c＃如何从其他类更改/访问WinForms控件

Question

So I'm trying to change the text from a WinForms project, from another class than the Form class. It should work like this:

But instead it does this:

The way I used to do it is pass along the object as a parameter to my other class and from that other class I could change the text. I do the same with the progressbar and it does work there, so it's weird that it works with the progressbar but not the label.

I use this method to change the progressbar:

public void IncreaseProgress(int progBarStepSize, String statusMsg, int currentProject=-1) {
   if (currentProject != -1) {
      lblStatus.Text = String.Format("Status: {0} | project {1} of {2}",statusMsg,currentProject,ProjectCount);
   }
   else {
      lblStatus.Text = String.Format("Status: {0}",statusMsg);
   }

   pb.Increment(progBarStepSize);
}

And here is where I use the method:

public void InitialiseFile(List<string> filePaths, int eurojobType)
{
    foreach (string sheet in outputSheets) {
        switch (sheet) {
            case "Summary":
                for (int i = 0; i < filePaths.Count; i++) {
                            var filePath = filePaths[i];
                    IncreaseProgress(1, "Reading Summary", i);
                    worksheetIn = excelReader.ReadExcelSummary(filePath);

                    IncreaseProgress(1, "Writing Summary", i);
                    excelWriter.WriteExcelSummary(worksheetIn);
                }
                break;
            case "Monthly_Cat1":
                for (int i = 0; i < filePaths.Count; i++) {
                    var filePath = filePaths[i];
                    IncreaseProgress(1, "Reading Monthly", i);
                    worksheetIn = excelReader.ReadExcelMonthly(filePath);

                    IncreaseProgress(1, "Writing Monthly", i);
                    excelWriter.WriteExcelMonthly(worksheetIn);
                }
                break;
        }
    }
    IncreaseProgress(1, "Completed!");
}

Now I know this code works because the progressbar increments. And it should jump in the first if-loop because i gets passed as a parameter, which is never -1 .

//manager class
private Label lblStatus;
private ProgressBar pb;

public Manager(ProgressBar pb, Label lbl){
    this.pb = pb;
    lblStatus = lbl;
}

//Form class
Manager mgr = new Manager(progressBar1, lblStatus, projectFilePaths.Count, outputSheets.ToArray(), exportPath);
mgr.InitialiseFile(projectFilePaths, eurjobType);

Answer 1

You can call lblStatus.Refresh(); to force the control to be redrawn, after setting its Text . But consider Slaks comment:

Don't do blocking work on the UI thread

You can consider using BackgroundWorker or Task.Run or async/await pattern instead.

As an example:

private async void button1_Click(object sender, EventArgs e)
{
    await Task.Run(() =>
    {
        for (int i = 0; i < 10000; i++)
        {
            this.Invoke(new Action(() =>
            {
                label1.Text = i.ToString();
                label1.Refresh();
            }));
        }
    });
}

This way the numbers increase, the label refreshes and shows the new value, while the UI is responsive and for example you can move your form or click on other button.

You should put your UI related codes in an action fired by Invoke to prevent receiving cross thread operation exception.