The first step in making the build system aware of our component is to generate an input file for autoconf to use during the configure step, which will build our the necessary Makefile automatically.

DEPTH = ../.. topsrcdir = @top_srcdir@ srcdir = @srcdir@ VPATH = @srcdir@

include $(DEPTH)/config/autoconf.mk

MODULE = firstxpcom

DIRS = public \

XPI_NAME = firstxpcom

# A Unique ID for your extension INSTALL_EXTENSION_ID = firstxpcom@senecac.on.ca

# Will create a .xpi in /mozilla/$(MOZ_OBJDIR)/dist/xpi-stage/ XPI_PKGNAME = firstxpcom

# install.rdf will tell Firefox how to install our extension and # this says, "copy install.rdf into our extension dir and xpi" DIST_FILES = install.rdf

include $(topsrcdir)/config/rules.mk

 Note the '''DIRS ''' variable. It says that the two directories, public and src, will be enteredduring the build. We That means we also need Makefile.in files in each of thosethese.

-----------start--------------  DEPTH = ../../.. topsrcdir = @top_srcdir@ srcdir = @srcdir@ VPATH = @srcdir@ include $(DEPTH)/config/autoconf.mk MODULE = firstxpcom XPIDL_MODULE = firstxpcom XPI_NAME = firstxpcom # The files under EXPORTS are copied directly to # /mozilla/$(MOZ_OBJDIR)/dist/include/myextension/firstxpcom # and are thus accessible from other modules #EXPORTS = \ # myHeader.h \ # $(NULL) XPIDLSRCS = IFirstXpcom.idl include $(topsrcdir)/config/rules.mk ----------end-------------------

Now a Makefile.in for in the srcdirectory:

DEPTH = . # The REQUIRES section tells make which modules your # components uses.This causes the relevant subdirectories # of /mozilla/$(MOZ_OBJDIR)/dist/..include/to be added to the # C++ compiler's include path.If you're including Mozilla # headers and the compiler isn't finding them, it could well # mean that you haven't listed all of the necessary modules here.topsrcdir REQUIRES = @top_srcdir@xpcom \ string \ $(NULL) # The .cpp source files to be compiledsrcdir CPPSRCS = @srcdir@FirstXpcom.cpp \ $(NULL) VPATH EXTRA_DSO_LDOPTS += @srcdir@\ $(XPCOM_GLUE_LDOPTS) \ $(NSPR_LIBS) \ $(NULL) include $(topsrcdir)/config/rules.mk

include $(DEPTH)/config/autoconf=== install.mkrdf ===

XPI_NAME <?xml version= "1.0" encoding="UTF-8"?> <RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:em="http://www.mozilla.org/2004/em-rdf#"> <Description about="urn:mozilla:install-manifest"> <em:id>firstxpcom@senecac.on.ca</em:id> <em:name>firstxpcom</em:name> <em:version>1.0</em:version> <em:creator>David Humphrey</em:creator> <em:description>A Simple XPCOM Extension.</em:description> <em:homepageURL>http://abc.com</em:homepageURL> <em:aboutURL>chrome://firstxpcom/content/about.xul</em:aboutURL> <em:targetApplication> <Description> <em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id> <!-- firefox --> <em:minVersion>2.0</em:minVersion> <em:maxVersion>3.0a3pre</em:maxVersion> </Description> </em:targetApplication> </Description> </RDF>

# The REQUIRES section tells make which modules your # components uses. This causes the relevant subdirectories# of /mozilla/$(MOZ_OBJDIR)/dist/include/ to be added to the# C++ compiler's include path. If you're including Mozilla# headers and the compiler isn't finding them, it could well# mean that you haven't listed all of the necessary modules here.REQUIRES = xpcom \ string \ $(NULL)= Building FirstXpcom ==

# The Now we're ready to build our component.cpp source files Add the following line to be compiledCPPSRCS = FirstXpcomyour '''.cpp \ $(NULL)mozconfig''' file in order to include firstxpcom during the build process:

