Nssarry usage in iOS

First, create an array

Create an empty array of  02.NSArray *array = [Nsarray array];      03.//creates an array of 1 elements  04.array = [Nsarray arraywithobject:@ "123"];  05.//creates an array with multiple elements  06.array = [Nsarray arraywithobjects:@ "a", @ "B", @ "C", nil Nil];  07.NSArray *array3 = [Array Arraybyaddingobjectsfromarray:[nsarray arraywithobjects:@ "4", @ "5", nil Nil]];  09.NSArray *array4 = [Nsarray arraywithobjects:@ "1", @ "2", @ "3", @ "4", nil Nil];  10.NSRange range = Nsmakerange (1, 2);  11.NSArray *array5 = [Array4 subarraywithrange:range];  

Ii. basic usage of arrays

int count = [array count];//number  02.//determines if an element 03.if is included  ([Array containsobject:@ "a"]) {  .    NSLog (@ "contains string a");  06.NSString *last = [array lastobject]; last element  07.NSString *str = [array objectatindex:1]; Gets the elements in the array according to the index  08.int index = [array indexofobject:@ "C"]; Gets the index of the specified element  09.//let all objects inside the array call the test method, 123 is the parameter  10.NSArray *array = [Nsarray arraywithobjects:stu1, STU2, STU3, nil Nil];  11.[array makeobjectsperformselector: @selector (test2:) withobject:@ "123"];  12.NSArray *array = [Nsarray arraywithobjects:@ "1", @ "2", @ "3", @ "4", nil Nil];  13.//1-2-3-4  14.//using separators-stitching all array elements  15.NSString *str = [Array componentsjoinedbystring:@ "-"];  16.//writes an array to the file (resulting in an XML file)  17.NSString *path = @ "/users/apple/desktop/array.xml";  18.[array Writetofile:path Atomically:yes];  19.path = @ "/users/apple/desktop/array.txt";  20.//reading array contents from a file (file has strict formatting requirements)  21.NSArray *array2 = [Nsarray Arraywithcontentsoffile:path];  

Third, iterating through the array

#pragma mark traverses the array 1 02.void arrayFor1 () {03.  Nsarray *array = [Nsarray arraywithobjects:stu1, @ "1", @ "2", @ "3", nil Nil];  *. int count = Array.count;        The. for (int i = 0; i<count; i++) {06.  ID obj = [array objectatindex:i];  07.} 08.}    #pragma mark traversed the array 2 fast traversal of 11.void ArrayFor2 () {12.  Student *STU1 = [Student Student];  Nsarray *array = [Nsarray arraywithobjects:stu1, @ "1", @ "2", @ "3", nil Nil];  int i = 0;        (ID obj in array) {16.  NSLog (@ "%i-%@", I, obj);  i++;  18.} 19.}    #pragma mark traverses the array 3 22.void ArrayFor3 () {23.  Student *STU1 = [Student Student];  Nsarray *array = [Nsarray arraywithobjects:stu1, @ "1", @ "2", @ "3", nil Nil];     [Array enumerateobjectsusingblock:26.        ^ (ID obj, Nsuinteger idx, Boolbool *stop) {27.  NSLog (@ "%i-%@", idx, obj);         28.//If the index is 1, stop traversing 29.             if (idx = = 1) {30.             Use the pointer to modify the value of the outer bool variable 31. *stop = YES;    32.} 33.  }];  34.} 35.    #pragma mark traverses the array 4 37.void ArrayFor4 () {38.  Student *STU1 = [Student Student];  Nsarray *array = [Nsarray arraywithobjects:stu1, @ "1", @ "2", @ "3", nil Nil];    40.//Gets the array iterator 41.  Nsenumerator *enumerator = [array objectenumerator];    42.//reverse-order iterator (traversing element from tail) 43.  Nsenumerator *enumerator = [array reverseobjectenumerator];    The.//AllObjects is to remove objects that have not been traversed 45.  Nsarray *array2 = [enumerator allobjects];  NSLog (@ "array2:%@", array2);    47.//Gets the next element that needs to be traversed 48.  ID obj = nil;        (obj = [Enumerator nextobject]) {50.  NSLog (@ "obj=%@", obj);   51.} 52.}

