I have a button in my application that return :
onPressed: () {
return context
.read(FavoriteIds.provider.notifier)
.toggle(doa.id.toString());
},
In this case, i used a riverpod provider. But when i want to import a flutter_bloc package, the read keyword will be error with this message
A member named 'read' is defined in extensions 'ReadContext' and 'BuildContextX' and neither is more specific. Try using an extension override to specify the extension you want to to be chosen.
Please help me solve this problem. thank you :)
Here the problem is read() is defined in both ReadContext & BuildContextX extensions. So the compiler is not getting which extension to use.
To solve the error, use : ReadContext(context).read if you wanna access bloc or BuildContextX(context).read() as per your need.
This means you are importing 2 extensions that both supply the same method read. Consider this example:
extension Ext1 on String {
void foo() => print("from extension 1");
}
extension Ext2 on String {
void foo() => print("from extension 2");
}
void main() {
String s = "hello";
s.foo();
}
What should this code print? There isn't an obvious answer, and to avoid accidental programming errors, Dart prohibits this.
You could try "go-to definition" (ctrl/cmd click in most IDEs) on the read method to navigate to one of the files that it is defined in, and then delete the corresponding import statement.
However, it might be quicker to just delete all the import statements in that file and add them back with autocomplete
Related
I am trying to know which class has called a specific function. I've been looking through the docs for this, but without success. I already know how to get the name of a class, but that is something different of what I'm looking for. I found already something related for java but for dart I haven't. Maybe I'm missing something.
Let's say for example that I have a print function like so:
class A {
void printSomethingAndTellWhereYouDidIt() {
// Here I would also include the class where this function is
// being called. For instance:
print('you called the function at: ...');
//This dot-dot-dot is where maybe should go what I'm looking for.
}
}
class B {
A a = A();
void test() {
a.printSomethingAndTellWhereYouDidIt();
}
}
The output should be something like:
you called the function at: B
Please let me know if there are ways to achieve this. The idea behind is to then use this with a logger, for instance the logging package. Thank you in advance.
You can use StackTrace.current to obtain a stack trace at any time, which is the object that's printed when an exception occurs. This contains the line numbers of the chain of invocations leading up to the call, which should provide the information you need.
class A {
void printSomethingAndTellWhereYouDidIt() {
print(StackTrace.current);
}
}
class B {
A a = A();
void test() {
a.printSomethingAndTellWhereYouDidIt();
}
}
If you are doing this for debugging purposes, you can also set a breakpoint in printSomethingAndTellWhereYouDidIt to check where it was called from.
With Dart 2.6, I can use extension methods like this :
extension on int {
int giveMeFive() {
return 5;
}
}
main(List<String> arguments) async {
int x;
x.giveMeFive();
}
Everything works perfectly ! :D
But now if I want to put my extension method in another file like this :
main.dart
import 'package:untitled5/Classes/ExtendInt.dart';
main(List<String> arguments) async {
int x;
x.giveMeFive();
}
ExtendInt.dart
extension on int {
int giveMeFive() {return 5;}
}
It fails with a depressing error ..
bin/main.dart:9:5: Error: The method 'giveMeFive' isn't defined for the class 'int'.
Try correcting the name to the name of an existing method, or defining a method named 'giveMeFive'.
x.giveMeFive();
^^^^^^^^^^
Is it not allowed to do that or am I doing something wrong ?
Thanks for reading ! :)
This is working as intended. An extension with no name is implicitly given a fresh name, but it is private. So if you want to use an extension outside the library where it is declared you need to give it a name.
This is also helpful for users, because they may need to use its name in order to be able to resolve conflicts and explicitly ask for the extension method giveMeFive from your extension when there are multiple extensions offering a giveMeFive on the given receiver type.
