I want to add the contents of a file to a list, but somehow the list seems to not get filled. Maybe we need some asynchronous code here.
Please help!
class App {
Map<String, List<Model>> models = {
'users': List<User>(),
'groups': List<Group>(),
'events': List<Event>()
};
App() {
loadUsers();
print(models['users']); // prints empty list: []
}
void loadUsers () {
Directory usersDirectory = Directory.fromUri(Uri(path: './app/data/users'));
usersDirectory.list(recursive: false).listen((FileSystemEntity userFile) async {
Map<String, dynamic> userFileContent = jsonDecode(await File(userFile.uri.path).readAsString());
models['users'].add(User.fromJson(userFileContent));
});
}
}
Thank you.
Try to get directories without listen:
usersDirectory.listSync(recursive: false).forEach((userFile) {
Map<String, dynamic> userFileContent = jsonDecode(await File(userFile.uri.path).readAsStringSync());
models['users'].add(User.fromJson(userFileContent));
);
Related
I want to create a map using the path
generateNestedMap("foo.bar.baz", "someValue")
and the output should be
Output: {'foo'{'bar':{'baz': 'someValue'}}}
Run this in dartpad. No recursion required. Just build it from inside-out:
void main() {
print(generateNestedMap("foo.bar.baz", "someValue"));
}
Map generateNestedMap(String path, String payload) {
var steps = path.split('.');
Object result = payload;
for (var step in steps.reversed) {
result = {step : result};
}
return result as Map;
}
EDIT: Or, as I suggested in one of the comments, a little fancier, but cool:
void main() {
print(generateNestedMap("foo.bar.baz", "someValue"));
}
Map generateNestedMap(String path, String payload) {
var steps = path.split('.');
var result = steps.reversed.fold(payload, (old, next) => {next: old});
return result as Map;
}
I try to localize a String in Flutter with the localization package. The problem is the location where my translation is needed. It is not related to the UI, rather it is somewhere deep in my model, where I don't have access to a BuildContext. Is there any other possibility to still make use of the translation function?
// I don't have a context variable here
MyLocalizations.of(context).trans("foo")
Yes there is. You don't need BuildContext to access strings. Here is my solution:
class Strings {
Strings._(Locale locale) : _localeName = locale.toString() {
current = this;
}
final String _localeName;
static Strings current;
static Future<Strings> load(Locale locale) async {
await initializeMessages(locale.toString());
final result = Strings._(locale);
return result;
}
static Strings of(BuildContext context) {
return Localizations.of<Strings>(context, Strings);
}
String get title {
return Intl.message(
'Hello World',
name: 'title',
desc: 'Title for the Demo application',
);
}
}
Future<Null> main() async {
final Locale myLocale = Locale(window.locale);
await Strings.load(myLocale);
runApp(MyApplication());
}
Now you can reference a string as follows:
final title = Strings.current.title;
I know this question is dated way back. But I came across this issue when implementing my application, and I dont see any "nice" way to handle it.
So here is my approach
class LanguageService {
static String defaultLanguage = 'en';
static Map<String, Map<String, String>> _localizedValues = {
'en': {
'title': 'Storefront',
'language': 'Language',
'googleLogin': 'Login with Google'
},
'vn': {
'title': 'Cửa hàng',
'language': 'Ngôn ngữ',
'googleLogin': 'Đăng Nhập với Google'
}
};
static set language(String lang) {
defaultLanguage = lang;
}
static String get title {
return _localizedValues[defaultLanguage]['title'];
}
static String get language {
return _localizedValues[defaultLanguage]['language'];
}
static String get googleLogin {
return _localizedValues[defaultLanguage]['googleLogin'];
}
}
Now you can reference a string as follows:
String title = LanguageService.title;
You can find the detailed tutorial here
AppLocalitzations needs the context.
You can create a class (e.g., Localization) to encapsulate AppLocalizations initialization and initialize it from the home widget using its context. After, can be used with a mixin:
import 'package:flutter/widgets.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
class Localization {
static AppLocalizations _loc;
AppLocalizations get loc => Localization._loc;
static void init(BuildContext context) => _loc = AppLocalizations.of(context);
}
In the home widget:
...
#override
Widget build(BuildContext context) {
Localization.init(context);
return Scaffold(
...
Access to loc in some class (it isn't necessary to be a Widget) using mixins:
class XXXWidget extends StatelessWidget with Localization {
...
Text(loc.xxxx)
...
}
class _XXXXWidgetState extends State<XXXWidget> with Localization {
...
Text(loc.xxxx)
...
}
class XXXXController with Localization {
...
cardNumberValidator = RequiredValidator(errorText: loc.commons_Required);
...
}
Null safety version:
class Localization {
static AppLocalizations? _l;
AppLocalizations get loc => Localization._l!;
static void init(BuildContext context) => _l = AppLocalizations.of(context)!;
}
No, there is no other way because it is stored using an InheritedWidget, which is a part of the build tree and thus can only be accessed with a reference to it (the BuildContext).
You will need to pass your context to somewhere deep in your model.
