Added a callback to listen the pref change by UI, added a function to nsIDBFolderInfo to check if default charset is used, bug 50054, r=bienvenu.

mailnews/base/util/nsMsgDBFolder.cpp

@@ -463,7 +463,10 @@ nsresult nsMsgDBFolder::ReadDBFolderInfo(PRBool force)
 				//folderInfo->GetImapTotalPendingMessages(&mNumPendingTotalMessages);
 				//folderInfo->GetImapUnreadPendingMessages(&mNumPendingUnreadMessages);
 
-				folderInfo->GetCharacterSet(&mCharset);
+				PRBool defaultUsed;
+				folderInfo->GetCharacterSet2(&mCharset, &defaultUsed);
+				if (defaultUsed)
+					mCharset.AssignWithConversion("");
         
 				if (db) {
 					PRBool hasnew;

mailnews/db/msgdb/public/nsIDBFolderInfo.idl

@@ -63,6 +63,7 @@ interface  nsIDBFolderInfo : nsISupports {
 	void	InitFromTransferInfo(in nsIDBFolderInfo transferInfo);
 
 	[noscript] void GetCharacterSet(in nsString result);
+	[noscript] void GetCharacterSet2(in nsString result, out boolean usedDefault);
 	[noscript] void SetCharacterSet(in nsString result);
 
 			   void GetCharPtrCharacterSet(out string result);

mailnews/db/msgdb/src/nsDBFolderInfo.cpp

@@ -51,8 +51,26 @@ static const char * kVersionColumnName = "version";
 static const char * kCharacterSetColumnName = "charSet";
 static const char * kLocaleColumnName = "locale";
 
+static const char * MAILNEWS_VIEW_DEFAULT_CHARSET = "mailnews.view_default_charset";
 static nsString gDefaultCharacterSet;	// default charset
 
+static int PR_CALLBACK defaultCharacterSetChanged(const char *prefName, void *closure)
+{
+	nsresult rv;
+	nsCOMPtr<nsIPref> prefs = do_GetService(NS_PREF_PROGID, &rv);
+	if (NS_SUCCEEDED(rv))
+	{
+		PRUnichar *prefCharset = nsnull;
+		rv = prefs->GetLocalizedUnicharPref(prefName, &prefCharset);
+		if (NS_SUCCEEDED(rv))
+		{
+			gDefaultCharacterSet.Assign(prefCharset);
+			PR_Free(prefCharset);
+		}
+	}
+	return 0;  
+} 
+
 NS_IMPL_ADDREF(nsDBFolderInfo)
 NS_IMPL_RELEASE(nsDBFolderInfo)
 
@@ -106,14 +124,15 @@ nsDBFolderInfo::nsDBFolderInfo(nsMsgDatabase *mdb)
 	m_mdbTokensInitialized = FALSE;
 
 	// Initialize a default charset to a pref default.
-	if (gDefaultCharacterSet.IsEmpty())
+	nsresult rv;
+	nsCOMPtr<nsIPref> prefs = do_GetService(NS_PREF_PROGID, &rv);
+	if (NS_SUCCEEDED(rv))
 	{
-		nsresult rv;
-		nsCOMPtr<nsIPref> prefs = do_GetService(NS_PREF_PROGID, &rv);
-		if (NS_SUCCEEDED(rv))
+		rv = prefs->RegisterCallback(MAILNEWS_VIEW_DEFAULT_CHARSET, defaultCharacterSetChanged, NULL);
+		if (gDefaultCharacterSet.IsEmpty())
 		{
 			PRUnichar *prefCharset = nsnull;
-			rv = prefs->GetLocalizedUnicharPref("mailnews.view_default_charset", &prefCharset);
+			rv = prefs->GetLocalizedUnicharPref(MAILNEWS_VIEW_DEFAULT_CHARSET, &prefCharset);
 			if (NS_SUCCEEDED(rv))
 			{
 				gDefaultCharacterSet.Assign(prefCharset);
@@ -144,6 +163,11 @@ nsDBFolderInfo::nsDBFolderInfo(nsMsgDatabase *mdb)
 
 nsDBFolderInfo::~nsDBFolderInfo()
 {
+	nsresult rv;
+	nsCOMPtr<nsIPref> prefs = do_GetService(NS_PREF_PROGID, &rv);
+	if (NS_SUCCEEDED(rv))
+		rv = prefs->UnregisterCallback(MAILNEWS_VIEW_DEFAULT_CHARSET, defaultCharacterSetChanged, NULL);
+
 	if (m_mdb)
 	{
 		if (m_mdbTable)
@@ -580,6 +604,22 @@ nsDBFolderInfo::GetCharacterSet(nsString *result)
 	return rv;
 }
 
+NS_IMETHODIMP
+nsDBFolderInfo::GetCharacterSet2(nsString *result, PRBool *usedDefault) 
+{
+	nsresult rv = GetProperty(kCharacterSetColumnName, result);
+	
+	*usedDefault = FALSE;
+
+	if (NS_SUCCEEDED(rv) && result->IsEmpty())
+	{
+		result->Assign(gDefaultCharacterSet.GetUnicode());
+		*usedDefault = TRUE;
+	}
+
+	return rv;
+}
+
 NS_IMETHODIMP
 nsDBFolderInfo::GetCharPtrCharacterSet(char **result)
 {