Visual Studio Windows 窗体 C# Interop.Excel - Excel 类对象

Question

I have created a C# Windows Form project in Visual Studio and I am trying to work with an Excel workbook via interop.excel . I have created a custom "excel class" and created an object of it in my Form1 .
What I am struggling with is whether it is possible to open an excel workbook via a button press, ie create the class object from a button press, and then be able to use that object in other button presses.

Two versions of code are shown below. One works，one does not. The one that works just opens the Excel workbook when the program is launched. The other attempts to use a button press on the form to open the workbook after the program is launched. In the code that does not work, the object does not exist in the current context .
Any help on how to make the button press code work is most appreciated!

This code works:

namespace XLtest1
{
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    ExcelClass ex  = new ExcelClass(@"C:\path\TestBook.xlsx", 1);

    private void ReadCell_Click(object sender, EventArgs e)
    {
        ex.ReadCell();
    }

...

This code does not:

namespace XLtest1
{
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    public void OpenFile()
    {
        ExcelClass ex  = new ExcelClass(@"C:\path\TestBook.xlsx", 1);
    }

    private void OpenWorkbook_Click(object sender, EventArgs e)
    {
      OpenFile();
    }

    private void ReadCell_Click(object sender, EventArgs e)
    {
        ex.ReadCell(); // "ex" does not exist in the current context 
    }

...

Answer 1

I think you are asking to be able to reuse the code on another button press? If so would it be an option for you to create a function with the code needed and just call that function inside each button press?

Answer 2

You are using a local variable inside ReadCell which has no knowledge of ex.

You could create a variable

public partial class Form1 : Form
{
public Form1()
{
    InitializeComponent();
}
private ExcelClass ex = null; //create your member field here

public void OpenFile()
{
    ex = new ExcelClass(@"C:\path\TestBook.xlsx", 1);
}

private void OpenWorkbook_Click(object sender, EventArgs e)
{
  OpenFile();
}

private void ReadCell_Click(object sender, EventArgs e)
{
    if (ex!= null) {
        ex.ReadCell();
    } else {
        //do nothing, or inform user they have to press other button to open the file
    }
}