Question

Writing a Windows 8 app in Javascript using Visual Studio Express. I’m not sure if I am missing a chaining dependency or something else, but I am giving my game users the ability to save their progress into a file (at least that’s the idea). However when I run the following code it appears that even though I can see the file out there, the file pointer is turning out to be undefined. See anything I’m missing?

var myStats = new Array();
myStats[0] = myTitle;
myStats[1] = currPage;
myStats[2] = currStep;
myStats[3] = currTune;
myStats[4] = musicon;
myStats[5] = gameComplete;

var save01File = null;

            Windows.Storage.KnownFolders.documentsLibrary.createFileAsync("Asave01.dat", Windows.Storage.CreationCollisionOption.replaceExisting).done(

                function (file) {
                    save01File = file;
                },
                function (error) {
                    WinJS.log && WinJS.log(error, "sample", "error");
                });
            Windows.Storage.FileIO.writeLinesAsync(save01File, myStats).done(
                function () {
                },
            function (error) {
                WinJS.log && WinJS.log(error, "sample", "error");
                errCount++;
            });
            if (errCount == 0) {
                fileMenuTitle.text = "File Saved - Click Cancel";
                fileMenuTitle.text = fileMenuTitle.text + "\nto Return or Select Another File to Load";
                fileMenuTitle.color = "green";
            }
            else {
                fileMenuTitle.text = "There was an error saving that file.";
                fileMenuTitle.text = fileMenuTitle.text + "\nPlease Make Another Selection.";
                fileMenuTitle.color = "firebrick";
            }

Answer 1

You need to use the promise pattern here:

var myStats = new Array();
myStats[0] = myTitle;
myStats[1] = currPage;
myStats[2] = currStep;
myStats[3] = currTune;
myStats[4] = musicon;
myStats[5] = gameComplete;

var save01File = null;

Windows.Storage.KnownFolders.documentsLibrary.createFileAsync("Asave01.dat", Windows.Storage.CreationCollisionOption.replaceExisting).then(function (file) {
    save01File = file;
    return Windows.Storage.FileIO.writeLinesAsync(file, myStats);
}).done(function() {
    fileMenuTitle.text = "File Saved - Click Cancel";
    fileMenuTitle.text = fileMenuTitle.text + "\nto Return or Select Another File to Load";
    fileMenuTitle.color = "green";
}, function (error) {
    WinJS.log && WinJS.log(error, "sample", "error");
    fileMenuTitle.text = "There was an error saving that file.";
    fileMenuTitle.text = fileMenuTitle.text + "\nPlease Make Another Selection.";
    fileMenuTitle.color = "firebrick";
});