MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

URI scheme, a subject that we’ll be covering later in Chapter 12, “Contracts.” An example of handling
state, in addition to the updates we’ll make to Here My Am! in the next section, can be found in
Scenario 3 of the App model sample.
Basic Session State in Here My Am!
To demonstrate some basic handling of session state, I’ve made a few changes to Here My Am! as given
in the HereMyAm3c example. Here we have two pieces of information we care about: the variables
lastCapture (a StorageFile with the image) and lastPosition (a set of coordinates). We want to make
sure we save these when we get suspended so that we can properly apply those values when the app
gets launched with the previous state of terminated.
With lastPosition, we can just move this into the sessionState object (prepending app.-
sessionState.) as in the completed handler for getGeopositionAsync:
gl.getGeopositionAsync().done(function (position) {
app.sessionState.lastPosition = {
latitude: position.coordinate.latitude,
longitude: position.coordinate.longitude
};
}
updatePosition();
}, function (error) {
console.log("Unable to get location.");
});
Because we’ll need to set the map location from here and from previously saved coordinates, I’ve
moved that bit of code into a separate function that also makes sure a location exists in sessionState:
function updatePosition() {
if (!app.sessionState.lastPosition) {
return;
}
}
callFrameScript(document.frames["map"], "pinLocation",
[app.sessionState.lastPosition.latitude, app.sessionState.lastPosition.longitude]);
Note also that app.sessionState is initialized to an empty object by default, { }, so lastPosition will
be undefined until the geolocation call succeeds. This also works to our advantage when rehydrating
the app. Here’s what the previousExecutionState conditions look like for this:
if (args.detail.previousExecutionState !==
activation.ApplicationExecutionState.terminated) {
//Normal startup: initialize lastPosition through geolocation API
} else {
//WinJS reloads the sessionState object here. So try to pin the map with the saved location
updatePosition();
}
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