四、一个小技巧
Masonry中的一个函数值得我们学习，其作用是对任何类型的值进行一层对象包装，函数如下：
//值包装宏
#define MASBoxValue(value) _MASBoxValue(@encode(__typeof__((value))), (value))
static inline id _MASBoxValue(const char *type, ...) {
va_list v;
va_start(v, type);
id obj = nil;
//进行类型判断 结构体包装成NSValue 基本类型包装成NSNumber
if (strcmp(type, @encode(id)) == 0) {
id actual = va_arg(v, id);
obj = actual;
} else if (strcmp(type, @encode(CGPoint)) == 0) {
CGPoint actual = (CGPoint)va_arg(v, CGPoint);
obj = [NSValue value:&actual withObjCType:type];
} else if (strcmp(type, @encode(CGSize)) == 0) {
CGSize actual = (CGSize)va_arg(v, CGSize);
obj = [NSValue value:&actual withObjCType:type];
} else if (strcmp(type, @encode(MASEdgeInsets)) == 0) {
MASEdgeInsets actual = (MASEdgeInsets)va_arg(v, MASEdgeInsets);
obj = [NSValue value:&actual withObjCType:type];
} else if (strcmp(type, @encode(double)) == 0) {
double actual = (double)va_arg(v, double);
obj = [NSNumber numberWithDouble:actual];
} else if (strcmp(type, @encode(float)) == 0) {
float actual = (float)va_arg(v, double);
obj = [NSNumber numberWithFloat:actual];
} else if (strcmp(type, @encode(int)) == 0) {
int actual = (int)va_arg(v, int);
obj = [NSNumber numberWithInt:actual];
} else if (strcmp(type, @encode(long)) == 0) {
long actual = (long)va_arg(v, long);
obj = [NSNumber numberWithLong:actual];
} else if (strcmp(type, @encode(long long)) == 0) {
long long actual = (long long)va_arg(v, long long);
obj = [NSNumber numberWithLongLong:actual];
} else if (strcmp(type, @encode(short)) == 0) {
short actual = (short)va_arg(v, int);
obj = [NSNumber numberWithShort:actual];
} else if (strcmp(type, @encode(char)) == 0) {
char actual = (char)va_arg(v, int);
obj = [NSNumber numberWithChar:actual];
} else if (strcmp(type, @encode(bool)) == 0) {
bool actual = (bool)va_arg(v, int);
obj = [NSNumber numberWithBool:actual];
} else if (strcmp(type, @encode(unsigned char)) == 0) {
unsigned char actual = (unsigned char)va_arg(v, unsigned int);
obj = [NSNumber numberWithUnsignedChar:actual];
} else if (strcmp(type, @encode(unsigned int)) == 0) {
unsigned int actual = (unsigned int)va_arg(v, unsigned int);
obj = [NSNumber numberWithUnsignedInt:actual];
} else if (strcmp(type, @encode(unsigned long)) == 0) {
unsigned long actual = (unsigned long)va_arg(v, unsigned long);
obj = [NSNumber numberWithUnsignedLong:actual];
} else if (strcmp(type, @encode(unsigned long long)) == 0) {
unsigned long long actual = (unsigned long long)va_arg(v, unsigned long long);
obj = [NSNumber numberWithUnsignedLongLong:actual];
} else if (strcmp(type, @encode(unsigned short)) == 0) {
unsigned short actual = (unsigned short)va_arg(v, unsigned int);
obj = [NSNumber numberWithUnsignedShort:actual];
}
va_end(v);
return obj;
}
其中@encode()是一个编译时特性，其可以将传入的类型转换为标准的OC类型字符串。
