已经成功从档案中读取数据。下面会提供解释和代码,但目前只是一种hack的方式,仅仅是为了看看是否可能实现。我一直在修改东西,直到我得到可行的结果;这只是可行的一个示例,绝不是生产质量的代码(起始位置没有再输入)。毫无疑问,有许多不好/不必要/令人困惑的事情,因此请随意使用注释来帮助清理。
如先前提到的那样,仅仅传递路径给库已经不够了——除非文件位于已知文件夹之一(documents、home、media、music、pictures、removable或videos),否则您将得到“拒绝访问”的消息。相反,图书馆必须能够接受StorageFile^,并从FileOpenPicker返回。至少我没有找到其他方法,也许有人知道更好的方法?
MiniZip通过iowin32.h/.c为zlib提供Windows文件系统访问层。虽然它仍然适用于旧式应用程序的桌面模式,但对于Metro应用程序却无法工作,因为它使用了弃用API并依赖路径。为了使MiniZip适用于Windows 8,需要完全重写iowin32。
为了重新让事情运作起来,第一件事就是找到一种方法将StorageFile^一直传递到iowinrt(iowin32的Windows 8替代品)中。幸运的是,MiniZip提供了两种样式的打开文件函数——一种接受char指针,另一种接受void指针。由于^仍然只是一个指针,因此将StorageFile^转换为void*,然后再转换回StorageFile^即可。
既然我已经能够将StorageFile^传递给我的新iowinrt,下一个问题是如何使新的异步C++文件访问API与Zlib配合工作。为了支持非常老的C编译器,Zlib是用旧版K&R风格的C编写的。VisualStudio编译器会拒绝将其编译为C ++,它必须被编译为C,并且新的iowinrt当然必须被编译为C ++——这一点在创建项目时需要记住。有关VS项目的其他注意事项是,尽管DLL也可以工作,但我将其设置为Visual C++ Windows Metro样式静态库,但那时您还必须定义宏以导出MiniZip API(我还没有尝试过,不知道应该使用哪个宏)。我认为我还必须设置“Consume Windows Runtime Extension”(/ZW),设置“Not Using Precompiled Headers”,并将_CRT_SECURE_NO_WARNINGS和_CRT_NONSTDC_NO_WARNINGS添加到Preprocessor Definitions中。
至于iowinrt本身,我将它分成了两个文件。一个包含两个密封的ref类——读取器和写入器对象;它们都接受StorageFile^。读取器实现了Read、Tell、SeekFromBeginning、SeekFromCurrent和SeekFromEnd(3种Seek方法的原因是因为ref sealed类必须坚持RT类型,而这显然排除了枚举,所以我选择了简单的路线)。目前,写入器仅实现了Write,但我还没有使用它。
这是FileReader代码:
#include "pch.h"
#include "FileAccess.h"
using namespace Concurrency;
using namespace Windows::Security::Cryptography;
using namespace CFileAccess;
FileReader::FileReader(StorageFile^ archive)
{
if (nullptr != archive)
{
create_task(archive->OpenReadAsync()).then([this](IRandomAccessStreamWithContentType^ archiveStream)
{
if (nullptr != archiveStream)
{
_readStream = archiveStream;
}
}).wait();
}
}
int32 FileReader::Read(WriteOnlyArray<byte>^ fileData)
{
int32 bytesRead = 0;
if ((nullptr != _readStream) && (fileData->Length > 0))
{
try
{
auto inputStreamReader = ref new DataReader(_readStream);
create_task(inputStreamReader->LoadAsync(fileData->Length)).then([&](task<unsigned int> dataRead)
{
try
{
bytesRead = dataRead.get();
if (bytesRead)
{
inputStreamReader->ReadBytes(fileData);
}
}
catch (Exception^ e)
{
bytesRead = -1;
}
inputStreamReader->DetachStream();
}).wait();
}
catch (Exception^ e)
{
bytesRead = -1;
}
}
return (bytesRead);
}
int64 FileReader::Tell(void)
{
int64 ret = -1;
if (nullptr != _readStream)
{
ret = _readStream->Position;
}
return (ret);
}
int64 FileReader::SeekFromBeginning(uint64 offset)
{
int64 ret = -1;
if ((nullptr != _readStream) && (offset < _readStream->Size))
{
_readStream->Seek(offset);
ret = 0;
}
return (ret);
}
int64 FileReader::SeekFromCurrent(uint64 offset)
{
int64 ret = -1;
if ((nullptr != _readStream) && ((_readStream->Position + offset) < _readStream->Size))
{
_readStream->Seek(_readStream->Position + offset);
ret = 0;
}
return (ret);
}
int64 FileReader::SeekFromEnd(uint64 offset)
{
int64 ret = -1;
if ((nullptr != _readStream) && ((_readStream->Size - offset) >= 0))
{
_readStream->Seek(_readStream->Size - offset);
ret = 0;
}
return (ret);
}
iowinrt位于MiniZip和FileReader(以及FileWriter)之间。这里无法详细介绍所有内容,但以下内容应该足以重建其余部分,因为它们大多只是不同的函数名称,再加上一堆fill_winRT_filefuncxxx(),这些都很明显:
#include "zlib.h"
#include "ioapi.h"
#include "iowinrt.h"
#include "FileAccess.h"
using namespace Windows::Security::Cryptography;
using namespace Platform;
using namespace CFileAccess;
static FileReader^ g_fileReader = nullptr;
static FileWriter^ g_fileWriter = nullptr;
static StorageFile^ g_storageFile = nullptr;
[...]
