今天终于把Message消息选择器看得有点头绪了，主要是这个官方英文文档理解起来有点抽象。

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编写IsMatchABC自定义Object，要求：

①若左入口（入口0）收到 "int" 型消息，则从出口发送数值 "888"；

②若左入口（入口0）收到 "ABC" 消息，则从出口发送 "Message match!!!(Send)"；

③若右入口（入口1）收到 "int" 型消息，则打印该int数值；

#include "ext.h"			// standard Max include, always required
#include "ext_obex.h"		// required for new style Max objecttypedef struct _IsMatchABC {t_object ob;			  // the object itself (must be first)// 可把t_symbol看成字符串类型t_symbol* messagePrintSymbol;  // 若消息选择器匹配，则打印messagePrintSymbolt_symbol* messageSendSymbol;   // 若消息选择器匹配，则从出口发送messageSendSymbolt_atom messageSendInt;         // 若消息选择器匹配，则从出口发送messageSendInt// t_atom类型可存储整型、浮点型、t_symbol类型、指针void* outLet;
} t_IsMatchABC;// function prototypes
// 必备函数
void* IsMatchABC_new(t_symbol* s, long argc, t_atom* argv);
void IsMatchABC_free(t_IsMatchABC* x);
void IsMatchABC_assist(t_IsMatchABC* x, void* b, long m, long a, char* s);
// 自定义函数
void IsMatchABC_testMessageSelector(t_IsMatchABC* x);
void handleInt(t_IsMatchABC* x);
void handleIn1(t_IsMatchABC* x, long n);// global class pointer variable
void* IsMatchABC_class;void ext_main(void* r) {t_class* c;// "IsMatchABC" 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("IsMatchABC", (method)IsMatchABC_new, (method)IsMatchABC_free, (long)sizeof(t_IsMatchABC),0L /* leave NULL!! */, A_GIMME, 0);/* you CAN'T call this from the patcher */class_addmethod(c, (method)IsMatchABC_assist, "assist", A_CANT, 0);// 收到"ABC"消息，则调用IsMatchABC_testMessageSelector方法class_addmethod(c, (method)IsMatchABC_testMessageSelector, "ABC", 0); class_addmethod(c, (method)handleInt, "int", A_LONG, 0);class_addmethod(c, (method)handleIn1, "in1", A_LONG, 0);class_register(CLASS_BOX, c); /* CLASS_NOBOX */IsMatchABC_class = c;post("I am the IsMatchABC object");
}void IsMatchABC_assist(t_IsMatchABC* 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 IsMatchABC_free(t_IsMatchABC* 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* IsMatchABC_new(t_symbol* s, long argc, t_atom* argv) { t_IsMatchABC* x = NULL;long i;if ((x = (t_IsMatchABC*)object_alloc(IsMatchABC_class))) { intin(x, 1);   // 创建入口1（入口0默认存在）x->outLet = outlet_new(x, NULL);   // 创建通用出口// t_symbol型数据得使用gensym函数进行赋值，返回t_symbol型指针x->messagePrintSymbol = gensym("Message match!!!(Print)");  x->messageSendSymbol = gensym("Message match!!!(Send)");atom_setlong(&(x->messageSendInt), 888);}return (x);
}// 入口0收到"ABC"消息，则调用IsMatchABC_testMessageSelector方法
void IsMatchABC_testMessageSelector(t_IsMatchABC* x) {post("%s", x->messagePrintSymbol->s_name);outlet_anything(x->outLet, gensym(x->messageSendSymbol->s_name), 0, 0);
}// 入口0收到int型消息，则发送"666"
void handleInt(t_IsMatchABC* x) {outlet_anything(x->outLet, gensym("int"), 1, &(x->messageSendInt));
}// 入口1收到int型消息，则发送收到的int数值
void handleIn1(t_IsMatchABC* x, long n) {t_atom t_int;atom_setlong(&t_int, n);outlet_anything(x->outLet, gensym("int"), 1, &t_int);
}

运行结果：