Proper way to update label with progress from a different thread-CodePudding

I have a windows form program. In the main form I have a label where I update with progress. I use the following code to perform my operations:

Thread workThread = new Thread(delegate ()
{
    for (int i = 1; i < bytes.Length; i  )
    {
        SliderOverBytesAndDoProcessing();
    }
});

workThread.Start();

The function SliderOverBytesAndDoProcessing() performs operations where I read 4 bytes and perform some operations on more bytes. I do this for each 4 bytes of the 200MB file (read 4 bytes process something and continue moving). Everything works fine until I decide to report my progress. Here is how I do the update:

Thread workThread = new Thread(delegate ()
{
    for (int i = 1; i < bytes.Length; i  )
    {
        Lbl.Invoke((Action)delegate { Lbl.Text = "Processing "   (ii / 1048576)   "/"   (bytes.Length / 1048576); }
        SliderOverBytesAndDoProcessing();
    }
});

workThread.Start();

If I add that one line the program becomes too slow. I mean the program runs in around a few minutes without that line but with that line it takes around 1.5 hours. Also, on some other operations if I do that, I end up in infinite loops. How do I report my progress from the other thread to form thread without facing this problem.

Thanks.

CodePudding user response：

It is slow because you’re dispatching to the UI thread on every byte, even though the progress message only seems to care about megabytes. So you change the label over a million times to the same value.

Consider

var totalMb = bytes.Length / 1024 / 1024;
var lastMb = -1;

for (int i = 1; i < bytes.Length; i  ) {
  var currentMb = i / 1024 / 1924;
  if (currentMb > lastMb) {
    Lbl.Invoke(() => { Lbl.Text = $"Processing {currentMb}/{totalMb} MiB" });
    lastMb = currentMb;
  }
  SliderOverBytesAndDoProcessing();
}