非静态字段错误需要对象引用

Question

I have a long method that ends up returning a DataTable. The method opens like this:

    public DataTable ImportCsvData(string folderPath, string[] csvFileNames, int compIdValue)
    {
        int countDupFiles = 0;// Count number of previously imported csv files
        int countImportedFiles = 0;// Count imported files

        for (int i = 0; i < csvFileNames.Length; i++)
        {
            frmImportCsvData.importProgressBar(i);

This method is inside a class where I am doing all of my SQL requests but is called from another class that controls my Form. The last line of code above calls a method back in my Form class which should update my progress bar. The code for that method is:

public void importProgressBar(int i)
        {
            progressTableLayoutPanel.Visible = true;//display progress bar

            int percProgress = 100 * (i + 1) / csvFileNames.Length;

            while (percProgress < 100)
            {
                if (percProgress <= 99)// Required to prevent values above 100 that crash the code
                    progressBar.Value = percProgress + 1;//hack that makes the progress bar update when progress value decreases
                progressBar.Value = percProgress;
                percProgressLabel.Text = percProgress.ToString();

                progressTableLayoutPanel.Update();//Required to display all progress bar table contents
                //Thread.Sleep(200);
            }
            progressTableLayoutPanel.Visible = false;
        }

This gives me the error: An object reference is required for the non-static field, method, or property 'BetfairDatabaseMDI.frmImportCsvData.importProgressBar(int)'. If I set the importProgressBar method to static I get a bunch of other similar errors. Could anybody advise me how to fix this please?

Answer 1

frmImportCsvData is a class, so a type , which is an abstract thing, not a real object in memory. The error message says you need an instance of a type, so a concrete, existing thing, an object in memory of that given type .

So, essentially, you need to pass the instance of frmImportCsvData into ImportCsvData . For example, like this:

public DataTable ImportCsvData(frmImportCsvData myForm, …)
{
    myForm.importProgressBar(i);
}

Then to call the method from within frmImportCsvData you just pass in this , which denotes the current instance (in run-time sense) of the enclosing class:

dataLayer.ImportCsvData(this, …);

Simplest doesn't mean best or correct in respect to the particular UI framework you are using (being it WinForms, WPF, whatever). BUT: You definitelly have to understand the differences between a type and an instance of a type first , before you run into any more complex constructs. So grab a C# book and get back to the basics, that will help you the most.

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Note: It is a common convention to start identifiers of methods, classes and properties with an upper-case letter.