其实消息选择器在simplemax示例中就接触到了,但这文档非要讲那么抽象。目前为止对消息选择器的理解是:可判断接收过来的消息是否符合本Object的处理要求,比如加法对象只可接收数值型的消息以处理,但不能接收t_symbol型的消息,如下:
1. Messages selector
如下面自定义的myObjectABC可从出口发送消息选择器为 "ABC" 的消息,myObjectInt可发送消息选择器为 "int" 的消息。MAX/MSP SDK学习03:Atoms and Messages的使用中的IsMatchABC组件可接收处理 "ABC" 消息和 "int" 消息。
myObjectABC:
#include "ext.h" // standard Max include, always required
#include "ext_obex.h" // required for new style Max object
typedef struct _myObjectABC {
t_object ob; // the object itself (must be first)
void* outLet; // 出口
} t_myObjectABC;
// function prototypes
void* myObjectABC_new(t_symbol* s, long argc, t_atom* argv);
void myObjectABC_free(t_myObjectABC* x);
void myObjectABC_assist(t_myObjectABC* x, void* b, long m, long a, char* s);
void myObjectABC_bang(t_myObjectABC* x);
// global class pointer variable
void* myObjectABC_class;
void ext_main(void* r) {
t_class* c;
// "myObjectABC" 建议和项目名一样,否则在max/msp中创建自定义组件会出问题
c = class_new("myObjectABC", (method)myObjectABC_new, (method)myObjectABC_free, (long)sizeof(t_myObjectABC),
0L /* leave NULL!! */, A_GIMME, 0);
/* you CAN'T call this from the patcher */
// Object将接收到的消息(int、bang、assist等)与消息选择器中的对比,比对成功则可调用相关C方法,否则"Object dosen't understand message"
// A_CANT、A_LONG等指定typed方法,A_GIMME:a list of atoms,适用于超过四个参数或者多个浮点数
class_addmethod(c, (method)myObjectABC_assist, "assist", A_CANT, 0);
class_addmethod(c, (method)myObjectABC_bang, "bang", 0);
class_register(CLASS_BOX, c); /* CLASS_NOBOX */
myObjectABC_class = c;
post("I am the myObjectABC object");
}
void myObjectABC_assist(t_myObjectABC* x, void* b, long m, long a, char* s) {
if (m == ASSIST_INLET) { // inlet
sprintf(s, "I am inlet %ld", a);
} else { // outlet
sprintf(s, "I am outlet %ld", a);
}
}
void myObjectABC_free(t_myObjectABC* x) {
;
}
/* argc指在创建组件时,直接跟在组件后面的参数个数;argv存储参数具体值*/
void* myObjectABC_new(t_symbol* s, long argc, t_atom* argv) { // 分配内存创建object,初始化属性,创建入口和出口(默认一个入口,无出口)
t_myObjectABC* x = NULL;
long i;
if ((x = (t_myObjectABC*)object_alloc(myObjectABC_class))) { // 使用全局指针创建新实例
object_post((t_object*)x, "a new %s object was instantiated: %p", s->s_name, x);
object_post((t_object*)x, "it has %ld arguments", argc);
x->outLet = outlet_new((t_object*)x, NULL);
}
return (x);
}
void myObjectABC_bang(t_myObjectABC* x) {
t_atom argv[3]; // t_atom类型可存储整型、浮点型、t_symbol类型、指针。
atom_setlong(argv, 666);
atom_setsym(argv + 1, gensym("MYM")); // 字符串需要用gensym转换成t_symbol* 类型
atom_setfloat(argv + 2, 0.123);
outlet_anything(x->outLet, gensym("ABC"), 3, argv);
}
myObjectInt:
#include "ext.h" // standard Max include, always required
#include "ext_obex.h" // required for new style Max object
typedef struct _myObjectInt {
t_object ob; // the object itself (must be first)
void* outLet; // 出口
} t_myObjectInt;
// function prototypes
void* myObjectInt_new(t_symbol* s, long argc, t_atom* argv);
void myObjectInt_free(t_myObjectInt* x);
void myObjectInt_assist(t_myObjectInt* x, void* b, long m, long a, char* s);
void myObjectInt_bang(t_myObjectInt* x);
// global class pointer variable
void* myObjectInt_class;
void ext_main(void* r) {
t_class* c;
// "myObjectInt" 建议和项目名一样,否则在max/msp中创建自定义组件会出问题
c = class_new("myObjectInt", (method)myObjectInt_new, (method)myObjectInt_free, (long)sizeof(t_myObjectInt),