Four, array sorting

Sort #pragma mark Array 1 02.void arraySort1 () {03.  Nsarray *array = [Nsarray arraywithobjects:@ "2", @ "3", @ "1", @ "4", nil Nil];    04.05.    Returns an ordered array that does not change the order of elements in the original array by 06.    The comparison method for the specified element: compare:07.  Nsarray *array2 = [Array sortedarrayusingselector: @selector (compare:)];  NSLog (@ "array2:%@", array2);  09.} 10.    #pragma mark Array sort 2 12.void arraySort2 () {13.  Student *STU1 = [Student studentwithfirstname:@ "Mingjie" lastname:@ "Li"];  Student *STU2 = [Student studentwithfirstname:@ "Longhu" lastname:@ "Huang"];  Student *STU3 = [Student studentwithfirstname:@ "Lianjie" lastname:@ "Li"];  Student *stu4 = [Student studentwithfirstname:@ "Jian" lastname:@ "Xiao"];  Nsarray *array = [Nsarray arraywithobjects:stu1,stu2,stu3, Stu4, nil Nil];    18.//Specify the sort comparison method 19.  Nsarray *array2 = [Array sortedarrayusingselector: @selector (comparestudent:)];  NSLog (@ "array2:%@", array2);  22.-} (Nscomparisonresult) Comparestudent: (Student *) Stu {23.//Sort by first name 24.  Nscomparisonresult result = [Self.lastname compare:stu.lastname];    25.//If you have the same surname, compare the name 26.        if (result = = Nsorderedsame) {27.  result = [Self.firstname compare:stu.firstname];    28.} 29.  return result;  30.} 31.    #pragma mark Array sort 3 33.void arraySort3 () {34.  Student *STU1 = [Student studentwithfirstname:@ "Mingjie" lastname:@ "Li"];  Student *STU2 = [Student studentwithfirstname:@ "Longhu" lastname:@ "Huang"];  Student *STU3 = [Student studentwithfirstname:@ "Lianjie" lastname:@ "Li"];  Panax Student *stu4 = [Student studentwithfirstname:@ "Jian" lastname:@ "Xiao"];  Nsarray *array = [Nsarray arraywithobjects:stu1,stu2,stu3, Stu4, nil Nil];    39.40.    Use block to sort 41.     Nsarray *array2 = [Array sortedarrayusingcomparator:42.         ^nscomparisonresult (Student *obj1, Student *obj2) {43.         Sort 44 by last name first.  Nscomparisonresult result = [Obj1.lastname compare:obj2.lastname]; 45.//If you have the same surname,Just compare the name 46.             if (result = = Nsorderedsame) {47.  result = [Obj1.firstname compare:obj2.firstname];           48.} 49.  . return result;  51.}];    52.53.  NSLog (@ "array2:%@", array2);  54.} 55.    #pragma mark Array Sort 4-advanced sort 57.void arraySort4 () {58.  Student *STU1 = [Student studentwithfirstname:@ "Mingjie" lastname:@ "Li" bookname:@ "Book1"];  Student *STU2 = [Student studentwithfirstname:@ "Longhu" lastname:@ "Huang" bookname:@ "Book2"];  Student *STU3 = [Student studentwithfirstname:@ "Lianjie" lastname:@ "Li" bookname:@ "Book2"];  Student *stu4 = [Student studentwithfirstname:@ "Jian" lastname:@ "Xiao" bookname:@ "Book1"];  Nsarray *array = [Nsarray arraywithobjects:stu1,stu2,stu3, Stu4, nil Nil];    63.64.    1. Sort by title first 65.    Here the key is written by the name of @property 66.  Nssortdescriptor *booknamedesc = [Nssortdescriptor sortdescriptorwithkey:@ "Book.name" Ascending:YES];    67.//2. Sort by last name 68. Nssortdescriptor *lastnamedesc = [Nssortdescriptor sortdescriptorwithkey:@ "LastName" Ascending:yes];    69.//3. Sort by name 70.  Nssortdescriptor *firstnamedesc = [nssortdescriptor sortdescriptorwithkey:@ "FirstName" Ascending:yes];    71.//Add Sort descriptor 72 sequentially.  Nsarray *descs = [Nsarray arraywithobjects:booknamedesc, Lastnamedesc, Firstnamedesc, nil Nil];    73.74.  Nsarray *array2 = [array Sortedarrayusingdescriptors:descs];    75.76.  NSLog (@ "array2:%@", array2);   77.}