DataWriter: flushing a stream requires a then call?

Question

Hello guys. I'm using the following code to create a new text file in a temp subfolder:

function createFolderAndFile() {
    //create new folder inside temp folder
    var tempFolder =
      Windows.Storage.ApplicationData.current.temporaryFolder;
    tempFolder.createFolderAsync("testFolder",
      Windows.Storage.CreationCollisionOption.openIfExists)
        .then(function (folder) {
            return folder.createFileAsync("testFile.txt")
        })
        .then( function (file) {
            return file.openAsync(
                        Windows.Storage.FileAccessMode.readWrite);
        })
        .then( function (dataStream) {
            var stream = dataStream.getOutputStreamAt(0);
            var writer = new Windows.Storage.Streams.DataWriter(stream);
            writer.writeString("Howdy, there!");
            return writer.storeAsync()
                .then(function () {
                stream.flushAsync()
                            .then(function () {},function () {});
                });
        });
}

If I remove the .then(function () {},function () {}); instruction from the code, the contents won't get written to the file. Is this a bug? I was under the impression that .then was only required if I needed to be notified when the flush operation has fnished. Comments?

thanks.

---

Luis Abreu

Answer 1

Are you by chance doing this in a background task?

---

Jeff Sanders (MSFT)

Answer 2

Nop. It's run when the click event of a button is fired:

WinJS.Utilities.ready(initializeSample, true);
  function initializeSample() {
      document.getElementById("ct").addEventListener("click", createFolderAndFile);
      document.getElementById("ct2").addEventListener("click", readFile);
  }

---

Luis Abreu

Answer 3

Hi Luis,

 

The stream is being left open because of the scoping of the stream variable.

You can solve this by propagating the return of the promise back:

return stream.flushAsync();

-Jeff

---

Jeff Sanders (MSFT)