如何在 IOS swift 中将 Double 转换为 Int

Question

tmp turned out to be nil in runtime. magneticField.x is a Double and when I printed it directly out it has a value.

Answer 1

The casting of the Double to an Int will work as written. The problem is that for some reason at runtime self.motion.magnetometerData is nil, so tmp becomes nil.

It's usually better to safely unwrap optionals, such as:

let tmp = self.motion.magnetometerData?.magneticField.x
if let tmpValue = tmp {
    let tmpInt = Int(tmpValue)
    print(tmpInt) //And whatever else
}

Or, if you intend not to continue if it ends up being nil, use a guard:

guard let tmp = self.motion.magnetometerData?.magneticField.x else {
    return //Or whatever is appropriate when the value is nil
}