Question

I have created one application in flex that is accessing the Java webservice using Actionscript3.0. In which I am getting the error during the accessing the one of the webservice method.That method is returning the list of child object I am taking this List of object in ArrayCollection class object.My code is:-

    [Bindable]
     private var photoFeed:Array; 
    public var user:SBTSWebService;

    public function initApp():void
    {
       user = new SBTSWebService();

       user.addSBTSWebServiceFaultEventListener(handleFaults);

    }

    public function displayString():void
    {
           // Instantiate a new Entry object.
           var newEntry:GetSBTSMobileAuthentication = new GetSBTSMobileAuthentication();
            newEntry.mobile=mobileno.text;
            newEntry.password=password.text;
            user.addgetSBTSMobileAuthenticationEventListener(authenticationResult);

            user.getSBTSMobileAuthentication(newEntry);

    }

    public function handleFaults(event:FaultEvent):void
    {
        Alert.show("A fault occured contacting the server. Fault message is: " + event.fault.faultString);
    }

    public function authenticationResult(event:GetSBTSMobileAuthenticationResultEvent):void
    {
        if(event.result != null) 
        {

           if(event.result._return > 0)
           {
             var UserId:int = event.result._return;
              getChildList(UserId);       
              viewstack2.selectedIndex=1;
           }
           else
           {
             Alert.show("Authentication fail");
           }


        }

    }
  public function getChildList(userId:int):void
  {
     var childEntry:GetSBTSMobileChildrenInfo = new GetSBTSMobileChildrenInfo();
     childEntry.UserId = userId;
     user.addgetSBTSMobileChildrenInfoEventListener(sbtsChildrenInfoResult);
     user.getSBTSMobileChildrenInfo(childEntry);
  }
   public function sbtsChildrenInfoResult(event:GetSBTSMobileChildrenInfoResultEvent):void
    {
        if(event.result != null && event.result._return!=null) 
        {

        photoFeed  = event.result._return as Array;
        childid.dataProvider = photoFeed; 

        }

    }


]]>

<mx:Move id="hideEffect"
    xTo="-500" />
<mx:Move id="showEffect"
    xFrom="500" />

<mx:Panel width="500" height="300"
    headerColors="[#000000,#FFFFFF]">

    <mx:TabNavigator id="viewstack2"
        selectedIndex="0"
        historyManagementEnabled="false"
        width="100%" height="100%">

        <mx:Form label="Login Form"
            hideEffect="{hideEffect}" showEffect="{showEffect}">
              <mx:FormItem>
                 <mx:TextInput id="mobileno"/>
              </mx:FormItem>
              <mx:FormItem>
                 <mx:TextInput id="password"/>
              </mx:FormItem>
              <mx:FormItem>
                 <mx:Button label="Login" click="displayString()"/>
              </mx:FormItem>
         </mx:Form>

        <mx:Form label="Child List"
            hideEffect="{hideEffect}" showEffect="{showEffect}">
           <mx:DataGrid id="childid" visible="false"/>



            <mx:Button label="click here to see location"
                click="viewstack2.selectedIndex=2" />
        </mx:Form>

        <mx:Form label="Bus Location"
            hideEffect="{hideEffect}" showEffect="{showEffect}">
            <mx:Text text="" />
        </mx:Form>
       <mx:Form label="Trace Path"
            hideEffect="{hideEffect}" showEffect="{showEffect}">
            <mx:Text text="" />
        </mx:Form>
    </mx:TabNavigator>

</mx:Panel>

I am getting the error like “TypeError: Error #1009: Cannot access a property or method of a null object reference”.when the line “photoFeed = event.result._return as Array;” is compile.
Please help me to remove this error.

Answer 1

It seems strange that you are getting the error on that line as you have already made the check that both result and result._return are not null. It is more likely that the line…

childid.dataProvider = photoFeed; 

…is causing the error because childid is null? This would probably be because you tab navigator has not created the second tab yet. Try adding creationPolicy=”all” to the tab navigator to make sure it has been created.

<mx:TabNavigator id="viewstack2"
        selectedIndex="0"
        creationPolicy="all"
        historyManagementEnabled="false"
        width="100%" height="100%">

By default it is set to ‘auto’ which means it will only create panels other than the default when you click on them.