这是个没有标题的文章

去除数组中重复的对象

NSArray *newArr = [oldArr valueForKeyPath:@“@distinctUnionOfObjects.self"];

强／弱引用

#define WeakSelf(type)  __weak typeof(type) weak##type = type; // weak

#define StrongSelf(type)  __strong typeof(type) type = weak##type; // strong

由角度转换弧度

#define DegreesToRadian(x) (M_PI * (x) / 180.0)

由弧度转换角度

#define RadianToDegrees(radian) (radian*180.0)/(M_PI)