Ios Swift类函数在for in循环后返回空

我试图在Swift中构建一个简单的图书馆书架图书模型，但遇到了一个奇怪的问题。在以下库类中，my func total book count每次都返回0。我知道这可能是我忽略的一些简单的事情，但任何帮助都会很棒。这是我的图书馆课：

class Library
{

var allShelves:[Shelf]=[]
var allBooksCount = 0

var description: String{
    return "This Library has \(allShelves.count) Shelves with \(allBooksCount) books"
}

func addNewShelf(newShelf: Shelf){
    var newShelf = Shelf()
    self.allShelves.append(newShelf)
    println("There are \(allShelves.count) SHELVES in this library")

}

func totalBookCount() -> Int{
    for currentShelf in allShelves{
        allBooksCount = currentShelf.numberOfBooks
    }
    return allBooksCount
}


}

这是我的书架课：

class Shelf
{

var allBooksOnShelf:[Book] = []
var numberOfBooks = 0

init(){
    self.allBooksOnShelf = []
}

var description: String{
    return "This Shelf has \(allBooksOnShelf.count) Books"
}

func addNewBook(newBookToAddToShelf: Book){
    let newBook = Book(bookName: newBookToAddToShelf.bookName)
    self.allBooksOnShelf += [newBookToAddToShelf]
    numberOfBooks = allBooksOnShelf.count
    println("new book called \(newBook.bookName)")

}
}

以下是我的测试：

let newLibrary = Library()
//println(newLibrary.description)


let libraryShelf1 = Shelf()
newLibrary.addNewShelf(libraryShelf1)

let libraryShelf2 = Shelf()
newLibrary.addNewShelf(libraryShelf2)

libraryShelf1.addNewBook(Book(bookName: "Game Of Thrones"))
libraryShelf1.addNewBook(Book(bookName: "Hunger Games"))
libraryShelf1.addNewBook(Book(bookName: "Return of the Jedi"))

println("this Shelf has \(libraryShelf1.allBooksOnShelf.count) books")

newLibrary.totalBookCount()

println(newLibrary.description)

newLibrary.totalBookCount（）始终返回0。

我看到两个错误：

错误1

func addNewShelf(newShelf: Shelf){
    var newShelf = Shelf()
    ^^^^^^^^^^^^
    self.allShelves.append(newShelf)
    println("There are \(allShelves.count) SHELVES in this library")        
}

在这里，您将

newShelf

参数重新定义为局部变量，从而丢失传入的内容。正确的实施方式是：

func addNewShelf(newShelf: Shelf){
    self.allShelves.append(newShelf)
    println("There are \(allShelves.count) SHELVES in this library")        
}

错误2

在这里：

在每次迭代中，您都会重新初始化

allBooksCount

属性，因此func最终返回的是循环中最后一个工具架的计数。您应该添加（使用

+=

运算符）-此外，在开始时重置计数器也是一个好主意（否则，如果多次调用该函数，则会得到错误的结果）：

---

使用调试器跟踪并观察变量值。哇！非常感谢！我知道这是一个小东西，它工作得很好，谢谢！！很高兴它成功了：）别忘了把答案标记为解决方案

func totalBookCount() -> Int{
    for currentShelf in allShelves{
        allBooksCount = currentShelf.numberOfBooks
    }
    return allBooksCount
}

func totalBookCount() -> Int{
    self.allBooksCount = 0
    for currentShelf in allShelves{
        allBooksCount += currentShelf.numberOfBooks
    }
    return allBooksCount
}