我們繼續(xù)學(xué)習(xí)D-Bus，參考http://dbus./doc/dbus/libdbus-tutorial.html ，相關(guān)的API接口reference參考http://dbus./doc/dbus/api/html/modules.html 。從底層，即libdbus學(xué)習(xí)如何發(fā)送Method以及如何等待應(yīng)答，在上上次學(xué)習(xí)中，給出了同步的方式 ，這是更為高層的處理方式，建議使用。監(jiān)聽(tīng)method和監(jiān)聽(tīng)signal的方式非常相似。在給出例子之前，我希望和上次學(xué)習(xí)一樣給出一個(gè)示意圖，更好地了解D-Bus的各個(gè)概念。

監(jiān)聽(tīng)Method call消息，并返回Method reply消息

　　Method的監(jiān)聽(tīng)和signal的監(jiān)聽(tīng)的處理時(shí)一樣，但是信號(hào)是不需要答復(fù)，而Method需要。在下面的例子中，我們將學(xué)習(xí)如何在消息中加入多個(gè)參數(shù)（在D-Bus學(xué)習(xí)（四）中，我們加入了一個(gè)參數(shù)）的情況。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dbus/dbus-glib.h>
#include <dbus/dbus.h>
#include <unistd.h>

/*讀取消息的參數(shù)，并且返回兩個(gè)參數(shù)，一個(gè)是bool值stat，一個(gè)是整數(shù)level*/ 
void reply_to_method_call(DBusMessage * msg, DBusConnection * conn){
    DBusMessage * reply;
    DBusMessageIter arg;
    char * param = NULL;
    dbus_bool_t stat = TRUE;
    dbus_uint32_t level = 2010;
    dbus_uint32_t serial = 0; 
    
    //從msg中讀取參數(shù)，這個(gè)在上一次學(xué)習(xí)中學(xué)過(guò) 
    if(!dbus_message_iter_init(msg,&arg))
        printf("Message has no args/n");
    else if(dbus_message_iter_get_arg_type(&arg) != DBUS_TYPE_STRING)
        printf("Arg is not string!/n");
    else
        dbus_message_iter_get_basic(&arg,& param);
    if(param == NULL) return;

    //創(chuàng)建返回消息reply 
    reply = dbus_message_new_method_return(msg); 
    //在返回消息中填入兩個(gè)參數(shù)，和信號(hào)加入?yún)?shù)的方式是一樣的。這次我們將加入兩個(gè)參數(shù)。 
    dbus_message_iter_init_append(reply,&arg); 
    if(!dbus_message_iter_append_basic (&arg,DBUS_TYPE_BOOLEAN,&stat)){
        printf("Out of Memory!/n");
        exit(1);
    }
    if(!dbus_message_iter_append_basic (&arg,DBUS_TYPE_UINT32,&level)){
        printf("Out of Memory!/n");
        exit(1);
    } 
  //發(fā)送返回消息 
      if( !dbus_connection_send (conn, reply, &serial)){
        printf("Out of Memory/n");
        exit(1);
    }
    dbus_connection_flush (conn);
    dbus_message_unref (reply);
}

/* 監(jiān)聽(tīng)D-Bus消息，我們?cè)谏洗蔚睦又羞M(jìn)行修改 */ 
void listen_dbus()
{
    DBusMessage * msg;
    DBusMessageIter arg;
    DBusConnection * connection;
    DBusError err;
    int ret;
    char * sigvalue;

    dbus_error_init(&err);
    //創(chuàng)建于session D-Bus的連接 
    connection = dbus_bus_get(DBUS_BUS_SESSION, &err);
    if(dbus_error_is_set(&err)){
        fprintf(stderr,"Connection Error %s/n",err.message);
        dbus_error_free(&err);
    }
    if(connection == NULL)
        return;
    //設(shè)置一個(gè)BUS name：test.wei.dest 
    ret = dbus_bus_request_name(connection,"test.wei.dest",DBUS_NAME_FLAG_REPLACE_EXISTING,&err);
    if(dbus_error_is_set(&err)){
        fprintf(stderr,"Name Error %s/n",err.message);
        dbus_error_free(&err);
    }
    if(ret != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
        return;

    //要求監(jiān)聽(tīng)某個(gè)singal：來(lái)自接口test.signal.Type的信號(hào) 
    dbus_bus_add_match(connection,"type='signal',interface='test.signal.Type'",&err);
    dbus_connection_flush(connection);
    if(dbus_error_is_set(&err)){
        fprintf(stderr,"Match Error %s/n",err.message);
        dbus_error_free(&err);
    } 

    while(true){ 
        dbus_connection_read_write (connection,0);
        msg = dbus_connection_pop_message (connection);

        if(msg == NULL){
            sleep(1);
            continue;
        } 

        if(dbus_message_is_signal(msg,"test.signal.Type","Test")){ 
            if(!dbus_message_iter_init(msg,&arg))
                fprintf(stderr,"Message Has no Param");
            else if(dbus_message_iter_get_arg_type(&arg) != DBUS_TYPE_STRING)
                g_printerr("Param is not string");
            else
                dbus_message_iter_get_basic(&arg,&sigvalue); 
        }else if(dbus_message_is_method_call(msg,"test.method.Type","Method")){ 
            //我們這里面先比較了接口名字和方法名字，實(shí)際上應(yīng)當(dāng)現(xiàn)比較路徑 
            if(strcmp(dbus_message_get_path (msg),"/test/method/Object") == TRUE)
               reply_to_method_call(msg, connection); 
        }
        dbus_message_unref(msg); 
    }
    
