Question

我是C＃的新手，我遇到了TextBox验证成绩字母（A，B，C，D，F）的问题。现在，下面的代码将执行if语句而不是else语句，因为如果我输入一个与其条件完全匹配的成绩字母，即使在单击“确定”按钮后设置了较低的套接字，然后是上部套接字。当我输入正确的成绩字母时，它应该跳过if并继续执行else语句，但是我没有看到错误。

    private void Button_Click(object sender, RoutedEventArgs e)
    {

        //automatically convert gradeLetter inputs to uppercase
        gradeLetter.Text = gradeLetter.Text.ToUpper();

        //check if gradeLetter entered is valid
        if (!string.IsNullOrWhiteSpace(gradeLetter.Text) || gradeLetter.Text != "A" || gradeLetter.Text != "B" || gradeLetter.Text != "C" || gradeLetter.Text != "D" || gradeLetter.Text != "F")
        {
            MessageBox.Show("Invalid grade letter or has an empty textbox!", "Caution!", MessageBoxButton.OK);
        }
        else
        {
            // switch statement to determine which 'gradeLetter' is being used 
            // and assign numerical numbers to 'gpa' to then be calculated.
            switch (gradeLetter.Text)
            {
                case "A": gradeW = 4.0;
                    break;
                case "B": gradeW = 3.0;
                    break;
                case "C": gradeW = 2.0;
                    break;
                case "D": gradeW = 1.0;
                    break;
                case "F": gradeW = 0.0;
                    break;
                default: // do nothing
                    break;
            }

            double result = (GPA += gradeW); //add to the gpa
            gCounter++; // increment the gpa entered
            result /= gCounter; // divide by the number of gpa entered
            result = Math.Round(result, 2, MidpointRounding.AwayFromZero); //round the result to two decimal places

            gpa.Text = result.ToString(); //convert result from int to string and display in 'gpa' TextBlock

            //append the input grade letters to 'gradeEntered' TextBlock
            gradeEntered.Text += gradeLetter.Text + System.Environment.NewLine;
       }
    }

Answer 1

您可以使用包含有效成绩字母的列表，而不是使用许多条件（这使得它更难以阅读）：

string gradeLetter = "A";

List<string> gradeLetters = new List<string> { "A", "B", "C", "D", "F" };

if (!gradeLetters.Contains(gradeLetter))
{
    // invalid grade letter
}

else
{
    // carry on
}

您的代码：

if (!string.IsNullOrWhiteSpace(gradeLetter.Text) || gradeLetter.Text != "A" || gradeLetter.Text != "B" || gradeLetter.Text != "C" || gradeLetter.Text != "D" || gradeLetter.Text != "F")

永远都是真的。假设等级为B.它将对gradeLetter.Text != "A"进行检查，短路，并且为真，因为“B”！=“A”。

Answer 2

当前if语句的问题是有效输入仍然会变为无效。如果输入是“B”，它将看到它不是“A”（在你的if语句中），这意味着整个标准都是真的。

将您的if语句更改为：

if (string.IsNullOrWhiteSpace(gradeLetter.Text) || !(gradeLetter.Text == "A" || gradeLetter.Text == "B" || gradeLetter.Text == "C" || gradeLetter.Text == "D" || gradeLetter.Text == "F"))

基本上问“你的输入是空的还是输入不是A，B，C，D或F？

Answer 3

您也可以使用词典方法：

gradeLetter.Text = gradeLetter.Text.ToUpper();
IDictionary<string, double> grades = new Dictionary<string, double>
{
    {"A", 4.0},
    {"B", 3.0},
    {"C", 2.0},
    {"D", 1.0},
    {"F", 0.0}
};

if (!grades.ContainsKey(gradeLetter.Text)){
    MessageBox.Show("Invalid grade letter or has an empty textbox!", "Caution!", MessageBoxButton.OK);
}
else{
    gradeW = grades[gradeLetter.Text];
    // other stuff
}

如何在C＃中正确验证TextBox？

3 个答案: