UWP Read write File -StorageFile

//
private void MainPage_Loaded(object sender, RoutedEventArgs e)
{
GetFileAsync();
}
public async void GetFileAsync()
{

        Uri uri = new Uri("ms-appx:///Resources/t.txt");
        StorageFile file = await StorageFile.GetFileFromApplicationUriAsync(uri);
        string s;
        using (Stream stream = await file.OpenStreamForReadAsync())
        {
            using (StreamReader read = new StreamReader(stream))
            {
                s = read.ReadToEnd();
                new MessageDialog("" + s, "title open file").ShowAsync();

            }
        }

    }

public async void testWriteFile2() {

        string file_name = "test.txt";
        StorageFolder   folder = ApplicationData.Current.LocalFolder;
        StorageFile file= await  folder.CreateFileAsync(file_name, CreationCollisionOption.ReplaceExisting);
        using (Stream stream = await file.OpenStreamForWriteAsync())
        {
            using (StreamWriter write = new StreamWriter(stream ))
            {
                write.Write("??0000000000000");
            }
        }


    }




     public async void WriteFileAsync()
    {
      
        Uri uri = new Uri("ms-appx:///Resources/t.txt");
        StorageFile file = await StorageFile.GetFileFromApplicationUriAsync(uri);//??
        string s;
        using (Stream stream = await file.OpenStreamForWriteAsync())//System.UnauthorizedAccessException: Access is denied.
        {
            using (StreamWriter writer = new StreamWriter(stream))
            {
                writer.Write("ffffffffffff"+DateTime.Now );
                new MessageDialog("write file ok", "title open file").ShowAsync();

            }
        }

    }

•   $exception	{System.UnauthorizedAccessException: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
  

  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
  at System.IO.WindowsRuntimeStorageExtensions.d__3.MoveNext()
  --- End of stack trace from previous location where exception was thrown ---
  at System.IO.WindowsRuntimeStorageExtensions.d__3.MoveNext()
  --- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
  at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
  at App1.MainPage.d__4.MoveNext()} System.UnauthorizedAccessException