Before enums were available in Dart I wrote some cumbersome and hard to maintain code to simulate enums and now want to simplify it. I need to get the name of the enum as a string such as can be done with Java but cannot.
For instance little test code snippet returns 'day.MONDAY' in each case when what I want is 'MONDAY"
enum day {MONDAY, TUESDAY}
print( 'Today is $day.MONDAY');
print( 'Today is $day.MONDAY.toString()');
Am I correct that to get just 'MONDAY' I will need to parse the string?
Dart 2.7 comes with new feature called Extension methods. Now you can write your own methods for Enum as simple as that!
enum Day { monday, tuesday }
extension ParseToString on Day {
String toShortString() {
return this.toString().split('.').last;
}
}
main() {
Day monday = Day.monday;
print(monday.toShortString()); //prints 'monday'
}
Bit shorter:
String day = theDay.toString().split('.').last;
Update Dart 2.15:
enum Day {
monday,
tuesday,
}
You can use name property on the enum.
String monday = Day.monday.name; // 'monday'
Old solution:
1. Direct way:
var dayInString = describeEnum(Day.monday);
print(dayInString); // prints 'monday'
2. Using Extension:
extension DayEx on Day {
String get name => describeEnum(this);
}
You can use it like:
void main() {
Day monday = Day.monday;
print(monday.name); // 'monday'
}
It used to be correct that the only way to get the source name
of the enum value was through the toString method which returns "day.MONDAY", and not the more useful "MONDAY".
Since Dart 2.15, enums have exposed a extension getter which returns just the source name, so day.MONDAY.name == "MONDAY".
Since Dart 2.17, you can also add your own members to enum declarations, and choose to provide another name for
a value than justits source name, e.g., with a more appropriate capitalization:
enum Day {
monday("Monday"),
tuesday("Tuesday"),
// ...
saturday("Saturday");
sunday("Sunday");
final String name;
Day(this.name);
// And other members too.
bool get isWorkday => index < saturday.index;
}
Then you get Day.sunday.name == "Sunday" (hiding the extension name getter which would return "sunday").
Before these features, you could only get the name from the toString string, extracting the rest of the string as:
day theDay = day.MONDAY;
print(theDay.toString().substring(theDay.toString().indexOf('.') + 1));
which was admittedly hardly convenient.
Another way to get the enum name as a string, one which is shorter, but also less efficient because it creates an unnecessary string for first part of the string too, was:
theDay.toString().split('.').last
If performance doesn't matter, that's probably what I'd write, just for brevity.
If you want to iterate all the values, you can do it using day.values:
for (day theDay in day.values) {
print(theDay);
}
Simplest way to get the name of an enum is a standard method from the flutter/foundation.dart
describeEnum(enumObject)
enum Day {
monday, tuesday, wednesday, thursday, friday, saturday, sunday
}
void validateDescribeEnum() {
assert(Day.monday.toString() == 'Day.monday');
assert(describeEnum(Day.monday) == 'monday');
}
enum day {MONDAY, TUESDAY}
print( 'Today is ${describeEnum(day.MONDAY)}' );
console output: Today is MONDAY
There is a more elegant solution:
enum SomeStatus {
element1,
element2,
element3,
element4,
}
const Map<SomeStatus, String> SomeStatusName = {
SomeStatus.element1: "Element 1",
SomeStatus.element2: "Element 2",
SomeStatus.element3: "Element 3",
SomeStatus.element4: "Element 4",
};
print(SomeStatusName[SomeStatus.element2]) // prints: "Element 2"
Sometimes I need to separate ui-value and real-value, so I defined keys and values using Map. This way, we have more flexiblity. And by using extension (since Dart 2.7), I made a method to read its key and value.
enum Status {
progess,
done,
}
extension StatusExt on Status {
static const Map<Status, String> keys = {
Status.progess: 'progess',
Status.done: 'done',
};
static const Map<Status, String> values = {
Status.progess: 'In Progress',
Status.done: 'Well done',
};
String get key => keys[this];
String get value => values[this];
// NEW
static Status fromRaw(String raw) => keys.entries
.firstWhere((e) => e.value == raw, orElse: () => null)
?.key;
}
// usage 1
Status status = Status.done;
String statusKey = status.key; // done
String statusValue = status.value; // Well done
// usage 2 (easy to make key and value list)
List<Status> statuses = Status.values;
List<String> statusKeys = statuses.map((e) => e.key).toList();
List<String> statusValues = statuses.map((e) => e.value).toList();
// usage 3. create Status enum from string.
Status done1 = StatusExt.fromRaw('done') // Status.done
Status done2 = StatusExt.fromRaw('dude') // null
With Dart 2.17 we now have general support for members on enums. That means we can add fields holding state, constructors that set that state, methods with functionality, and even override existing members.
