Swift Learning-strings & arrays & Dictionaries

String

• Differences between the strings in OC and Swift
  • When the string type is nsstring in OC, the string type in Swift
  • The string @ "" In OC, the string "" in Swift
  • String in Swift is the first struct with higher performance
  • String supports direct traversal
  • Swift provides a seamless transition between string and NSString

Use of Strings

• Use backslashes \ and parentheses () to interpolate the string (insert the constant \ variable into the string)
  • Let hand = 2
    var age1 = 20
    Let string1 = "I am (age1) year old, have \ (hand) only Hand"
  • You can also use string concatenation, but you must turn it into a string
    var string2 = "I this year" +string (age1) + "old, have \ (hand) only Hand"

• Traversing strings
  • var string = "Hi Siri"
    For s in string.characters {//String.characters represents all the characters in a string
    Print (s)//printing 7 characters in sequence, space is also
    }

• Concatenation of strings and other data types
  • Let name = "Siri"
    Let age = 10
    Let Siriinfo = "My name was \ (name), Age was \ (age)"

           My name is Siri, which is 10

• Formatting time for string: 03:04
  • Let min = 3
    Let second = 4
    Let time = String (format: "%02d:%02d", arguments: [min, second])

• Interception of strings
  • A special interception method is provided in Swift, but it is cumbersome and index is difficult to create
  • The simple way to do this is to turn the string into NSString to use. String-NSString After the identifier: as NSString
    • Let Baidu = "www.baidu.com"
      var subStr = (Baidu as NSString). Substringfromindex (4)//"baidu.com"
      SUBSTR = (Baidu as NSString). Substringtoindex (3)//"www"
      SUBSTR = (Baidu as NSString). Substringwithrange (Nsrange (Location:4, Length:5))//"Baidu"

• Note: In swift, String has a method called ToInt that can convert a string to an int type. It is important to note that not all strings can be converted to integers.
  • Let Numstr = "123"
    Let number = Numstr.toint ()//It doesn't seem to work.

Array

• Array: (array) is a set of ordered sets of elements of the same type, the immutable array when let is modified, the variable group when VAR is modified
  • Defines a mutable array that must be initialized to use
    var array1: [String] = [string] ()
    Define an immutable group
    Let array2: [nsobject] = ["WWL", 18]

• Statement
  • Declaration method one: Var myarray1:array<string>
    Declaration method Two: Var myArrray2: [String]

• Initialization
  • Initialize directly when defining
    var array3 = ["AAA", "SSS", "ddd"]//type derivation of string type
    Define first, then initialize
    var array4:array<string>
    Array4 = ["fff", "GGG", "HHH"]

Note: Arrays must be initialized to be used, and array types are specified at the time of declaration

• Array operations:
  • Add data
    Array.append ("DD")
    Delete Element
    Array.removefirst ()
    modifying elements
    Array[0] = "ee"
    Take value
    ARRAY[1]
    inserting elements
    Array.insert ("TTT", atindex:0)
  • The array can also be used for interval
    ARRAY[1...2]

• Traversal of an array
  • Normal traversal array
    For I in 0..<array.count {
    Print (Array[i])//with subscript
    }
    
    For in mode
    For item in array {
    Print (item)//no subscript required
    }
    
    Set the traversal interval
    For item in ARRAY[0..<2] {//0..<2 open interval 0,1 0...2 closed interval 0,1,2
    Print (item)
    }

• Merging of arrays
  • Only arrays of the same type can be merged
    • var stringArr1 = ["AA", "BB", "CC"]
      var stringArr2 = ["dd", "EE"]
      var stringArr3 = array + array1;
      
      It is not recommended to store multiple types of data in an array
      var = [objectArr1, "AA"]
      var objectArr2 = ["BB", 44]
      OBJECTARR1 + OBJECTARR2

• Checks whether the length of the array is 0 through a IsEmpty property that returns a Boolean type
  • var stringarr = ["AA", "BB", "CC"]
    
