CODEWITHSUNDEEP
iosswiftreflection
Johnathan
Johnathan

Reputation: 33

How to set a member variable value using reflection in Swift?

I've read through numerous tutorials and tried countless things to get this to work but can't seem to find a solution.

All I want to do is use reflection to set the value for a named member variable. I can read the values just fine, but how do I write a value?

Here is my sample code:

class MyObject
{
    public var myString : String = "Not working"
}

func test()
{
    let value = "It works!"
    let member = "myString"
    var myObject = MyObject()

    let mirror = Mirror(reflecting: myObject)
    for (_, var attr) in mirror.children.enumerated() {
        if attr.label == member {
            print("Setting value of \(member)")

            // attempt to set the member variable value
            attr.value = value

            break
        }
    }

    print("New value: \(myObject.myString)")
}

Running this example, the output prints the old value of myString. I'm using Swift 4 for iOS.

Any help would be appreciated. Thank you!

Upvotes: 3

Views: 2801

Answers (2)

Andrew
Andrew

Reputation: 1538

Unfortunately, you cannot modify value with built-in Mirror.

Maybe try Runtime named library instead (which's the successor of now deprecated Reflection library).

OR

You can make it without reflection if it is acceptable for you, like:

class MyObject: NSObject {
    @objc public var myString : String = "Not working"
}

func test() {
    let value = "It works!"
    let member = "myString"
    let myObject = MyObject()
    
    myObject.setValue(value, forKey: member)
   
    print("New value: \(myObject.myString)")
}

Hope it helps you.

Upvotes: 3

Dharmesh Kheni
Dharmesh Kheni

Reputation: 71854

Swift's reflection capabilities are based around a struct called Mirror. You create a mirror for a particular subject and the mirror will then let you query it.

Means with Mirror you can not modify the subject in your case MyObject.

Read HERE for more info.

EDIT:

You can simply update your class property as shown below:

func test() {

    let myObject = MyObject()
    myObject.myString = "It works!"
    print("New value: \(myObject.myString)") // "New value: It works!"
}

Upvotes: 0

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