The KVC of Kvc/kvo's violence

This chapter will be divided into two sections:

• The Set/get of KVC
• KVC Key-value path

The Set/get of KVC

There are 3 variables in Class A, all private permissions, and for access rights, see the OBJECTIVE-C member Variable "

A.h

@interface a:nsobject{@private    *str;    Nsinteger value; //Note there are no asterisks    here oh oh *array;} @end

a.m.: Override the description function for NSLog

@implementation A /* * *     */-(NSString *)    description{return [nsstring stringWithFormat:@ "\n%@ \n%li\n%@", str, (long) value, array];} @end

MAIN.M: In theory, external variables are not accessible to these 3 private variables, but the KVC of violence comes.

A *a =[[A alloc] init];//set of KVC[A SetValue:@"HelloWorld"Forkey:@"Str"]; [A setvalue:@ -Forkey:@"value"]; [A setvalue:@[@"Hearthstone", @2] Forkey:@"Array"]; NSLog (@"%@", a);//KVC's GetNSString *str = [a valueforkey:@"Str"]; Nsinteger value= [[A Valueforkey:@"value"] IntegerValue];//ID to NsintegerNsarray *array = [a valueforkey:@"Array"]; NSLog (@"\n%@\n%ld\n%@", str, (Long) value, array);

Output to

HelloWorld
2015
(
Hearthstone,
2
)

HelloWorld
2015
(
Hearthstone,
2
)

Analysis:

KVC Set Method (emphasis)

[A setValue:@ "HelloWorld" forkey:@ "str"];

Is the set method of KVC, where key must be a property name for the message receiver, not a custom one.

Get method for KVC (focus)

NSString *str = [a valueforkey:@ "str"];

Is the Get method of KVC, where key must be a property name for the message receiver, and cannot be customized.

When the set method encounters a basic data type

[A setvalue:@ forkey:@ "value"];

Nsinteger is the basic data type, when setting the basic data type, you need to convert the basic type to NSNumber, when setting the value, the system will have the process of automatic unpacking, NSNumber will unpack the value of the assignment.

when the Get method encounters a base data type

Nsinteger value = [[a valueforkey:@ 'value'] integervalue];  // ID to Nsinteger

Valueforkey returns the ID type, the method of ID conversion to Nsinteger should be the above, and the following notation is wrong!

Nsinteger value = (nsinteger) [a valueforkey:@ "value"];

Off-topic: Rewrite description to facilitate NSLog output

-(NSString *) description{    return [nsstring stringWithFormat:@ "\n%@\n%li\n%@  ", str, (long) value, array];} NSLog (@ "%@", a);

Will print out

HelloWorld
2015
(
Hearthstone,
2
)

The KVC Key-Value path

The KVC of Kvc/kvo's violence