Gobject - Inherit (Chinese)

Gobject Inherit elpam.tw@gmail.com elpam@Taiwan, Taipei, 2008

LICENSE ● 本投影片授權方式為： – 姓名標示─非商業性─相同方式分享 3.0 台灣版 – http://creativecommons.org/licenses/byncsa/3.0/tw/ ● 所有的範例程式皆為 Public Domain elpam.tw@gmail.com

About This Slides ● All example was build by (Ubuntu 9.10) – GCC4.3.4 – GLIB2.22.2 elpam.tw@gmail.com

Agenda ● GObject 's Introduction ● First Gobject Klass ● Inherit elpam.tw@gmail.com

GObject's Introduction elpam.tw@gmail.com

GTK+ (The GIMP Toolkit) ● GTK+ 最初是 GIMP 的專用開發庫，後來發展為 Unixlike 系統下開發圖形界面的應用程序的主流開發工具之一 – 相較於 QT ● GLib/GObject/GDK/GTK 都是為了發展 GIMP 而產生的，而 GTK+ 2.0 之後將 GLib 與 GObject 獨立出來讓其他的軟體使用 – March 11, 2002 elpam.tw@gmail.com

GLib ● 大部份的程式語言都提供 OO 以及內建方便的演算法 ● GLib 也提供了基本的資料結構 (Hash/Linked Lists) ● GLib Object System 則提供了簡單的 OO Framework for C elpam.tw@gmail.com

GObject ● GTK+, Pango 等函式庫裡的物件都繼承了 GOjbect 而實作 ● 提供 – 管理 Construction/ Destruction – property access method ● 不好用 .... – message passing/ signal support elpam.tw@gmail.com

Before GObject ● 學習 GObject 最好的管道 – Official Documents – Trace Code/ GTK+ 裡頭的數十個範例 ●Gobject 因為沒有語法的限制，所以很容易 '' 無意 / 惡意 '' 的造成 Memory leaking ，所以： ● 依造前人留下來的方式使用。 ( 勿異想天開 ) ● 真正的了解到每一個 Macro 的用法 / 意義，並嘗試展開之 elpam.tw@gmail.com

GObject 41 First Klass Step By Step elpam.tw@gmail.com

範例 ● mamanbar.{h|c} ● main.c elpam.tw@gmail.com

Step 1 ：定義物件 ● mamanbar.h typedef struct _MamanBar MamanBar; typedef struct _MamanBarClass MamanBarClass; struct _MamanBar { 繼承 GObject GObject parent; /* instance members */ int a; int b; }; struct _MamanBarClass { GObjectClass parent; /* class members */ }; elpam.tw@gmail.com

將 function 與 value 分開 ● 在 GObject 的設計裡，與 C++ 最大的概念上的不同就是 member function 與 member value 擺放的位置 – maman_bar 放 member value – maman_bar_class 放 member function ● Why? – member value 是每一個物件都要有一份 – member function 則是每一個物件都使用同一份 elpam.tw@gmail.com

精確的說 ● class 裡頭放的資料是所有的物件都存取同一份 – C++ 的 static member value – 是的， class 裡不一定要放 function point – 不是 static member function ● 而 base 裡頭放則是各個物件都保存一份 elpam.tw@gmail.com

Step 2 ：註冊 GType ● /* mamanbar.c */ 請注意：此 Function 為 Singleton ，而此函式只 GType maman_bar_get_type (void) 會 if(){} 裡只會被執行一次 { static GType type = 0; if (type == 0) { 將自已所撰寫的 function 填寫於此 static const GTypeInfo info = { /* You fill this structure. */ }; type = g_type_register_static (G_TYPE_OBJECT, "MamanBarType", &info, 0); } return type; } elpam.tw@gmail.com

Step 2 ：註冊 GType (cont') type = g_type_register_static (G_TYPE_OBJECT, "MamanBarType", &info, 0); GType g_type_register_static (GType parent_type, const gchar *type_name, const GTypeInfo *info, GTypeFlags flags); parent_type : Type from which this type will be derived. type_name : 0terminated string used as the name of the new type. info : The GTypeInfo structure for this type. flags : Bitwise combination of GTypeFlags values. Returns : The new type identifier. elpam.tw@gmail.com

