MAX/MSP SDK学习04：Messages selector的使用-编程知识

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 objecttypedef 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) { // inletsprintf(s, "I am inlet %ld", a);} else {	// outletsprintf(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 objecttypedef 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) { // inletsprintf(s, "I am inlet %ld", a);} else {	// outletsprintf(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 objecttypedef 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) { // inletsprintf(s, "I am inlet %ld", a);} else {	// outletsprintf(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：