36-oc Nsarray

Nsarray Basic Concepts

What is Nsarray

Nsarray is an array class in OC, and in development it is recommended to use Nsarray instead of arrays in the C language.

What are the use notes of Nsarray

Only any OC objects can be stored, and are ordered

Cannot store non-OC objects, such as int\float\double\char\enum\struct, etc.

It is immutable, and once initialized, the contents of it are always fixed, the elements inside cannot be deleted, and no elements can be added to it.

Nsarray is printed with NSLog (), and the output is in the form of parentheses.

Nil is not stored in Nsarray because Nsarray considers nil to be the end of the array (nil is the tag at the end of the array element). Nil is 0. 0 is also the basic data type and cannot be stored in the Nsarray.

What are the common methods of Nsarray?

-(Nsuinteger) count;

Get the number of collection elements

-(ID) Objectatindex: (Nsuinteger) index;

Gets the element of the index position

-(BOOL) Containsobject: (ID) anobject;

Whether to include an element

-(ID) lastobject;

Returns the last element

-(ID) firstobject;

Returns the last element

-(Nsuinteger) Indexofobject: (ID) anobject;

Finds the position of the AnObject element in the array (returns-1 if not found)

-(Nsuinteger) Indexofobject: (ID) anobject inrange: (nsrange) range;

Find the position of the AnObject element in the array within range range

Writing Nsarray Shorthand form

Nsarray *arr = [Nsarray arraywithobjects:@ "LJ", @ "LM", @ "JJJ", nil];

Nsarray *arr = @[@ "Lnj", @ "LM", @ "JJJ"];

Gets the shorthand for the array element

NSLog (@ "%@", [arr objectatindex:0]);

NSLog (@ "%@", arr[0]);

Nsarray traversal

Enhancing the use of a For loop

How to use the enhanced for loop to traverse the Nsarray array

Remove elements from arr one by one and assign the extracted elements to obj

Note: The type of obj can be written according to the type of elements in the array, not necessarily written nsobject

For (NSString *obj in arr) {

NSLog (@ "obj =%@", obj);

}

How to iterate through an array using an iterator to an OC array

Each time an element is taken, the block is called.

Each call to block will pass to us the index of the element and element that is currently taken out.

Obj is the currently removed element, and IDX is the index of the current element.

Stop is used to control when to stop traversing

[arr enumerateobjectsusingblock:^ (id obj, Nsuinteger idx, BOOL *stop) {

if (idx = = 1) {

*stop = YES;

}

NSLog (@ "obj =%@, idx =%lu", obj, idx);

}];

To all object method messages in the Nsarray

How do I send a message to all the objects in the array?

For:

Person *P1 = [person new];

Person *P2 = [person new];

Person *P3 = [person new];

Person *P4 = [person new];

Nsarray *arr = @[p1, p2, p3, P4];

Method One:

[Arr enumerateobjectsusingblock:^ (person *obj, Nsuinteger idx, BOOL *stop) {

[obj say];

}];

2. Method Two:

If you use the OC array to store the object, you can call the OC array method to have all elements in the array execute the specified method

Note: If the array does not hold the same type of data, and there is no same method, then an error will be

[Arr makeobjectsperformselector: @selector (say)];

Withobject: Arguments that need to be passed to the calling method

[Arr makeobjectsperformselector: @selector (saywithname:) withobject:@ "WC"];

Array sorting

How to sort the data

Nsarray *arr = @[@10, @20, @5, @7, @15];

NSLog (@ "sort before:%@", arr);

Note: To use the Compare method to sort elements in a group, the elements in the array must be objects in the foundation framework, that is, they cannot be custom objects

Nsarray *newarr = [arr sortedarrayusingselector: @selector (compare:)];

NSLog (@ "After sorting:%@", NEWARR);

To sort an object

Person *P1 = [person new];

P1.age = 10;

Person *P2 = [person new];

P2.age = 20;

Person *P3 = [person new];

P3.age = 5;

Person *P4 = [person new];

P4.age = 7;

Nsarray *arr = @[p1, p2, p3, P4];

NSLog (@ "sort before:%@", arr);

Sort by age of person

The method is sorted by default in ascending order

Nsarray *newarr = [arr sortedarraywithoptions:nssortstable usingcomparator:^nscomparisonresult (person *obj1, person * OBJ2) {