    
}
int main( int argc , char ** argv){
    listen_dbus(); 
    return 0;
}

發(fā)送Method call消息，并等待Method reply消息

　　下面的例子在上次學(xué)習(xí)信號(hào)發(fā)送的例子上進(jìn)行修改。如下：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dbus/dbus-glib.h>
#include <dbus/dbus.h>
#include <unistd.h> 
//建立與session D-Bus daemo的連接，并設(shè)定連接的名字，相關(guān)的代碼已經(jīng)多次使用過(guò)了 
DBusConnection *  connect_dbus(){
    DBusError err;
    DBusConnection * connection;
    int ret;

    //Step 1: connecting session bus 
    /* initialise the erroes */ 
    dbus_error_init(&err); 
    /* Connect to Bus*/ 
    connection = dbus_bus_get(DBUS_BUS_SESSION, &err); 
    if(dbus_error_is_set(&err)){
        fprintf(stderr,"Connection Err : %s/n",err.message);
        dbus_error_free(&err);
    }
    if(connection == NULL)
        return NULL;

    //step 2: 設(shè)置BUS name，也即連接的名字。 
    ret = dbus_bus_request_name(connection,"test.wei.source",DBUS_NAME_FLAG_REPLACE_EXISTING,&err); 
    if(dbus_error_is_set(&err)){
        fprintf(stderr,"Name Err : %s/n",err.message);
        dbus_error_free(&err);
    }
    if(ret != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
        return NULL;

    return connection;    
} 

void send_a_method_call(DBusConnection * connection,char * param)
{
    DBusError err;
    DBusMessage * msg;
    DBusMessageIter    arg;
    DBusPendingCall * pending;
    dbus_bool_t * stat;
    dbus_uint32_t * level;    
    
    dbus_error_init(&err); 

    //針對(duì)目的地地址，請(qǐng)參考圖，創(chuàng)建一個(gè)method call消息。 Constructs a new message to invoke a method on a remote object. 
    msg = dbus_message_new_method_call ("test.wei.dest","/test/method/Object","test.method.Type","Method"); 
    if(msg == NULL){
        g_printerr("Message NULL");
        return;
    } 

    //為消息添加參數(shù)。Append arguments 
    dbus_message_iter_init_append(msg, &arg); 
    if(!dbus_message_iter_append_basic (&arg, DBUS_TYPE_STRING,&param)){
        g_printerr("Out of Memory!");
        exit(1); 
    }

    //發(fā)送消息并獲得reply的handle 。Queues a message to send, as with dbus_connection_send() , but also returns a DBusPendingCallused to receive a reply to the message. 
    if(!dbus_connection_send_with_reply (connection, msg,&pending, -1)){ 
        g_printerr("Out of Memory!");
        exit(1);
    }      

    if(pending == NULL){
        g_printerr("Pending Call NULL: connection is disconnected ");
        dbus_message_unref(msg);
        return;
    } 

    dbus_connection_flush(connection);
    dbus_message_unref(msg); 
 
    //waiting a reply，在發(fā)送的時(shí)候，已經(jīng)獲取了method reply的handle，類(lèi)型為DBusPendingCall。 
    // block until we recieve a reply， Block until the pending call is completed. 
    dbus_pending_call_block (pending); 
    // get the reply message，Gets the reply, or returns NULL if none has been received yet. 
    msg = dbus_pending_call_steal_reply (pending); 
    if (msg == NULL) {
        fprintf(stderr, "Reply Null/n");
         exit(1);
    }
     // free the pending message handle 
     dbus_pending_call_unref(pending); 
    // read the parameters 
    if (!dbus_message_iter_init(msg, &arg)) 
        fprintf(stderr, "Message has no arguments!/n");
    else if ( db us_message_iter_get_arg_type (&arg) != DBUS_TYPE_BOOLEAN)
        fprintf(stderr, "Argument is not boolean!/n");
    else
        dbus_message_iter_get_basic (&arg, &stat);
 
    if (!dbus_message_iter_next(&arg)) 
        fprintf(stderr, "Message has too few arguments!/n");
    else if ( db us_message_iter_get_arg_type (&arg) != DBUS_TYPE_UINT32 )
        fprintf(stderr, "Argument is not int!/n");
    else
        dbus_message_iter_get_basic (&arg, &level);

    printf("Got Reply: %d, %d/n", stat, level);
    dbus_message_unref(msg); 
}

int main( int argc , char ** argv){
    DBusConnection * connection;
    connection = connect_dbus();
    if(connection == NULL)
        return -1;

    send_a_method_call(connection,"Hello, D-Bus");
    return 0;
}