Custom data source with WinJS? - windows-8

Question

I am currently implementing a custom data source in a Windows8 application. However, I got some trouble with it: no data is displayed.
First, here is the code:
var dataArray = [
{ title: "Basic banana", text: "Low-fat frozen yogurt", picture: "images/60banana.png" },
// Other data taken from Windows8 ListView quick start
{ title: "Succulent strawberry", text: "Sorbet", picture: "images/60strawberry.png" }
];
var searchAdDataAdapter = WinJS.Class.define(
function () {}, // Constructor
{
itemsFromIndex: function (requestIndex, countBefore, countAfter) {
var that = this;
if (requestIndex >= that._maxCount) {
return WinJS.Promise.wrapError(new WinJS.ErrorFromName(UI.FetchError.doesNotExist));
}
var fetchSize, fetchIndex;
// See which side of the requestIndex is the overlap.
if (countBefore > countAfter) {
// Limit the overlap
countAfter = Math.min(countAfter, 10);
// Bound the request size based on the minimum and maximum sizes.
var fetchBefore = Math.max(
Math.min(countBefore, that._maxPageSize - (countAfter + 1)),
that._minPageSize - (countAfter + 1)
);
fetchSize = fetchBefore + countAfter + 1;
fetchIndex = requestIndex - fetchBefore;
} else {
countBefore = Math.min(countBefore, 10);
var fetchAfter = Math.max(Math.min(countAfter, that._maxPageSize - (countBefore + 1)), that._minPageSize - (countBefore + 1));
fetchSize = countBefore + fetchAfter + 1;
fetchIndex = requestIndex - countBefore;
}
// Create an array of IItem objects:
// results =[{ key: key1, data : { field1: value, field2: value, ... }}, { key: key2, data : {...}}, ...];
for (var i = 0, itemsLength = dataArray.length ; i < itemsLength ; i++) {
var dataItem = dataArray[i];
results.push({
key: (fetchIndex + i).toString(),
data: dataArray[i]
});
}
// Get the count.
count = dataArray.length;
return {
items: results, // The array of items.
offset: requestIndex - fetchIndex, // The index of the requested item in the items array.
totalCount: count
};
},
getCount: function () {
return dataArray.length;
}
}
);
var searchAdDataSource = WinJS.Class.derive(WinJS.UI.VirtualizedDataSource, function () {
this._baseDataSourceConstructor(new searchAdDataAdapter());
});
// Create a namespace to make the data publicly
// accessible.
var publicMembers = {
itemList: new searchAdDataSource()
};
WinJS.Namespace.define("DataExample", publicMembers);
I know the code is a little bit long, but the major part of it is taken from official Microsoft custom data source quick start.
I tried to debug it, but it seems the code contained in itemFromIndex is never used (my breakpoint is never reached).
The HTML code is:
<div id="basicListView" data-win-control="WinJS.UI.ListView"
data-win-options="{itemDataSource : DataExample.itemList.dataSource}">
</div>
I do not use any template for the moment, to simplify the code as more as I can. Data are normally displayed in text this way (but nothing appears).
Have one of this great community any idea?
Furthermore, I do not understand the countBefore and countAfter parameters, even with the documentation. Can somebody explain it to me with other words?
Thanks a lot! :)

Answer 1

Try modifying your HTML code to the following:
<div id="basicListView" data-win-control="WinJS.UI.ListView"
data-win-options="{itemDataSource : DataExample.itemList}">
</div>
No need to call the .datasource member, as you are talking to the datasource directly.