3]};
  print(unique);
}

String Methods

Also remember:

• '$name' puts a variable in text. '${a + b}' puts an expression.
• '''...''' makes text over many lines.
• For many joins, use StringBuffer: sb.write('x'), then sb.toString().

Date and Time

Strings and dates

void main() {
  var parts = 'Asha,8A,91'.split(',');
  print('${parts[0].toUpperCase()} ${parts.length}');
  var exam = DateTime(2026, 11, 14, 9, 30);
  var end = exam.add(Duration(hours: 3));
  print('${end.hour}:${end.minute.toString().padLeft(2, '0')}');
  print(DateTime(2026, 12, 25).difference(exam).inDays);
}

Classes and Objects

Inheritance, Polymorphism and Mixins

The class modifiers:

A small class family

abstract class Shape {
  double area();
}

class Square extends Shape {
  final double side;
  Square(this.side);
  @override
  double area() => side * side;
}

mixin Named {
  String get label => 'Shape #1';
}

class LabelledSquare extends Square with Named {
  LabelledSquare(super.side);
}

void main() {
  var s = LabelledSquare(2.5);
  print('${s.label}: ${s.area()}');
}

Enums and Generics

Records and Patterns

Records and patterns

(int, int) minMax(List<int> xs) {
  var sorted = [...xs]..sort();
  return (sorted.first, sorted.last);
}

void main() {
  var (low, high) = minMax([72, 95, 64]);
  print('$low to $high');
  var data = {'name': 'Ravi', 'marks': 75};
  if (data case {'name': String n, 'marks': int m} when m >= 35) {
    print('$n passed');
  }
}

Exception Handling

Exception = something that can go wrong in normal use, like bad input. Error = a bug in the program, like a wrong index. Catch exceptions, fix errors.

Async: Futures, Streams and Isolates

File Handling and JSON

Async, exceptions and JSON together

import 'dart:convert';

Future<String> fetch() => Future.delayed(Duration(seconds: 1), () => '{"name": "Asha", "marks": [92, 88]}');

Future<void> main() async {
  try {
    var data = jsonDecode(await fetch());
    print('${data['name']}: ${data['marks']}');
    jsonDecode('oops');
  } on FormatException {
    print('Bad JSON skipped');
  } finally {
    print('done');
  }
}

TL;DR

1. Types = int, double, String, bool, List, Set, Map, and ? for null.
2. Variables = var, final, const, late.
3. Control flow = if, switch expressions, for, for-in, while.
4. Functions = arrow =>, optional [], named {}, closures.
5. OOP = classes, extends, implements, with, modifiers, generics, enums.
6. Records and patterns = (a, b), var (x, y) =, case, when.
7. Safety = try / on / catch / finally.
8. Async and data = async / await, Streams, isolates, dart:io, dart:convert.

Common mistakes

The most common mistakes from the whole course, in one place.

Check Yourself

Exercises

What to Remember

• Nobody remembers everything. Know a tool exists, and look up the spelling.
• Type . after a value and your editor lists what it can do.
• / gives a double. ~/ gives an int.
• T? allows null. Handle it with ??, ?. or a check, not with !.
• final is set once at run time. const is fixed before the program runs.
• {} is an empty map. Write <int>{} for an empty set.
• Months in DateTime start at 1.
• async functions give a Future. await it before you use the value.
• The first matching on block wins, so go specific to general.
• Writing a file replaces it. Use FileMode.append to add.

You have finished the Dart course. Next, try building a small app of your own, like a marks tracker that saves to a JSON file.