create_task IAsyncOperation error winrt c++ metro

Question

the same code for two functions , but  the TestASync  worked error [error reports:Unhandled exception at 0x5FA42BF8 (msvcr110.dll) in CPPApp_testwinrtcomponent.exe: An invalid parameter was passed to a function that considers invalid parameters fatal.] ,yet

the function [ bool test] worked right.

IAsyncOperation<bool>^  ClassTest::TestASync(Platform::String^ aFpath)
{

 return Concurrency::create_async([aFpath]() ->Boolean 
 {
   Platform::String^ Fpath=aFpath;
       
      create_task(StorageFile::GetFileFromPathAsync(Fpath)).then([](task<StorageFile^> taskgetfile)
   {
     try
     {
      StorageFile^ file=taskgetfile.get();
      if(file==nullptr) return false;
   
      create_task(file->OpenAsync(FileAccessMode::ReadWrite)).then([](IRandomAccessStream^ rastream)
      {
       IOutputStream^ outputStream =rastream->GetOutputStreamAt(0);
       DataWriter^ dwrite = ref new DataWriter(outputStream);
       dwrite->UnicodeEncoding=UnicodeEncoding::Utf8;

       int Fill[4];
       for(int i=0;i<4;i++)
        Fill[i]=rand();
       Array<unsigned char,1>^ inarray =ref new Array<unsigned char,1>(16);
     
       memcpy(inarray->Data,Fill,16);
       dwrite->WriteBytes(inarray);

         create_task(dwrite->StoreAsync()).then([outputStream](task<unsigned int> taskoutstream)
       {
        
        try
        {
           
         outputStream->FlushAsync(); 
           // return ;
        }
        catch(...)
        {
         return ;
        }

       });
      }); 

 

     }
     catch(...)
     {
               return false;
     }

   });
   return true;
   
 });

}

 


bool ClassTest::test(Platform::String^ aFpath)
{


   Platform::String^ Fpath=aFpath;
       
      create_task(StorageFile::GetFileFromPathAsync(Fpath)).then([](task<StorageFile^> taskgetfile)
   {
     try
     {
      StorageFile^ file=taskgetfile.get();
      if(file==nullptr) return false;
   
      create_task(file->OpenAsync(FileAccessMode::ReadWrite)).then([](IRandomAccessStream^ rastream)
      {
       IOutputStream^ outputStream =rastream->GetOutputStreamAt(0);
       DataWriter^ dwrite = ref new DataWriter(outputStream);
       dwrite->UnicodeEncoding=UnicodeEncoding::Utf8;

       int Fill[4];
       for(int i=0;i<4;i++)
        Fill[i]=rand();
       Array<unsigned char,1>^ inarray =ref new Array<unsigned char,1>(16);
     
       memcpy(inarray->Data,Fill,16);
       dwrite->WriteBytes(inarray);

         create_task(dwrite->StoreAsync()).then([outputStream](task<unsigned int> taskoutstream)
       {
        
        try
        {
           
         outputStream->FlushAsync(); 
           // return ;
        }
        catch(...)
        {
         return ;
        }

       });
      }); 

 

     }
     catch(...)
     {
               return false;
     }

   });
   return true;

}

what's wrong ?

Answer 1

The bool Test will retuen true immediately while the task is running. It may not return the correct value in your create_task  lambda. So that works fine.

And how do you call your async method? Did you do create_task to invoke the TestASync?

---

Bob Bao [MSFT]
MSDN Community Support | Feedback to us

Answer 2

你好，

Windows runtime 需要返回Windows runtime的数据类型。

Boolean 是Windows runtime的数据类型， bool是C++的基本类型。

如果你的函数不是private的话，返回值必须是Windows runtime的数据类型。

http://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh700121.aspx

请参考这段代码。

// In .h file
Windows::Foundation::IAsyncOperation<Platform::Boolean>^  TestASync(Platform::String^ aFpath);


// In cpp file
IAsyncOperation<Platform::Boolean>^  MainPage::TestASync(Platform::String^ aFpath)
{

 return Concurrency::create_async([aFpath]() ->Platform::Boolean{
   Platform::String^ Fpath=aFpath;
       return true;});

}

---

Jesse Jiang [MSFT]
MSDN Community Support | Feedback to us

Answer 3

你好， 问题已经解决。 我的 上述异步代码，含多层异步操作， 每层确实需要加入关键字 return ,同时 只有最后一个task 返回 true。

但问题又来了， 这是最理想的 代码。 其中在任何一层加入异常处理， try catch , 或者希望跳出，终止， 编译就不通过。

return taskA.then

{

// try catch.......

// 报错，无法通过

 return taskB.then

{

return taskC.then

{

return true;

}

}

}