1、valueForKeyPath可以获取数组中的最小值、最大值、平均值、求和。代码如下：

NSArray *array = @[@10, @23, @43, @54, @7, @17, @5];

+ (NSString *)caculateArray:(NSArray *)array
{
    CGFloat sum = [[array valueForKeyPath:@"@sum.floatValue"] floatValue];
    CGFloat avg = [[array valueForKeyPath:@"@avg.floatValue"] floatValue];
    CGFloat max =[[array valueForKeyPath:@"@max.floatValue"] floatValue];
    CGFloat min =[[array valueForKeyPath:@"@min.floatValue"] floatValue];
    NSLog(@"%fn%fn%fn%f",sum,avg,max,min);
    return [NSString stringWithFormat:@"%f",sum];
}

2、valueForKeyPath可以获取数组中相同key的元素

如下所示：

NSArray *arr = @[@{@"city":@"beijing",@"person":@{@"name":@"zhangsan"}},@{@"city":@"chengdu"}];

[arr valueForKeyPath:@"city"] 可以获取到city数组 @[@"beijing",@"chengdu"]

3、valueForKeyPath 可以使用. 来一层一层向下索引，当多个字典层级时，取子层级中的属性就非常简单了

NSDictionary *dict1 = @{@"dict1":@{@"dict2":@{@"name":@"lishi",@"info":@{@"age":@"12"}}}};

id res = [dict1 valueForKeyPath:@"dict1.dict2.name"];//(http://dict1.dict2.name/)
NSLog(@"res = %@",res);// 输出lishi

4、删除重复的数据

NSArray *array = @[@"qq", @"wechat", @"qq", @"msn", @"wechat"];
NSArray *deleltNewA = [array valueForKeyPath:@"@distinctUnionOfObjects.self"];
NSLog(@"deleltNewA = %@",deleltNewA);// 输出( qq,  wechat,    msn)

5、嵌套使用（先删除对应值的重复数据再取值）

NSArray *array = @[@{@"name" : @"xiaoming",
                  @"code" : @1},
                 @{@"name": @"judy",
                  @"code" : @2},
                 @{@"name": @"judy",
                  @"code" : @3},
                 @{@"name": @"xiaohua",
                  @"code" : @4}];
NSArray *deleltNewA =  [array valueForKeyPath:@"@distinctUnionOfObjects.name"];
NSLog(@"deleltNewA = %@",deleltNewA);// 输出(judy, xiaohua, xiaoming); 

6、改变 UITextfield 的 placeholder 的颜色

[addressTextField  setValue:[UIColor redColor] forKeyPath:@”_placeholderLabel.textColor”];

比起重写 - (void)drawPlaceholderInRect:(CGRect)rect; 要方便太多！