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Bug 1254194: Add XPCOMUtils.defineLazyPreferenceGetter. r=billm
MozReview-Commit-ID: JBVelZ0Xg2H --HG-- extra : rebase_source : 3909e75aa6b24ed2a1d2663c11be69c27f4de1e7
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@ -283,6 +283,63 @@ this.XPCOMUtils = {
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});
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},
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/**
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* Defines a getter on a specified object for preference value. The
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* preference is read the first time that the property is accessed,
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* and is thereafter kept up-to-date using a preference observer.
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*
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* @param aObject
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* The object to define the lazy getter on.
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* @param aName
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* The name of the getter property to define on aObject.
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* @param aPreference
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* The name of the preference to read.
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* @param aDefaultValue
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* The default value to use, if the preference is not defined.
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*/
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defineLazyPreferenceGetter: function XPCU_defineLazyPreferenceGetter(
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aObject, aName, aPreference, aDefaultValue = null)
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{
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// Note: We need to keep a reference to this observer alive as long
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// as aObject is alive. This means that all of our getters need to
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// explicitly close over the variable that holds the object, and we
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// cannot define a value in place of a getter after we read the
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// preference.
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let observer = {
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QueryInterface: this.generateQI([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
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value: undefined,
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observe(subject, topic, data) {
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if (data == aPreference) {
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this.value = undefined;
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}
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},
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}
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let defineGetter = get => {
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Object.defineProperty(aObject, aName, {
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configurable: true,
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enumerable: true,
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get,
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});
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};
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function lazyGetter() {
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if (observer.value === undefined) {
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observer.value = Preferences.get(aPreference, aDefaultValue);
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}
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return observer.value;
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}
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defineGetter(() => {
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Services.prefs.addObserver(aPreference, observer, true);
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defineGetter(lazyGetter);
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return lazyGetter();
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});
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},
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/**
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* Convenience access to category manager
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*/
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@ -382,6 +439,11 @@ this.XPCOMUtils = {
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},
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};
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XPCOMUtils.defineLazyModuleGetter(this, "Preferences",
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"resource://gre/modules/Preferences.jsm");
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XPCOMUtils.defineLazyModuleGetter(this, "Services",
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"resource://gre/modules/Services.jsm");
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/**
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* Helper for XPCOMUtils.generateQI to avoid leaks - see bug 381651#c1
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*/
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@ -8,6 +8,7 @@
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* This file tests the methods on XPCOMUtils.jsm.
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*/
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Components.utils.import("resource://gre/modules/Preferences.jsm");
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Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
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const Cc = Components.classes;
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@ -116,6 +117,44 @@ add_test(function test_defineLazyServiceGetter()
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});
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add_test(function test_defineLazyPreferenceGetter()
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{
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const PREF = "xpcomutils.test.pref";
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let obj = {};
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XPCOMUtils.defineLazyPreferenceGetter(obj, "pref", PREF, "defaultValue");
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equal(obj.pref, "defaultValue", "Should return the default value before pref is set");
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Preferences.set(PREF, "currentValue");
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do_print("Create second getter on new object");
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obj = {};
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XPCOMUtils.defineLazyPreferenceGetter(obj, "pref", PREF, "defaultValue");
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equal(obj.pref, "currentValue", "Should return the current value on initial read when pref is already set");
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Preferences.set(PREF, "newValue");
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equal(obj.pref, "newValue", "Should return new value after preference change");
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Preferences.set(PREF, "currentValue");
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equal(obj.pref, "currentValue", "Should return new value after second preference change");
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Preferences.reset(PREF);
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equal(obj.pref, "defaultValue", "Should return default value after pref is reset");
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run_next_test();
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});
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add_test(function test_categoryRegistration()
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{
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const CATEGORY_NAME = "test-cat";
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