nsIPrefBranch

このオブジェクトは自身が指し示す"branch"の起点となるpreference木の"root"値を伴って生成されます。各preferencesにはこのrootに続く最後の部分のみを使ってアクセスすることができます。 例えばオブジェクトが"browser.startup."をrootとして生成された場合、"browser.startup.page"、"browser.startup.homepage"、"browser.startup.homepage_override"などに対してGet/Setを行う際には"page"、"homepage"、"homepage_override"と指定することができます。

Method overview

Attributes

Constants

Methods

preference change observerを追加します。preferenceに変化があると以下の引数がnsIObserver.observe()に渡されます：

aSubject - nsIPrefBranch オブジェクト (this)。

aTopic - NS_PREFBRANCH_PREFCHANGE_TOPIC_ID で定義される文字列。

aData - 変更があったpreferenceの名前（aSubjectの"root"に対する相対値）

aSubject.get*Pref(aData) で変更後の新しい値を得ることができます。例えば observer がaddObserver("bar.", ...)で"foo."を起点とするbranchに対して登録を行った場合、"foo.bar.baz"に対する変更がそのobserverを起こします。その時のaDataは"bar.baz"になります。

void addObserver(
  in string aDomain, 
  in nsIObserver aObserver, 
  in boolean aHoldWeak
);

Parameters

aDomain

変更を監視したい preference 。完全なbranchを指定することもできます。 例えば "root" prefbranch から addObserver("foo.bar.", ...) を呼ぶと foo.bar.baz と foo.bar.bzipを監視できます。

aObserver

preference の変更通知を受け取るオブジェクト。

aHoldWeak

true を指定すると aObserver の weak reference を保持します。この場合オブジェクトは nsISupportsWeakReference インターフェースを実装する必要があり、実装されていない場合は失敗します。false を指定すると strong reference を保持します。

clearUserPref()

Called to clear a user set value from a specific preference. This will, in effect, reset the value to the default value. If no default value exists the preference will cease to exist.

void clearUserPref(
  in string aPrefName
);

Parameters

aPrefName

The preference to be cleared.

Remarks

deleteBranch()

Called to remove all of the preferences referenced by this branch.

void deleteBranch(
  in string aStartingAt
);

Parameters

aStartingAt

The point on the branch at which to start the deleting preferences. Pass in "" to remove all preferences referenced by this branch.

getBoolPref()

Called to get the state of an individual boolean preference.

boolean getBoolPref(
  in string aPrefName
);

Parameters

aPrefName

The boolean preference to get the state of.

Return value

The value of the requested boolean preference.

getCharPref()

Called to get the state of an individual string preference.

string getCharPref(
  in string aPrefName
);

Parameters

aPrefName

The string preference to retrieve.

Return value

Returns string - The value of the requested string preference.

getChildList()

Returns an array of strings representing the child preferences of the root of this branch.

(To call from javascript use children = nsIPrefBranch.getChildList("",obj), which will fill in obj.value with the count and return an array of keys! (It is not void in javascript)

void getChildList(
  in string aStartingAt,
  out unsigned long aCount,
  [array, size_is(aCount), retval] out string aChildArray
);

Parameters

aStartingAt

The point on the branch at which to start enumerating the child preferences. Pass in "" to enumerate all preferences referenced by this branch.

aCount Optional from Gecko 2.0

Receives the number of elements in the array.

aChildArray

Receives the array of child preferences.

getComplexValue()

Called to get the state of an individual complex preference. A complex preference is a preference which represents an XPCOM object that can not be easily represented using a standard boolean, integer or string value.

void getComplexValue(
  in string aPrefName,
  in nsIIDRef aType,
  [iid_is(aType), retval] out nsQIResult aValue
);

Parameters

aPrefName

The complex preference to get the value of.

aType

The XPCOM interface that this complex preference represents. Interfaces currently supported are:

• NsILocalFile
• NsISupportsString (UniChar)
• NsIPrefLocalizedString (Localized UniChar)
• NsIFileSpec (deprecated - to be removed eventually)

aValue

The XPCOM object into which to the complex preference value should be retrieved.

getIntPref()

Called to get the state of an individual integer preference.

long getIntPref(
  in string aPrefName
);

Parameters

aPrefName

The integer preference to get the value of.

