KVC之valueForKeyPath进阶

KVC 常用方法

setValue:forKey:
setValue: forKeyPath:
valueForKey:
valueForKeyPath:
setValuesForKeysWithDictionary:

注：valueForKey会自动把基本类型转成NSNumber或NSValue中包装成对象,同样,动态设置setValue: forKey:的属性也必须先包装成NSNumber对象类型才可以.

高阶用法

把字典中的key单独生成数组

NSDictionary *dic1 = @{@"city":@"北京",@"count":@"22"};
NSDictionary *dic2 = @{@"city":@"上海",@"count":@"18"};
NSDictionary *dic3 = @{@"city":@"深圳",@"count":@"17"};
NSArray *arr = @[dic1,dic2,dic3];

NSLog(@"city:%@",[arr valueForKeyPath:@"city"]);
NSLog(@"count:%@",[arr valueForKeyPath:@"count"]);

输出结果为：
    city:(
    "北京",
    "上海",
    "深圳"c4
    )   

    count:(
    22,
    18,
    17
    )

把数组中的数取整

NSArray *array = [NSArray arrayWithObjects:@"10.11",@"20.22", nil];
NSArray *resultArray = [array valueForKeyPath:@"doubleValue.intValue"];
NSLog(@"resultArray:%@", resultArray);

输出结果为：
    resultArray:(
    10,
    20
    )

valueForKeyPath 运算符

在路径中,可以引用一下运算符 @xxx 来进行一些运算,例如获取一组值得平均值,最值或者总数.

1. 常规操作符：@avg @count @max @min @sum

   NSMutableArray *personsArray = [[NSMutableArray alloc] initWithCapacity:5];
   for (NSInteger i = 0; i < 5; i ++) {
       NSString *tempName = [NSString stringWithFormat:@"people%ld",(long)i];
       NSDictionary *personInfoDictionary = @{
                                              @"name" : tempName,
                                              @"age" : @(10 + i),
                                              @"school" : @"Hist"
                                              };
       Person *tempPerson = [Person yy_modelWithDictionary:personInfoDictionary];
       [personsArray addObject:tempPerson];
   }
   NSNumber *count = [personsArray valueForKeyPath:@"@count"];
   NSNumber *sumAge = [personsArray valueForKeyPath:@"@sum.age"];
   NSNumber *avgAge = [personsArray valueForKeyPath:@"@avg.age"];
   NSNumber *maxAge = [personsArray valueForKeyPath:@"@max.age"];
   NSNumber *minAge = [personsArray valueForKeyPath:@"@min.age"];
   NSLog(@"%@  %@  %@  %@  %@",count,sumAge,avgAge,maxAge,minAge);

   输出结果为：
       5  60  12  14  10

2. 对象操作符：@distinctUnionOfObjects(去掉重复) @unionOfObjects(不去重复)，都返回数组

   NSArray *values = [object valueForKeyPath:@"@distinctUnionOfObjects.value"];

• 注：@distinctUnionOfObjects 操作符返回被操作对象指定属性的集合并做去重操作，而@unionOfObjects则允许重复。如果其中任何涉及的对象为nil，则抛出异常。

3. Array和Set操作符: @distinctUnionOfArrays、@unionOfArrays对象是嵌套型的集合对象

• 普通去重

  NSArray *array = @[@"name", @"w", @"aa", @"zxp", @"aa"];
   //返回的是一个新的数组
   NSArray *newArray = [array valueForKeyPath:@"@distinctUnionOfObjects.self"];
   NSLog(@"%@", newArray);

• 单独取出字典中的 key/value 并去重

  NSArray myArray = @[@{@300:@"5 min"},
                      @{@900:@"15 min"},
                      @{@1800:@"30 min"},
                      @{@3600:@"1 hour"}];
                      
  NSArray *values = [myArray valueForKeyPath: @"@unionOfArrays.@allValues"];
  NSArray *keys   = [myArray valueForKeyPath: @"@unionOfArrays.@allKeys"];

  // 相当于如下代码
  values = @[@"5 min",@"15 min",@"30 min",@"1 hour"];
  keys = @[@300, @900, @1800, @3600];
  

参考链接：
iOS监听模式之KVO、KVC的高阶应用
valueForKeyPath 妙用