Swift教程13-字典Dictionary與NSDictionary

標籤：swift字典   dictionary與nsdiction   

與Oc的字典不太一樣,Swift的字典不僅可以儲存 物件類型的值,還可以儲存 基礎資料型別 (Elementary Data Type)值,結構體,枚舉值;

Swift字典的使用方式也更加簡潔,功能更加強大.

字典本質上也是結構體,查看文檔可以看到:

/// A hash-based mapping from `Key` to `Value` instances.  Also a/// collection of key-value pairs with no defined ordering.struct Dictionary<Key : Hashable, Value> : CollectionType, DictionaryLiteralConvertible {    typealias Element = (Key, Value)    typealias Index = DictionaryIndex<Key, Value>    /// Create a dictionary with at least the given number of    /// elements worth of storage.  The actual capacity will be the    /// smallest power of 2 that's >= `minimumCapacity`.    init()    /// Create a dictionary with at least the given number of    /// elements worth of storage.  The actual capacity will be the    /// smallest power of 2 that's >= `minimumCapacity`.    init(minimumCapacity: Int)    /// The position of the first element in a non-empty dictionary.    ///    /// Identical to `endIndex` in an empty dictionary    ///    /// Complexity: amortized O(1) if `self` does not wrap a bridged    /// `NSDictionary`, O(N) otherwise.    var startIndex: DictionaryIndex<Key, Value> { get }    /// The collection's "past the end" position.    ///    /// `endIndex` is not a valid argument to `subscript`, and is always    /// reachable from `startIndex` by zero or more applications of    /// `successor()`.    ///    /// Complexity: amortized O(1) if `self` does not wrap a bridged    /// `NSDictionary`, O(N) otherwise.    var endIndex: DictionaryIndex<Key, Value> { get }    /// Returns the `Index` for the given key, or `nil` if the key is not    /// present in the dictionary.    func indexForKey(key: Key) -> DictionaryIndex<Key, Value>?    subscript (position: DictionaryIndex<Key, Value>) -> (Key, Value) { get }    subscript (key: Key) -> Value?    /// Update the value stored in the dictionary for the given key, or, if they    /// key does not exist, add a new key-value pair to the dictionary.    ///    /// Returns the value that was replaced, or `nil` if a new key-value pair    /// was added.    mutating func updateValue(value: Value, forKey key: Key) -> Value?    /// Remove the key-value pair at index `i`    ///    /// Invalidates all indices with respect to `self`.    ///    /// Complexity: O(\ `count`\ ).    mutating func removeAtIndex(index: DictionaryIndex<Key, Value>)    /// Remove a given key and the associated value from the dictionary.    /// Returns the value that was removed, or `nil` if the key was not present    /// in the dictionary.    mutating func removeValueForKey(key: Key) -> Value?    /// Remove all elements.    ///    /// Postcondition: `capacity == 0` iff `keepCapacity` is `false`.    ///    /// Invalidates all indices with respect to `self`.    ///    /// Complexity: O(\ `count`\ ).    mutating func removeAll(keepCapacity: Bool = default)    /// The number of entries in the dictionary.    ///    /// Complexity: O(1)    var count: Int { get }    /// Return a *generator* over the (key, value) pairs.    ///    /// Complexity: O(1)    func generate() -> DictionaryGenerator<Key, Value>    /// Create an instance initialized with `elements`.    init(dictionaryLiteral elements: (Key, Value)...)    /// True iff `count == 0`    var isEmpty: Bool { get }    /// A collection containing just the keys of `self`    ///    /// Keys appear in the same order as they occur as the `.0` member    /// of key-value pairs in `self`.  Each key in the result has a    /// unique value.    var keys: LazyBidirectionalCollection<MapCollectionView<[Key : Value], Key>> { get }    /// A collection containing just the values of `self`    ///    /// Values appear in the same order as they occur as the `.1` member    /// of key-value pairs in `self`.    var values: LazyBidirectionalCollection<MapCollectionView<[Key : Value], Value>> { get }}

可以看到 字典的key必須是實現了  Hashable協議的類型;也就是說key的類型不僅限於 字串!

1.字典的聲明

//定義一個空的字典var dic:[String:Int]=[:]

形式:

var dicName:[key類型 : 值類型] 

或者,使用範型的方式類約束其類型

//字典的範型定義方式var myDic:Dictionary<String,String>

2.字典的建立.

(1)我們觀察上面給出的 字典定義可以看到有兩個init 方法,這是兩個構造器,我們可以使用這兩個構造器來建立字典對象

init()

<span style="font-family: Arial, Helvetica, sans-serif;">init(minimumCapacity: Int)</span>

第二個構造器指定了 字典的最小容量

//使用init()構造器var mydic:[String:String]=Dictionary<String,String>()

//使用init(minimumCapacity:Int)var dic2:[String:Int]dic2=Dictionary<String,Int>(minimumCapacity: 5)

(2)直接賦值建立字典

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];

3.字典或數組的判空操作

isEmpty

是用該屬性返回的布爾值,可以判斷數組或字典中的元素個數是否為0

4.訪問或修改字典的元素

(1)字典可以直接通過類似下標的方式  key來訪問,字典的元素;var  定義的可變字典可以直接使用Key來修改其值

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];myDic["語文"]="99.9222"//可變字典可以直接修改內容println(myDic["語文"])

輸出:

Optional("99.9222")

可以看到,通過 key我們拿到的是一個 可選類型,我們需要對其進行解析;因為 該key對應的值可能不存在!!!

(2) 解析可選類型值

我們必須使用可選類型來接收 Key對應的值,否則會導致編譯錯誤

var yuwen:String? = myDic["語文"]

完整樣本:

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];myDic["語文"]="99.9222"//可變字典可以直接修改內容var yu:String? = myDic["語文"]if yu != nil{    println(yu!)}

輸出:

99.9222

可以看到,我們把之前的可選類型解析為我們需要的普通類型,就可以直接使用了

5.修改,新增字典元素的幾種方式

(1)可以直接使用  下標方式,形如 

dic["key"] = value   的形式來修改或新增字典元素;如果該key對應的元素不存在則會新增這個key的鍵值對,否則會直接修改該key對應的值;

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];println(myDic)myDic["2語文"]="99.9222"println(myDic)

輸出:

[數學: 100, 語文: 99][數學: 100, 語文: 99, 2語文: 99.9222]

上面的  key  "2語文"  在 原來的字典中並不存在,此時會新增一個 元素,對應的 key是  該 "2語文",值 是  "99.922"

(2)使用字典的方法

mutating func updateValue(value: Value, forKey key: Key) -> Value?

使用樣本:

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];println(myDic)myDic.updateValue("888", forKey: "新增的key")println(myDic)

輸出:

[數學: 100, 語文: 99][新增的key: 888, 數學: 100, 語文: 99]

可以看到,此方法對於  不存在的 key也會新增 鍵值對;當然如果該 key存在就會直接修改該key對應的值

6.擷取所有的keys和 values, 方法  和 Oc中的方法類似

查看 字典的定義文檔可以知道  如下的 兩個屬性,可以獲得所有的 keys  和 values

    var keys: LazyBidirectionalCollection<MapCollectionView<[Key : Value], Key>> { get }    /// A collection containing just the values of `self`    ///    /// Values appear in the same order as they occur as the `.1` member    /// of key-value pairs in `self`.    var values: LazyBidirectionalCollection<MapCollectionView<[Key : Value], Value>> { get }

使用方法:

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];println(myDic.keys)println(myDic.values)

輸出:

Swift.LazyBidirectionalCollectionSwift.LazyBidirectionalCollection

可以看到,輸出的是集合類型;如果我們想要看到它的值,則可以把它放在數組中即可:

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];var keys1 = Array(myDic.keys)println(keys1)var values1 = Array(myDic.values)println(values1)

輸出,所有keys  values

[數學, 語文][100, 99]

7.刪除字典元素的幾種方式

(1)刪除單個數組元素

可以使用  dic[key] = nil來刪除一個元素

或者使用 removeValueForKey方法來刪除

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];myDic.removeValueForKey("語文")println(myDic)myDic["新增"] = "77"println(myDic)myDic["數學"] = nilprintln(myDic)

[數學: 100][數學: 100, 新增: 77][新增: 77]

(2)清空字典元素

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];myDic = [:]println(myDic)

直接  把字典賦值為 空

myDic = [:]即可

或者:

var myDic:Dictionary<String,String>myDic=["語文":"99","數學":"100"];myDic.removeAll(keepCapacity: false)println(myDic)

對於  keepCapacity :false /true  ,根據需求選擇 即可;

區別是true的話,會保持資料容量,佔據空間?

8.字典的複製

字典的複製規律和數組類似

如果字典內的元素是實值型別的,如整型,那麼字典複製時,會把源字典複製出元素的副本;如果字典內的元素是參考型別的,如對象,那麼 字典複製時,只是複製出元素的指標,修改該指標則也會修改源字典的內容

關於Swift數組請參見http://blog.csdn.net/yangbingbinga/article/details/44747877

更多Swift教程:http://blog.csdn.net/yangbingbinga

           

Swift教程13-字典Dictionary與NSDictionary