在WinForm中声明一个全局整数

Question

I am trying to declare the int

 private int i = 15 - textBox1.Text.Length;

as a global integer for this code

    private void checkBox1_CheckedChanged(object sender, EventArgs e)
    {
        if (checkBox1.Checked == true)
        {
            i = 15 - textBox1.Text.Length;
            timer1.Enabled = true;
            timer1.Start();
        }
        else
        {
            timer1.Enabled = false;
        }
    }
    private int i = 15 - textBox1.Text.Length; //this wont work but i need it to
    private int y = 15 - textBox1.Text.Length; //this wont work either but i also need it to
    private void timer1_Tick(object sender, EventArgs e)
    {

        if (i <= 11)
        {
            i++;
            string ping = new string(' ', i) + textBox1.Text;
            label1.Text = ping;
            if (i == 10)
            {
                y = 11;
            }
        }
        else if (y > 0)
        {
            y--;
            string pong = new string(' ', y) + textBox1.Text;
            label1.Text = pong;
            if (y == 0)
            {
                i = 0;
            }
        }
    }

but i get the error

A field initializer cannot reference the non-static field, method, or property 'text_test.Form1.textBox1'

help?

Answer 1

You're trying to set the initial value of the variable i (which is a bad variable name, by the way -- variable names should be descriptive!).

You'll need to set the value of i at some point in your workflow -- without any context, I'd guess probably in an OnTextChange event or something similar.

Answer 2

private int i;

然后在那之后（在构造函数中）

i = textBox1.Text.Length;

Answer 3

It is important to understand the order in which code runs. You put the field declaration in the middle of your code, perhaps hoping that it would get initialized after the checkBox1_CheckedChanged() method runs. But no, fields are initialized before the constructor of the class runs.

That could never come to a good end. The textBox1 object doesn't exist yet, it gets created by the constructor in the InitializeComponent() method. It will most certainly not have a Length yet, that won't happen until much later when the user types something. The compiler error keeps you out of trouble.

I have no idea what the code tries to do. But assuming the i variable needs to be initialized with something, you do so when the user types something in the text box. Which makes the Text.Length property change. Add an event handler for the textbox' TextChanged event:

    private void textBox1_TextChanged(object sender, EventArgs e) {
        if (textBox1.Text.Length <= 15) {
            i = 15 - textBox1.Text.Length;
        }
    }