这将返回一个数组，其中包含myCars数组中每个项目的licensePlate值:

This will return an array containing the value of licensePlate from each item in the myCars array:

NSArray *licensePlates = [myCars valueForKeyPath:@"licensePlate"]

例如，如果只需要唯一项，则可以执行以下操作:

If you want only unique items (for example), you can do something like this:

NSArray *licensePlates = [myCars valueForKeyPath:@"@distinctUnionOfObjects.licensePlate"];

有关更多可能性，请参见键值编码编程指南.

For more possibilities, see the Collection Operators documentation in the Key-Value Coding Programming Guide.