I am not sure if i did it right (from performance point of view) and maybe someone can comment on this but i have rx BehaviorSubject in my AppLocalization and fire event once new locales are loaded. I am listening to it in my main.dart and doing setState on receiving an event.
I checked performance tab but did not noticed any big changes in it once comparing my method vs accessing translations through context (inherited widget).
I have defined a static var as Map for all instances of my element. If it contains a specific key, it should use the value. If the key is not contains the instance should get the data with a request and save it in the static map, so other instances could use it.
static var data = new Map();
func() {
if (Elem.data.containsKey(['key']) {
list = Elem.data['key'];
}
else {
Helper.getData().then((requestedData) {
list = requestedData;
Elem.data.addAll({ 'key' : requestedData });
}
}
The Problem is that all my instances go into the else, since the key is not contained in the Map at the moment the other instances are at the if. So i need them to wait, until the Data is in the Map.
static var data = new Map();
static Completer _dataCompleter;
Future<bool> func() {
if(_dataCompleter == null) {
_dataCompleter = new Completer();
Helper.getData().then((requestedData) {
list = requestedData;
Elem.data.addAll({ 'key' : requestedData });
_dataCompleter.complete(true);
})
}
if(_dataCompleter.isCompleted) {
return new Future.value(true);
}
return _dataCompleter.future;
}
and call it like
func().then((success) => /* continue here when `key` in `data` has a value.
In response to Günter Zöchbauer. I generally avoid using Completers directly:
static var data = new Map();
static Future _pendingFuture;
Future func() {
if (_pendingFuture == null) {
_pendingFuture = Helper.getData().then((requestedData) {
list = requestedData;
Elem.data.addAll({ 'key' : requestedData });
});
}
return _pendingFuture;
}
I am trying to write an i18n app. The program read a json file, that contains translation from languages and it based on json structure.
{
"EN": {
"TEXT1": "Hello",
"TEXT2": "March"
},
"DE": {
"TEXT1": "Hallo",
"TEXT2": "März"
}
}
My program read the json file in async way with the file class, the whole code
import 'dart:io';
import 'dart:async';
import 'package:json_object/json_object.dart';
abstract class I18n {
static _I18n _i18n;
factory I18n(String file, String lang) {
if(_i18n == null) {
_i18n = new _I18n(file, lang);
return _i18n;
}
return _i18n;
}
Future<String> getTextByMap(String textId);
}
class _I18n implements I18n {
File _file;
String _lang;
JsonObject _jsonContainer;
JsonObject _jsonFiltered;
Future<JsonObject> _imme;
// Parameters:
// file: The whole path and filename
// lang: Expected language
_I18n(String file, this._lang) {
this._file = new File(file);
}
// Read file and return the content of file.
Future<String> _readFileFromStream() {
var com = new Completer();
this._file.exists()
.then((fileExists) {
if(!fileExists) {
throw new StateError('File not found');
}
return this._file.readAsString()
.then((stream) => com.complete(stream));
});
return com.future;
}
void _convertContentToJson(String stream) {
this._jsonContainer = new JsonObject.fromJsonString(stream);
}
Future<JsonObject> _prepareData() {
return this._readFileFromStream().then((stream) {
_convertContentToJson(stream);
this._jsonFiltered = this._jsonContainer[this._lang];
return this._jsonFiltered;
});
}
Future<String> getTextByMap(String textId) {
return this._prepareData().then((filterd) {
return filterd[textId];
});
}
}
and the main code
import 'package:i18n/i18n.dart';
void main() {
var i18n = new I18n('../hello.json', 'EN');
i18n.getTextByMap('TEXT1').then((val) => print(val));
i18n.getTextByMap('TEXT2').then((val) => print(val));
}
Everything here, happen in dart async way, read json file etc. And everytime, when i call the method
i18n.getTextByMap('TEXT1').then((val) => print(val));
it gonna read the json file again and again. I tried to rewrite the method to prevent reading json file many times
Future<String> getTextByMap(String textId) {
if(this._jsonFiltered == null)
{
return this._prepareData().then((filterd) {
return filterd[textId];
});
}
return new Future(() => this._jsonFiltered[textId]);
}
but it doesn't work too, because dart works in async way.
My question is, how can i keep this json file content in an object? Read json file only one time and keep the contents in an object, it is better then read json file everytime, that is my opinion.
It could do everything in sync way, then i wouldn't have such as problem but this is not dart terminology.
In which order do dart execute I/O operations, like this?
Future
I/O Events
My solution would be to create a class with a factory constructor. The factory constructor always returns a object of that file.
Your problem is that futures are parallel. So both calls are executed in parallel. The solution is to let the first future complete and then do other stuff to be able to get cached results.
Then you can have a read() method that reads the value of the file if it is not present in the classes "contents" attribute for example - or if that attribute is not null, it loads the file in background.
In both cases a completer or future is returned you can listen on.
