Using isKindOfClass with Swift

问题

I\'m trying to pick up a bit of Swift lang and I\'m wondering how to convert the following Objective-C into Swift:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesBegan:touches withEvent:event];

    UITouch *touch = [touches anyObject];

    if ([touch.view isKindOfClass: UIPickerView.class]) {
      //your touch was in a uipickerview ... do whatever you have to do
    }
}

More specifically I need to know how to use isKindOfClass in the new syntax.

override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {

    ???

    if ??? {
        // your touch was in a uipickerview ...

    }
}

回答1:

The proper Swift operator is is:

if touch.view is UIPickerView {
    // touch.view is of type UIPickerView
}

Of course, if you also need to assign the view to a new constant, then the if let ... as? ... syntax is your boy, as Kevin mentioned. But if you don't need the value and only need to check the type, then you should use the is operator.

回答2:

override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {

    super.touchesBegan(touches, withEvent: event)
    let touch : UITouch = touches.anyObject() as UITouch

    if touch.view.isKindOfClass(UIPickerView)
    {

    }
}

Edit

As pointed out in @Kevin's answer, the correct way would be to use optional type cast operator as?. You can read more about it on the section Optional Chaining sub section Downcasting.

Edit 2

As pointed on the other answer by user @KPM, using the is operator is the right way to do it.

回答3:

You can combine the check and cast into one statement:

let touch = object.anyObject() as UITouch
if let picker = touch.view as? UIPickerView {
    ...
}

Then you can use picker within the if block.

回答4:

I would use:

override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {

    super.touchesBegan(touches, withEvent: event)
    let touch : UITouch = touches.anyObject() as UITouch

    if let touchView = touch.view as? UIPickerView
    {

    }
}

回答5:

Another approach using the new Swift 2 syntax is to use guard and nest it all in one conditional.

guard let touch = object.AnyObject() as? UITouch, let picker = touch.view as? UIPickerView else {
    return //Do Nothing
}
//Do something with picker

来源：https://stackoverflow.com/questions/24019707/using-iskindofclass-with-swift

标签

ios

swift

reflection

introspection