gecko-dev/xpcom/sample/nsSample.cpp

188 lines
6.3 KiB
C++

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
*
* The contents of this file are subject to the Netscape Public
* License Version 1.1 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at http://www.mozilla.org/NPL/
*
* Software distributed under the License is distributed on an "AS
* IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
* implied. See the License for the specific language governing
* rights and limitations under the License.
*
* The Original Code is mozilla.org code.
*
* The Initial Developer of the Original Code is Netscape
* Communications Corporation. Portions created by Netscape are
* Copyright (C) 1998 Netscape Communications Corporation. All
* Rights Reserved.
*
* Contributor(s):
* Pierre Phaneuf <pp@ludusdesign.com>
*/
/**
*
* A sample of XPConnect. This file contains an implementation nsSample
* of the interface nsISample.
*
*/
#include "nsIAllocator.h"
#include "plstr.h"
#include "stdio.h"
#include "nsSample.h"
////////////////////////////////////////////////////////////////////////
/**
* This is the static constructor for the sample component. Notice that
* the prototype for this function is included in the {C++ ... } section
* of nsISample.idl. This prototype is not actually part of the nsISample
* interface, it only gets included, verbatim, in nsISample.h.
* This is so that the factory for this class (nsSampleFactory.cpp)
* can create a nsSample object. Normally you would expect to use
* "nsSampleImpl s = new nsSampleImpl();" to create the object, the catch here
* is that nsSampleImpl is not declared anywhere except in this file, so the
* factory has no idea what a nsSampleImpl is. Instead, this static function's
* prototype is declared in in nsISample.h (generated from nsISample.idl),
* which any nsISample factory would require for the declaration of
* nsISample anyway.
*/
nsresult
NS_NewSample(nsISample** aSample)
{
NS_PRECONDITION(aSample != nsnull, "null ptr");
if (! aSample)
return NS_ERROR_NULL_POINTER;
*aSample = new nsSampleImpl();
if (! *aSample)
return NS_ERROR_OUT_OF_MEMORY;
/**
* XPCOM automatically frees up memory used by objects when they are
* no longer in use. It determines that an object is no longer in use
* by checking how many unique, owning references there are to it.
* Unfortunately, there is no automatic procedure for determining
* what an owning reference is. Ownership is determined by conventions,
* and you must be very careful to adhere to these conventions, or you
* will forever be plagued by circular dependancies, and memory leaks.
* The first rule of ownership is, "If You Created It, You Own It"
* The other part of this convention is, when you create a new
* object, the factory has already added you as an owning reference.
* It is the clients responsibility to call Release() when it is finished
* using the object.
* NS_ADDREF() takes care of calling AddRef on the nsISupports interface
* of the object you pass it.
*/
NS_ADDREF(*aSample);
return NS_OK;
}
////////////////////////////////////////////////////////////////////////
nsSampleImpl::nsSampleImpl() : mValue(nsnull)
{
NS_INIT_REFCNT();
mValue = PL_strdup("initial value");
}
nsSampleImpl::~nsSampleImpl()
{
if (mValue)
PL_strfree(mValue);
}
/**
* NS_IMPL_ISUPPORTS expands to a simple implementation of the nsISupports
* interface. This includes a proper implementation of AddRef, Release,
* and QueryInterface. If this class supported more interfaces than just
* nsISupports,
* you could use NS_IMPL_ADDREF() and NS_IMPL_RELEASE() to take care of the
* simple stuff, but you would have to create QueryInterface on your own.
* nsSampleFactory.cpp is an example of this approach.
* Notice that the second parameter to the macro is the static IID accessor
* method, and NOT the #defined IID.
*/
NS_IMPL_ISUPPORTS(nsSampleImpl, NS_GET_IID(nsISample));
/**
* Notice that in the protoype for this function, the NS_IMETHOD macro was
* used to declare the return type. For the implementation, the return
* type is declared by NS_IMETHODIMP
*/
NS_IMETHODIMP
nsSampleImpl::GetValue(char** aValue)
{
NS_PRECONDITION(aValue != nsnull, "null ptr");
if (! aValue)
return NS_ERROR_NULL_POINTER;
if (mValue) {
/**
* GetValue's job is to return data known by an instance of
* nsSampleImpl to the outside world. If we were to simply return
* a pointer to data owned by this instance, and the client were to
* free it, bad things would surely follow.
* On the other hand, if we create a new copy of the data for our
* client, and it turns out that client is implemented in JavaScript,
* there would be no way to free the buffer. The solution to the
* buffer ownership problem is the nsAllocator singleton. Any buffer
* returned by an XPCOM method should be allocated by the nsAllocator.
* This convention lets things like JavaScript reflection do their
* job, and simplifies the way C++ clients deal with returned buffers.
*/
*aValue = (char*) nsAllocator::Alloc(PL_strlen(mValue) + 1);
if (! *aValue)
return NS_ERROR_NULL_POINTER;
PL_strcpy(*aValue, mValue);
}
else {
*aValue = nsnull;
}
return NS_OK;
}
NS_IMETHODIMP
nsSampleImpl::SetValue(const char* aValue)
{
NS_PRECONDITION(aValue != nsnull, "null ptr");
if (! aValue)
return NS_ERROR_NULL_POINTER;
if (mValue) {
PL_strfree(mValue);
}
/**
* Another buffer passing convention is that buffers passed INTO your
* object ARE NOT YOURS. Keep your hands off them, unless they are
* declared "inout". If you want to keep the value for posterity,
* you will have to make a copy of it.
*/
mValue = PL_strdup(aValue);
return NS_OK;
}
NS_IMETHODIMP
nsSampleImpl::Poke(const char* aValue)
{
return SetValue((char*) aValue);
}
NS_IMETHODIMP
nsSampleImpl::WriteValue(const char* aPrefix)
{
NS_PRECONDITION(aPrefix != nsnull, "null ptr");
if (! aPrefix)
return NS_ERROR_NULL_POINTER;
printf("%s %s\n", aPrefix, mValue);
return NS_OK;
}