In the context of a Flutter 2.0.5 app whose state I'd like to manage with Riverpod, I thought I can declare a StateNotifierProvider like this:
import 'package:flutter_riverpod/flutter_riverpod.dart';
final counterProvider = StateNotifierProvider<CounterStateNotifier>((ref) => CounterStateNotifier());
class CounterStateNotifier extends StateNotifier<int> {
CounterStateNotifier([int count = 0]) : super(count);
void increment() => state++;
}
But Android Studio (and later the Dart compiler as well) complains about the line where I declare the counterProvider variable:
The type 'StateNotifierProvider' is declared with 2 type parameters, but 1 type arguments were given.
Removing the <CounterStateNotifier> type parameter in StateNotifierProvider<CounterStateNotifier> removes the error. However, attempting to read the provider and call its increment method (setting () => context.read(counterProvider).increment() as the onPressed of an ElevatedButton, then pressing the button) gives the following runtime error:
'increment'
method not found
Receiver: 0
Arguments: []
Why is context.read(counterProvider) returning the int state instead of the notifier? And what is the reason behind the type parameter error mentioned in the first part of my question?
I should mention that I'm running my app on the web (with flutter run -d Chrome).
As of Riverpod 0.14.0, State is the default value exposed by StateNotifierProvider.
The syntax for declaring your StateNotifierProvider is now as follows:
final counterProvider = StateNotifierProvider<CounterStateNotifier, int>((ref) => CounterStateNotifier());
Accessing functions now requires adding .notifier (accessing the StateNotifier itself):
context.read(counterProvider.notifier).increment();
And like you've noticed, you now access the state like so:
final count = context.read(counterProvider);
More on the changes here.
You may also use dynamic to accept any type if value for the StateNotifierProvider
final modelProvider =
StateNotifierProvider.autoDispose<ModelClassName, dynamic>(
(ref) => ModelClassName());
This question already has answers here:
Safely turning a JSON string into an object
(28 answers)
Closed 7 years ago.
I want to parse a JSON string in JavaScript. The response is something like
var response = '{"result":true,"count":1}';
How can I get the values result and count from this?
The standard way to parse JSON in JavaScript is JSON.parse()
The JSON API was introduced with ES5 (2011) and has since been implemented in >99% of browsers by market share, and Node.js. Its usage is simple:
const json = '{ "fruit": "pineapple", "fingers": 10 }';
const obj = JSON.parse(json);
console.log(obj.fruit, obj.fingers);
The only time you won't be able to use JSON.parse() is if you are programming for an ancient browser, such as IE 7 (2006), IE 6 (2001), Firefox 3 (2008), Safari 3.x (2009), etc. Alternatively, you may be in an esoteric JavaScript environment that doesn't include the standard APIs. In these cases, use json2.js, the reference implementation of JSON written by Douglas Crockford, the inventor of JSON. That library will provide an implementation of JSON.parse().
When processing extremely large JSON files, JSON.parse() may choke because of its synchronous nature and design. To resolve this, the JSON website recommends third-party libraries such as Oboe.js and clarinet, which provide streaming JSON parsing.
jQuery once had a $.parseJSON() function, but it was deprecated with jQuery 3.0. In any case, for a long time, it was nothing more than a wrapper around JSON.parse().
WARNING!
This answer stems from an ancient era of JavaScript programming during which there was no builtin way to parse JSON. The advice given here is no longer applicable and probably dangerous. From a modern perspective, parsing JSON by involving jQuery or calling eval() is nonsense. Unless you need to support IE 7 or Firefox 3.0, the correct way to parse JSON is JSON.parse().
First of all, you have to make sure that the JSON code is valid.
After that, I would recommend using a JavaScript library such as jQuery or Prototype if you can because these things are handled well in those libraries.
On the other hand, if you don't want to use a library and you can vouch for the validity of the JSON object, I would simply wrap the string in an anonymous function and use the eval function.
This is not recommended if you are getting the JSON object from another source that isn't absolutely trusted because the eval function allows for renegade code if you will.
Here is an example of using the eval function:
var strJSON = '{"result":true,"count":1}';
var objJSON = eval("(function(){return " + strJSON + ";})()");
alert(objJSON.result);
alert(objJSON.count);
If you control what browser is being used or you are not worried people with an older browser, you can always use the JSON.parse method.
