Save value EditorGUILayout.Popup in custom edtior with javascirpt

Hi, I'm just 18 years old who is noob in unity. I tried to make custom editor about fps and finally I almost finished. But unfortunately my popup list doesn't work well which saves the keycode of the weapon. So I want you to teach me how to make it work. Here is my code about the weapon keys editor. Other value saved well like damage or range with slider but only popup list work don't well.

 @CustomEditor(WeaponDefine)
 
 class WeaponDefineEditor extends Editor {
 
         private var Keys : String[] = new String[10];
 
         @SerializeField
         private var selectedIndex : int;
         function OnInspectorGUI() {
 
         for(var i = 0; i < 10; i++)
             Keys[i] = "Alpha " + i.ToString();
         selectedIndex = EditorGUILayout.Popup("Weapon Key ", selectedIndex, Keys);
 
         if(GUILayout.Button("Save Key Setting"))
                 KeySetting();
     
         function KeySetting() {
             switch(selectedIndex) {
                 case 0 : target.WeaponKey = KeyCode.Alpha0;
                          break;
                 case 1 : target.WeaponKey = KeyCode.Alpha1;
                          break;
                 case 2 : target.WeaponKey = KeyCode.Alpha2;
                          break;
                 case 3 : target.WeaponKey = KeyCode.Alpha3;
                          break;
                 case 4 : target.WeaponKey = KeyCode.Alpha4;
                          break;
                 case 5 : target.WeaponKey = KeyCode.Alpha5;
                          break;
                 case 6 : target.WeaponKey = KeyCode.Alpha6;
                          break;
                 case 7 : target.WeaponKey = KeyCode.Alpha7;
                          break;
                 case 8 : target.WeaponKey = KeyCode.Alpha8;
                          break;
                 case 9 : target.WeaponKey = KeyCode.Alpha9;
                          break;
             }
         }
       }
    }

I also serialize the value "target.WeaponKey" in the code. Like this.

 @SerializeField
 var WeaponKey : KeyCode;

How can I solve this problem?