Small talk about the set operator of KeyPath in KVC

Because the knowledge point is relatively simple, there is no longer a large set of principles, straight into the subject.

The set operators in KVC have the following three categories:

1. Simple set Operator: @avg, @sum, @max, @min, @count ( can only be used in collection objects, object properties must be numeric types )

　　 2. Object operators:

               @ unionofobjects: Returns an array of the values of the specified property, without the weight

@distinctUnionOfObjects: returns an array of values after the specified property is de-weighed

3. array/Collective operators: is similar to the object operator, except that it works in a NSArray NSSet set of components.

@unionOfArrays: Returns an array that consists of the elements of each sub-array, not the weight

@distinctUnionOfArrays: Returns an array that consists of the elements of each sub-array, to remove the weight

@distinctUnionOfSets: similar to @distinctunionofarrays, except that it expects a nsset that contains the Nsset object and returns a Nsset object. Because the collection cannot have duplicate values, only the distinct operation.

On the code:

Scenario: There is a person class with the name and age two properties. Instantiate 5 objects to find their average age, sum of age, maximum age and minimum age.

Person class header file:

1 #import<Foundation/Foundation.h>2 3 @interfacePerson:nsobject4 5 /**6 name7  */8@property (nonatomic,copy) NSString *name;9 Ten /** One Age A  */ - @property (nonatomic,assign) Nsinteger age; -  the /** - Custom Constructors -  - @param Name + @param age -  + @return object that returns person A  */ at-(Instancetype) Initwithname: (NSString *) name Andage: (Nsinteger) age; -  - @end

. m files for Person:

1 #import "Person.h"2 3 @implementation Person4 5-(Instancetype) Initwithname: (NSString *) name Andage: (nsinteger) age{6     if(self =[Super Init]) {7_name =name;8_age =Age ;9     }Ten     returnSelf ; One } A  - @end

The controller invokes the Person object implementation function:

1 @interfaceViewcontroller ()2 3 @end4 5 @implementationViewcontroller6 7- (void) Viewdidload {8 [Super Viewdidload];9     TenPerson *P1 = [[Person alloc] Initwithname:@"xiaoming"Andage:Ten]; OnePerson *P2 = [[Person alloc] Initwithname:@"xiaoming"Andage: the]; APerson *P3 = [[Person alloc] Initwithname:@"Xiaohong"Andage: -]; -Person *P4 = [[Person alloc] Initwithname:@"Xiaoli"Andage: -]; -Person *P5 = [[Person alloc] Initwithname:@"Xiaoli"Andage: -]; the      -     //Simple set operators cannot be used in a single object, so there will be an error -     //int res = [[P1 valueforkeypath:@] @sum. Age "] integervalue]; -      +Nsarray *perarray =@[p1, p2, P3, P4, P5]; -      +     //Simple Set Operators ANsinteger avg = [[Perarray valueforkeypath:@"@avg. Age"] IntegerValue]; atNsinteger sum = [[Perarray valueforkeypath:@"@sum. Age"] IntegerValue]; -Nsinteger max = [[Perarray valueforkeypath:@"@max. Age"] IntegerValue]; -Nsinteger min = [[Perarray valueforkeypath:@"@min. Age"] IntegerValue]; -      -     //Count: Take the number of elements in the array, the following 3 kinds of notation are equivalent -Nsinteger count = [[Perarray valueforkeypath:@"@count. Age"] IntegerValue]; inNsinteger count1 = [[Perarray valueforkeypath:@"@count"] IntegerValue]; -Nsinteger Count2 =Perarray.count; to      +      -     //Object operators: Working with array objects the     //@unionOfObjects: Returns an array of the values of the specified property, without the weight *     //@distinctUnionOfObjects: Returns an array of values after the specified property is de-weighed $nsarray<nsstring *> *namearray = [Perarray valueforkeypath:@"@unionOfObjects. Name"];Panax Notoginsengnsarray<nsstring *> *namearray2 = [Perarray valueforkeypath:@"@distinctUnionOfObjects. Name"]; -      the     //array/Collective operators: Operations on collections composed of Nsarray and Nsset +     //unionofarrays: Returns an array whose values consist of the elements of each sub-array, not the weight A     //distinctunionofarrays: Returns an array whose values consist of the elements of each sub-array to the     //distinctunionofsets: Similar to distinctunionofarrays, except that it expects a nsset that contains Nsset objects and returns a Nsset object. Because a collection cannot contain duplicate values, it has only distinct operations.  +Person *P1 = [[Person alloc] Initwithname:@"PP1"Andage:Ten]; -Person *P2 = [[Person alloc] Initwithname:@"PP1"Andage: -]; $Person *P3 = [[Person alloc] Initwithname:@"PP2"Andage: -]; $Person *P4 = [[Person alloc] Initwithname:@"PP3"Andage: +]; -Person *P5 = [[Person alloc] Initwithname:@"PP3"Andage: -]; -Nsarray *perarray2 =@[p1, P2, P3, P4, P5]; the      -Nsarray *arr1 = [@[perarray,perarray2] Valueforkeypath:@"@unionOfArrays. Name"];WuyiNsarray *ARR2 = [@[perarray,perarray2] Valueforkeypath:@"@distinctUnionOfArrays. Name"]; the } -  Wu @end

Small talk about the set operator of KeyPath in KVC