Question

我有一个textbox，只需要接受数字（可以是十进制值）和负值。

目前我在KeyPress事件

中有类似的内容

   if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && e.KeyChar != '.')
    {
        e.Handled = true;                
    }

为了允许负值，我还应该做些什么？

由于

Answer 1

if (!char.IsControl(e.KeyChar) && (!char.IsDigit(e.KeyChar)) 
        && (e.KeyChar != '.')  && (e.KeyChar != '-'))
    e.Handled = true;

// only allow one decimal point
if (e.KeyChar == '.' && (sender as TextBox).Text.IndexOf('.') > -1)
    e.Handled = true;

// only allow minus sign at the beginning
if (e.KeyChar == '-' && (sender as TextBox).Text.Length > 0)
    e.Handled = true;

正如L.B在评论中正确提到的那样，这将不允许使用3E-2这样的高级符号，但对于简单的数字，它可以解决这个问题。

Answer 2

我认为文本框有一个属性，您可以在其中设置插入内容的输入。虽然我目前无法检查这一点。

否则作为替代方案，您可以在提交值时尝试将输入解析为double。类似的东西：

double myDouble;
try
{
    myDouble = double.parse(textbox.Text)
}
catch (Exception e)
{
    MessageBox.Show("Input is incorrect", "Error")
}

它可能不是最好的解决方法，但它可能只是诀窍。

Answer 3

连接Validating事件，如下所示：

private void myTextBox_Validating(object sender, CancelEventArgs event) {
    decimal d;
    if(!decimal.TryParse(myTextBox.Text, out d) {
        event.Cancel = true;
        //this.errorProvider1.SetError(myTextBox, "My Text Box must be a negative number."); //optional
        return;
    }

    if(d >= 0) {
        event.Cancel = true;
        //this.errorProvider1.SetError(myTextBox, "My Text Box must be a negative number."); //optional
        return;
    }
}

Answer 4

@DennisTraub的作品，但有些遗漏的角落情况。例如，如果文本框中的文本是“-11”并且用户将光标放在文本的开头，则他或她可以输入另一个字符，使得文本可以是“1-11”或“.- 11" 。以下是他的回答的扩展，似乎对我有用。

TextBox textBox = sender as TextBox;
// If the text already contains a negative sign, we need to make sure that 
//    the user is not trying to enter a character at the start
// If there is already a negative sign and the negative sign is not selected, the key press is not valid
// This allows the user to highlight some of the text and replace it with a negative sign
if ((textBox.Text.IndexOf('-') > -1) && textBox.SelectionStart == 0 && !textBox.SelectedText.Contains('-'))
{
    e.Handled = true;
}
// Do not accept a character that is not included in the following
if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && e.KeyChar != '.' && e.KeyChar != '-')
{
    e.Handled = true;
}
// Only allow one decimal point
if ((e.KeyChar == '.') && (textBox.Text.IndexOf('.') > -1))
{
    e.Handled = true;
}            
// The negative sign can only be at the start
if ((e.KeyChar == '-'))
{
    // If the cursor is not at the start of the text, the key press is not valid
    if (textBox.SelectionStart > 0)
    {
        e.Handled = true;
    }
    // If there is already a negative sign and the negative sign is not selected, the key press is not valid
    // This allows the user to highlight some of the text and replace it with a negative sign
    if (textBox.Text.IndexOf('-') > -1 && !textBox.SelectedText.Contains('-'))
    {
        e.Handled = true;
    }
}

我打破了一些可以组合成一行的东西。但基本上你还需要检查文本中是否已经有负号，以及用户是否将光标放在文本的开头。

Answer 5

类似的东西：

var regex = new Regex("^[-]?\d+(\.\d+)?$", RegexOptions.Compiled);
Match m = regex.Match(textbox.Text + e.KeyChar);
e.Handled = m.Success;

修改：现在允许任何实数

Answer 6

// Boolean flag used to determine when a character other than a number is entered. 
        private bool nonNumberEntered = false;

        // Handle the KeyDown event to determine the type of character entered into the control. 
        private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
        {
            // Initialize the flag to false.
            nonNumberEntered = false;

            // Determine whether the keystroke is a number from the top of the keyboard. 
            if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
            {
                // Determine whether the keystroke is a number from the keypad. 
                if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
                {
                    // Determine whether the keystroke is a backspace. 
                    if(e.KeyCode != Keys.Back)
                    {
                        // A non-numerical keystroke was pressed. 
                        // Set the flag to true and evaluate in KeyPress event.
                        nonNumberEntered = true;
                    }
                }
            }
            //If shift key was pressed, it's not a number. 
            if (Control.ModifierKeys == Keys.Shift) {
                nonNumberEntered = true;
            }
        }

        // This event occurs after the KeyDown event and can be used to prevent 
        // characters from entering the control. 
        private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
        {
            // Check for the flag being set in the KeyDown event. 
            if (nonNumberEntered == true)
            {
                // Stop the character from being entered into the control since it is non-numerical.
                e.Handled = true;
            }
        }

Answer 7

试试这个正则表达式

"/^(?!0*[.,]0*$|[.,]0*$|0*$)\d+[,.]?\d{0,2}$/"

并使用System.Text.RegularExpressions命名空间

请参阅此处的示例：http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex.aspx

仅允许数字和负值

7 个答案: