Question

I have a synchronism logic makes sendOrder from db in android to server by web service which runs on doInBackgroud().

first I start app.
then click SyncClick and It Sync database without error.
after that I go into application add someorder to orderTable
return to main screen(which has SyncClick) and I click SyncClick again.
It sends order (which means sendOrder() function works well)
after that reset database and get latest data on doInBackgroud().
but It getting this error;

07-11 23:38:15.406: E/AndroidRuntime(7864): java.lang.RuntimeException: An error occured while executing doInBackground()

07-11 23:38:15.406: E/AndroidRuntime(7864): Caused by: java.lang.NullPointerException

after I start app and click SyncClick works well again. so It doesn’t work after I add some order then Sync but works well without any order added.

looking for problem.
thanks for your time in advance.

public void SyncClick(View v) 
    {
        Loading = (ImageView)findViewById(R.id.imgLoadingAnim);
        LoadingLayout = (LinearLayout)findViewById(R.id.loLoadingAnim);
        LoadingLayout.setVisibility(VISIBLE);
        Loading.setBackgroundResource(R.drawable.loading);
        frameAnimation= (AnimationDrawable)Loading.getBackground();
        frameAnimation.setCallback(Loading);
        frameAnimation.setVisible(true, true);
        frameAnimation.start();

        if(!this.dhn.isTableExists("Orders"))
        {
            updateDB();
        }

        sendOrder();    
    }


    public void sendOrder()
    {
        ArrayList<Object[]> argumentsList = new ArrayList<Object[]>();
        Object[] stuff = {this.dhn, this};
        //SEND
        ArrayList<Order> orders = this.dhn.GetOrders();

        for(int i = 0 ; i < orders.size(); i++)
        {
            ArrayList<OrderItem> orderItems = this.dhn.GetOrderItems(orders.get(i).ID);

            String orderItemsS = "";

            for(int r = 0 ; r < orderItems.size(); r++)
            {
                orderItemsS = orderItemsS + orderItems.get(r).FinalCode + "|" + orderItems.get(r).Quantity + "|" +
                orderItems.get(r).Price + "|" + orderItems.get(r).Discount + "|" + orderItems.get(r).Status + "|" + "#";
            }

            orderItemsS = orderItemsS.substring(0, orderItemsS.length() - 1);

            Object[] arguments = { 
                    new String("OrderAdd"), 
                    stuff,

                    new String("UserId"),
                    new Integer (orders.get(i).UserId),
                    new String("int"),

                    new String("CustomerId"),
                    new Integer (orders.get(i).CustomerId),
                    new String("int"),

                    new String("Price"),
                    new Double (orders.get(i).Price),
                    new String("double"),

                    new String("Discount"),
                    new Double (orders.get(i).Discount),
                    new String("double"),

                    new String("Status"),
                    new Integer (orders.get(i).Status),
                    new String("int"),

                    new String("orderItems"),
                    new String (orderItemsS),
                    new String("String")
                    };

            argumentsList.add(arguments);
        }

        Object[] stuffALL = {this.dhn, this, argumentsList};


        Object[] argumentsALL = { 
                new String("recieveALL"), 
                stuffALL
                };

        //ConnectXML runXMLALL = new ConnectXML();
        new ConnectXML().execute(argumentsALL);


        Status = 1;

        updateDB();

        receive();
    }

    public void receive()
    {
        Object[] stuff = {this.dhn, this};
        ArrayList<Object[]> argumentsList1 = new ArrayList<Object[]>();

        //receive
        Object[] arguments = { 
                new String("ProductListGet"), 
                stuff,
                new String("CatID"),
                new Integer (-1),
                new String("int")
                };
        argumentsList1.add(arguments);
        Object[] arguments1 = { 
                new String("CustomerListGet"), 
                stuff
                };
        argumentsList1.add(arguments1);
        Object[] arguments2 = { 
                new String("CategoryListGet"), 
                stuff,
                new String("ParentID"),
                new Integer (-2),
                new String("int")
                };
        argumentsList1.add(arguments2);
        Object[] arguments3 = { 
                new String("UserListGet"), 
                stuff
                };
        argumentsList1.add(arguments3);
        Object[] arguments5 = { 
                new String("ProductCategoriesListGet"), 
                stuff
                };
        argumentsList1.add(arguments5);
        Object[] arguments6 = { 
                new String("ProductOptionListGet"), 
                stuff
                };
        argumentsList1.add(arguments6);
        Object[] arguments7 = { 
                new String("FinalProductListGet"), 
                stuff
                };
        argumentsList1.add(arguments7);
        Object[] arguments8 = { 
                new String("ProductDiscountsListGet"), 
                stuff
                };
        argumentsList1.add(arguments8);
        Object[] arguments9 = { 
                new String("ProductPriceGroupListGet"), 
                stuff
                };
        argumentsList1.add(arguments9);
        Object[] arguments10 = { 
                new String("OptionListGet"), 
                stuff
                };
        argumentsList1.add(arguments10);


        Object[] stuffALL1 = {this.dhn, this, argumentsList1};


        Object[] argumentsALL1 = { 
                new String("recieveALL"), 
                stuffALL1
                };

        //ConnectXML runXMLALL1 = new ConnectXML();
        new ConnectXML().execute(argumentsALL1);
    }

    int Stat;
    int Status;
    public void LoadAnim()
    {   
        if(Status == 1)
        {
            Stat++;
            if(Stat > 0)
            {
                LoadingLayout.setVisibility(GONE);
                if(frameAnimation !=null && frameAnimation.isRunning())
                { 
                    frameAnimation.stop();
                    Stat = 0;
                    Status = 0;
                }
            }
        }
    }

    public void updateDB()
    {
        this.dhn.close();

        try {
            InputStream myInput;

                myInput = getAssets().open("sistem.db");

            // Path to the just created empty db
            String outFileName = "/data/data/sistem.ss/databases/"
                    + "sistem.db";

            // Open the empty db as the output stream
            OutputStream myOutput = new FileOutputStream(outFileName);

            // transfer bytes from the inputfile to the outputfile
            byte[] buffer = new byte[1024];
            int length;
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }

            // Close the streams
            myOutput.flush();
            myOutput.close();
            myInput.close();
            buffer = null;
            outFileName = null;
            this.dhn.close();
            this.dhn = null;
            this.dhn = DataHelper.getDataHelper(this);
        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
    }

LogCat

07-12 07:31:59.879: E/AndroidRuntime(2873): FATAL EXCEPTION: AsyncTask #1
07-12 07:31:59.879: E/AndroidRuntime(2873): java.lang.RuntimeException: An error occured while executing doInBackground()
07-12 07:31:59.879: E/AndroidRuntime(2873):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at java.lang.Thread.run(Thread.java:1096)
07-12 07:31:59.879: E/AndroidRuntime(2873): Caused by: java.lang.NullPointerException
07-12 07:31:59.879: E/AndroidRuntime(2873):     at sistem.ss.ConnectXML.doInBackground(ConnectXML.java:79)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at sistem.ss.ConnectXML.doInBackground(ConnectXML.java:1)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
07-12 07:31:59.879: E/AndroidRuntime(2873):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
07-12 07:31:59.879: E/AndroidRuntime(2873):     ... 4 more

Answer 1

I haven’t yet had a chance to work with AsyncTask, but the documentation says:

The task can be executed only once (an exception will be thrown if a second execution is attempted.)

That means you just need to create a new instance and execute on that one. E.g.

new WhateverYourTaskIsCalled().execute(...);

Rather than calling execute() on the instance you’ve already used.