How can I "blindly inject" an object variable with arbitrary value? - swift

Question

For example, I have a variable with type AnyObject. I do not know what class is that. But I want to test, whether if the object can accept specific attribute, and want to assign value to it.
For example, if I have:
class BaseViewController : UIViewController {
var containerVc : UIViewController?;
}
If I know that a variable can be typecasted into BaseViewController, then, of course, I can just typecast it to BaseViewController, and then assign the variable to it.
let vc : UIViewController?;
vc = BaseViewController();
(vc as? BaseViewController)?.containerVc = self;
The problem is if the BaseViewController type itself is inaccessible or unknowable.
So what I want to do is that I just want to test if an attribute is available to be set, if the operation can't be performed, it can fail silently. So for example, the code I have in mind if this is possible:
var vc : UIViewController? = generateUnknownVc();
vc.setValue(self, forAttribute: "containerVc");
or genericaly:
var abc : AnyObject = generateRandomObject();
abc.setValue(123, forAttribute: "randomAttribute");
I ask this because I remember somewhere that you can supply value to an object the way Storyboard does (User Defined Runtime Attributes). But I don't know how that works programmatically.
CONCLUSION:
This is the code I finally ended up with, borrowed heavily from Ehsan Saddique's answer. This code has been improved to also check the ancestors (superclass).
extension NSObject {
func safeValue(forKey key: String) -> Any? {
var copy : Mirror? = Mirror(reflecting: self);
while copy != nil {
for child in copy!.children.makeIterator() {
if let label = child.label, label == key {
return child.value
}
}
copy = copy?.superclassMirror;
}
return nil
}
func setValueSafe(_ value: Any?, forKey key: String) {
if safeValue(forKey: key) != nil { self.setValue(value, forKey: key); }
}
}
And from Andreas Oetjen's answer, I need to make mental note that this only works if the object is descendant from NSObject or tagged with #objc, and the function is also tagged with #objc.
Thanks!

Answer 1

UIViewController is inherited from NSObject. You can use Key-Value-Coding to find if the key exists. Add this extension to your code.
extension NSObject {
func safeValue(forKey key: String) -> Any? {
let copy = Mirror(reflecting: self)
for child in copy.children.makeIterator() {
if let label = child.label, label == key {
return child.value
}
}
return nil
}
}
Now you can use if-let to check if key exists.
if let key = yourViewController.safeValue(forKey: "someKey") {
print("key exists")
yourViewController.setValue("someValue", forKey:"someKey")
}
else {
print("key doesn't exist")
}
You will have to mark your properties with #objc to use KVC.

Answer 2

You would use Key-Value-Coding, which is supported in swift if (and only if)
Your class is somehow a subclass of NSObject or tagged with #objc
Your properties you want to access are tagged with #objc
I currently have no Xcode available, but this sample code should work:
class A : NSObject {
#objc var name:String = "hello"
}
var theA = A()
theA.setValue("world", forKey:"name")
print(theA.name) // shoud print "world"
To check if an property exists (instead of just crashing), see this answer: Check if class has a value for a key