0L /* leave NULL!! */, A_GIMME, 0);
/* you CAN'T call this from the patcher */
// Object将接收到的消息(int、bang、assist等)与消息选择器中的对比,比对成功则可调用相关C方法,否则"Object dosen't understand message"
// A_CANT、A_LONG等指定typed方法,A_GIMME:a list of atoms,适用于超过四个参数或者多个浮点数
class_addmethod(c, (method)myObjectInt_assist, "assist", A_CANT, 0);
class_addmethod(c, (method)myObjectInt_bang, "bang", 0);
class_register(CLASS_BOX, c); /* CLASS_NOBOX */
myObjectInt_class = c;
post("I am the myObjectInt object");
}
void myObjectInt_assist(t_myObjectInt* x, void* b, long m, long a, char* s) {
if (m == ASSIST_INLET) { // inlet
sprintf(s, "I am inlet %ld", a);
} else { // outlet
sprintf(s, "I am outlet %ld", a);
}
}
void myObjectInt_free(t_myObjectInt* x) {
;
}
/* argc指在创建组件时,直接跟在组件后面的参数个数;argv存储参数具体值*/
void* myObjectInt_new(t_symbol* s, long argc, t_atom* argv) { // 分配内存创建object,初始化属性,创建入口和出口(默认一个入口,无出口)
t_myObjectInt* x = NULL;
long i;
if ((x = (t_myObjectInt*)object_alloc(myObjectInt_class))) { // 使用全局指针创建新实例
object_post((t_object*)x, "a new %s object was instantiated: %p", s->s_name, x);
object_post((t_object*)x, "it has %ld arguments", argc);
x->outLet = outlet_new((t_object*)x, NULL);
}
return (x);
}
void myObjectInt_bang(t_myObjectInt* x) {
t_atom argv[3]; // t_atom类型可存储整型、浮点型、t_symbol类型、指针。
atom_setlong(argv, 666);
atom_setsym(argv + 1, gensym("MYM")); // 字符串需要用gensym转换成t_symbol* 类型
atom_setfloat(argv + 2, 0.123);
outlet_anything(x->outLet, gensym("int"), 3, argv);
}
将myObjectABC和myObjectInt的出口都接入IsMatchABC的左入口,测试消息选择器的使用。
运行结果:
2. anything method
若某t_symbol消息匹配不到消息选择器,则可定义通用处理方法anything method,如下:
#include "ext.h" // standard Max include, always required
#include "ext_obex.h" // required for new style Max object
typedef struct _anything {
t_object ob; // the object itself (must be first)
} t_anything;
void* anything_new(t_symbol* s, long argc, t_atom* argv);
void anything_free(t_anything* x);
void anything_assist(t_anything* x, void* b, long m, long a, char* s);
void anything_anything(t_anything* x, t_symbol* s, long argc, t_atom* argv);
void* anything_class;
void ext_main(void* r) {
t_class* c;
// "anything" 建议和项目名一样,否则在max/msp中创建自定义组件会出问题
c = class_new("anything", (method)anything_new, (method)anything_free, (long)sizeof(t_anything),
0L /* leave NULL!! */, A_GIMME, 0);
class_addmethod(c, (method)anything_assist, "assist", A_CANT, 0);
class_addmethod(c, (method)anything_anything, "anything", A_GIMME, 0);
class_register(CLASS_BOX, c); /* CLASS_NOBOX */
anything_class = c;
post("I am the anything object");
}
void anything_assist(t_anything* x, void* b, long m, long a, char* s) {
if (m == ASSIST_INLET) { // inlet
sprintf(s, "I am inlet %ld", a);
} else { // outlet
sprintf(s, "I am outlet %ld", a);
}
}
void anything_free(t_anything* x) {
;
}
/* argc指在创建组件时,直接跟在组件后面的参数个数;argv存储参数具体值*/
void* anything_new(t_symbol* s, long argc, t_atom* argv) { // 分配内存创建object,初始化属性,创建入口和出口(默认一个入口,无出口)
t_anything* x = NULL;
x = (t_anything*)object_alloc(anything_class);
return (x);
}
void anything_anything(t_anything* x, t_symbol* s, long argc, t_atom* argv) {
object_post((t_object*)x, "Invoked by [%s] message", s->s_name);
}
运行结果: