WinJS loading local json file

Question

I am banging my head on this one.

I cannot find a way to open a simple json file from a subfolder in my WinJS App.

I have tried Ajax and WinJS.xhr, both to no avail.

I have also looked into opening the file the "old fashioned" way with something like File.Open in .NET, but I couldn't find anything besides WinJS.Application.local.readText, which I tried with both an absolute and a relative path.

I'm at the end of my rope here, does anyone have a working snippet that you can share?

Answer 1

You can refer to files in the app package using URLs in the form:

ms-appx:///data/data.json

(Notice that there are three / characters - if you miss the third one out, you'll have problems)

To read and parse a file that contains a JSON object, you can use the objects in the Windows.Storage namespace. There are three steps - to get a StorageFile object that points to the file, read the contents of the file and then parse the JSON data. Here is the code that I used to do this:

var url = new Windows.Foundation.Uri("ms-appx:///data/data.json");
Windows.Storage.StorageFile.getFileFromApplicationUriAsync(url).then(function (file) {
    Windows.Storage.FileIO.readTextAsync(file).then(function (text) {
        var parsedObject = JSON.parse(text);
        // do something with object
    });
});

There are lots of ways of reading the data from the file, but I find the FileIO object the most convenient. The code above assumes there is one JSON object description in the file. If you have a file that contains one object per line, then you'll need this:

var url = new Windows.Foundation.Uri("ms-appx:///data/data.json");
Windows.Storage.StorageFile.getFileFromApplicationUriAsync(url).then(function (file) {
    Windows.Storage.FileIO.readLinesAsync(file).then(function (lines) {
        lines.forEach(function (line) {
            var parsedObject = JSON.parse(line);
            // do something with object
        });
    });
});

This is a slight variation that uses the FileIO.readLinesAsync method to create an array of strings, each of which is parsed as a JSON object.