Return value

Returns long - The value of the requested integer preference.

getPrefType()

Called to determine the type of a specific preference.

long getPrefType(
  in string aPrefName
);

Parameters

aPrefName

The preference to get the type of.

Return value

Returns long - A value representing the type of the preference. This value will be PREF_STRING, PREF_INT, PREF_BOOL, or PREF_INVALID.

lockPref()

Called to lock a specific preference. Locking a preference will cause the preference service to always return the default value regardless of whether there is a user set value or not.

void lockPref(
  in string aPrefName
);

Parameters

aPrefName

The preference to be locked.

prefHasUserValue()

Called to check if a specific preference has a user value associated to it.

boolean prefHasUserValue(
  in string aPrefName
);

Parameters

aPrefName

The preference to be tested.

Return value

Returns boolean - true The preference has a user set value. false The preference only has a default value.

prefIsLocked()

Called to check if a specific preference is locked. If a preference is locked calling its Get method will always return the default value.

boolean prefIsLocked(
  in string aPrefName
);

Parameters

aPrefName

The preference to be tested.

Return value

Returns boolean - true The preference is locked. false The preference is not locked.

Remove a preference change observer.

  void removeObserver(
     in string aDomain, 
     in nsIObserver aObserver
  );

Parameters

aDomain

The preference which is being observed for changes.

aObserver

An observer previously registered with addObserver.

resetBranch()

Called to reset all of the preferences referenced by this branch to their default values.

void resetBranch(
  in string aStartingAt
);

Parameters

aStartingAt

The point on the branch at which to start the resetting preferences to their default values. Pass in "" to reset all preferences referenced by this branch.

setBoolPref()

Called to set the state of an individual boolean preference.

void setBoolPref(
  in string aPrefName,
  in long aValue
);

Parameters

aPrefName

The boolean preference to set the state of.

aValue

The boolean value to set the preference to.

setCharPref()

Called to set the state of an individual string preference.

void setCharPref(
  in string aPrefName,
  in string aValue
);

Parameters

aPrefName

The string preference to set.

aValue

The string value to set the preference to.

setComplexValue()

Called to set the state of an individual complex preference. A complex preference is a preference which represents an XPCOM object that can not be easily represented using a standard boolean, integer or string value.

void setComplexValue(
  in string aPrefName,
  in nsIIDRef aType,
  in nsISupports aValue
);

Parameters

aPrefName

The complex preference to set the value of.

aType

The XPCOM interface that this complex preference represents. Interfaces currently supported are:

• NsILocalFile
• NsISupportsString (UniChar)
• NsIPrefLocalizedString (Localized UniChar)
• NsIFileSpec (deprecated - to be removed eventually)

aValue

The XPCOM object from which to set the complex preference value.

setIntPref()

Called to set the state of an individual integer preference.

void setIntPref(
  in string aPrefName,
  in long aValue
);

Parameters

aPrefName

The integer preference to set the value of.

aValue

The integer value to set the preference to.

unlockPref()

Called to unlock a specific preference. Unlocking a previously locked preference allows the preference service to once again return the user set value of the preference.

void unlockPref(
  in string aPrefName
);

Parameters

aPrefName

The preference to be unlocked.

Remarks

Registering as a preference observer can open an object to potential cyclical references which will cause memory leaks. These cycles generally occur because an object both registers itself as an observer (causing the branch to hold a reference to the observer) and holds a reference to the branch object for the purpose of getting/setting preference values. There are 3 approaches which have been implemented in an attempt to avoid these situations:

1. The nsPrefBranch object supports nsISupportsWeakReference. Any consumer may hold a weak reference to it instead of a strong one.
2. The nsPrefBranch object listens for xpcom-shutdown and frees all of the objects currently in its observer list. This ensures that long lived objects (services for example) will be freed correctly.
3. The observer can request to be held as a weak reference when it is registered. This insures that shorter lived objects (say one tied to an open window) will not fall into the cyclical reference trap.

The list of registered observers may be changed during the dispatch of nsPref:changed notification. However, the observers are not guaranteed to be notified in any particular order, so you can't be sure whether the added/removed observer will be called during the notification when it is added/removed. 

It is possible to change preferences during the notification.

It is not safe to change observers during this callback in releases before Gecko 1.9. If you want a safe way to remove a preference observer, please use an nsITimer.