MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

var localSettings = Windows.Storage.ApplicationData.current.localSettings;
var settingName = "exampleSetting";
var settingValue = "Hello World";
function settingsWriteSetting() {
localSettings.values[settingName] = settingValue;
}
function settingsDeleteSetting() {
localSettings.values.remove(settingName);
}
Many settings, like that shown above, are just simple key-value pairs, but other settings will be
objects with multiple properties. This presents a particular challenge: although you can certainly write
and read the individual properties of that object within the values array, what happens if a failure
occurs with one of them? That would cause your state to become corrupt.
To guard against this, the app data APIs provide for composite settings, which are groups of
individual properties that are guaranteed to be managed as a single unit. (Again, each composite has a
64K limit.) It’s like the perfect group consciousness: either we all succeed or we all fail, with nothing in
between! That is, if there’s an error reading or writing any part of the composite, the whole composite
fails; with roaming, either the whole composite roams or none of it roams.
A composite object is created using Windows.Storage.ApplicationDataCompositeValue, as shown
in Scenario 4 of the Application data sample (js/compositeSettings.js):
var roamingSettings = Windows.Storage.ApplicationData.current.roamingSettings;
var settingName = "exampleCompositeSetting";
var settingName1 = "one";
var settingName2 = "hello";
function compositeSettingsWriteCompositeSetting() {
var composite = new Windows.Storage.ApplicationDataCompositeValue();
composite[settingName1] = 1; // example value
composite[settingName2] = "world"; // example value
roamingSettings.values[settingName] = composite;
}
function compositeSettingsDeleteCompositeSetting() {
roamingSettings.values.remove(settingName);
}
function compositeSettingsDisplayOutput() {
var composite = roamingSettings.values[settingName];
// ...
}
The ApplicationDataCompositeValue object has, as you can see in the documentation, some
additional methods and events to help you manage it such as clear, insert, and mapchanged.
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