gecko-dev/xpcom/sample/nsSample.cpp

150 lines
4.5 KiB
C++

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/**
*
* A sample of XPConnect. This file contains an implementation nsSample
* of the interface nsISample.
*
*/
#include <stdio.h>
#include "nsSample.h"
#include "nsMemory.h"
#include "nsEmbedString.h"
#include "nsIClassInfoImpl.h"
////////////////////////////////////////////////////////////////////////
nsSampleImpl::nsSampleImpl() : mValue(nullptr)
{
mValue = (char*)nsMemory::Clone("initial value", 14);
}
nsSampleImpl::~nsSampleImpl()
{
if (mValue)
nsMemory::Free(mValue);
}
/**
* NS_IMPL_ISUPPORTS1 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 name of the interface, and
* NOT the #defined IID.
*
* The _CI variant adds support for nsIClassInfo, which permits introspection
* and interface flattening.
*/
NS_IMPL_CLASSINFO(nsSampleImpl, nullptr, 0, NS_SAMPLE_CID)
NS_IMPL_ISUPPORTS1_CI(nsSampleImpl, 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 != nullptr, "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 nsMemory singleton. Any buffer
* returned by an XPCOM method should be allocated by the nsMemory.
* This convention lets things like JavaScript reflection do their
* job, and simplifies the way C++ clients deal with returned buffers.
*/
*aValue = (char*) nsMemory::Clone(mValue, strlen(mValue) + 1);
if (! *aValue)
return NS_ERROR_NULL_POINTER;
}
else {
*aValue = nullptr;
}
return NS_OK;
}
NS_IMETHODIMP
nsSampleImpl::SetValue(const char* aValue)
{
NS_PRECONDITION(aValue != nullptr, "null ptr");
if (! aValue)
return NS_ERROR_NULL_POINTER;
if (mValue) {
nsMemory::Free(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 = (char*) nsMemory::Clone(aValue, strlen(aValue) + 1);
return NS_OK;
}
NS_IMETHODIMP
nsSampleImpl::Poke(const char* aValue)
{
return SetValue((char*) aValue);
}
static void GetStringValue(nsACString& aValue)
{
NS_CStringSetData(aValue, "GetValue");
}
NS_IMETHODIMP
nsSampleImpl::WriteValue(const char* aPrefix)
{
NS_PRECONDITION(aPrefix != nullptr, "null ptr");
if (! aPrefix)
return NS_ERROR_NULL_POINTER;
printf("%s %s\n", aPrefix, mValue);
// This next part illustrates the nsEmbedString:
nsEmbedString foopy;
foopy.Append(PRUnichar('f'));
foopy.Append(PRUnichar('o'));
foopy.Append(PRUnichar('o'));
foopy.Append(PRUnichar('p'));
foopy.Append(PRUnichar('y'));
const PRUnichar* f = foopy.get();
uint32_t l = foopy.Length();
printf("%c%c%c%c%c %d\n", char(f[0]), char(f[1]), char(f[2]), char(f[3]), char(f[4]), l);
nsEmbedCString foopy2;
GetStringValue(foopy2);
//foopy2.AppendLiteral("foopy");
const char* f2 = foopy2.get();
uint32_t l2 = foopy2.Length();
printf("%s %d\n", f2, l2);
return NS_OK;
}