I want to make a setter for the fontSize property of my WrappedLabel class because I need to do some additional stuff when someone changes it.
So when someone uses my class like this:
<comp:WrappedLabel fontSize="10"/>
I want to know.
I tried to override setStyle but looks like it doesn't get called when fontSize is initialized in mxml.
That's actually easier to accomplish then you might think, but it involves metadata. All you need to do is add a Style metadata declaration to your class definition, like so:
[Style(name="fontSize", type="Number", inherit="no")]
public class WrappedLabel {
...
}
If you want more information on the parameters of the metadata, read the docs.
Related
I would like to check if a mixin has been applied to a custom element, but I don't think I can use 'instanceof', since a mixin is not properly a base class (I tried, of course).
I would need to enforce that an element added to a collection can be only of a kind with a particular class mixin applied...
Any suggestions?
Not sure I understand you question correctly.
I assume you want to check something like MyCustomElement has already apply MyMixin or not?
You can check from the instance
let instance = new MyCustomElement()
console.log(instance instanceof MyMixin)
This will only work when MyMixin is a class not a factory function. If you follow documentation you need to change it.
Another way, you can declare some static function in MyMixin. Then you can call from MyCustomElement to check it.
I'm currently working on a project where I have a ton of classes inheriting from other classes which inherit from other classes and so on. It's probably more complex than it should be, but I am a sucker for abstraction.
Anyway, at times I need to change a getter/setter from being public to private. I suppose it's not really a need, but a desire to cut off things that are preset in child classes, but still need to be publicly accessible in the parent classes.
So an example would be:
Class Base {
public function set label( value:String ):void{};
}
Class A extends Base {}
Class B extends A {
public function B() {
super();
this.label = "stuff";
}
override public function set label( value:String ):void {
//this setter should not be publicly available since the label should not be possible to change in this class
}
}
Currently, I am doing one of two things in these cases:
override the setter to do nothing or set it to the default value so that it can still update/render/whatever
throw an error saying it is unavailable in that class
I've done some searching and everything seems to point to this being impossible, but I've never found it explicitly stated that it is impossible. So is it possible to change the access modifier on an inherited property/function?
It is not possible, and it really should not be, because it leads to confusing and unpredictable class hierarchies. For starters, if you did something like that, you would break the Liskov Substitution Principle: A super class should at all times be replaceable by its derived classes. Changing the API would clearly prevent that - and thus possibly lead to runtime errors and/or inexplicable glitches, if another programmer accidentally exchanged types.
If the classes you are modeling have different behavior in such a way that would make you "hide" an otherwise public API method, you should probably not use inheritance for this - or perhaps in a different way. From what you are describing, I would guess that in a larger part of your hierarchy, you should probably be using composition instead of inheritance, anyway.
It is not possible for the very reason in the comments by Marty Wallace. But it's not an uncommon thing to do.
However in the alternative you used, The property owner is the base class & hence it should always know of anything that the derived class does with it's own properties.
Instead of your hack I would thus prefer something like this :
public class Base {
protected var _isLabelUsable:Boolean = true;
public function set label( value:String ):void {
if (!_isLabelUsable)
throw new Error("Access of undefined property label.");
// Set Label here
}
}
public class A extends Base {
}
public class B extends A {
public function B() {
super();
_isLabelUsable = false;
}
}
These are all valid points, but...
There are cases where they are all void.
Given a base class that comes from an external source. Like, say, mx:Panel.
It has the property 'titleIcon:Class'
The derived class inherits all properties and functions. But people using it shall never set the titleIcon directly, because part of the derived class' functionality depends on the availability of an icon name being known. It provides a property iconName:String. Setting it will also set the titleIcon.
Now how to prevent people from still setting the icon directly? The UI is offering the old property for AS3 and MXML, and the compiler will (of course) not complain.
If titleIcon is a setter/getter pair (in this case, it is), and not final, then the derived class can override the setter and throw an error, while the iconName setter will assign the icon class to super.titleIcon.
However, this is clumsy and will not work for final functions or variables.
If there were a way to at least tell the UI to not offer the property anymore or show a warning...
I always created additional property to MovieCLips using the syntax
myMC.myProperty
without any sort of declaration... But i can use this method only with MovieClips.. What about if i want to add a property to a button or any different type of object? I need to extend the class? Do you can me suggest how? Many thanks
You can add property to movieclips in runtime because MovieClip is dynamic class. If the class is not dynamic, you should extend it to create methods and properties.
Read about dynamic classes.
I tend to create custom classes for nearly everything.
I would extend the relevant class and set up a private var for your new property. You can then pass in the value to the constructor or add a getter/setter method to call externally.
private function _myProperty:int;
public function get myProperty():int
{
return _myProperty;
}
public function set myProperty(newVal:int):void
{
_myProperty = newVal;
}
Getter/setter methods add a few lines of code that may seem unnecessary but on big projects when you find a property is being set and you don't know why, you can put a break point in your set myProperty
Subclass is main solution.