EXTRA_DSO_LDOPTS += \ $(XPCOM_GLUE_LDOPTS) \ $(NSPR_LIBS) \ $(NULL) include $(topsrcdir)/config/rules.mk ----------end------------------- Last, we need to create a file telling Firefox how to install our extension, install.rdf (see http://developer.mozilla.org/en/docs/Install_Manifests for details). -----------start-------------- <?xml version="1.0"?> <RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:em="http://www.mozilla.org/2004/em-rdf#"> <Description about="urn:mozilla:install-manifest"> <em:id>firstxpcom@senecac.on.ca</em:id> <em:version>0.1</em:version> <em:type>2</em:type>  <em:targetApplication> <!-- Firefox --> <Description> <em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id> <em:minVersion>2.0+</em:minVersion> <em:maxVersion>3.0a3</em:maxVersion> </Description> </em:targetApplication> <!-- front-end metadata --> <em:name>My First XPCOM Extension</em:name> <em:description>Just a simple XPCOM component.</em:description> <em:creator>David Humphrey</em:creator> <em:homepageURL>http://zenit.senecac.on.ca/wiki</em:homepageURL> </Description></RDF> ----------end-------------------  * Now let's build our component Add the following line to your .mozconfig file in order to enable your extension in the build system:  ac_add_options --enable-extensions=default,firstxpcom

$ cd mozilla $ make -f client.mk build

$ cd $(objdir) $ ../build/autoconf/make-makefile extensions/firstxpcom

$ cd $(objdir)/extensions/firstxpcom $ make

This will create the '''public ''' and '''src ''' directories, as well as generate the Makefiles necessary in each. Go into the public directory and call make again, in order to have your .h and .cpp stubs generated:

$ cd $(objdir)/extensions/firstxpcom/public $ make

<code> IFirstXpcom.idl ../../../dist/bin/xpidl.exe -m header -w -I../../../../extensions/firstxpcom/public -I../../../dist/idl -o _xpidlgen/IFirstXpcom /c/temp/proj/ff-trunk/mozilla/obj-fftrunk/extensions/firstxpcom/public/../../../../extensions/firstxpcom/public/IFirstXpcom.idl Here it is processing our IDL file. As a result of this first partially successful run make, exported and generated header files (i.e.,from our IDL) will be placed in dist/include/firstxpcom. Within $(obdir)/dist/include</firstxpcom/IFirstXpcom.h you'll see a block that begins:code>

#if 0/* Use Here we can see the code below as build processing our IDL file. As a template for the implementation class for result of this interfacefirst (partially) successful run of make, exported and generated header files (i.e. *,from our IDL) will be placed in '''$(objdir)/dist/...include/* End of implementation class templatefirstxpcom'''. */#endif

The code in the middle of this block is what you want to start working with in order to implement your .cpp file Within '''$(and obdir)/dist/include/firstxpcom/IFirstXpcom.h if ''' you choose to split it out, which we won't). Copy this implementation stub into ll see the following fileblock of code:

mozilla #if 0 /extensions* Use the code below as a template for the implementation class for this interface. */firstxpcom ... /FirstXpcom* End of implementation class template.cpp*/ #endif

You'll need The code in the middle of this block is what you want to do a search/replace on _MYCLASS_ use as the basis for implementing your .cpp file (and change .h if you choose to split it to out, which we won't). Copy and paste this implementation stub into the name of your classfollowing file: '''mozilla/extensions/firstxpcom/FirstXpcom.cpp'''

You'll need to do a search/replace on '''_MYCLASS_ > ''' and change it to the name of your class, in our case, '''FirstXpcom'''.

$ cd $(objdir)/extensions/firstxpcom $ make

This will produce a host of errors, mostly related to the fact that we don't have proper includes setup set-up and it can't find declarations it needs. You need to add an include for your interface's generated .hfile:

#include "IFirstXpcom.h"

Now reRe-run make.