EDIT Example Code:
example_async_file_factory.dart
import 'dart:io';
import 'dart:async';
class FileHolder {
String _contents = null;
String path;
static Map<String, FileHolder> _files;
factory FileHolder(String path) {
if (_files == null) {
_files = {};
}
if (_files.containsKey(path)) {
return _files[path];
} else {
final fh = new FileHolder._internal(path);
_files[path] = fh;
return fh;
}
}
FileHolder._internal(this.path);
Future<String> getContents() {
if(_contents != null) {
print("cached");
return new Future.value(_contents);
} else {
print("read");
File f = new File(this.path);
Future<String> future = f.readAsString();
Completer completer = new Completer();
future.then((String c) {
_contents = c;
completer.complete(_contents);
});
return completer.future;
}
}
}
void main() {
FileHolder f = new FileHolder("example_async_file_factory.dart");
f.getContents().then((String contents) {
print(contents.length);
FileHolder f2 = new FileHolder("example_async_file_factory.dart");
f2.getContents().then((String contents) {
print(contents.length);
});
f2.getContents().then((String contents) {
print(contents.length);
});
f.getContents().then((String contents) {
print(contents.length);
});
});
}
Output:
read
1411
cached
cached
cached
1411
1411
1411
Regards
Robert
I would like to be able to back a dynamic property with a Map using a lookup in noSuchMethod(). However the latest changes makes the incoming property reference name unavailable. I can understand the minification scenario requiring us to use Symbols rather than Strings for names, but this makes implementing serializable dynamic properties difficult. Anyone have good ideas on how to approach this problem?
I can't use String names since the String names are not fixed between calls to the minifier. (This would completely break serialization)
You can access the original name with MirrorSystem.getName(symbol)
So a dynamic class could look like :
import 'dart:mirrors';
class A {
final _properties = new Map<String, Object>();
noSuchMethod(Invocation invocation) {
if (invocation.isAccessor) {
final realName = MirrorSystem.getName(invocation.memberName);
if (invocation.isSetter) {
// for setter realname looks like "prop=" so we remove the "="
final name = realName.substring(0, realName.length - 1);
_properties[name] = invocation.positionalArguments.first;
return;
} else {
return _properties[realName];
}
}
return super.noSuchMethod(invocation);
}
}
main() {
final a = new A();
a.i = 151;
print(a.i); // print 151
a.someMethod(); // throws
}
You could do something like this:
import 'dart:json' as json;
main() {
var t = new Thingy();
print(t.bob());
print(t.jim());
print(json.stringify(t));
}
class Thingy {
Thingy() {
_map[const Symbol('bob')] = "blah";
_map[const Symbol('jim')] = "oi";
}
final Map<Symbol, String> _map = new Map<Symbol, String>();
noSuchMethod(Invocation invocation) {
return _map[invocation.memberName];
}
toJson() => {
'bob': _map[const Symbol('bob')],
'jim': _map[const Symbol('jim')]};
}
Update - dynamic example:
import 'dart:json' as json;
main() {
var t = new Thingy();
t.add('bob', 'blah');
t.add('jim', 42);
print(t.bob());
print(t.jim());
print(json.stringify(t));
}
class Thingy {
final Map<Symbol, String> _keys = new Map<Symbol, String>();
final Map<Symbol, dynamic> _values = new Map<Symbol, dynamic>();
add(String key, dynamic value) {
_keys[new Symbol(key)] = key;
_values[new Symbol(key)] = value;
}
noSuchMethod(Invocation invocation) {
return _values[invocation.memberName];
}
toJson() {
var map = new Map<String, dynamic>();
_keys.forEach((symbol, name) => map[name] = _values[symbol]);
return map;
}
}
If you only need "dynamic properties", it should be enough to use Symbols as keys in the Map. If you also want to serialize that map, then you need to keep track of the original String names and use those for serialization. When deserializing, you'd have to create new Symbols from those Strings.
Note that all these scenarios (and basically everything that involves new Symbol) require a compiler to create a mapping of original names to the minified ones and put this mapping into the program, which of course makes it bigger.
Thanks for the solution of #Alexandre Ardhuin, I made some modification to make it runnable.
import 'dart:mirrors';
class object {
final _properties = new Map<String, Object>();
object();
object.from(Map<String, Object> initial) {
initial.entries.forEach((element) => _properties[element.key] = element.value);
}
noSuchMethod(Invocation invocation) {
if (invocation.isAccessor) {
final realName = MirrorSystem.getName(invocation.memberName);
if (invocation.isSetter) {
// for setter realname looks like "prop=" so we remove the "="
final name = realName.substring(0, realName.length - 1);
_properties[name] = invocation.positionalArguments.first;
return;
} else {
return _properties[realName];
}
}
return super.noSuchMethod(invocation);
}
#override
String toString() {
return _properties.toString();
}
}
main() {
// we can't use var or object type here, because analysis will consider
// https://dart.dev/tools/diagnostic-messages#undefined_setter
// The setter 'i' isn't defined for the type 'object'
// So dynamic is required here!
dynamic a = object.from({'a': 123, 'b': 234});
a.i = 151;
print(a); // print {a: 123, b: 234, i: 151}
try {
a.someMethod(); // throws NoSuchMethodError
} catch (e) {
print(e);
}
}