Whats the use of UIControlState “application” of U

问题:

I went through the apple doc too but it just states that its

Additional control-state flags available for application use.

Its just a getter method so when does it get set?

回答1:

application and reserved are basically markers. That is more clear when looking at the objective-c documentation for them:

disabled: UIControlStateDisabled = 1 << 1

application: UIControlStateApplication = 0x00FF0000

reserved: UIControlStateReserved = 0xFF000000

That means that the second least significant bit of a UIControlState for example is responsible for determining wether or not a UIControl is disabled or not. All the bits from 17 - 24 (from 1 << 16 until 1 << 23) are there for your application to use while 25 - 32 (from 1 << 24 until 1 << 31) are there for internal frameworks to use.

That basically means that Apple is able / allowed to define new state flags of controls while using the lowest 16 bits, you have the guarantee to be able to use 8 bits for custom flags of your own.

Defining custom flags can be done e.g. via:

let myFlag = UIControlState(rawValue: 1 << 18)

class MyButton : UIButton {
    var customFlags = myFlag
    override var state: UIControlState {
        get {
            return [super.state, customFlags]
        }
    }

    func disableCustom() {
        customFlags.remove(myFlag)
    }
}

which can be used via

let myButton = MyButton()
print(myButton.state.rawValue) // 262144 (= 2^18)
myButton.isEnabled = false
myButton.isSelected = true
print(myButton.state.rawValue) // 262150 (= 262144 + 4 + 2)
myButton.disableCustom()
print(myButton.state.rawValue) // 6 (= 4 + 2)