Let's examine the code more closely and try to make sense of things ($(objdir)/dist/include/firstxpcom/== Examining IFirstXpcom.h): -----------start-------------- /* * DO NOT EDIT. THIS FILE IS GENERATED FROM c:/temp/proj/ff-trunk/mozilla/obj-fftrunk/extensions/firstxpcom/public/../../../../extensions/firstxpcom/public/IFirstXpcom.idl */ #ifndef __gen_IFirstXpcom_h__#define __gen_IFirstXpcom_h__  #ifndef __gen_nsISupports_h__#include "nsISupports.h"#endif /* For IDL files that don't want to include root IDL files. */#ifndef NS_NO_VTABLE#define NS_NO_VTABLE#endif /* starting interface: IFirstXpcom */#define IFIRSTXPCOM_IID_STR "78af1749-014a-47aa-baec-2669670b7601" #define IFIRSTXPCOM_IID \ {0x78af1749, 0x014a, 0x47aa, \ { 0xba, 0xec, 0x26, 0x69, 0x67, 0x0b, 0x76, 0x01 }} class NS_NO_VTABLE IFirstXpcom : public nsISupports { public:   NS_DECLARE_STATIC_IID_ACCESSOR(IFIRSTXPCOM_IID)  /* attribute AString name; */ NS_IMETHOD GetName(nsAString & aName) = 0; NS_IMETHOD SetName(const nsAString & aName) = 0;  /* long add (in long a, in long b); */ NS_IMETHOD Add(PRInt32 a, PRInt32 b, PRInt32 *_retval) = 0; };

NS_DEFINE_STATIC_IID_ACCESSORLet's examine the code more closely and try to make sense of things. Here is the code in '''$(objdir)/dist/include/firstxpcom/IFirstXpcom, IFIRSTXPCOM_IID).h''':

/* Use this macro when declaring classes * DO NOT EDIT. THIS FILE IS GENERATED FROM c:/temp/proj/ff-trunk/mozilla/obj-fftrunk/extensions/firstxpcom/public/../../../../extensions/firstxpcom/public/IFirstXpcom.idl */ #ifndef __gen_IFirstXpcom_h__ #define __gen_IFirstXpcom_h__ #ifndef __gen_nsISupports_h__ #include "nsISupports.h" #endif /* For IDL files that implement this interfacedon't want to include root IDL files. */ #ifndef NS_NO_VTABLE #define NS_DECL_IFIRSTXPCOM \NS_NO_VTABLE NS_IMETHOD GetName(nsAString & aName); \ #endif NS_IMETHOD SetName(const nsAString & aName); \ NS_IMETHOD Add(PRInt32 a, PRInt32 b, PRInt32 /* starting interface: IFirstXpcom *_retval); / #define IFIRSTXPCOM_IID_STR "78af1749-014a-47aa-baec-2669670b7601"

/* Use this macro to declare functions that forward the behavior of this interface to another object. */ #define NS_FORWARD_IFIRSTXPCOM(_to) IFIRSTXPCOM_IID \ NS_IMETHOD GetName(nsAString & aName) { return _to GetName(aName); } 0x78af1749, 0x014a, 0x47aa, \ NS_IMETHOD SetName(const nsAString & aName) { return _to SetName(aName); } \ NS_IMETHOD Add(PRInt32 a0xba, 0xec, 0x26, 0x69, PRInt32 b0x67, PRInt32 *_retval) { return _to Add(a0x0b, b0x76, _retval); 0x01 }}

