I have a short of Find a primeNumber simple code below.
void main() {
PrimeNumber primeNumber = new PrimeNumber(17);
}
class PrimeNumber {
int remainder;
int numberToCheck;
PrimeNumber(this.numberToCheck){...}
bool findingPrime(int numberToCheck){...}
}
Once the findingPrime method have been declared inside class body, I wonder, If it can implement outside class body. unlike C++ or Java use
bool PrimeNumber::findingPrime(){...} // it show error in Dart
Related
I'm trying to call a static method from a generic type I receive.
Is that even possible?
Furthermore, I apply a Type constraint in order to only manipulate the object from its parent class.
Here is a short example of what I'm trying to achieve:
class A {
static func() {
print("A");
}
}
class B extends A {
static func() {
print("B");
}
}
concret<T extends A>() {
T.func(); // I expected a print('B')
}
main() {
concret<B>();
}
No, it's not possible.
Dart static method invocations are resolved at compile-time, so it's not possible to call them on type variables which only have a value at run-time.
If it was possible, it would be completely unsafe. Anyone can create a class C extending A which does not have a static func member and invoke concret<C>();. Since static members are not inherited, it would have to give you a run-time error, and there is nothing you can do to detect that at compile-time. That is the primary reason why it is not allowed.
I would like to make a generic class which only accepts Lists as a type parameter. But I also want the type parameter of the List. Something like this:
class MyClass<L extends List<T>> {
T foo() {
// ....
}
}
The problem is that that does not work. T is not found. But this does:
class MyClass<L extends List<T>, T> {
T foo() {
// ....
}
}
My only issue with this is that I have to always pass in the extra parameter T which should be inferred from the List type.
var instance = MyClass<List<int>>();
var instance = MyClass<List<int>, int>(); // Extra int kind of redundant
Is there any workaround to this?
The solution is similar to the one provided in this question (the same problem, but in Java): basically, you can't do that in Dart. What you can do is
create a new subclass:
class MyClass2<T> extends MyClass<List<T>, T> { ... }
or
create a factory method:
class MyClass<L extends List<T>, T> {
static MyClass<List<T>, T> fromList<T>(List<T> list) {
return MyClass(...);
}
}
I want to invoke functions of a class by their names inside a string. I know my best option are Mirrors.
var ref = reflect(new TestClass());
ref.invoke(Symbol("test"), []);
It works fine, I can call the function test by a string. But I also want to put "TestClass" inside a string. Is it possible somehow ?
var ref = reflect("TestClass");
ref.invoke(Symbol("test"), []);
Jonas
You can do something like this:
import 'dart:mirrors';
class MyClass {
static void myMethod() {
print('Hello World');
}
}
void main() {
callStaticMethodOnClass('MyClass', 'myMethod'); // Hello World
}
void callStaticMethodOnClass(String className, String methodName) {
final classSymbol = Symbol(className);
final methodSymbol = Symbol(methodName);
(currentMirrorSystem().isolate.rootLibrary.declarations[classSymbol]
as ClassMirror)
.invoke(methodSymbol, <dynamic>[]);
}
Note, that this implementation does require that myMethod is static since we are never creating any object but only operate directly on the class itself. You can create new objects from the class by calling newInstance on the ClassMirror but you will then need to call the constructor.
But I hope this is enough. If not, please ask and I can try add some more examples.
I have a XAML page with WebView inside (for example MainPage.xaml). Also I have WinRT Component with class marked with [AllowForWeb] attribute. This component is referenced from project where MainPage.xaml located and in code-behind AddWebAllowedObject method is used. And I can't reference main project back because of circular dependency.
How to call MainPage.xaml.cs methods from component class? Very usual situation. Is there are some standard way to do it?
For example. I have a method inside RT component that could be called from JavaScript
public void ShowMessage(string message)
{
// I want to call here function from MainPage.xaml.cs
}
How to call MainPage.xaml.cs methods from component class? Very usual situation. Is there are some standard way to do it?
Yes, you can pass the method from MainPage.xaml.cs to Windows Runtime Component through delegate(Currently it's very limited to use delegate in Runtime Component using C#, see this case, so I use C++ as demo).
For Runtime Component Class MyClass.h:
public delegate Platform::String^ MyFunc(int a, int b);
public ref class MyClass sealed
{
public:
MyClass();
static Platform::String^ MyMethod(MyFunc^ func)
{
Platform::String^ abc=func(4, 5);
return abc;
}
};
And you can use the delegate in code behind like below:
using MyComponentCpp;
private void myBtn_Click(object sender, RoutedEventArgs e)
{
String abc=MyClass.MyMethod(MyMethod);
myTb.Text = abc;
}
private String MyMethod(int a, int b)
{
return (a.ToString() + b.ToString());//replace this line with your own logic.
}
And here is the complete Demo: TestProject.
Thankfully to #Elvis Xia who has gived me idea, I has found a solution how to do it without C++.
I have create a third project as Class Library. It doesn't has restrictions to use Action. This library I have referenced from main project and from WinRT component. Code of class inside library:
public class BridgeClass
{
public static event Action<string> MessageReceived;
public static void Broadcast(string message)
{
if (MessageReceived != null) MessageReceived(message);
}
}
Code inside main project with webview is:
// place somewhere
BridgeClass.MessageReceived += ShowMessage;
// ....... and add a method
void ShowMessage(string msg)
{
}
And now i can call this code from WinRT component:
public void ShowMessage(string message)
{
BridgeClass.Broadcast("lalala");
}
I apologize in advance for the newbiness of this question; I think I'm not grasping the basics of Actionscript but haven't been able to find an answer elsewhere.
What I want is some global constants like one would have in C++. In C++, I would simply have a file where I would #define MAP_HEIGHT 20, or something like that, and they would be globally accessible when I included the file at the top. In Actionscript, I've tried making a static class instead, like so:
package
{
public class Settings {
public const mapx:int = 20;
public function Settings() {}
}
}
But when I try to reference it in my code with colon syntax
var a:int = Settings::mapx;
I get the error "[Fault] exception, information=TypeError: Error #1034: Type Coercion failed: cannot convert Settings$ to Namespace."
I tried dot syntax:
var a:int = Settings.mapx;
and got a different error, "Access of possibly undefined property mapx through a reference with static type Class."
But what I really want is a file of global static variables, like in C++, and can't find a way to do it in Actionscript.
Mark variables, constants, and functions with the static keyword, as in:
package
{
public class MathUtil
{
public static const PI:Number = 3.141592653589;
public static function deg2rad(angle:Number):Number
{
angle = !isNaN(angle) ? (angle) : (0);
return angle * PI / 180;
}
}
}
Then you may use dot notation.
var pi:Number = MathUtil.PI;
var angle:Number = MathUtil.deg2rad(45);
From ActionScript 3.0 Reference for the Adobe Flash Platform: Statements, Keywords & Directives
Usage
class someClassName {
static var varName;
static const kName;
static function methodName() { }
}
You can use static in class definitions only, not in interface
definitions.
Static class members are not inherited. You cannot refer to a static
class member using the name of a subclass, as you can in Java or C++.
You can, however, refer to a static variable or method within a class
or subclass, without using any qualifier. See the example below.
You cannot use the super statement or the this keyword inside a static
method.