static voidpf winRT_translate_open_mode(int mode)
{
if (nullptr != g_storageFile)
{
if ((mode & ZLIB_FILEFUNC_MODE_READWRITEFILTER)==ZLIB_FILEFUNC_MODE_READ)
{
g_fileWriter = nullptr;
g_fileReader = ref new FileReader(g_storageFile);
}
else if (mode & ZLIB_FILEFUNC_MODE_EXISTING)
{
g_fileReader = nullptr;
g_fileWriter = ref new FileWriter(g_storageFile);
}
else if (mode & ZLIB_FILEFUNC_MODE_CREATE)
{
g_fileReader = nullptr;
g_fileWriter = ref new FileWriter(g_storageFile);
}
}
return (nullptr != g_fileReader ? reinterpret_cast<voidpf>(g_fileReader) : reinterpret_cast<voidpf>(g_fileWriter));
}
voidpf ZCALLBACK winRT_open64_file_func (voidpf opaque,const void* storageFile,int mode)
{
g_storageFile = reinterpret_cast<StorageFile^>(const_cast<void*>(storageFile));
return (winRT_translate_open_mode(mode));
}
[...]
Long ZCALLBACK winRT_read_file_func (voidpf opaque, voidpf stream, void* buf,uLong size)
{
uLong bytesRead = 0;
if (nullptr != g_fileReader)
{
auto fileData = ref new Platform::Array<byte>(size);
bytesRead = g_fileReader->Read(fileData);
memcpy(buf, fileData->Data, fileData->Length);
}
return (bytesRead);
}
uLong ZCALLBACK winRT_write_file_func (voidpf opaque,voidpf stream,const void* buf,uLong size)
{
uLong bytesWritten = 0;
if (nullptr != g_fileWriter)
{
auto bytes = ref new Array<uint8>(reinterpret_cast<uint8*>(const_cast<void*>(buf)), size);
IBuffer ^writeBuffer = CryptographicBuffer::CreateFromByteArray(bytes);
bytesWritten = g_fileWriter->Write(writeBuffer);
}
return (bytesWritten);
}
long ZCALLBACK winRT_tell_file_func (voidpf opaque,voidpf stream)
{
long long ret = 0;
if (nullptr != g_fileReader)
{
ret = g_fileReader->Tell();
}
return (static_cast<long>(ret));
}
ZPOS64_T ZCALLBACK winRT_tell64_file_func (voidpf opaque, voidpf stream)
{
ZPOS64_T ret = 0;
if (nullptr != g_fileReader)
{
ret = g_fileReader->Tell();
}
return (ret);
}
[...]
long ZCALLBACK winRT_seek64_file_func (voidpf opaque, voidpf stream,ZPOS64_T offset,int origin)
{
long long ret = -1;
if (nullptr != g_fileReader)
{
switch (origin)
{
case ZLIB_FILEFUNC_SEEK_CUR :
ret = g_fileReader->SeekFromCurrent(offset);
break;
case ZLIB_FILEFUNC_SEEK_END :
ret = g_fileReader->SeekFromEnd(offset);
break;
case ZLIB_FILEFUNC_SEEK_SET :
ret = g_fileReader->SeekFromBeginning(offset);
break;
default:
ret = -1;
break;
}
}
return (static_cast<long>(ret));
}
int ZCALLBACK winRT_close_file_func (voidpf opaque, voidpf stream)
{
g_fileWriter = nullptr;
g_fileReader = nullptr;
return (0);
}
int ZCALLBACK winRT_error_file_func (voidpf opaque,voidpf stream)
{
return (0);
}
这已经足够让MiniZip运行起来(至少是读取),但你必须注意如何调用MiniZip函数,因为Metro使用的全是异步操作,如果阻塞UI线程,会导致异常,所以必须在任务中包装访问:
FileOpenPicker^ openPicker = ref new FileOpenPicker();
openPicker->ViewMode = PickerViewMode::List;
openPicker->SuggestedStartLocation = PickerLocationId::ComputerFolder;
openPicker->FileTypeFilter->Append(".zip");
task<IVectorView<StorageFile^>^>(openPicker->PickMultipleFilesAsync()).then([this](IVectorView<StorageFile^>^ files)
{
if (files->Size > 0)
{
std::for_each(begin(files), end(files), [this](StorageFile ^file)
{
create_task([this, file]()
{
OpenArchive(file);
[...]
});
});
}
else
{
rootPage->NotifyUserBackgroundThread("No files were returned.", NotifyType::ErrorMessage);
}
});
[...]
bool OpenArchive(StorageFile^ archive)
{
bool isArchiveOpened = false;
if (nullptr != archive)
{
zlib_filefunc64_def ffunc;
fill_winRT_filefunc64(&ffunc);
unzFile archiveObject = NULL;
create_task([this, &ffunc, archive]()
{
archiveObject = unzOpen2_64(reinterpret_cast<const void*>(archive), &ffunc);
}).wait();
if (NULL != archiveObject)
{
[...]