    If!stringarr.isempty {
    Print ("Stringarr has \ (stringarr.count) items")
    } else {
    Print ("Stringarr is Empty")
    }
    Stringarr has 3 items

• Use the (+ =) operator to add an array to the end of another array
• (+ =) operator to add an element to the end of the array as if it had been deleted
  • var stringarr = ["AA", "BB", "CC"]
    var stringArr1 = ["dd", "EE", "FF"]
    STRINGARR1 + = Stringarr
    Print (STRINGARR1)//["DD", "EE", "ff", "AA", "BB", "CC"]

• The SWIFT array type also provides an initialization method to create an array that determines the length and provides a default value. You can add a new array by this initialization method, the number of elements becomes count, and the appropriate default value is Repeatedvalue
  • var Threestringarr = [String] (Count:3, Repeatedvalue: "HI")
    You can also not specify a type, thanks to type inference
    var Threedoublearr = Array (Count:3, repeatedvalue:2.0)

Dictionary

• The dictionary type in Swift is dictionary, a generic collection. var modifiers are mutable dictionaries, let modifiers when mutable dictionaries

• declaring Dictionary types:
  • var dict1:dictionary<int, string>
    var dict2: [Int:string]

• Initialization
  • Must be initialized to use
  • var dict1:dictionary<int, string> = Dictionary ()

• • Define a mutable dictionary
    var dict3: [String:nsobject] = [String:nsobject] ()
    
    Initializing a dictionary while defining it
    Let dict4 = [' name ': ' Xiaosan ', ' age ': 18]//Type deduced [String:nsobject] Type
    
    Any object in swift, usually without the use of nsobject, using Anyobject
    var dict5:dictionary<string, anyobject>
    DICT5 = ["name": "DD", "age": 18]

• Basic operation of the dictionary
  • Operation of the Dictionary
    var dict: [String:anyobject] = [String:anyobject] ()
    
    Dict = ["Age": +, "height": 1.74, "name": "Xiaocan"]
    
    Add data
    dict["weight"] = 60.0
    
    Delete data
    Dict.removevalueforkey ("Age")
    
    Modify Dictionary
    dict["name"] = "Xiaoer"
    Dict["Age"] = 18//If you do not have this key, add the data
    
    Inquire
    dict["Name"]

• The traversal of a dictionary
  • Iterate through all the values in the dictionary
    For value in Dict.values {
    Print (value)
    }
    Iterate through all the keys in the dictionary
    For key in Dict.keys {
    Print (key)
    }
    
    Traverse all key-value pairs
    For (key, value) in Dict {
    Print (key)
    Print (value)
    }

• Merging of dictionaries
  • var myDict1 = ["Name": "Xiaosan", "Age": 20]
    var myDict2 = ["Height": 1.77, "Address": "Taikang"]
    
    Dictionaries cannot be added and merged in different types and cannot be merged
    For (key, value) in MyDict1 {
    Mydict2[key] = value
    }

• Removevalueforkey && Updatevalue (forkey:)

• • Dictionary of Updatevalue (forkey:) method to set or update a value for a particular key, set its value if the key does not exist, and update its value if the key exists, Updatevalue (forkey:). method if it is updated, the original old value is returned rthis enables you can use this to determine if an update has occurred.
    • var dict = ["name": "Siri", "Age": "Address": "Nanjing"]
      
      Iflet OldValue = Dict.updatevalue ("Siri", Forkey: "name") {
      Print (OldValue)//Siri
      }
      
      Use the following banner to assign his value to nil to remove the key-value pair.
      Dict["Age" = Nil
      
      Print (DICT)//["Address": Nanjing, "name": Siri]
  • With the Removevalueforkey method, if there is a value corresponding to the key, a key-value pair is removed and the removed value is returned, otherwise nil is returned.
    • If Let Removedvalue = Dict.removevalueforkey ("address") {
      Print ("The Remove dict ' s adddress is \ (removedvalue)")//The Remove dict ' s adddress are Nanjing
      } else {
      Print ("The dict does not contain a value for address")
      }

Swift Learning-strings & arrays & Dictionaries