1、valueForKeyPath可以獲取數組中的最小值、最大值、平均值、求和。代碼如下：

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可以獲取數組中相同key的元素

如下所示：

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

[arr valueForKeyPath:@"city"] 可以獲取到city數組 @[@"beijing",@"chengdu"]

3、valueForKeyPath 可以使用. 來一層一層向下索引，當多個字典層級時，取子層級中的屬性就非常簡單了

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

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

4、刪除重復的數據

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

5、嵌套使用（先刪除對應值的重復數據再取值）

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);// 輸出(judy, xiaohua, xiaoming); 

6、改變 UITextfield 的 placeholder 的顏色

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

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