UWP，C++/Cx FileOpenPicker

Question

有人知道我做错什么了吗。

    // STORAGE FILE
    StorageFile^ saveFile;

    // FILE PICKER, FOR SELECTING A SAVE FILE
    FileOpenPicker^ filePicker = ref new FileOpenPicker;

    // ARRAY OF FILE TYPES
    Array<String^>^ fileTypes = ref new Array<String^>(1);
    fileTypes->Data[0] = ".txt";

    filePicker->ViewMode = PickerViewMode::Thumbnail;
    filePicker->SuggestedStartLocation = PickerLocationId::Desktop;
    filePicker->FileTypeFilter->ReplaceAll(fileTypes);

    // THIS SHOULD HOPEFULLY LET US PICK A FILE

    saveFile = filePicker->PickSingleFileAsync();

具体而言，最后一行：

saveFile = filePicker->PickSingleFileAsync();

我得到以下错误。

错误C2440：'='：无法从'Windows::Foundation::IAsyncOperation ^‘转换为'Windows::Storage::StorageFile ^’

Answer 1

错误C2440：'='：无法从'Windows::Foundation::IAsyncOperation ^‘转换为'Windows::Storage::StorageFile ^’

PickSingleFileAsync是异步方法，返回类型是Windows::Foundation::IAsyncOperation，不能转换为StorageFile类型。正如Hans所说，您可以使用create_task()等待这个异步操作。

create_task(folderPicker->PickSingleFolderAsync()).then([this](StorageFolder^ folder)
{
    if (folder)
    {
        //do some stuff
    }
    else
    {
        //do some stuff
    }
});

有关更多信息，请参考Asynchronous programming in C++。