Xcode 9.3 - NSPredicate Bool crash

问题:

After the Xcode 9.3 update, I've noticed that if you want to have Predicate like this:

let predicate = NSPredicate(format: "preferred = %@", true as CVarArg)

You have a crash. But in Xcode 9.2 this wasn't a problem. Any idea?

回答1:

// Solution 3 [ Apple Documentation ]

let predicate = NSPredicate(format: "preferred == TRUE")

---

The exception occurs because true is not an object (%@). You need the %d placeholder

let predicate = NSPredicate(format: "preferred = %d", true)

回答2:

I think you can also use this:

NSPredicate(format: "preferred = true")

回答3:

After a bit of investigation, I've discovered how to fix this. In short:

// Solution 1 [ NSNumber ]
let bool = NSNumber(booleanLiteral: true)
let predicate = NSPredicate(format: "preferred = %@", bool as CVarArg)

// Solution 2 [ Bool ] (static example)
let predicate = NSPredicate(format: "preferred == YES")

As also explained here, it's simply better to deal with Obj-C type instead of Swift type when we have to deal with this kind of methods.