This is really the ideal solution for the future.
If you are getting this from an outside site it might be helpful to use jQuery's getJSON. If it's a list you can iterate through it with $.each
$.getJSON(url, function (json) {
alert(json.result);
$.each(json.list, function (i, fb) {
alert(fb.result);
});
});
If you want to use JSON 3 for older browsers, you can load it conditionally with:
<script>
window.JSON ||
document.write('<script src="//cdnjs.cloudflare.com/ajax/libs/json3/3.2.4/json3.min.js"><\/scr'+'ipt>');
</script>
Now the standard window.JSON object is available to you no matter what browser a client is running.
The following example will make it clear:
let contactJSON = '{"name":"John Doe","age":"11"}';
let contact = JSON.parse(contactJSON);
console.log(contact.name + ", " + contact.age);
// Output: John Doe, 11
If you pass a string variable (a well-formed JSON string) to JSON.parse from MVC #Viewbag that has doublequote, '"', as quotes, you need to process it before JSON.parse (jsonstring)
var jsonstring = '#ViewBag.jsonstring';
jsonstring = jsonstring.replace(/"/g, '"');
You can either use the eval function as in some other answers. (Don't forget the extra braces.) You will know why when you dig deeper), or simply use the jQuery function parseJSON:
var response = '{"result":true , "count":1}';
var parsedJSON = $.parseJSON(response);
OR
You can use this below code.
var response = '{"result":true , "count":1}';
var jsonObject = JSON.parse(response);
And you can access the fields using jsonObject.result and jsonObject.count.
Update:
If your output is undefined then you need to follow THIS answer. Maybe your json string has an array format. You need to access the json object properties like this
var response = '[{"result":true , "count":1}]'; // <~ Array with [] tag
var jsonObject = JSON.parse(response);
console.log(jsonObject[0].result); //Output true
console.log(jsonObject[0].count); //Output 1
The easiest way using parse() method:
var response = '{"a":true,"b":1}';
var JsonObject= JSON.parse(response);
this is an example of how to get values:
var myResponseResult = JsonObject.a;
var myResponseCount = JsonObject.b;
JSON.parse() converts any JSON String passed into the function, to a JSON object.
For better understanding, press F12 to open the Inspect Element of your browser, and go to the console to write the following commands:
var response = '{"result":true,"count":1}'; // Sample JSON object (string form)
JSON.parse(response); // Converts passed string to a JSON object.
Now run the command:
console.log(JSON.parse(response));
You'll get output as Object {result: true, count: 1}.
In order to use that object, you can assign it to the variable, let's say obj:
var obj = JSON.parse(response);
Now by using obj and the dot(.) operator you can access properties of the JSON Object.
Try to run the command
console.log(obj.result);
Without using a library you can use eval - the only time you should use. It's safer to use a library though.
eg...
var response = '{"result":true , "count":1}';
var parsedJSON = eval('('+response+')');
var result=parsedJSON.result;
var count=parsedJSON.count;
alert('result:'+result+' count:'+count);
If you like
var response = '{"result":true,"count":1}';
var JsonObject= JSON.parse(response);
you can access the JSON elements by JsonObject with (.) dot:
JsonObject.result;
JsonObject.count;
I thought JSON.parse(myObject) would work. But depending on the browsers, it might be worth using eval('('+myObject+')'). The only issue I can recommend watching out for is the multi-level list in JSON.
An easy way to do it:
var data = '{"result":true,"count":1}';
var json = eval("[" +data+ "]")[0]; // ;)
If you use Dojo Toolkit:
require(["dojo/json"], function(JSON){
JSON.parse('{"hello":"world"}', true);
});
As mentioned by numerous others, most browsers support JSON.parse and JSON.stringify.
Now, I'd also like to add that if you are using AngularJS (which I highly recommend), then it also provides the functionality that you require:
var myJson = '{"result": true, "count": 1}';
var obj = angular.fromJson(myJson);//equivalent to JSON.parse(myJson)
var backToJson = angular.toJson(obj);//equivalent to JSON.stringify(obj)
I just wanted to add the stuff about AngularJS to provide another option. NOTE that AngularJS doesn't officially support Internet Explorer 8 (and older versions, for that matter), though through experience most of the stuff seems to work pretty well.
