为什么我的退格返回一个新文本而不是更新当前文本？

Question

I am trying my hand at a self teaching project by creating a calculator. I am having trouble getting my backspace to update the text in my textbox. My goal is to be able to Backspace using my backspace button and add a number afterward and having my result being exactly whats expected with any backspace ie

(1) string of 701 (2) Backspace used (3) Adding 4 to the string (4) return 704

What I am thinking is that when I click the button it is returning a new string and when I enter a new number, it is updating the old string. I have tried this code in the btnBck_Click function as well as what I am showing in my current code(the BackSpaceFunction(); is my attempt to tell the program to return the updated string).

    private void btnBck_Click(object sender, EventArgs e)
    {
        BackSpaceFunction();
    }

    private string BackSpaceFunction()
    {
        string textBoxText = textBox1.Text;
        textBoxText = textBox1.Text.Remove(textBoxText.Length - 1);
        if (textBox1.Text.Length >= 1)
        {
            textBox1.Text = textBox1.Text.Replace(textBox1.Text, textBoxText);
            return textBox1.Text;
        }

        else if (textBox1.Text.Length == 0)
        {
            textBox1.Text = "0";
            input = string.Empty;
            operand1 = string.Empty;
            operand2 = string.Empty;
        }
        return textBox1.Text;
    }

(Please understand my excessive explaining and use of examples is to make sure everyone can understand in case I myself missed the point. Thank you in advance)

Answer 1

I am having trouble getting my backspace to update the text in my textbox

The TextBox control supports use of the backspace key directly. As long as the TextBox has the input focus, pressing the backspace key will delete the character just before the current insertion point.

Your code example is incomplete, but it looks like you have a separate Button object that is intended to provide similar functionality. You aren't taking into account the insertion point for the TextBox , so presumably you just always want to remove the last character. If that's the case, your method is far more complicated than it needs to be. You can just use string.Substring() to remove the last character:

private string BackSpaceFunction()
{
    if (textBox1.Length > 0)
    {
        textBox1.Text = textBox1.Text.Substring(0, textBox1.Text.Length - 1);
    }

    if (textBox1.Text.Length == 0)
    {
        textBox1.Text = "0";
        input = string.Empty;
        operand1 = string.Empty;
        operand2 = string.Empty;
    }

    return textBox1.Text;
}

(You never actually use the return value, so it's not clear why the method has a return value. But I left that in because it's not inherently a problem.)

Answer 2

So to answer my own question, I took the time to try and figure it out for myself. I ended up succeeding and found that this code worked (look at the "if" portion of my if statement).

    private void btnBck_Click(object sender, EventArgs e)
    {

        BackSpaceFunction();

    }

    private string BackSpaceFunction()
    {
        //textBoxText = textBox1.Text.Remove(textBoxText.Length - 1);
        if (textBox1.Text.Length >= 1)
        {
            string textBoxText = textBox1.Text.Remove(textBox1.Text.Length - 1);
            string updatedText = textBox1.Text = textBox1.Text.Replace(textBox1.Text, textBoxText);
            textBox1.Text = updatedText;
            input = string.Format(textBox1.Text, updatedText);
            operand1 = string.Format(textBox1.Text, updatedText);
            operand1 = string.Format(textBox1.Text, updatedText);
        }

        else if (textBox1.Text.Length == 0)
        {
            textBox1.Text = "0";
            input = string.Empty;
            operand1 = string.Empty;
            operand2 = string.Empty;
        }
        return textBox1.Text;

    }'''

I'm not exactly sure why I had to use Format for input , operand1 , and operand2 but it ended up doing exactly what I needed. If there are any explanations as to why this worked I will gladly accept the learning opportunity. :)