(I'm new to Swift and iOS development in general).
I'm porting some Objective-C code over to Swift and I don't know how to translate this:
-(void) fooDidBar:(NSNotification *)notification
{
Foo* foo = [[notification userInfo] objectForKey:BarKey];
// do stuff with foo
}
So far I have this:
private func fooDidBar(notification: NSNotification) {
var foo: Foo = notification.userInfo.objectForKey(BarKey)
}
But I get a compiler error:
/Users/me/src-me/project/FooBarViewController.swift:53:57: Value of type '[NSObject : AnyObject]?' has no member 'objectForKey'
As userInfo
is declared as an NSDictionary
in UIApplicationShortcutItem.h
:
@property (nullable, nonatomic, copy) NSDictionary<NSString *, id <NSSecureCoding>> *userInfo;
...I thought I'd try this:
= notification.userInfo[BarKey]
but then I get this error:
/Users/me/src-me/project/FooBarViewController.swift:53:65: Type '[NSObject : AnyObject]?' has no subscript members
Your idea to use subscripts was correct, however as you can see by the presence of ?
, the userInfo
dictionary is Optional , meaning that it can be nil (in Objective-C, no distinction is made). Furthermore, Swift's Dictionary is not as lenient with types as NSDictionary, so you'll need to use as?
to ensure the value is a Foo
instance as you expect.
You can't directly subscript the optional dictionary, but if you use a ?
for optional chaining , then you can access the value if the dictionary is non-nil. I would also recommend if let
to access the final value if it's non-nil. (Or you might choose to use guard let
with a fatalError
or return
in case the Foo is not present.)
if let foo = notification.userInfo?[BarKey] as? Foo {
// foo is non-nil (type `Foo`) in here
}
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