Example:
enum Day {
MONDAY("Monday"),
TUESDAY("Tuesday");
const Day(this.text);
final String text;
}
Output:
void main() {
const day = Day.MONDAY;
print(day.text); /// Monday
}
For above functionality override dart version like below which target 2.17 and greater
environment:
sdk: ">=2.17.0 <3.0.0"
I got so over this I made a package:
https://pub.dev/packages/enum_to_string
Also has a handy function that takes enum.ValueOne and parses it to "Value one"
Its a simple little library but its unit tested and I welcome any additions for edge cases.
I use the functions below to get the name of the enum value and, vise versa, the enum value by the name:
String enumValueToString(Object o) => o.toString().split('.').last;
T enumValueFromString<T>(String key, Iterable<T> values) => values.firstWhere(
(v) => v != null && key == enumValueToString(v),
orElse: () => null,
);
When using Dart 2.7 and newer, extension methods would work here (as well as for any other Objects):
extension EnumX on Object {
String asString() => toString().split('.').last;
}
The implementation above is not dependant on the specific enums.
Usage examples:
enum Fruits {avocado, banana, orange}
...
final banana = enumValueFromString('banana', Fruits.values);
print(enumValueToString(banana)); // prints: "banana"
print(banana.asString()); // prints: "banana"
Edit from 2020-04-05: Added nullability checks. values parameter could be Iterable, not necessarily List. Added extensions method implementation. Removed <Fruits> annotation from the example to show that the class name duplication is not required.
I use structure like below:
abstract class Strings {
static const angry = "Dammit!";
static const happy = "Yay!";
static const sad = "QQ";
}
Dart 2.15 includes an extension to make this easy:
enum day {MONDAY, TUESDAY}
print( 'Today is ${day.MONDAY.name}');
Until the changes in https://github.com/dart-lang/sdk/commit/18f37dd8f3db6486f785b2c42a48dfa82de0948b are rolled out to a stable version of Dart, the other clever but more complex answers here are very useful.
One more way:
enum Length {
TEN,
TWENTY,
THIRTY,
NONE,
}
extension LengthValue on Length {
static const _values = [10, 20, 30, 0];
int get value => _values[this.index];
}
since dart 2.15 just use ".name"
enum day {monday, tuesday}
print( 'Today is ${day.monday.name}');
My approach is not fundamentally different, but might be slightly more convenient in some cases:
enum Day {
monday,
tuesday,
}
String dayToString(Day d) {
return '$d'.split('.').last;
}
In Dart, you cannot customize an enum's toString method, so I think this helper function workaround is necessary and it's one of the best approaches. If you wanted to be more correct in this case, you could make the first letter of the returned string uppercase.
You could also add a dayFromString function
Day dayFromString(String s) {
return Day.values.firstWhere((v) => dayToString(v) == s);
}
Example usage:
void main() {
Day today = Day.monday;
print('Today is: ${dayToString(today)}');
Day tomorrow = dayFromString("tuesday");
print(tomorrow is Day);
}
enum day {MONDAY, TUESDAY}
print(day.toString().split('.')[1]);
OR
print(day.toString().split('.').last);
Create a class to help:
class Enum {
Enum._();
static String name(value) {
return value.toString().split('.').last;
}
}
and call:
Enum.name(myEnumValue);
One of the good ways I found in the answer is
String day = theDay.toString().split('.').last;
But I would not suggest doing this as dart provide us a better way.
Define an extension for the enum, may be in the same file as:
enum Day {
monday, tuesday, wednesday, thursday, friday, saturday, sunday
}
extension DayExtension on Day {
String get value => describeEnum(this);
}
You need to do import 'package:flutter/foundation.dart'; for this.
I had the same problem in one of my projects and existing solutions were not very clean and it didn't support advanced features like json serialization/deserialization.
Flutter natively doesn't currently support enum with values, however, I managed to develop a helper package Vnum using class and reflectors implementation to overcome this issue.
Address to the repository:
https://github.com/AmirKamali/Flutter_Vnum
To answer your problem using Vnum, you could implement your code as below:
#VnumDefinition
class Visibility extends Vnum<String> {
static const VISIBLE = const Visibility.define("VISIBLE");
static const COLLAPSED = const Visibility.define("COLLAPSED");
static const HIDDEN = const Visibility.define("HIDDEN");
const Visibility.define(String fromValue) : super.define(fromValue);
factory Visibility(String value) => Vnum.fromValue(value,Visibility);
}
You can use it like :
var visibility = Visibility('COLLAPSED');
print(visibility.value);
There's more documentation in the github repo, hope it helps you out.
