diff --git a/webapp/services/NftService.php b/webapp/services/NftService.php
index 1396bfbd..ae588126 100644
--- a/webapp/services/NftService.php
+++ b/webapp/services/NftService.php
@@ -18,71 +18,71 @@ class NftService extends BaseService {
     public static function isHeroOwner($tokenId)
     {
         self::mustBeHeros();
-        $nftDB = getXVal(self::heroHash, $tokenId);
+        $nftDB = getXVal(self::$heroHash, $tokenId);
         return $nftDb && $nftDB['owner_address'] == myself()->_getOpenId();
     }
 
     public static function isEquipOwner($tokenId)
     {
         self::mustBeEquips();
-        $nftDb = getXVal(self::equipHash, $tokenId);
+        $nftDb = getXVal(self::$equipHash, $tokenId);
         return $nftDb && $nftDB['owner_address'] == myself()->_getOpenId();
     }
 
     public static function isChipOwner($tokenId)
     {
         self::mustBeChips();
-        $nftDb = getXVal(self::chipHash, $tokenId);
+        $nftDb = getXVal(self::$chipHash, $tokenId);
         return $nftDb && $nftDB['owner_address'] == myself()->_getOpenId();
     }
 
     public static function getHeros()
     {
         self::mustBeHeros();
-        return self::heroList;
+        return self::$heroList;
     }
 
     public static function getEquips()
     {
         self::mustBeEquips();
-        return self::equipList;
+        return self::$equipList;
     }
 
     public static function getChips()
     {
         self::mustBeChips();
-        return self::chipList;
+        return self::$chipList;
     }
 
     private static function mustBeHeros()
     {
-        if (is_null(self::heroList)) {
-            self::heroList = Nft::GetNftListByType(myself()->_getOpenId(), Nft::HERO_TYPE);
-            self::heroHash = array();
-            foreach (self::heroList as $nftDb) {
-                self::heroHash[$nftDb['token_id']] = $nftDb;
-            }
+        if (is_null(self::$heroList)) {
+            self::$heroList = Nft::GetNftListByType(myself()->_getOpenId(), Nft::HERO_TYPE);
+            self::$heroHash = array();
+            foreach (self::$heroList as $nftDb) {
+                self::$heroHash[$nftDb['token_id']] = $nftDb;
+                }
         }
     }
 
     private static function mustBeEquips()
     {
-        if (is_null(self::equipList)) {
-            self::equipList = Nft::GetNftListByType(myself()->_getOpenId(), Nft::EQUIP_TYPE);
-            self::equipHash = array();
-            foreach (self::equipList as $nftDb) {
-                self::equipHash[$nftDb['token_id']] = $nftDb;
+        if (is_null(self::$equipList)) {
+            self::$equipList = Nft::GetNftListByType(myself()->_getOpenId(), Nft::EQUIP_TYPE);
+            self::$equipHash = array();
+            foreach (self::$equipList as $nftDb) {
+                self::$equipHash[$nftDb['token_id']] = $nftDb;
             }
         }
     }
 
     private static function mustBeChips()
     {
-        if (is_null(self::chipList)) {
-            self::chipList = Nft::GetNftListByType(myself()->_getOpenId(), Nft::CHIP_TYPE);
-            self::chipHash = array();
-            foreach (self::chipList as $nftDb) {
-                self::chipHash[$nftDb['token_id']] = $nftDb;
+        if (is_null(self::$chipList)) {
+            self::$chipList = Nft::GetNftListByType(myself()->_getOpenId(), Nft::CHIP_TYPE);
+            self::$chipHash = array();
+            foreach (self::$chipList as $nftDb) {
+                self::$chipHash[$nftDb['token_id']] = $nftDb;
             }
         }
     }