C ++ CX Windows RT create_task使用return vs C＃Confusion [英] C++ CX Windows RT create_task working with returns vs C# Confusion

问题描述

首先道歉，如果这不是正确的论坛，其次，如果我完全忽略了这一点。

如何在不使用静态变量的情况下实现C ++ CX中下面的C＃代码示例这样简单的事情当然如果
太可怕了？

C＃

 var folder = awaitWindows.ApplicationModel.Package.Current.InstalledLocation.GetFolderAsync（" Assets"）; 
 var file = await folder.GetFileAsync（" customTile.xml"）; 
 string szCustomTileXML = await Windows.Storage.FileIO.ReadTextAsync（file）; 
 HttpClient c = new HttpClient（）; 
 await var s = c-> GetStringAsync（new Uri（" www.bing.com"））; 
 Border tile = XamlReader.Load（szCustomTileXML）as Border; 
 //获取http数据，拆分并使用'tile'设置一些TextBlocks 

C ++ CX 

 static String ^ markup = ref new String（）; 
 
返回create_task（Package :: Current-> InstalledLocation-> GetFolderAsync（" Assets"））
 .then（[inputMarkupFilename]（StorageFolder ^ assetsFolder） - > IAsyncOperation< StorageFile ^> ^ 
 {
 return assetsFolder-> GetFileAsync（inputMarkupFilename）; 
} 
）.then（[]（StorageFile ^ markupStorageFile） - > IAsyncOperation< Platform :: String ^> ^ 
 {
返回FileIO :: ReadTextAsync（markupStorageFile）; 
} 
 //）.then（[this，outputImageFilename，size]（平台： ：String ^ markupContent）
）.then（[this，outputImageFilename，size]（Platform :: String ^ markupContent） - > Windows :: Foundation :: IAsyncOperationWithProgress< Platform :: String ^，Windows :: Web： ：Http :: HttpProgress> ^ 
 {
 markup = markupContent; 
 
 HttpClient ^ hc = ref new HttpClient（）; 
 
 return hc-> ; GetStringAsync（ref new Uri（" www.bing.com"））; 
} 
）.t hen（[this，outputImageFilename，size]（Platform :: String ^ httpContent）
 {
 Border ^ border =（Border ^）XamlReader :: Load（markup）; 
 
 //获取http数据，拆分并使用'tile'设置一些TextBlocks 
 //返回... 
 
}）; 

解决方案

您需要通过引用捕获变量

http://en.cppreference.com/w/cpp/language/lambda

例如

 String ^ value = nullptr; 
 
 create_task（MyAsyncMethod（））。then（[& value]（T ^ asyncResult）
 {
 value =" this is the information" ;; 
 }）; 

Firstly apologies if this isn't the right forum and secondly if I am totally missing the point.

How do I achieve something as simple as the C# code sample below in C++ CX without using a static variable which of course if horrible?

C#

var folder = awaitWindows.ApplicationModel.Package.Current.InstalledLocation.GetFolderAsync("Assets");
var file = await folder.GetFileAsync("customTile.xml");
string szCustomTileXML = await Windows.Storage.FileIO.ReadTextAsync(file);
HttpClient c = new HttpClient();
await var s = c->GetStringAsync(new Uri("www.bing.com"));
Border tile = XamlReader.Load(szCustomTileXML) as Border;
// Take http data, split it and using 'tile' set some TextBlocks

C++ CX 

static String^ markup = ref new String();

    return create_task(Package::Current->InstalledLocation->GetFolderAsync("Assets"))
    .then([inputMarkupFilename](StorageFolder^ assetsFolder) ->IAsyncOperation<StorageFile^>^ 
    {
        return assetsFolder->GetFileAsync(inputMarkupFilename);
    }
    ).then([](StorageFile^ markupStorageFile)  ->IAsyncOperation<Platform::String^>^ 
    {
        return FileIO::ReadTextAsync(markupStorageFile);
    }
    //).then([this, outputImageFilename, size](Platform::String^ markupContent)
    ).then([this, outputImageFilename, size](Platform::String^ markupContent) -> Windows::Foundation::IAsyncOperationWithProgress<Platform::String^, Windows::Web::Http::HttpProgress>^
    {
        markup = markupContent;

        HttpClient ^hc = ref new HttpClient();

        return hc->GetStringAsync(ref new Uri("www.bing.com"));
    }
    ).then([this, outputImageFilename, size](Platform::String^ httpContent) 
    {
        Border^ border = (Border^)XamlReader::Load(markup);

// Take http data, split it and using 'tile' set some TextBlocks
// return ...

});

解决方案

you need to capture a variable by reference

http://en.cppreference.com/w/cpp/language/lambda

And for example

String^ value=nullptr;

create_task(MyAsyncMethod()).then([&value](T^ asyncResult)
{
   value="this is the information";
});

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