How can I know, trying to access dynamically, if a given setter exists for an object, assuming a getter does exist. So the point is to know if a value can be set for that property, but using hasOwnProperty returns true as a property by that name does exist.
You can ram it with blunt front attack, but there's no telling if this corrupts the property data (in case there's a pre-processing setter):
try
{
obj.propertyName = obj.propertyName
trace("Setter is avaliable!");
}
catch (fail:Errot)
{
trace("There's no setter...");
}
Alternately, use http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/utils/package.html#describeType(), it seems that < accessor > tag is what you want.
Related
I was just wondered which is better way for returning some result of function or instance of Class?
1)
FN() {
var result = callSomeFN();
return result;
}
InitClass(int typeId): MyClass {
MyClass class = new MyClass(typeId);
return class;
}
2)
FN() {
return callSomeFN();
}
InitClass(int typeId): MyClass {
return new MyClass(typeId);
}
The only difference I see here is the declaration of a variable. I wouldn't say one is better than the other. If the variable is never going to be used why bother defining it? Just return.
I suppose if you really wanted to nitpick it would depend on if you're returning a value or reference type. If it's a reference it doesn't matter since you're going to store something in memory and return a pointer (both the variable and the return value are just pointers to the same memory space). If it's a value type it will end up copying the value and disposing of the version within the function scope. If the variable is never used why create something just to destroy it? The default behavior would be highly language dependent, which you didn't specify.
I'm writing my own language from ActionScript as a personal project (yeah, I guess AS3 is not the best language to build a language from, but never mind that).
NOTE: I have checked several times, and my compiler's option 'Enable Strict Mode' is set to True. I have tried setting it to False to try, but I didnt get a different result.
At any rate, I have a this:
package NodyCode.Classes
{
public class NCString
{
var value:String;
public function NCString(expression:String = "") {
value = expression;
}
public function rindex(substr:NCString, startIndex:int = 0x7fffffff):uint {
//code here
}
}
}
Since I'm writing my own language, I need to make sure functions and methods can take un unlimited number of arguments. For this reason, I'm using an anonymous function so that I can use the apply method. Like so:
//This code is in a class named ClassMethods
public static var StringMethods:Object = {
rindex: function(substr:NCString, startIndex:int = 0x7fffffff):uint {
return this.rindex(substr, startIndex);
}
}
And, somewhere else in my code, I do the call:
return ClassMethods.StringMethods["rindex"].apply(ncstr1, [ncstr2, [5]]);
I would like an error to be thrown whenever the user uses the wrong type of argument.
So, in this case, I call the rindex method on ncstr1, with arguments: substr = ncstr2 and startIndex = [5]. Notice that, according to my anonymous function's definition, startIndex is supposed to be an int, not an Array.
So, I expected an error to be thrown. Instead, though, rindex is called with startIndex = 5.
Why is [5] converted to 5, and is there any way for me to prevent that? If there isn't, I can always work around this problem, but I'd rather not if I can do otherwise.
EDIT: Finally understood that I did not mention I was using an anonymous function.
Are you compiling with strict mode set to false? (See here also.)
The strict option: "Prints undefined property and function calls; also performs compile-time type checking on assignments and options supplied to method calls".
It defaults to true, but if it got set to false somehow, compile-time checks might be disabled. I'd check your compiler settings (whether in an IDE or if you're compiling on the command-line) and make sure they're correct.
Okay, so here's what was said in the comments:
I did have my compiler on strict mode. The reason for which I was not getting an error is because I was using the apply method of an anonymous function. The type checks are loosened when using the apply method. That's why [5] was coerced to 5.
There is apparently no way to prevent this.
I am trying to use an instance variable as a parameter value in a method, but it is giving me an error. "Parameter initializer is unknown or is not a compile-time constant"
I want to use a non-constant instance variable though, and I assume there has to be some way around this besides calling this method from another method. Here is the code I'm referring to:
public function attack(target:Fighter=this.target):void {
}
What about:
public function attack(target:Fighter):void
{
if(target == null)
target = this.target;
}
and to be honest maybe it's easier to name one of variables _target to avoid confusion. You can use target = _target; instead of this..
You cannot set an optional parameter that way. You can set optional parameters to a default value but not a reference. In this case if you want to keep it optional you could do something like this (or what #George Profenza suggested):
public function attack(target:Fighter=null):void {
target = target ? target : this.target;
}
I see that you marked a correct answer already, but I'll explain that since you are defaulting any null parameters to this.target you would benefit from using this solution so you don't have to pass null each time you call attack() i.e. - you can do attack() instead of attack(null).
Using a value converter in WPF, you can return something like DependecyProperty.UnsetValue or Binding.DoNothing as special values to say leave the binding alone. Is there a similar mechanism in MVVMCross?
To be more specific about what I'm trying to do, is I have a view model property that is a three-state enum that I need to bind to 3 binary controls. So I thought I could bind each of the controls to a MyEnum -> bool converter that will have a conversion parameter set to the value of the converter and in the Convert method it will return true if the MyEnum state is equal to the parameter and false otherwise. So far so good. But I want this binding to be two-way, so I need to convert back. My convert back works something like this:
protected override MyEnum ConvertBack(bool value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (parameter is MyEnum)
{
if (value)
{
return (MyEnum)parameter; // this is fine
}
else
{
return ???
}
}
return base.ConvertBack(value, targetType, parameter, culture);
}
Basically, what I want to be able to do is say, if the state of my control is true update the bound property on my view model to be the same as the parameter, if not, leave the view model property alone.
Maybe this is the problem with using the strongly typed value converters?
If anybody else encounters a similar problem, in addition to Stuart's suggestions, this is what I actually ended up doing.
In the View Model
private MyEnum _selectedValue = MyEnum.SomeValue;
public MyEnum ? SelectedValue
{
get
{
return _selectedTab;
}
set
{
if (value.HasValue)
{
_selectedTab = value.Value;
RaisePropertyChanged(() => SelectedTab);
}
}
}
Then in my converter (now a MvxValueConverter<MyEnum?, bool>):
protected override MyEnum? ConvertBack(bool value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (parameter is MyEnum) // this is just a sanity check
{
if (value)
{
return (MyEnum)parameter;
}
else
{
return null
}
}
return base.ConvertBack(value, targetType, parameter, culture);
}
It's not a general solution, but it fits my immediate need.
Update: UnsetValue is now available in mvvmcross - so this answer is no longer required.
Binding.DoNothing, DependencyProperty.UnsetValue or equivalent are currently not implemented in the MvvmCross binding system, and I don't believe there are any feature or pull requests currently open on this.
I'm afraid I don't really understand your example - the 'conversion parameter set to the value of the converter' and the if (parameter is MyEnum) snippet rather threw me - as far as I know, the parameter in windows xaml binding is a constant so I don't quite understand this example. Sorry if I've misunderstood.
Regardless, some possible approaches that might be used to assist with getting this functionality up and running in your mvx app are:
You could throw an exception from the ValueConverter:
For the Convert direction, the binding FallbackValue is used if a ValueConverter fails (throws an exception)
For the ConvertBack direction, the binding does nothing if an exception is thrown (although this would unfortunately generate some trace "error" output each time)
You could implement a custom binding for your control - something which only fires change updates when the change is one you are interested in (some custom bindings are introduced in N=28 in http://mvvmcross.wordpress.com which creates bindings like BinaryEditFooTargetBinding.cs - it would be straight-forward to customise/filter the TargetOnMyCountChanged behaviour in that class)
You could implement a custom binary control - which only fires change updates when the change is one you are interested in (for various platforms, some custom controls are introduced in N=18 to N=20 in http://mvvmcross.wordpress.com)
You could implement ViewModel binary properties which mirror your View and map to your three state enum
You could use a ValueCombiner within the Tibet binding system - it should be relatively straight-forward to work out a combiner based on top of something like MvxSingleValueCombiner.cs
Alternatively/additionally, please do also consider raising a Feature and/or Pull Request for this 'do nothing' type of functionality to be included in the TryGetValue/SetValue methods in https://github.com/slodge/MvvmCross/blob/v3/Cirrious/Cirrious.MvvmCross.Binding/Bindings/SourceSteps/MvxSourceStep.cs#L66 - but obviously the timeline on that might be longer.
How does one get a reference the the getter and setter functions in actionscript 3?
if a method is defined on the calls, e.g.
public function blah():String { ...}
I can get a reference to it by just saying blah or this.blah
How do get a reference to
public function get blah2():String {}
public function set blah2(b:String):void {}
Thanks!
Original response:
Unfortunately, you will not be able to store references to those as functions. The getter and setter methods are actually built around the idea that you shouldn't be able to and they therefore function as a property.
Is there a reason that you need to reference the functions specifically?
The comment I'm responding to:
I want to dynamically add external interface methods based on custom metadata tags, e.g. [External]. I was able to do this for the regular methods, but I'm trying to extend this to getter/setters as well. To do this, I need to get a reference to the function dynamically, so I can execute it with the right args using the apply function.
I think you're better off using a multi-step approach in that case. Since getters and setters function as a property and not a method, it would make sense to test to see if it is a property and then simply assign it a value directly. Would you be able to use this:
if( foo.blah2 is Function )
{
foo.blah2.apply( foo, arr );
}
else
{
foo.blah2 = arr[ 0 ];
}