Next works only with mx components (flex sdk 3).
Most components have data : Object property that you can freely use to store data.
Monkey patching sometimes is the only way to go. It allows you to add custom properties to flex sdk classes. I don't think you should use it in your case. But I used it to change core logic that is locked by private keyword in flex sdk.
Hope that helps.
I have a custom component called ButtonPanel written in Actionscript. Basically it's just a panel that displays a mx:ButtonBar in the upper right of the mx:Panel title bar and responds to the clicks of the buttons in the bar.
A ButtonBar has three styles available for the buttons: buttonStyleName, firstButtonStyleName, and lastButtonStyleName. I want to write these styles for the ButtonPanel so that if it is declared as such:
<comp:ButtonPanel buttonStyleName="myButtonStyle" ... />
then the ButtonPanel will pass the style through and set the corresponding style of the ButtonBar.
I really have no clue where to start on this because I've never messed with defining styles. Can someone help?
What you refer to as "pass-through" styles are actually called inheriting styles. The solution to your question is in fact quite simple.
You use the style metadata on your custom component to declare that ButtonPanel has a stylename called 'buttonStyleName':
[Style(name="buttonStyleName", inherit="yes")]
public class ButtonPanel extends Panel {
....
}
Note the 'inherit' flag which is set to true: this will make sure that any component inside your custom Panel that has the same style will inherit the value that you've given to that style at the Panel level.
Setting this metadata will make sure that FlashBuilder will suggest buttonStyleName as a style and not as a property (as would happen with Sam's solution).
Edit: already defined styles
I didn't realize at first that you were referring to the mx ButtonBar (as it's not explicitly mentioned). The reason this is not working for you is that mx:ButtonBar already has these styles defined as not inheriting. Look at the source code:
[Style(name="firstButtonStyleName", type="String", inherit="no")]
[Style(name="buttonStyleName", type="String", inherit="no")]
[Style(name="lastButtonStyleName", type="String", inherit="no")]
Because of this the compiler will complain when you try to override that definition in your custom Panel, because it simply wouldn't know which of the contradictory instructions to pick. So we'll have to do a little more work if you want to stick with mx:ButtonBar.
First define the styles on ButtonPanel exactly as they are defined in mx:ButtonBar so they have the same signature (you can just copy/paste the three lines above). This will shut up the compiler but the styles won't be inherited anymore, right?
So we'll have to pass them on manually: in your custom Panel skin, override the updateDisplayList() method and - assuming that the ButtonBar's id is 'buttonBar' - add the following:
private const buttonStyles:Array = [
"firstButtonStyleName",
"buttonStyleName",
"lastButtonStyleName"
];
override protected function updateDisplayList(unscaledWidth:Number,
unscaledHeight:Number):void
{
if (buttonBar)
for each (var buttonStyle:String in buttonStyles)
buttonBar.setStyle(buttonStyle, getStyle(buttonStyle));
//some other code
super.updateDisplayList(unscaledWidth, unscaledHeight);
}
This will take the styles from the host Panel and pass them on to the ButtonBar.
In order to pass these styles through, you only have to store them as string variables, and then pass them to the internal ButtonBar.
<mx:ButtonBar ... buttonStyleName="{buttonStyleName}" ... />
[Bindable]public var buttonStyleName:String;
If these two lines of code don't explain it fully to you, let me know and I can flesh out my example.
The problem I'm having is while using Linq2Sql with inheritance after declaring a new instance of the inherited class the discriminator property is still set to its initial value, not the correct value for the sub-type. It gets the correct value after attaching it to a context and calling SubmitChanges(). There are times where I want to declare a new object of the inherited type and call methods on the base class with the base class knowing inherited type it is working with and the most logical choice would be to use the discriminator property.
Is there a way to force the setting of the discriminator property? I don't want to go to all my sub-classes and implement the OnCreated() partial method for something the context already knows how to do.
I did come up with a slightly better workaround than putting code in the OnCreated() method of each inheriting class and figured I'd leave it here in case anyone stumbles here.
In the OnCreated() of the base class I added code that looked similar to this:
partial void OnCreated()
{
if (this is BaseClass1)
{
this.[DiscriminatorProperty] = DiscriminatorValueForBaseClass1;
}
else if(this is BaseClass2)
{
this.[DiscriminatorProperty] = DiscriminatorValueForBaseClass2;
}
}
It is still duplicating the functionality that the context already knows how to do but at least I'm not implementing the OnCreated() in every base class. I also don't like the fact that if a new class is added or a discriminator value changes you have to update it in the DBML and in the OnCreated(). For this reason I'd still like a way for the context to assign the value, in fact it should be doing this when the inherited class is created.