I have TestStore and observable property fields.
When I click to any name, i call action changeOneName and change some object inside fields. Computed getter hasError called again and i see console.log("hasError computed");
Why don't I see console.log("valueFields computed"); second time after changing name to 'ErrorName'?
https://codesandbox.io/s/vibrant-lumiere-cv2tp?file=/src/TestStore.js
You only changed name property of the object, not the object itself. And Object.values only dereferences direct values (objects) of your fields object, not the inner things, like name. So computed don't need to rerun because things that were referenced in that computed didn't change.
hasError did rerun because you actually dereference name property inside of it, so when name changes it reruns.
Hope it makes sense.
Related
I'm trying to understand something about type properties in swift.
The Swift Programming Language says
For classes, you can define computed type properties only
So a computed property does not store a value itself, but it is calculated. That I understand. But I don't get how such a thing can apply to type properties. Such properties belong to the class itself and not to an instance of it.
So if you use a getter for such a computed type property, what could you possibly use to calculate it? It can't be any other type properties, as they too can only be computed properties. You would get a sort of loop of computed properties because there aren't any stored type properties.
In the same way, I also don't get what a setter would do. If you call the setter of a computed type property, what can it set? There are no stored type properties to be set.
Bear in mind that stored class properties are only unsupported at the moment. The compiler error you get when you try to use them—"Class variables not yet supported"— suggests that they're on their way. Computed class properties don't necessarily have to make sense on their own.
However, computed properties don't always have to be based on the values of stored data. As it stands, you could use them for "static" read-only values associated with the class, say:
class var ThisIsAClassConstant: String { return "Woo" }
And people have already come up with ways to store associated values, for example, in the first two singleton patterns in this answer, the class property stores its state in either a global (but private) variable, or in a static variable inside a nested structure.
These are obviously a bit "workaroundy", but they're a way of achieving class-like storage while it's not officially implemented.
I have an Structure in a Class where i have a property named 'Name'. and other properties values inside the structure depends of the set of this value, is there any way to make them publics only when this first property is Set ?.
When i create an instance of the class , and access to this structure all the properties are available.
I would hook up these properties with an ICommand implementation.
For each property that depends on Name, they can use CanExecute to determine if Name is set. If so, CanExecute will return true, and the Command will be executed for the property (which can hook up to a method to do anything you want...get a value, set a value, etc.)
More information here
I remember coming across some way to declare multiple Set handlers in a property but now I can't figure out how it's done. It's useful in that one can assign different data types and the Set handler does the conversion, but I get the error
'Set' is already declared
thoughts anyone?
It's not possible
It would be nice to be able to write both
sQuantity = "1234"
and
sQuantity = 1234
with two setter functions, but trying to write even one setter function with the wrong parameter type seems doomed to failure:-
error BC31064: 'Set' parameter must have the same type as the containing property.
If Visual Basic doesn't allow conversion between setter parameter type and property type then there is no way it would be possible to have two setter functions. If setter functions are forced to have the same type as the property, then it could not know which to run if there were more than one!
So I'd argue 'not only does it not seem possible, but it is actually not possible!'
There is a workaround
What you can do however, is have two properties of different types changing the same underlying variable, so that you can write
sQuantityFromString = "1234"
and
sQuantityFromInt = 1234
using
Public Shared WriteOnly Property sQuantityFromInt () As Integer
with a setter function that takes an integer as a parameter and with both properties setter functions modifying the same underlying string member variable.
Private Shared m_sQuantity As String = Nothing
As far as I know, you cannot have multiple Set statements for a class property. A property cannot be overridden.
You can use a setter functions (this is mostly a paradigm in Java) and overload that if you need to. Then I would also suggest making the property readonly.
One other option is to have the property be defined as an Object and in the set check the TypeOf of the value being used to set the property and do whatever business logic you want. The only problem with this approach is that then your property doesn't have type checking.
I want to make a custom getter that should return two fields of the model instead of one. I have the attribute name like first_name. And the getter I am making is
public function getFirstName(){
return 1;
}
And then I try to get it called in a CDetailView like this
'client.first_name:raw:Client',
But it returns the standard attribute of the model. How to do it right?
Yii's order of operations to retrieve an attribute is as follows:
AR attribute
public variable
custom getter
I'm not sure whether AR attributes or public variables are pulled first, but I do know that if either of them exist, your custom getter won't be called.
If you already have a first_name attribute (from AR), then you'll need to use a different name for your getter and use that.
I have a ListView bound to an ObjectDataSource, I'm passing some custom parameters to the Insert and Update methods on my bound class methods by adding them to the event.Values map in the ListView ItemInserting/ItemUpdating events.
However when I try to do the same thing on the ItemDeletingEvent the additional parameters do not seem to be passed to the datasource ( If I register a listener for ObjectDataSource.ItemSourceDeleting I only see one parameter, effectively the 'id' of the row).
Is this an expected behavior? I can't see anything in the documentation that indicates as such.
I found a solution -
I Added a 'DeleteParameter' value with the same name as my desired 'custom' parameter to the ObjectDataSource declaration.
Then in the ItemDeleting Event get the ObjectDataSource.DeleteParameters["myparam"] and set the DefaultValue property. Seems like a hack, but it does work.