Each time the block is called, the two elements in the array are taken out to us

Two points

NSLog (@ "obj1 =%@, Obj2 =%@", obj1, OBJ2);

return obj1.age > Obj2.age; Descending

return Obj1.age < Obj2.age; Ascending

/*

The method of modification, which produces random numbers

if (Obj1.age > Obj2.age) {

5 4

return nsordereddescending;

}else if (Obj1.age < obj2.age)

{

4 5

return nsorderedascending;

}else

{

return nsorderedsame;

}

*/

}];

NSLog (@ "After sorting:%@", NEWARR);

Nsarray and NSString conversions

Nsarray *arr = @[@ "LJ", @ "LM", @ "JJJ"];

How to stitch each element in an array into a string

Method One

1. Define a variable string to save the result after stitching

nsmutablestring *STRM = [nsmutablestring string];

2. Iterate through the array, take each element in the array, add the element to the variable string

For (NSString *str in arr) {

[StrM APPENDSTRING:STR];

//3. Add another one after each add-

[StrM appendstring:@ "-"];

}

[StrM Deletecharactersinrange:nsmakerange (Strm.length-1, 1)];

NSLog (@ "StrM =%@", StrM);

Method Two:

Link an array element to a string, using a * * as a concatenation character to stitch an array element into a string

NSString *str = [Arr componentsjoinedbystring:@ "* *"];

NSLog (@ "str =%@", str);

How to generate an array from a string

String Segmentation method

NSString *str = @ "LNJ**LMJ**JJJ";

Nsarray *arr = [str componentsseparatedbystring:@ "* *"];

NSLog (@ "arr =%@", arr);

Nsarray file read/write

How to write an array to a file

Nsarray *arr = @[@ "ln", @ "LJ", @ "JJ"];

BOOL flag = [arr writetofile:@ "/users/xiaomage/desktop/abc.plist" atomically:yes];

NSLog (@ "flag =%i", flag);

What are the considerations for writing an array to a file

Note 1: If an array is written to a file, it is essentially written to an XML file in iOS development generally we will save the XML file extension as Plist

Note that 2:writetofile can only write to the elements that are saved in the array are objects created by classes in the foundation framework and cannot be written if the custom object is saved

How to read data from a file into Nsarray

Reads an array from a file, which is often used in dictionary-to-model

Nsarray *newarray = [Nsarray arraywithcontentsoffile:@ "/users/xiaomage/desktop/abc.plist"];

NSLog (@ "%@", NewArray);

Nsmutablearray

"Variable array additions and deletions"

What is a mutable array? What's the difference with Nsarray?

Nsmutablearray is a subclass of Nsarray

Nsarray is immutable, once initialized, the contents of it will always be fixed, can not delete the elements inside, and can no longer add elements inside

Nsmutablearray is variable, can add \ change \ delete element at any time

How do I create an empty array? To create a mutable array what's the point of note

1. Creating an empty array

Nsmutablearray *ARRM = [Nsmutablearray array];

Nsmutablearray *ARRM = [[Nsmutablearray alloc] init];

2. Note the point:

You cannot create a mutable array by @[], because @[] creates an immutable array

If you use an immutable group as a mutable array, a run-time error is raised

For example:

Nsmutablearray *arrm = @[@ "LJ" @ "LM"];

[Arrm addobject:@ "JJJ"];

How to add content to a mutable array

[Arrm addobject:@ "LJ"];

Method Two:

The elements in the specified array are removed and placed in ARRM \

Not adding an entire array as an element to the ARRM

[Arrm addobjectsfromarray:@[@ "LJ", @ "JJ"];

Note: The following is the addition of an entire array as an element

[Arrm addobject:@[@ "LJ", @ "JJJ"];

NSLog (@ "%@", ARRM);

How to insert content into a mutable array

[Arrm insertobject:@ "Xcq" atindex:1];

Nsrange range = Nsmakerange (2, 2);

Nsindexset *set = [Nsindexset indexsetwithindexesinrange:range];

Inserts a set of data, specifies where the array needs to be inserted, and inserts how many

[Arrm insertobjects:@[@ "A", @ "B"] atindexes:set];

How to delete content in a mutable array

To delete the specified element:

[Arrm removeobjectatindex:0];

Delete the last element in an array

[Arrm Removelastobject];

Delete an element of the index position

[Arrm removeobject:@ "A"];

How to replace content in a mutable array

[Arrm replaceobjectatindex:1 withobject:@ "M"];

Shorthand:

Arrm[0] = @ "ZS";

NSLog (@ "%@", ARRM);

How to get the contents of a mutable array

NSLog (@ "%@", [Arrm objectatindex:0]);

36-oc Nsarray