We can easily put Doc comments for Dart Class variables e.g.
class SomeClass {
/// Class variable Doc Comment.
var someVariable;
}
How can I do the same for Dart Function parameters e.g. I tried this
void someFunction(
{/// Function parameter documentation
String funParameter="Some Default Value"}
) {
}
But it's not showing anything. If it's not possible please suggest me any alternative.
It is against the Effective Dart conventions to document parameters of functions using a direct syntax like that. Instead, use prose to describe the parameter and how it relates to the function's purpose.
// Instead of this
/// someFunction
/// #funParameter Does something fun
void someFunction({ String funParameter="Some Default Value" }) ...
// Or this
/// someFunction
void someFunction({
/// Does something fun
String funParameter="Some Default Value"
}) ...
// Do this
/// Does something fun with the [funParameter].
void someFunction({ String funParameter="Some Default Value" }) ...
Here's perhaps a more practical example:
/// Takes the values [a] and [b] and returns their sum. Optionally a
/// third parameter [c] can be provided and it will be added to the
/// sum as well.
int add(int a, int b, [int c = 0]) ...
You should use the doc comment like this:
/// the function uses [funParameter] to do stuff
void someFunction({String funParameter = "Some Default Value"}) {
// ..
}
Related
I am writing a native plugin that, in some cases, has to call functions in the Flutter portion of the app, written in Dart.
How it's achieved, is explained here:
https://flutter.io/platform-channels/
Furthermore, an example of invoking a method from the native/platform part towards the Dart/non-native is here:
https://github.com/flutter/plugins/tree/master/packages/quick_actions
Now, this example is really nice in case the platform only needs to invoke a method, i.e. that call returns nothing/void, but in case it needs to invoke a function, i.e. needs a return value from the non-native/Dart part, I could not have found an example or documentation on the internet. I believe it can be implemented though, because in the native Java part, there is a method:
public void invokeMethod(String method, Object arguments, MethodChannel.Result callback)
So, there is a callback object that could have a return value from the non-native part - or, I am mistaken here, and there is currently no way of returning a value from the non-native Dart portion of the app?
The signature is void setMethodCallHandler(Future<dynamic> handler(MethodCall call)), so we need to provide a function at the Dart end that returns Future<dynamic>, for example _channel.setMethodCallHandler(myUtilsHandler);
Then implement the handler. This one handles two methods foo and bar returning respectively String and double.
Future<dynamic> myUtilsHandler(MethodCall methodCall) async {
switch (methodCall.method) {
case 'foo':
return 'some string';
case 'bar':
return 123.0;
default:
throw MissingPluginException('notImplemented');
}
}
At the Java end the return value is passed to the success method of the Result callback.
channel.invokeMethod("foo", arguments, new Result() {
#Override
public void success(Object o) {
// this will be called with o = "some string"
}
#Override
public void error(String s, String s1, Object o) {}
#Override
public void notImplemented() {}
});
In Swift, the return value is an Any? passed to the result closure. (Not implemented is signaled by the any parameter being the const NSObject value FlutterMethodNotImplemented.)
channel.invokeMethod("foo", arguments: args, result: {(r:Any?) -> () in
// this will be called with r = "some string" (or FlutterMethodNotImplemented)
})
I am writing a native plugin that, in some cases, has to call functions in the Flutter portion of the app, written in Dart.
How it's achieved, is explained here:
https://flutter.io/platform-channels/
Furthermore, an example of invoking a method from the native/platform part towards the Dart/non-native is here:
https://github.com/flutter/plugins/tree/master/packages/quick_actions
Now, this example is really nice in case the platform only needs to invoke a method, i.e. that call returns nothing/void, but in case it needs to invoke a function, i.e. needs a return value from the non-native/Dart part, I could not have found an example or documentation on the internet. I believe it can be implemented though, because in the native Java part, there is a method:
public void invokeMethod(String method, Object arguments, MethodChannel.Result callback)
So, there is a callback object that could have a return value from the non-native part - or, I am mistaken here, and there is currently no way of returning a value from the non-native Dart portion of the app?
The signature is void setMethodCallHandler(Future<dynamic> handler(MethodCall call)), so we need to provide a function at the Dart end that returns Future<dynamic>, for example _channel.setMethodCallHandler(myUtilsHandler);
Then implement the handler. This one handles two methods foo and bar returning respectively String and double.
Future<dynamic> myUtilsHandler(MethodCall methodCall) async {
switch (methodCall.method) {
case 'foo':
return 'some string';
case 'bar':
return 123.0;
default:
throw MissingPluginException('notImplemented');
}
}
At the Java end the return value is passed to the success method of the Result callback.
channel.invokeMethod("foo", arguments, new Result() {
#Override
public void success(Object o) {
// this will be called with o = "some string"
}
#Override
public void error(String s, String s1, Object o) {}
#Override
public void notImplemented() {}
});
In Swift, the return value is an Any? passed to the result closure. (Not implemented is signaled by the any parameter being the const NSObject value FlutterMethodNotImplemented.)
channel.invokeMethod("foo", arguments: args, result: {(r:Any?) -> () in
// this will be called with r = "some string" (or FlutterMethodNotImplemented)
})
I can assign an arrow function, which returns a value to a function variable that requires a void signature. But I can not assign a block function that returns a value. Why? Should the not be arrow function restricted as well, as it returns a value?
arrow function
block function
That is because by doing
void Function(int) function=(a)=>b=a;
Dart assumes that you don't want to return the value of the assignation, that normally you could use, for example:
void main() {
int a=10,b;
print(b=a);
}
So, dart just thinks that you want to assign the variable, nothing more. Another more detailed example here:
int number=10;
late int target;
void main() {
print(test());
number+=10;
test2();
print(target);
}
int test()=>target=number;
void test2()=>target=number;
//Note: there aren't many best practices here (For example, global variables)
//Is just an example to make you understand, nothing more
but if you specify the return, dart will think you reeeeally want to return that value, and that's not possible, as it is a void function.
when i make widget ,
i have many arguments that #required.
so, my function looks like this,
function doSomething (#required this.a ,#required this.b,#required this.c,#required this.d,#required this.e .... )
is there a way to make this arguments clear? like
function doSomething (#requiredALL this.a,this.b,this.c,this.d ... )...
No, There is No #requiredAll. But you can make class like
class A {
String a ;
String b;
A(this.a, this.b);
}
When you use make the object of A()
like A a = A() this will give a compile error. means you have to put required paraments in A() like
A a = A("valueA","valueB")
Or in Function call. it will also work in the same manner
I have class with void method and optional argument looking like this:
class A
{
public:
void method(int par1, bool par2 = false) { ... }
};
BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(method, A::method, 1, 2)
class_<A>("A")
.def("method", &A::method, return_value_policy<reference_existing_object>(),method())
;
What is correct return_value_policy in this case? I've tried to avoid return policy completely however I've received following compile error then.
'boost::mpl::vector17<RT,most_derived<Target,ClassT>::type&,T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14> boost::python::detail::get_signature(RT (__cdecl ClassT::* )(T0,T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14) volatile const,Target *)' : expects 2 arguments - 1 provided
Any suggestion appreciated.
I've scrambled few things together. Bur I realized I do not need to use BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS but rather named arguments something like:
def("method", &A::method, (arg("par1"), arg("par2") = false))