Instead of defining extension for every enum, we can define extension on object and get access to .enumValue from any enum.
void main() {
// ❌ Without Extension ❌
print(Countries.Cote_d_Ivoire.toString().split('.').last.replaceAll("_", " ")); // Cote d Ivoire
print(Movies.Romance.toString().split('.').last.replaceAll("_", " ")); //Romance
// ✅ With Extension ✅
print(Countries.Cote_d_Ivoire.enumValue); // Cote d Ivoire
print(Movies.Romance.enumValue); //Romance
}
enum Countries { United_States, United_Kingdom, Germany, Japan, Cote_d_Ivoire }
enum Movies { Romance, Science_Fiction, Romantic_Comedy, Martial_arts }
extension PrettyEnum on Object {
String get enumValue => this.toString().split('.').last.replaceAll("_", " ");
}
With this, you can even define multi-word enum where words are separated by _(underscore) in its name.
As from Dart 2.15, you can get enum value from
print(MyEnum.one.name);
// and for getting enum from value you use
print(MyEnum.values.byName('two');
try this solution:
extension EnumValueToString on Enum {
String valueAsString() {
return describeEnum(this);
}
}
how to used it:
enum.valueAsString()
dart 2.15 is now supporting this
you can just type
print(day.MONDAY.name); //gives you: MONDAY
Since Dart 2.15, we can just do Day.monday.name, where
enum Day { monday, tuesday }
As from Dart version 2.15, you can access the String value of an enum constant using .name:
enum day {MONDAY, TUESDAY}
void main() {
print('Today is ${day.MONDAY.name}');
// Outputs: Today is MONDAY
}
You can read in detail about all the enum improvements in the official Dart 2.15 release blog post.
as of dart 2.15 you can use .name to get the name of enum elements.
enum day {MONDAY, TUESDAY}
print(day.MONDAY.name); // prints MONDAY
Dart version 2.15 has introduced name property on enums.
Example
void main() {
MyEnum.values.forEach((e) => print(e.name));
}
enum MyEnum { value1, Value2, VALUE2 }
Output:
value1
Value2
VALUE2
For those who require enum with values use this approach as Dart doesn't support this:
class MyEnumClass {
static String get KEY_1 => 'value 1';
static String get KEY_2 => 'value 2';
static String get KEY_3 => 'value 3';
...
}
// Usage:
print(MyEnumClass.KEY_1); // value 1
print(MyEnumClass.KEY_2); // value 2
print(MyEnumClass.KEY_3); // value 3
...
And sure you may put whatever types you need.
now with null safety it looks like this
String enumToString(Object? o) => o != null ? o.toString().split('.').last : '';
T? enumFromString<T>(String key, List<T> values) {
try {
return values.firstWhere((v) => key == enumToString(v));
} catch(e) {
return null;
}
}
I'm getting a Bluetooth Characteristic from a Bluetooth controller with flutter blue as a List. This characteristic contains weight measurement of a Bluetooth scale. Is there a function to convert this list of ints to a Double?
I tried to find some background on float representations by reading the IEEE 754 standard. There is the dart library typed_data but I am new to dart and have no experience with this lib.
Example:
I have this List: [191, 100, 29, 173] which is coming from a bluetooth controller as a IEEE754 representation for a float value.
Now i believe i have to convert each int to hex and concat these values: bf 64 1d ad
Next thing need to do is convert this to double, but i cannot find a function to convert hex to double. Only int.parse("0xbf641dad").
I guess your mean to convert the list of ints to a list of floats, not to a single float, right?
First, dart has no type called float. Instead it has type double. To convert it, you can use the map() function:
var listInt = [1, 2, 3];
var listDouble = list.map((i) => i.toDouble()).toList();
Had this same issue.
I think you mean how do you make the four bytes into a float32 ?
I needed to do the same thing.
you will want to do something like this:
first take the List value as a byte buffer, then take the byte data, then you can use the getFloat32 function.
ByteBuffer buffer = new Int8List.fromList(value_in).buffer;
ByteData byteData = new ByteData.view(buffer);
result = byteData.getFloat32(0);
Just be a little aware that the order of bytes from the Bluetooth may be back to front, as the convention varys.
Also you will need the typed_data library:
import 'dart:typed_data'; //for data formatting
I'm trying to go in the other direction now . . . for the obvious reason.
You may need this:
double parseHexString(String hexStr, bool littleEndian){
if(hexStr.length % 2 != 0){
return 0;
}
if(littleEndian == true){
List<int> bytes = hex.decode(hexStr).reversed.toList();
hexStr = hex.encode(bytes);
}
var byteConvert = ByteData(12);
byteConvert.setInt64(0, int.parse(hexStr,radix: 16));
return byteConvert.getFloat64(0);}
And demo :
double lat = parseHexString("0000004069665E40",true);
//lat = 121.60017395019531
If you already have:
int.parse("0xbf641dad")
I don't see why this wouldn't work:
int.parse("0xbf641dad").toDouble();
I used dart:typed_data for this:
import 'dart:typed_data';
List<int> intList = [191, 100, 29, 173];
double asFloat = ByteData.view(Uint8List.fromList(List.from(intList)).buffer).getFloat32(0, Endian.little);
Library reference: https://api.dart.dev/be/136883/dart-typed_data/dart-typed_data-library.html