swift - 转义闭包捕获非转义参数派发

Question

我收到错误:转义闭包捕获非转义参数分派(dispatch)。此错误出现在 MovieService().getMovies 行。

typealias ActionCreator = (_ dispatch: (Action) -> (), _ getState: () -> AppState) -> ()

func fetchMovies() -> ActionCreator   {
    
    return { dispatch, getState in
        
        MovieService.getMovies(url: "http://www.omdbapi.com/?s=Batman&page=2&apikey=YOURKEY") { result in
            
            switch result {
            case .success(let movies):
                if let movies = movies {
                    dispatch(.populateMovies(movies))
                }
            case .failure(let error):
                print(error.localizedDescription)
            }
            
        }
    }
    
}

有什么想法吗？

Answer 1

作为closures文档状态:

A closure is said to escape a function when the closure is passed asan argument to the function, but is called after the function returns.When you declare a function that takes a closure as one of itsparameters, you can write @escaping before the parameter’s type toindicate that the closure is allowed to escape.

默认情况下，闭包是 nonescaping 就像你的 dispatch 参数，但你在 escaping 闭包中调用它，这可能是闭包您在 getMovies 函数中作为参数传递。

解决方法很简单，在dispatch参数类型前加上@escaping即可:

typealias ActionCreator = (_ dispatch: @escaping (Action) -> (), _ getState: () -> AppState) -> ()