在Objective-C中处理快速关闭

Question

I've an objective-c function that looks like below

+ (void) invokeSortingWithClassName: (NSString*) className functionName: (NSString*) functionName closure: (id(^)(NSArray* arr))closure;

and I've to call this method from a swift class. The swift code that calls this method looks like below

SortHandler.invokeSorting(withClassName: className, functionName: functionName, closure:
{
    args in 
    let something = unwrap(args!)
    do
    {
        let returnValue = try closure(something as NSArray!) //this is another closure coming as a parameter in the function in which this code is written and this throws
        return returnValue;
    }
    catch
    {
        throw error

    }
    return "-1" as! T
})

At the start of closure definition, I get this attached error

Essentially, this closure throws an error and I am not sure, how to handle this error in objective-c definition of this function. Please help me fix this error

Answer 1

While a closure can be declared with throws , this closure has not been declared with throws , so your closure cannot throw - this is exactly what the error message is telling you.

Since the function is declared in Objective-C, the function signature can't be changed to include throws as Objective-C doesn't know anything about Swift exceptions.

The standard way in which error handling is translated between Swift and Objective-C is for the Objective-C block to receive an &NSError parameter.

If you have the ability to change the Objective-C method signature, it should be declared as

+(void) invokeSortingWithClassName: (NSString* _Nullable) className functionName: (NSString* _Nullable) functionName closure: (id _Nullable (^_Nullable)(NSArray* _Nullable arr, NSError* _Nullable * _Nullable error))closure;

This will allow you to throw from swift with the error being received via the error parameter in Objctive-C.

If you cannot change the method signature, then you will need to catch the exception in your closure and simply return an 'error' value, such as nil