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AechoLiu
AechoLiu

Reputation: 18368

UITextField `setText` in Swift

With Objective-C, I can override the setText function by following codes. The text is a property of UITextField, and I sub-class it for some custom UI design.

- (void)setText:(NSString *)text
{
   [super setText:text];
   ....
}

My question is, how to do such thing by Swift ?

There is no such function setText when I program with Swift. How to override the setter and getter methods of property with Swift ?

Upvotes: 4

Views: 10607

Answers (2)

Michaël Azevedo
Michaël Azevedo

Reputation: 3894

In your subclass of UITextField, override the textproperty :

override public var text:String?  {
    didSet {            
         NSLog("text = \(text)")
    }
}

Be careful though, this didSet observer is called after the property was changed, so you can't decide to revert to the previous value since it's already replaced. If you want to perform operations before the value is changed, you can use the willSet observer, which is called before you value change.

override public var text:String?  {
    didSet {            
         NSLog("text = \(text)")
    }
    willSet {
        NSLog("will change from \(text) to \(newValue)")
    }
}

Small example with this code :

var testTextfield = MyTextFieldClass()
testTextfield.text = "test"
testTextfield.text = "test1"

And the output is 

will change from Optional("") to Optional("test")
text = Optional("test")
will change from Optional("test") to Optional("test1")
Optional("test1")

Upvotes: 1

Tommie C.
Tommie C.

Reputation: 13181

You can use variable observers in this case.

var variableName: someType = expression {
    willSet(valueName) {
    // code called before the value is changed
    }
    didSet(valueName) {
    // code called after the value is changed
    }
}

A practical example.

“class StepCounter {
    var totalSteps: Int = 0 {
        willSet(newTotalSteps) {
            print("About to set totalSteps to \(newTotalSteps)")
        }
        didSet {
            if totalSteps > oldValue  {
                print("Added \(totalSteps - oldValue) steps")
            }
        }
    }
}”

Excerpt From: Apple Inc. “The Swift Programming Language (Swift 2.1 Prerelease).” iBooks. https://itun.es/us/k5SW7.l

Upvotes: 2

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