WPF multitasking along with a timer and background worker

Few days ago I started using tasks in my WPF application for parallelization purposes. My application needs to perform some work every 5 seconds. This work has to be parallelized by 4 tasks. And in addition to that the background worker needs to be implemented in order to avoid freezing of UI while doing the work by tasks. I found lots of examples to understand how tasks work. However, I couldn't find any simple examples to understand how tasks work along with timers, background worker and locks of course. I wrote some simple example to show you how I understood. Please, give me advises whether I do it correctly. By this way I will have better understanding in multitasking in WPF. I'm looking forward to your replies.

namespace timer_and_thread{/// <summary>/// Interaction logic for MainWindow.xaml/// </summary>publicpartialclassMainWindow:Window{DispatcherTimerTimerObject;Task[] tasks;readonlyobject _countLock =newobject();int[]Summ=newint[10];intIndex=0;publicMainWindow(){InitializeComponent();TimerObject=newDispatcherTimer();TimerObject.Tick+=newEventHandler(timer_Elapsed);TimerObject.Interval=newTimeSpan(0,0,5);}// call the method every 5 secondsprivatevoid timer_Elapsed(object sender,EventArgs e){TimerObject.Stop();BackgroundWorker backgroundWorkerObject =newBackgroundWorker();
                backgroundWorkerObject.DoWork+=newDoWorkEventHandler(StartThreads);
                backgroundWorkerObject.RunWorkerAsync();TimerObject.Start();}privatevoidStartThreads(object sender,DoWorkEventArgs e){
                tasks =newTask[4];
                tasks[0]=Task.Factory.StartNew(()=>DoSomeLongWork());
                tasks[1]=Task.Factory.StartNew(()=>DoSomeLongWork());
                tasks[2]=Task.Factory.StartNew(()=>DoSomeLongWork());
                tasks[3]=Task.Factory.StartNew(()=>DoSomeLongWork());// Give the tasks a second to start.Thread.Sleep(1000);}privatevoidDoSomeLongWork(){while(Index<Summ.Length){int localIndex =0;// lock the global variable from accessing by multiple threads at a timelock(_countLock){
                        localIndex =Index;Index++;}//I wrote rundom number generation just a an example of doing some calculation and getting some result. It can also be some long calculation. Random rnd =newRandom();int someResult = rnd.Next(1,100000);// lock the global variable (Summ) to give it the result of calculation lock(_countLock){Summ[localIndex]= someResult;}}}// button by which I start the application workingprivatevoidStart_Button_Click_1(object sender,RoutedEventArgs e){TimerObject.Start();}}}