If you use jQuery, it is simple:
var response = '{"result":true,"count":1}';
var obj = $.parseJSON(response);
alert(obj.result); //true
alert(obj.count); //1
I have two environmental variables set.
1] firstName = "abc"
2] firstNameUpdate = "{{firstName}}Update"
when I say -
console.log(postman.getEnvironmentVariable("firstNameUpdated"));
I am getting --> {{firstName}}Update instead of abcUpdate in the console log.
which fails my below code
tests["Success"] = jsonData.data.firstName === postman.getEnvironmentVariable("firstNameUpdated");
Problem is postman.getEnvironmentVariable() returns the value of the variable, but it does not resolve the variable. How to achieve it?
I don't want to use regular expression here, want to achieve it from Postman itself. Any help guys?
Other details :
Postman for Chrome
Version 5.0.2
win / x86-64
Chrome 59.0.3071.115
I don't think it is possible for postman to resolve your environment variable like this. If it is a matter of building your variable dynamically you may proceed like this in your "tests" tab:
postman.setEnvironmentVariable("firstname","abc");
var name_update = postman.getEnvironmentVariable("firstname")+"update";
console.log(name_update); // you can see your second env var name
postman.setEnvironmentVariable("firstnameupdate",name_update);
// you can check your env var content:
var check_env = postman.getEnvironmentVariable("firstnameupdate");
console.log(check_env); // this should give you abcupdate
hope this helps
Alexandre
Hi guys faily newbie here tons to learn in IOS
I am using messageUI and I want to pass a text value to MFmailComposeviewController
this is why I have try so far
var userdata = String(txtUserEmail.Text)
let mail = MFMailComposeViewController()
mail.setToRecipients([" \(userdata)"])
for somereason when I enter a email address it does not show in the composer of course there are other parts to the code that I have not included on here. As the main problem is i am unable to pass this value to the setToRecipients([])
any support would be most welcome here
Is txtUserEmail a UITextField?
If so declare your userdata like this:
let userdata = txtUserEmail.text
mail.setToRecipients(userdata!)
A UITextField.text (not "Text") already returns a string.
I am using F# and Foq to write unit tests for a C# project.
I am trying to set up a mock of an interface whose method has an out parameter, and I have no idea how to even start. It probably has to do with code quotations, but that's where my understanding ends.
The interface is this:
public interface IGetTypeNameString
{
bool For(Type type, out string typeName);
}
In C# Foq usage for the interface looks like this:
[Fact]
public void Foq_Out()
{
// Arrange
var name = "result";
var instance = new Mock<IGetTypeNameString>()
.Setup(x => x.For(It.IsAny<Type>(), out name))
.Returns(true)
.Create();
// Act
string resultName;
var result = instance.For(typeof(string), out resultName);
// Assert
Assert.True(result);
Assert.Equal("result", resultName);
}
As for how to achieve that with F#, I am completely lost. I tried something along the lines of
let name = "result"
let instance = Mock<IGetTypeNameString>().Setup(<# x.For(It.IsAny<Type>(), name) #>).Returns(true).Create();
which results in the quotation expression being underlined with an error message of
This expression was expected to have type IGetTypeNameString -> Quotations.Expr<'a> but here has type Quotations.Expr<'b>
Without any indication what types a and b are supposed to be, I have no clue how to correct this.
:?>
(It gets even wilder when I use open Foq.Linq; then the Error List window starts telling me about possible overloads with stuff like Action<'TAbstract> -> ActionBuilder<'TAbstract>, and I get even loster....)
Any assistance or explanation greatly appreciated!
Edit:
So, as stated here, byref/out parameters can not be used in code quotations. Can this be set up at all then in F#?
Foq supports setting up of C# out parameters from C# using the Foq.Linq namespace.
The IGetTypeNameString interface can be easily setup in F# via an object expression:
let mock =
{ new IGetTypeNameString with
member __.For(t,name) =
name <- "Name"
true
}
For declarations that have no analog in F#, like C#'s protected members and out parameters, you can also use the SetupByName overload, i.e.:
let mock =
Mock<IGetTypeNameString>()
.SetupByName("For").Returns(true)
.Create()
let success, _ = mock.For(typeof<int>)