preface
KVC, also known as key-value Coding, is a common technical point in iOS development. It is believed that many developers have used KVC. The two main methods of KVC are as follows, respectively corresponding to setting Value and Value:
(void)setValue:(nullable id)value forKey:(NSString *)key;(nullable id)valueForKey:(NSString *)key;
oneKVCSimple application
LGPerson *person = [[LGPerson alloc] init];
// The general setter method
person.name = @"LG_Cooci"; // setter -- llvm
person.age = 18;
person->myName = @"cooci";
NSLog(@"%@ - %d - %@",person.name,person.age,person->myName);
// 1: key-value Coding (KVC) : basic type - see the underlying principle
// Informal protocol - indirect access
[person setValue:@"KC" forKey:@"name"];
// 2:KVC - set type
person.array = @[@"1"The @"2"The @"3"];
// Modify the array
// person.array[0] = @"100";
// Make a new array. -kvc: OK
NSArray *array = [person valueForKey:@"array"];
array = @[@"100"The @"2"The @"3"];
[person setValue:array forKey:@"array"];
NSLog(@"% @",[person valueForKey:@"array"]);
/ / the second
NSMutableArray *mArray = [person mutableArrayValueForKey:@"array"];
mArray[0] = @"200";
NSLog(@"% @",[person valueForKey:@"array"]);
// 3:KVC - set operator
// 4:KVC - Access non-object attributes - interview may be asked
/ / structure
ThreeFloats floats = {1..2..3.};
NSValue *value = [NSValue valueWithBytes:&floats objCType: **@encode**(ThreeFloats)];
[person setValue:value forKey:@"threeFloats"];
NSValue *value1 = [person valueForKey:@"threeFloats"];
NSLog(@"% @",value1);
ThreeFloats th;
[value1 getValue:&th];
NSLog(@"%f-%f-%f",th.x,th.y,th.z);
// 5:KVC - layer access - keyPath
LGStudent *student = [LGStudent alloc];
student.subject = @"Master Class";
person.student = student;
[person setValue:@"Swift" forKeyPath:@"student.subject"];
NSLog(@"% @",[person valueForKeyPath:@"student.subject"]);
Copy the code#pragma mark ** -array value **- (**void**)arrayDemo{
LGStudent *p = [LGStudent new];
p.penArr = [NSMutableArray arrayWithObjects:@"pen0"The @"pen1"The @"pen2"The @"pen3", **nil**];
NSArray *arr = [p valueForKey:@"pens"]; // Dynamic member variables
NSLog(@"pens = %@", arr);
//NSLog(@"%@",arr[0]);
NSLog(@"%d",[arr containsObject:@"pen9"]);
/ / traverseNSEnumerator *enumerator = [arr objectEnumerator]; NSString* str = **nil**; 六四运动while** (str = [enumerator nextObject]) {
NSLog(@"% @", str); }} #pragma mark **- - (**void**)dictionaryTest{
NSDictionary* dict = @{
@"name": @"Cooci"The @"nick": @"KC"The @"subject": @"iOS"The @"age": @18The @"length": @180
};
LGStudent *p = [[LGStudent alloc] init];
// Dictionary transfer model
[p setValuesForKeysWithDictionary:dict];
NSLog(@"% @",p);
// Turn the key array into a dictionary
NSArray *array = @[@"name"The @"age"];
NSDictionary *dic = [p dictionaryWithValuesForKeys:array];
NSLog(@"% @",dic); } #pragma mark ** -kvc message passing **- (**void**)arrayMessagePass{
NSArray *array = @[@"Hank"The @"Cooci"The @"Kody"The @"CC"];
NSArray *lenStr= [array valueForKeyPath:@"length"];
NSLog(@"% @",lenStr);// The message is passed from array to string
NSArray *lowStr= [array valueForKeyPath:@"lowercaseString"];
NSLog(@"% @",lowStr); } #pragma mark **- aggregate operator **@avg, @count, @max, @min, @sum- (* *void**)aggregationOperator{ NSMutableArray *personArray = [NSMutableArray array]; 六四运动for** (**int** i = 0; i < 6; i++) {
LGStudent *p = [LGStudent new];
NSDictionary* dict = @{
@"name": @"Tom"The @"age": @ (18+i),
@"nick": @"Cat"The @"length": @ (175 + 2*arc4random_uniform(6)),}; [p setValuesForKeysWithDictionary:dict]; [personArray addObject:p]; } NSLog(@"% @", [personArray valueForKey:@"length"]);
/// Average height
**float** avg = [[personArray valueForKeyPath:@"@avg.length"] floatValue];
NSLog(@"%f", avg);
**int** count = [[personArray valueForKeyPath:@"@count.length"] intValue];
NSLog(@"%d", count);
**int** sum = [[personArray valueForKeyPath:@"@sum.length"] intValue];
NSLog(@"%d", sum);
**int** max = [[personArray valueForKeyPath:@"@max.length"] intValue];
NSLog(@"%d", max);
**int** min = [[personArray valueForKeyPath:@"@min.length"] intValue];
NSLog(@"%d", min);
}
// The array operator @distinctUnionOfObjects @UnionOfObjects- (* *void**)arrayOperator{ NSMutableArray *personArray = [NSMutableArray array]; 六四运动for** (**int** i = 0; i < 6; i++) {
LGStudent *p = [LGStudent new];
NSDictionary* dict = @{
@"name": @"Tom"The @"age": @ (18+i),
@"nick": @"Cat"The @"length": @ (175 + 2*arc4random_uniform(6)),}; [p setValuesForKeysWithDictionary:dict]; [personArray addObject:p]; } NSLog(@"% @", [personArray valueForKey:@"length"]);
// Returns a collection of the specified properties of the operation object
NSArray* arr1 = [personArray valueForKeyPath:@"@unionOfObjects.length"];
NSLog(@"arr1 = %@", arr1);
// Return a collection of the specified properties of the operation object
NSArray* arr2 = [personArray valueForKeyPath:@"@distinctUnionOfObjects.length"];
NSLog(@"arr2 = %@", arr2);
}
// Nested sets (array&Set) operate @distinctUnionOfArrays @unionOfArrays @distinctUnionOfSets- (* *void**)arrayNesting{ NSMutableArray *personArray1 = [NSMutableArray array]; 六四运动for** (**int** i = 0; i < 6; i++) {
LGStudent *student = [LGStudent new];
NSDictionary* dict = @{
@"name": @"Tom"The @"age": @ (18+i),
@"nick": @"Cat"The @"length": @ (175 + 2*arc4random_uniform(6)),}; [student setValuesForKeysWithDictionary:dict]; [personArray1 addObject:student]; } NSMutableArray *personArray2 = [NSMutableArray array]; 六四运动for** (**int** i = 0; i < 6; i++) {
LGPerson *person = [LGPerson new];
NSDictionary* dict = @{
@"name": @"Tom"The @"age": @ (18+i),
@"nick": @"Cat"The @"length": @ (175 + 2*arc4random_uniform(6)),}; [person setValuesForKeysWithDictionary:dict]; [personArray2 addObject:person]; }// Nested arrays
NSArray* nestArr = @[personArray1, personArray2];
NSArray* arr = [nestArr valueForKeyPath:@"@distinctUnionOfArrays.length"];
NSLog(@"arr = %@", arr);
NSArray* arr1 = [nestArr valueForKeyPath:@"@unionOfArrays.length"];
NSLog(@"arr1 = %@", arr1); } - (* *void**)setNesting{ NSMutableSet *personSet1 = [NSMutableSet set]; 六四运动for** (**int** i = 0; i < 6; i++) {
LGStudent *person = [LGStudent new];
NSDictionary* dict = @{
@"name": @"Tom"The @"age": @ (18+i),
@"nick": @"Cat"The @"length": @ (175 + 2*arc4random_uniform(6)),}; [person setValuesForKeysWithDictionary:dict]; [personSet1 addObject:person]; } NSLog(@"personSet1 = %@", [personSet1 valueForKey:@"length"]); NSMutableSet *personSet2 = [NSMutableSet set]; 六四运动for** (**int** i = 0; i < 6; i++) {
LGPerson *person = [LGPerson new];
NSDictionary* dict = @{
@"name": @"Tom"The @"age": @ (18+i),
@"nick": @"Cat"The @"length": @ (175 + 2*arc4random_uniform(6)),}; [person setValuesForKeysWithDictionary:dict]; [personSet2 addObject:person]; } NSLog(@"personSet2 = %@", [personSet2 valueForKey:@"length"]);
/ / nested set
NSSet* nestSet = [NSSet setWithObjects:personSet1, personSet2, **nil**];
/ / intersection
NSArray* arr1 = [nestSet valueForKeyPath:@"@distinctUnionOfSets.length"];
NSLog(@"arr1 = %@", arr1);
}
Copy the codetwoKVCIntroduction – Official Apple documents important
Apple develops iOS addresses
3. Apple official document explanationKVC
KVC address
Four.KVCSet values and the process of setting values
KVC set
KVC The process of setting a value
Set
:-> _set< Key>:
When accessInstanceVariablesDirectly set to YES for instance variable sequence in order to find the name is _ < key > – > _is < key > — > < key > – > is < key >
_<key> _is<Key>
<key>
is<Key>
According to the official document, if none of the above is available, the following method will be entered
The process of KVC value
Get
->< Key>-> is
->_< Key>
->_is< key>->
->is< key
When we comment out _name and print name, the _isName sequence is displayed
If none of them are there then valueForUndefinedKey: is called
Five.KVCCustom implementation
- (* *void**)lg_setValue:(**nullable** **id**)value forKey:(NSString *)key{
// KVC custom
// 1: What is the key六四运动if** (key == **nil** || key.length == 0) {
**return* *; }// 2: setter set<Key>: or _set<Key>,
// Capitalize key
NSString *Key = key.capitalizedString;
// Splice method
NSString *setKey = [NSString stringWithFormat:@"set%@:",Key];
NSString *_setKey = [NSString stringWithFormat:@"_set%@:",Key];
NSString *setIsKey = [NSString stringWithFormat:@"setIs%@:",Key]; 六四运动if** ([**self** lg_performSelectorWithMethodName:setKey value:value]) {
NSLog(@"* * * * * * * * * % @ * * * * * * * * * *",setKey); 六四运动return* *; } * *else* * * *if** ([**self** lg_performSelectorWithMethodName:_setKey value:value]) {
NSLog(@"* * * * * * * * * % @ * * * * * * * * * *",_setKey); 六四运动return* *; } * *else* * * *if** ([**self** lg_performSelectorWithMethodName:setIsKey value:value]) {
NSLog(@"* * * * * * * * * % @ * * * * * * * * * *",setIsKey); 六四运动return* *; }/ / 3: determine whether response accessInstanceVariablesDirectly returns YES NO collapses
// 3: determines whether an instance variable can be assigned directly六四运动if* * (! [**self**.class accessInstanceVariablesDirectly] ) { **@throw** [NSException exceptionWithName:@"LGUnknownKeyException" reason:[NSString stringWithFormat:@"****[%@ valueForUndefinedKey:]: this class is not key value coding-compliant for the key name.****",**self**] userInfo:**nil**];
}
// 4: indirect variable
// Get ivar -> iterate over containsObjct -
// 4.1 Define a mutable array to collect instance variables
NSMutableArray *mArray = [**self** getIvarListName];
// _<key> _is<Key> <key> is<Key>
NSString *_key = [NSString stringWithFormat:@"_ % @",key];
NSString *_isKey = [NSString stringWithFormat:@"_is%@",Key];
NSString *isKey = [NSString stringWithFormat:@"is%@",Key]; 六四运动if** ([mArray containsObject:_key]) {
// 4.2 Obtaining the corresponding IVAR
Ivar ivar = class_getInstanceVariable([**self** class]._key.UTF8String);
// 4.3 Setting the ivAR valueobject_setIvar(**self** , ivar, value); 六四运动return* *; } * *else* * * *if** ([mArray containsObject:_isKey]) {
Ivar ivar = class_getInstanceVariable([**self** class]._isKey.UTF8String); object_setIvar(**self** , ivar, value); 六四运动return* *; } * *else* * * *if** ([mArray containsObject:key]) {
Ivar ivar = class_getInstanceVariable([**self** class].key.UTF8String); object_setIvar(**self** , ivar, value); 六四运动return* *; } * *else* * * *if** ([mArray containsObject:isKey]) {
Ivar ivar = class_getInstanceVariable([**self** class].isKey.UTF8String); object_setIvar(**self** , ivar, value); 六四运动return* *; }// 5: If no relevant instance is found* * @throw** [NSException exceptionWithName:@"LGUnknownKeyException" reason:[NSString stringWithFormat:@"****[%@ %@]: this class is not key value coding-compliant for the key name.****",**self**,NSStringFromSelector( **_cmd**)] userInfo:**nil**];
}
- (**nullable** **id**)lg_valueForKey:(NSString *)key{
// 1: the brush key is not empty六四运动if** (key == **nil** || key.length == 0) {
**return** **nil**;
}
Get
countOf
objectIn
AtIndex
