WinJS.Binding.List - key value isn't found - windows-8

Question

I've got a WinRT/javaScript app where I use a list. As a test, I've got the following code:
var testList = new WinJS.Binding.List();
var item = {
key: "mykey",
value: "hello",
value2: "world"
};
testList.push(item);
var foundItem = testList.getItemFromKey("mykey");
I would expect to be able to find my item using the key supplied; however foundItem always comes back undefined. Is there something I'm doing wrong in the setup and use of my list?
Also, when I examine my list at debug time, I can see that the key for the item I push is "1" instead of "mykey."

Answer 1

What you are pushing is the value of the object in the list, the key is assigned internally as a incrementing integer value. If you crack open base.js in the Windows Library for JavaScript 1.0 reference in your project, you'll see the following implementation for push.
Note the call to this._assignKey(). This value is returned to you in the oniteminserted handler
push: function (value) {
/// <signature helpKeyword="WinJS.Binding.List.push">
/// <summary locid="WinJS.Binding.List.push">
/// Appends new element(s) to a list, and returns the new length of the list.
/// </summary>
/// <param name="value" type="Object" parameterArray="true" locid="WinJS.Binding.List.push_p:value">The element to insert at the end of the list.</param>
/// <returns type="Number" integer="true" locid="WinJS.Binding.List.push_returnValue">The new length of the list.</returns>
/// </signature>
this._initializeKeys();
var length = arguments.length;
for (var i = 0; i < length; i++) {
var item = arguments[i];
if (this._binding) {
item = WinJS.Binding.as(item);
}
var key = this._assignKey();
this._keys.push(key);
if (this._data) {
this._modifyingData++;
try {
this._data.push(arguments[i])
} finally {
this._modifyingData--;
}
}
this._keyMap[key] = { handle: key, key: key, data: item };
this._notifyItemInserted(key, this._keys.length - 1, item);
}
return this.length;
},
so if you add the following to your code, you'll get the value that you could then use later (assuming you associate it with the 'key' you pushed).
testList.oniteminserted = function (e) {
var newKey = e.detail.key;
};