Threading.Timer with WinForm

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I'm polling a database every 1/2 second via Threading.Timer and displaying the results in a Windows Form listview control. The query results return about 150 rows that I initial 'ADD' to listview. Once the listview is populated I no longer 'ADD' items I iterate through each row of the listview and access the TEXT property to change the contents of each row. I do this so I won't have to clear the listview on each query causing the listview to paint and lose it's current scroll position...

The winForm is a little unresponsive. I thought if I moved the updating of the control off of the main thread that the form would say responsive and this would improve the performance.

Can someone please clarify what's going on here and what do I need to do to make the form more responsive and improve the efficiency of updating the listview with new result but without repainting the listview and losing it's current scroll position.

Thanks in advance,
-Dee

Posted 1-Dec-11 13:24pm

d.allen101

Updated 29-Apr-19 13:23pm

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BillWoodruff 1-Dec-11 20:31pm

This may be a dumb question, but it sounds like you are not using DataBinding where any change in the underlying DataBase, ideally, is propagated to the changed segment presentation control, ideally: very quickly.

Why ?

2 solutions

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Sergey Alexandrovich Kryukov · Answer 1 · 2011-12-01T13:39:00

Solution 1

What's wrong about my solution Polling Database with Timer[^]?

If you run polling in a separate thread, UI update will go via UI thread invocation. Even it you "updating of the control off of the main thread" (I read it as "UI thread"), the actual update will happen in UI thread due to invocation. You simply cannot call anything related to UI from non-UI thread. Instead, you need to use the method Invoke or BeginInvoke of System.Windows.Threading.Dispatcher (for both Forms or WPF) or System.Windows.Forms.Control (Forms only).

You will find detailed explanation of how it works and code samples in my past answers:
Control.Invoke() vs. Control.BeginInvoke()[^],
Problem with Treeview Scanner And MD5[^].

See also more references on threading:
How to get a keydown event to operate on a different thread in vb.net[^],
Control events not firing after enable disable + multithreading[^].

—SA

Posted 1-Dec-11 13:39pm

Sergey Alexandrovich Kryukov

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d.allen101 2-Dec-11 14:52pm

I'm struggling! what am I doing wrong! my listview control isnt updating and my form is freezing. here's what my code looks like:

MyDataObject myDatObj = new MyDataObject;
Thread thrd = new Thread(new ParameterizedThreadStart(ListviewMethod));
thrd.Start(myDatObj);
EventWaitHandle ewh = new AutoResetEvent(false);
delegate void ListviewDel(object dataObj);
Timer tmr = new Timer();
tmr.Interval = 500;
tmr.Tick += new EventHandler(OnListview_Tick);
tmr.Start();

void OnListviewTick(object sender, EventArgs e)
{
ewh.Set();
}

void ListviewMethod(object obj)
{
while(true)
{
ewh.WaitOne();

if(listview1.InvokeRequired)
{
listview1.Invoke((ListveiwDel)ListviewMethod, myDatObj);
continue;
}

double a = myDatObj.Number1;
double b = myDataObj.Number2;
double c = myDataObj.Number3;

listview1.Add(a);
listview1.Add(b);
listview2.Add(c);
}
}

Sergey Alexandrovich Kryukov 2-Dec-11 23:59pm

You don't need ParameterizedThreadStart -- you don't use obj. ParameterizedThreadStart is bad thing. Instead, did I tell you to use thread wrapper. ListView method is non-static (instance) method, it already passed "this". Try using manual reset event. (Auto might work, too, but I did it with manual.) I don't know what else...

Oh, I see!!! Problem found!!!
In ListviewMethod, you invoke the same very method. How could you do it??!!! This method waits AGAIN. No, don't do it. Create two separate method: a separate one for UI update, and ListviewMethod should only wait and then Invoke UI update method.

I cannot stand it: such a common flaw. Why you try to "save" (something :-) on methods? Makes no sense.
--SA

d.allen101 4-Dec-11 1:49am

SA, I'm confused! can you I've ready your solution several times and read your articles on threading: i'm trying to implement what you suggested but I can't seem to get it right. can you point to an example that implements this please?

d.allen101 4-Dec-11 2:07am

is this correct? :

delegate void LstVwDel();

MyDataObj myDatObj = new MyDataObj();
LstVwDel lstVwDel = new LstVwDel(updateLv);
Thread thrd = new Thread(updateThread);
thrd.Start();
EventWaitHandle ewh = AutoResetEvent(false);
Timer tmr = new Timer();
tmr.Interval = 500;
tmr.Tick += new EventHandler(threadThrottle_Tick);
tmr.Start();

void threadThrottle_Tick(object sender, EventArgs e)
{
ewh.Set();
}

void updateThread()
{
while(true)
{
ewh.WaitOne();
Invoke(lstVwDel);
}
}

void updateLv()
{
if(listview1.Items.Count < 1)
{
listview1.BeginUpdate();

for(i = 0; i < myDatObj.Numbers.Count; i++)
{
double a = myDatObj.Number1[i];
double b = myDatObj.Number2[i];
double c = myDatObj.Number3[i]

listview1.Items.Add(a);
listview1.Items.SubItems.Add(b);
listview1.Items.SubItems.Add(c);
}
listview1.EndUpdate();
}
else
{
listview1.BeginUpdate();

for(int i = 0; i < myDatObj.Numbers.Count; i++)
{
double a = myDatObj.Number1[i];
double b = myDatObj.Number2[i];
double c = myDatObj.Number3[i];

listview1.Items[i].Text = a;
listview1.Items[i].SubItems[1].Text = b;
listview1.Items[i].SubItems[2].Text = c;
}
listview1.EndUpdate();
}
}

d.allen101 4-Dec-11 2:32am

that 'seems' to work but my form is VERY slugglish! and there is a lot of latency in my listview displaying the results...

saberw · Answer 2 · 2019-04-29T13:24:00

Solution 2

Try setting the double buffered property in true.

Also you could use:

this.SuspendLayout();
this.listview.SuspendLayout();

//update control  
//put listview manipulation code hrer to not cause refresh form

this.listview.ResumeLayout(false);
this.ResumeLayout(false);

Posted 29-Apr-19 13:24pm

saberw

Comments

Dave Kreskowiak 29-Apr-19 22:03pm

You do understand that the question you posted this to is over seven years old?

saberw 1-May-19 1:57am

Did you know that each question has a more correct answer without considering time.
Dear learners can use it.

Dave Kreskowiak 1-May-19 8:22am

Yes I know. What I also see is more information and discussion in Solution 1 than in your answer, which is just a small subset of what was discussed.