什麼是 Type ( 形別 ) ● TypeInfo 裡記錄了物件的 Constructor/ Destructor/ 記憶體大小及 Parent 為何 ● Glib 有實作 Type System ，管理所有的 Type – 動態的 , interpreted languages – 靜態的 , compiled languages elpam.tw@gmail.com

typedef struct { /* interface types, classed types, instantiated types */ guint16 class_size; GbaseInitFunc base_init; GbaseFinalizeFunc base_finalize; /* interface types, classed types, instantiated types */ GclassInitFunc class_init; GclassFinalizeFunc class_finalize; gconstpointer class_data; /* instantiated types */ guint16 instance_size; guint16 n_preallocs; GinstanceInitFunc instance_init; /* value handling */ const GtypeValueTable *value_table; } GTypeInfo; elpam.tw@gmail.com

Step 2 ：註冊 GType(cont') ● 目前可以填寫的資料 static const GTypeInfo info = { sizeof (MamanBarClass), NULL, /* base_init */ NULL, /* base_finalize */ NULL, /* class_init */ NULL, /* class_finalize */ NULL, /* class_data */ sizeof (MamanBar), 0, /* n_preallocs */ NULL /* instance_init */ }; elpam.tw@gmail.com

Step 3 ：撰寫 basic_init ● 也就是 Constructor static void maman_bar_init ( MamanBar* self ) { self > a = 1; self > b = 2; } elpam.tw@gmail.com

● Register function pointer into structure static const GTypeInfo info = { sizeof (MamanBarClass), NULL, /* base_init */ NULL, /* base_finalize */ NULL, /* class_init */ NULL, /* class_finalize */ NULL, /* class_data */ sizeof (MamanBar), 0, /* n_preallocs */ ????? /* instance_init */ }; elpam.tw@gmail.com

Step 4 ： use it ● Add print out information in the maman_bar_init ● Please monitor the order of function launched int main (int argc, char *argv[]) { /* this function should be executed first. Before everything */ g_type_init(); You can find out the constructor/ type register will be launched by this function /* Create our object */ MamanBar *bar = g_object_new (MAMAN_TYPE_BAR, NULL); printf(" bar>a = (%d) bar>b = (%d)n", bar>a, bar>b ); return 0; } elpam.tw@gmail.com

GObject 42 Inherit Step By Step elpam.tw@gmail.com

Step 1 ： Define SubBar ● Please Notice This Color /* subbar.h */ typedef struct _MamanBar MamanBar; typedef struct _MamanBarClass MamanBarClass; struct _SubBar { 繼承 GObject MamanBar parent; /* instance members */ int c; int d; }; elpam.tw@gmail.com

Step 2 ： Register SubBar's GType ● Please Notice This Color /* subbar.c */ GType maman_bar_get_type (void) { static GType type = 0; if (type == 0) { static const GTypeInfo info = { sizeof (SubBarClass), NULL, /* base_init */ NULL, /* base_finalize */ NULL, /* class_init */ NULL, /* class_finalize */ NULL, /* class_data */ sizeof (SubBar), 0, /* n_preallocs */ sub_bar_init /* instance_init */ }; type = g_type_register_static (MAMAN_BAR_TYPE, "SubBarType", &info, 0); } return type; } elpam.tw@gmail.com

Step 3 ： Try Casting ● /* main.c */ ● When we need to access parent's member value ((MamanBar*)subbar)>a, ((MamanBar*)subbar)>b elpam.tw@gmail.com

Step 4 ： .... ● Yes, it's very simple. No trick like previous slide ● Please monitor the order of function launched elpam.tw@gmail.com

Conclusion ● The above example show the inheritance implementation by using Gobject. ● Reader can write to child inherit subbar, and monitor the timing of constructor. elpam.tw@gmail.com

Next ● We''ll talk about Virtual Function later elpam.tw@gmail.com

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Gobject - Inherit (Chinese)

by Kai-Feng Chou on Nov 30, 2009

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