基于 GObject 信号的事件响应
基于 GObjet 信号的解决方案大致像下面这样：
void
file_write (File *self, const char *buffer)
{
/* 向文件写入数据 */
... ... ...
/* 发射“文件改变了”这一信号 */
g_signal_emit (self, CHANGED, 0);
}
int
main (void)
{
File *file = file_new ("test.txt");
g_signal_connect (file, "changed", file_print, NULL);
g_signal_connect (file, "changed", file_print_xml, NULL);
g_signal_connect (file, "changed", file_print_tex, NULL);
... ... ...
}
上述代码的含义如下：
- 在 file_write 函数中，文件数据写入操作完毕后，就这一事件向外发射一个“CHANGED”信号，告诉所有响应者，文件内容改变了。至于哪些函数是这一信号的响应者，file_write 函数不必知道。
- file_write 函数的使用者，如果希望哪些函数用于响应 file_write 函数修改文件内容这一事件，那么就使用 g_signal_connect 函数（实际上它是一个宏）将响应函数与信号挂接到一起。这样，一旦事件的对应信号被 g_signal_emit 所发射，这些响应函数便会被自动调用。
为了实现上述的“信号/响应”模拟，那么 file_write 函数的参数便不可能再是 FILE 类型的文件指针了，而是我们自定义的 File 类型的对象，其中封装了“信号/响应”功能。事实上，GObject 类的内部便封装了这些功能，所有经由 GObject 子类化而产生的对象，便可拥有这些功能。
GObject 子类对象的信号处理
首先，我们定义 GObject 子类 MyFile。这个过程，我们应当已经不再陌生，参考文档。
my-file.h 头文件内容如下：
#ifndef MY_FILE_H
#define MY_FILE_H
#include <glib-object.h>
#define MY_TYPE_FILE (my_file_get_type ())
#define MY_FILE(object) G_TYPE_CHECK_INSTANCE_CAST ((object), MY_TYPE_FILE, MyFile)
#define MY_IS_FILE(object) G_TYPE_CHECK_INSTANCE_TYPE ((object), MY_TYPE_FILE))
#define MY_FILE_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), MY_TYPE_FILE, MyFileClass))
#define MY_IS_FILE_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), MY_TYPE_FILE))
#define MY_FILE_GET_CLASS(object) (\
G_TYPE_INSTANCE_GET_CLASS ((object), MY_TYPE_FILE, MyFileClass))
typedef struct _MyFile MyFile;
struct _MyFile {
GObject parent;
};
typedef struct _MyFileClass MyFileClass;
struct _MyFileClass {
GObjectClass parent_class;
};
GType my_file_get_type (void);
#endif
my-file.c 源文件内容如下：
#include "my-file.h"
G_DEFINE_TYPE (MyFile, my_file, G_TYPE_OBJECT);
#define MY_FILE_GET_PRIVATE(object) (\
G_TYPE_INSTANCE_GET_PRIVATE ((object), MY_TYPE_FILE, MyFilePrivate))
typedef struct _MyFilePrivate MyFilePrivate;
struct _MyFilePrivate {
GString *name;
GIOChannel *file;
};
enum PropertyDList {
PROPERTY_FILE_0,
PROPERTY_FILE_NAME
};
static void
my_file_dispose (GObject *gobject)
{
MyFile *self = MY_FILE (gobject);
MyFilePrivate *priv = MY_FILE_GET_PRIVATE (self);
if (priv->file){
g_io_channel_unref (priv->file);
priv->file = NULL;
}
G_OBJECT_CLASS (my_file_parent_class)->dispose (gobject);
}
static void
my_file_finalize (GObject *gobject)
{
MyFile *self = MY_FILE (gobject);
MyFilePrivate *priv = MY_FILE_GET_PRIVATE (self);
g_string_free (priv->name, TRUE);
G_OBJECT_CLASS (my_file_parent_class)->finalize (gobject);
}
static void
my_file_set_property (GObject *object, guint property_id,
const GValue *value, GParamSpec *pspec)
{
MyFile *self = MY_FILE (object);
MyFilePrivate *priv = MY_FILE_GET_PRIVATE (self);
switch (property_id){
case PROPERTY_FILE_NAME:
if (priv->name)
g_string_free (priv->name, TRUE);
priv->name = g_string_new (g_value_get_string (value));
priv->file = g_io_channel_new_file (priv->name->str, "a+", NULL);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
break;
}
}
static void
my_file_get_property (GObject *object, guint property_id,
GValue *value, GParamSpec *pspec)
{
MyFile *self = MY_FILE (object);
MyFilePrivate *priv = MY_FILE_GET_PRIVATE (self);
switch (property_id){
case PROPERTY_FILE_NAME:
g_value_set_string (value, priv->name->str);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
break;
}
}
static
void my_file_init (MyFile *self)
{
}
static
void my_file_class_init (MyFileClass *klass)
{
g_type_class_add_private (klass, sizeof (MyFilePrivate));
GObjectClass *base_class = G_OBJECT_CLASS (klass);
base_class->set_property = my_file_set_property;
base_class->get_property = my_file_get_property;
base_class->dispose = my_file_dispose;
base_class->finalize = my_file_finalize;
GParamSpec *pspec;
pspec = g_param_spec_string ("name",
"Name",
"File name",
NULL,
G_PARAM_READABLE | G_PARAM_WRITABLE | G_PARAM_CONSTRUCT);
g_object_class_install_property (base_class, PROPERTY_FILE_NAME, pspec);
g_signal_new ("file_changed",
MY_TYPE_FILE,
G_SIGNAL_RUN_LAST | G_SIGNAL_NO_RECURSE | G_SIGNAL_NO_HOOKS,
0,
NULL,
NULL,
g_cclosure_marshal_VOID__VOID,
G_TYPE_NONE,
0);
}
void
my_file_write (MyFile *self, gchar *buffer)
{
MyFilePrivate *priv = MY_FILE_GET_PRIVATE (self);
g_io_channel_write_chars (priv->file, buffer, -1, NULL, NULL);
g_io_channel_flush (priv->file, NULL);
g_signal_emit_by_name(self, "file_changed");
}
MyFile 类的使用者——main.c 文件内容如下：
#include "my-file.h"
static void
file_print (gpointer gobject, gpointer user_data)
{
g_printf ("invoking file_print!\n");
}
static void
file_print_xml (gpointer gobject, gpointer user_data)
{
g_printf ("invoking file_print_xml!\n");
}
static void
file_print_tex (gpointer gobject, gpointer user_data)
{
g_printf ("invoking file_print_tex!\n");
}
int
main (void)
{
g_type_init ();
MyFile *file = g_object_new (MY_TYPE_FILE, "name", "test.txt", NULL);
g_signal_connect (file, "file_changed", G_CALLBACK (file_print), NULL);
g_signal_connect (file, "file_changed", G_CALLBACK (file_print_xml), NULL);
g_signal_connect (file, "file_changed", G_CALLBACK (file_print_tex), NULL);
my_file_write (file, "hello world!\n");
g_object_unref (file);
return 0;
}
首先，是在 MyFile 类的类结构题初始化函数 my_file_class_init 中，除了设置类属性之外，我们调用了 g_signal_new 函数用于建立 MyFile 类型与 "file_changed" 信号的关联。至于究竟是何种关联，那不是我们所关心的！还有，g_signal_new 函数的参数有很多。
其次，是 MyFile 对象的析构函数。在 my-file.c 源文件中，函数 my_file_dispose 与 my_file_finalize 构成了 MyFile 对象的析构函数，前者用于解除 MyFile 对象对其它对象（是指那些具有引用计数且被 GObject 库的类型系统所管理的对象）的引用，后者用于 MyFile 对象属性的内存释放。至于分何要分为两个阶段进行 GObject 子类对象析构以及相关细节知识，还是另外开一篇文章来讨论吧，否则问题会被越搞越复杂。