Custom component attribute types - dart

I was wondering if i can pass other types of arguments than int, String to custom components explained here.
My problem is that i want to make a component and i want to pass data of type List, especially List<Map<String, String>> to the component itself. How can i achive this functionality? In other words, how can i pass other arguments to a component in angulardart than int or String?
My related code looks like this:
#NgComponent(
...
)
class MyComponent {
List<Map<String, String>> myList;
...
#NgAttr('myAttr')
set setMyAttribute(List<Map<String, String>> myList) {
this.myList = myList;
}
...
}
Where i use the component:
<div>
...
<mycomponent myAttr="ctrl.returnsAListOfMaps"></mycomponent>
...
</div>
Any idea? Is it possible?
Cheers

With #NgAttr the literal value of the attribute is assigned to the fild.
With #NgOneWay, #NgTwoWay, #NgOneWayOneTime the attribute value is evaluated and the result gets assigned.
#NgCallback is for assigning callback functions.

It is possible to use many kind of types with component attributes (map, list and even object/class).
Here you can find a couple of examples: https://stackoverflow.com/a/21961449/2777805

Related

Dart accessing class fields like map values

I was wondering if it was possible to access the values of fields in an object with their names in a manner analogous to accessing values in a map with the key names. For example, something like this
void main() {
MyData d=MyData();
List<String> fieldNames=['a','b','c'];
for(var name in fieldNames){
print('This is the value of the $name field: ${d[name]}}');
}
}
class MyData{
String a='A';
String b='B';
String c='C';
}
Of course, this doesn't work because Dart doesn't quite know what to make of d[name] because d is an object. But if d was a map, it would work. Like this.
void main() {
Map d=myData;
List<String> fieldNames=['a','b','c'];
for(var name in fieldNames){
print('This is the value of the $name field: ${d[name]}}');
}
}
Map myData={
'a':'A',
'b':'B',
'c':'C',
};
So my question is this. If I have a class, is there any way to treat it like a Map in the situations where I might want to refer to several of the field values indirectly via their names like I tried to do above? Or is this sort of trick not possible in a compiled language like Dart?
The short answer is "no". The longer answer is "noooooooo". :)
But seriously, the namespace of your program code is very separate from the data values that are managed by your code. This isn't JavaScript, where we can freely flow from code to data to code again.

Dart Generic Function with Subtype function call

I am not sure if this is even possible but here's my setup:
I have basically 2 Maps holding a special identifier to get some objects.
these identifier is like a versioning number, i may have data in version 8 that belongs to meta version 5. But at the same time, Meta versions up to 10 may exist and not every meta version holds information about every data, so here's where the _filter kicks in.
The filter is able to find to any given value the correct object. So far so good.
My question belongs to the following: (last codeline)
how am i able to say "if you have no matching candidate, generate me a default value"
For this purpose, i tried to force a named constructor with a super class for "Data" and "Meta" called "BasicInformation".
But even if i implement this, how do i call something like T.namedConstructor(); ?
class Repo{
Map<int, Data> mapData;
Map<int, Meta> mapMeta;
Data getData(int value)
{
return _filter<Data>(mapData, value);
}
Meta getMeta(int value)
{
return _filter<Data>(mapMeta, value);
}
T _filter<T extends BasicInformation>(Map<int, T>, int value)
{
//fancy filtering technique
//....
//speudo code
if (found) return map[found]; //speudo code
else return T.generateDefault();
}
}
I've found the following stackoverflow entry: Calling method on generic type Dart
which says, this is not possible without adding a function call.

Get type of Key and Value from a Map variable?

Given a Map variable, how can I determine the type of Key and Value from it?
For example:
void doSomething(Map m){
print('m: ${m.runtimeType}');
print('keys: ${m.keys.runtimeType}');
print('values: ${m.values.runtimeType}');
print('entries: ${m.entries.runtimeType}');
}
void main() async {
Map<String, int> m = {};
doSomething(m);
}
This will print
m: _InternalLinkedHashMap<String, int>
keys: _CompactIterable<String>
values: _CompactIterable<int>
entries: MappedIterable<String, MapEntry<String, int>>
But how can I get the actual type of Key and Value (i.e. String and int), so that I can use them in type checking code (i.e. if( KeyType == String ))?
You cannot extract the type parameters of a class if it doesn't provide them to you, and Map does not.
An example of a class which does provide them is something like:
class Example<T> {
Type get type => T;
R withType<R>(R Function<X>() callback) => callback<T>();
}
If you have an instance of Example, you can get to the type parameter, either as a Type (which is generally useless), or as a type argument which allows you to do anything with the type.
Alas, providing access to types variables that way is very rare in most classes.
You can possibly use reflection if you have access to dart:mirrors, but most code does not (it doesn't work with ahead-of-time compilation, which includes all web code, or in Flutter programs).
You can try to guess the type by trying types that you know (like map is Map<dynamic, num>, then map is Map<dynamic, int> and map is Map<dynamic, Never>. If the first two are true, and the last one is false, then the value type is definitely int. That only works if you know all the possible types.
It does work particularly well for platform types like int and String because you know for certain that their only subtype is Never.
If you can depend on the static type instead of the runtime type, you could use a generic function:
Type mapKeyType<K, V>(Map<K, V> map) => K;
Otherwise you would need to have a non-empty Map and inspect the runtime types of the actual elements.

AutoFixture constrained string parameter

Is there a simple way to specify a list of possible values for the parameter orderBy? Not one by one please, otherwise I would not be making the question. I want to specify that orderby makes sense only if it is chosen from a predetermined list. Suppose the list is very large...still not random. This cannot be that hard...no single example of such a simple task.
[Test, AutoData]
public override void IndexReturnsView(int? pageIndex, int? pageSize, string orderBy, bool? desc)
{
.....
}
EDIT:
All I want is to read the possible values from a list as I would do with the ValueSource attribute. However, it seems not to work with AutoFixture. If I specified e.g. [ValueSource("GetOrderByColumnNames")] my test does not work anymore. I have no idea of what I am doing wrong. Unfortunately AutoFixture lacks useful documentation and the examples are very basic. Is there a working example of this scenario that I can use to guide myself here?
This has to be a very common situation, however I have been looking for days with no luck :(.
Appreciated!
If I understand the question correctly, the problem is that the orderBy value should be randomly selected from a list of predefined values, but that list might be too large to use with [InlineAutoData].
The easiest way to do this that I can think of is to introduce a helper type. This might actually be a valuable addition to the application code itself, as it makes the role of various values more explicit, but if not, you can always add the wrapper type to the test code base.
Something like this is the minimum you'll need:
public class OrderCriterion
{
public OrderCriterion(string value)
{
Value = value;
}
public string Value { get; }
}
If we also imagine that this class exposes a list of ValidValues, you can implement an AutoFixture Customization using the ElementsBuilder class:
public class OrderCriterionCustomization : ICustomization
{
public void Customize(IFixture fixture)
{
fixture.Customizations.Add(
new ElementsBuilder<OrderCriterion>(OrderCriterion.ValidValues));
}
}
Then you create a data source attribute for your test code base:
public class TestConventionsAttribute : AutoDataAttribute
{
public TestConventionsAttribute() : base(
() => new Fixture().Customize(new OrderCriterionCustomization()))
{
}
}
This enables you to write a test like this, which passes:
[Theory, TestConventions]
public void IndexReturnsView(
int? pageIndex,
int? pageSize,
OrderCriterion orderBy,
bool? desc)
{
Assert.Contains(orderBy.Value, OrderCriterion.ValidValues.Select(x => x.Value));
}
Notice that instead of declaring the orderBy parameter as a string, you declare it as an OrderCriterion, which means that AutoFixture will be detect its presence, and the Customization then kicks in.
See also https://stackoverflow.com/a/48903199/126014

Default stringify for objects, equivalent to Java's toString?

I have just take a look at the 3ยบ tutorial from dart, creating the rating component. I was wondering if there is same method which is called when stringifying an object, something similar to Java's toString.
For example:
MyClass myObject = new MyClass();
System.out.println(myObject);
Will call MyClass.toString() if overwriten, else will call it's parent until java.lang.Object is reached giving a default toString.
I find kind ugly (completely subjective) doing:
<span ng-repeat="star in cmp.stars" > {{star.toString()}} </span>
I would rather do:
<span ng-repeat="star in cmp.stars" > {{star}} </span>
And give the implementation of how I want it to display at an averwritten method. Is this possible?
If you have something like this:
class MyClass {
String data;
MyClass(this.data);
#override
String toString() {
return data;
}
}
MyClass myObject = new MyClass("someData");
print(myObject); // outputs "someData", not 'Instance of MyClass'
I think this might be what you are looking for.
Yes it works like this for print, String interpolation or Angular mustaches.
By overriding the String toString() method on your object the displayed value will be the result of this toString() call. If there's no toString() defined in the class hierarchy the toString() of Object will be called (which will return Instance of 'MyClass' for class MyClass{}).
You may be interesting look how Rating component was implemented in Angular Dart UI project. Check this out.
Sergey.

Resources