class NS_NO_VTABLE IFirstXpcom : public nsISupports { public: NS_DECLARE_STATIC_IID_ACCESSOR(IFIRSTXPCOM_IID) /* attribute AString name; */ NS_IMETHOD GetName(nsAString & aName) = 0; NS_IMETHOD SetName(const nsAString & aName) = 0; /* long add (in long a, in long b); */ NS_IMETHOD Add(PRInt32 a, PRInt32 b, PRInt32 *_retval) = 0; }; NS_DEFINE_STATIC_IID_ACCESSOR(IFirstXpcom, IFIRSTXPCOM_IID) /* Use this macro when declaring classes that implement this interface. */ #define NS_DECL_IFIRSTXPCOM \ NS_IMETHOD GetName(nsAString & aName); \ NS_IMETHOD SetName(const nsAString & aName); \ NS_IMETHOD Add(PRInt32 a, PRInt32 b, PRInt32 *_retval); /* Use this macro to declare functions that forward the behavior of this interface to another object in a safe way. */ #define NS_FORWARD_SAFE_IFIRSTXPCOMNS_FORWARD_IFIRSTXPCOM(_to) \ NS_IMETHOD GetName(nsAString & aName) { return !_to ? NS_ERROR_NULL_POINTER : _to->GetName(aName); } \ NS_IMETHOD SetName(const nsAString & aName) { return !_to ? NS_ERROR_NULL_POINTER : _to->SetName(aName); } \ NS_IMETHOD Add(PRInt32 a, PRInt32 b, PRInt32 *_retval) { return !_to ? NS_ERROR_NULL_POINTER : _to->Add(a, b, _retval); } #if 0 /* Use this macro to declare functions that forward the code below as a template for the implementation class for behavior of this interfaceto another object in a safe way. */ /* Header file */class _MYCLASS_ : public IFirstXpcom{public: NS_DECL_ISUPPORTS NS_DECL_IFIRSTXPCOM  _MYCLASS_ #define NS_FORWARD_SAFE_IFIRSTXPCOM(_to);\ private: ~_MYCLASS_ NS_IMETHOD GetName(nsAString & aName); protected: /* additional members */}; /* Implementation file */NS_IMPL_ISUPPORTS1(_MYCLASS_, IFirstXpcom) _MYCLASS_::_MYCLASS_(){ /* member initializers and constructor code */} _MYCLASS_::~_MYCLASS_(){ /* destructor code */} /* attribute AString name; */NS_IMETHODIMP _MYCLASS_:return !_to ? NS_ERROR_NULL_POINTER : _to->GetName(nsAString & aName){ return NS_ERROR_NOT_IMPLEMENTED;}\NS_IMETHODIMP _MYCLASS_:: NS_IMETHOD SetName(const nsAString & aName){ return NS_ERROR_NOT_IMPLEMENTED;} /* long add !_to ? NS_ERROR_NULL_POINTER : _to->SetName(in long a, in long baName); */} \NS_IMETHODIMP _MYCLASS_:: NS_IMETHOD Add(PRInt32 a, PRInt32 b, PRInt32 *_retval){ return NS_ERROR_NOT_IMPLEMENTED!_to ? NS_ERROR_NULL_POINTER : _to->Add(a, b, _retval);} /* End of implementation class template. */#endif  #endif /* __gen_IFirstXpcom_h__ */ ----------end-------------------

* === Use of header guards===

Header guards (or Include Guards, see [http://en.wikipedia.org/wiki/Include_guardInclude Guards]) are a portable technique for ensuring that includes or defines are only done once. Another way of doing this, especially with the Microsoft compiler, is to use

#pragma once

* Use of macros Mozilla provides many convenience macros to help C++ developers do common tasks more efficiently. Much of the code involved in making a module/component is generic, and has to be repeated ever every time. You can spot macros in the code by the fact that they are all capitals, and often begin with '''NS_*'''. Examples include:

* NS_DECL_ISUPPORTS* NS_ENSURE_TRUE* NS_IMPL_NSGETMODULE(* see http://developer.mozilla.org/en/docs/Category:XPCOM_Macros for more examples)

NS_DECL_ appended with any interface name in all caps will declare all of the methods of that interface for you. Looking at the code above shows you how this is possible. For example, NS_DECL_NSIFOO will declare all of the methods of nsIFoo , provided that it exists and that nsIFoo.h was generated by the XPIDL compiler. Consider the following real class:

class myClass : public nsISomeClass { public: NS_DECL_ISUPPORTS // declares AddRef, Release, and QueryInterface NS_DECL_NSISOMECLASS // declares all methods of nsISomeClass myClass(); virtual ~myClass() {} };

The declaration of nsISomeClass doesn't include any methods other than the contructor and destructor. Instead, the class uses the NS_DECL_ macro Also note the use of NS_METHOD and NS_METHODIMP for return type signatures. All XPCOM functions are required to return a result code ('''nsresult'''), which indicates whether or not the function worked (e.g., NS_OK).

NS_IMPL_ISUPPORTS1(classname, interface1)

Also, if If your class implements more than one interface, you can simply change the number 1 in the macro to the number of interfaces you support and list the interfaces, separated by commas. For example:

NS_IMPL_ISUPPORTS2(classname, interface1, interface2) NS_IMPL_ISUPPORTSn(classname, interface1, ..., interfacen)

These macros automatically add the nsISupports entry for you, so you ''don't '' need to do something like thisthe following:

NS_IMPL_ISUPPORTS2(classname, interface1, nsISupports)

62 NS_IMPL_ISUPPORTS3(nsBinaryOutputStream, nsIObjectOutputStream, nsIBinaryOutputStream, nsIOutputStream) 

* === Use of never before-seen types===