So you need to do something like
extension MyExtension on int {
int giveMeFive() => 5;
}
I have the following class in my code
abstract class DatabaseKey<T> implements Built<DatabaseKey<T>, DatabaseKeyBuilder<T>> {
DatabaseKey._();
factory DatabaseKey([void Function(DatabaseKeyBuilder<T>) updates]) = _$DatabaseKey<T>;
String get name;
}
Then, I define the following generic typedef function:
typedef ObserveDatabaseEntity = Observable<DatabaseEntity<T>> Function<T>(DatabaseKey<T> key);
But, when I try to use it as follows, the code has an error.
static ObserveConfigurationValue observe(
GetConfigurationState getState,
ObserveDatabaseEntity observeDatabaseEntity,
) {
assert(getState != null);
assert(observeDatabaseEntity != null);
return <KT>(ConfigKey<KT> key) {
return Observable.just(getState())
.flatMap((state) {
final dbKey = _databaseKeyFromConfig<KT>(key);
return observeDatabaseEntity(dbKey)
.map(_configValueFromDatabaseEntity);
});
}
}
DatabaseKey<T> _databaseKeyFromConfig<T>(ConfigKey<T> key) {
return DatabaseKey((build) => build
..name = key.value,
);
}
The error I am getting is:
The argument type DatabaseKey can't be assigned to the parameter DatabaseKey.
I see nothing wrong with this code or why it shouldn't work, but maybe my understanding of what can be written in Dart is wrong. What would be the correct way to write this, if possible at all?
EDIT#1:
Note:
The typedef ObserveDatabaseEntity is in one file
The static ObserveConfigurationValue observe(GetConfigurationState getState, ObserveDatabaseEntity observeDatabaseEntity) is is another file
From playing around, it seems that placing them in a single file, the error disappears.
Still, I believe that this should work in separate files as well,
This error looks like an import mismatch.
In dart, you can import file either through relative path or package.
import 'lib/some_file.dart'; //relative
import 'package:myapp/lib/some_file.dart'; //package
There's really no better way but once you choose one, you have to stick to it. If you don't (meaning you have imported a file using a package import and the same file elsewhere with a relative path) Dart will place them in two different namespaces and think they are two different classes.
Let me be more specific here: This is used in Unity 2017 so the syntax they are using is this:
class CameraMotionBlurEditor extends Editor
{
var preview : SerializedProperty;
var previewScale : SerializedProperty;
...
function OnInspectorGUI () {
if (preview.boolValue) dosomething()
}
}
What I'm getting errors in is this preview.boolValue reference.. it claims it's ambiguous so therefore whatever this class is extending, must also have a declaration of that variable name. What I don't know is how to specify the local one.
The this keyword is used to refer to the current instance of the class. Retrieving the preview.boolValue from the current instance of the class hence becomes this.preview.boolValue:
function OnInspectorGUI () {
if (this.preview.boolValue) dosomething()
}
Note that UnityScript is slowly becoming deprecated, and the recommended route of action is to instead program Unity scripts in C#.
I need a special keyword in my code to be replaced by a consequence of symbols before the build.
For example, I want hello to be replaced by Debug.Log("Hello");
According to this, MonoDevelop didn't have this feature in 2006. Has anything changed?
If no, are there any plugins/external tools implementing it?
I don't think that switching to another IDE will be helpful unless it can use code completion for unity3d.
Please, don't answer that macro definitions are evil.
Update:
I understood that my example was too abstract. In fact, I want to replace read("name"); with
var name;
name=gameObject.Find("name");
if(!name)
return;
name=name.param;
1)Every script should have all needed variables declared + a variable called "self".
2)They should be public.
3)
public static function set_var(target,name:String,value)
{
var fi=typeof(target).GetField(name);
fi.SetValue(target,value);
}
public static function read(name:String,target):String
{
set_var(target,"self",target);
return "var rtmp=self.gameObject.GetComponent(\""+name+"\");"+"if(!rtmp)return;"+name+"=rtmp.param;";
}
4)eval(read("name",this));
5)As far as I know, it wouldn't work in unity C#
6)Probably, set_var can be replaced by assignment
Far better solution:
var component_names = ["hello","thing","foo"];
var component;
for(var name:String in component_names)
{
component = gameObject.GetComponent(name);
if(!component)
return;
set_var(this,name,component.param);
}
(Requires set_var() from the first one)