Question

我编写Windows Store App，我遇到了以下问题。我使用此代码将数字数组记录到文件中：

auto item = KnownFolders::PicturesLibrary;
task<StorageFile^> getFileTask(item->CreateFileAsync(filename, CreationCollisionOption::ReplaceExisting));
getFileTask.then([=](StorageFile^ storageFile)
{
    return storageFile->OpenAsync(FileAccessMode::ReadWrite);
}).then([](IRandomAccessStream^ m_istream)mutable
{
    unsigned char a[] = { 1, 2, 3 };
    auto arr = ref new Array<unsigned char>(a, sizeof(a));
    auto outs = m_istream->GetOutputStreamAt(0);
    auto dw = ref new DataWriter(outs);
    dw->WriteBytes(arr);
    return dw->StoreAsync();
}).wait();

代码已成功编译，但它提供了一个错误： MyTest.exe已触发断点。它指向_REPORT_PPLTASK_UNOBSERVED_EXCEPTION();行，ppltasks.h。

如果我使用.then([](DataWriterStoreOperation^){})代替.wait()，我的应用程序不会使用此错误进行编译：

error C2338: incorrect parameter type for the callable object in 'then'; 
consider _ExpectedParameterType or task<_ExpectedParameterType> (see below).

为什么？我用的是VS2013。请帮帮我。

Answer 1

我找到了解决这个问题的方法！正确的代码：

unsigned char a[] = { 1, 2, 3 };
auto arr = ref new Array<unsigned char>(a, sizeof(a));
auto m_istream = ref new InMemoryRandomAccessStream();
auto outs = m_istream->GetOutputStreamAt(0);
auto dw = ref new DataWriter(outs);
dw->WriteBytes(arr);
task<unsigned int>(dw->StoreAsync()).then([=](unsigned int)
{
    return item->CreateFileAsync(filename, CreationCollisionOption::ReplaceExisting);
}).then([=](StorageFile^ storageFile)
{
    return storageFile->OpenAsync(FileAccessMode::ReadWrite);
}).then([=](IRandomAccessStream^ new_stream)
{
    return RandomAccessStream::CopyAsync(m_istream->GetInputStreamAt(0), new_stream->GetOutputStreamAt(0));
}).then([=](UINT64 copiedBytes)
{
    return;
});

C＃ - 当我使用task :: wait（）方法时，抛出异常

1 个答案: