Question

从2个具有相同测量单词的不同列表框中进行选择时，我尝试从3个选项中选择1个。

用户在文本框中输入一个数字，然后在FromList列表框中选择3个单位中的一个（单位为英寸，英尺和码），然后在“列表”列表框中选择3个单位中的一个（单位为还有英寸，英尺和码。）

当点击计算按钮时，它会将测量英寸转换为英寸（不做数学，只是吐出他们输入到标签的内容）或英寸到英尺或英寸到码，如果FromList选择了英寸，并显示输出到标签。它也可以做到英尺，英尺到英尺（没有数学），脚到码。最后，它会做到英寸，码距离，码距离（不做数学）。

两个列表框都将SelectionMode设置为One，因此用户只能从每个列表框中选择1个项目。我可以将第一个列表框设置为具有SelectedItem的值，但是它突出显示的代码中的9个错误是如果我尝试设置它，如果选择了第二个列表框中的项目。这是我到目前为止所尝试的内容：

    public frmConverter()
    {
        InitializeComponent();
    }
    private void btnExit_Click(object sender, EventArgs e)
    {
        this.Close();
    }

    private void btnClear_Click(object sender, EventArgs e)
    {
        txtEntered.Text = "";
        lblOutput.Text = "";
    }

    private void btnCalc_Click(object sender, EventArgs e)
    {
        string Fromlist;
        string ToList;
        double Entered, Output;

        Entered = Convert.ToDouble(txtEntered.Text);

        if (FromList == "Inches" && ToList == "Inches")
        {
            lblOutput.Text = txtEntered.Text + " Inches";
        }
        else if (FromList == "Inches" && ToList =="Feet")
        {
            Output = Entered / 12;
            lblOutput.Text = Output.ToString("N2") + (" Feet");
        }
        else if (FromList == "Inches" && ToList == "Yards")
        {
            Output = Entered / 36;
            lblOutput.Text = Output.ToString("N2") + (" Yards");
        }
        else if (FromList == "Feet" && ToList == "Inches")
        {
            Output = Entered * 12;
            lblOutput.Text = Output.ToString("N2") + (" Inches");
        }
        else if (FromList == "Feet" && ToList == "Feet")
        {
            lblOutput.Text = txtEntered.Text + " Feet";
        }
        else if (FromList == "Feet" && ToList == "Yards")
        {
            Output = Entered / 3;
            lblOutput.Text = Output.ToString("N2") + (" Yards");
        }
        else if (FromList == "Yards" && ToList == "Inches")
        {
            Output = Entered * 36;
            lblOutput.Text = Output.ToString("N2") + (" Inches");
        }
        else if (FromList == "Yards" && ToList == "Feet")
        {
            Output = Entered * 12;
            lblOutput.Text = Output.ToString("N2") + (" Feet");
        }
        else if (FromList == "Yards" && ToList == "Yards")
        {
            lblOutput.Text = txtEntered + " Yards";
        }
    }
}

Answer 1

您的一个问题是您在if语句中使用赋值运算符=而不是相等运算符==。

if (FromList.SelectedItem.ToString() == "Inches" && ToList.SelectedItem.ToString() == "Inches")
{
    lblOutput.Text = txtEntered.Text + " Inches";
}

Entered永远不会给出值。

您可能想要考虑的事情是使用枚举来简化代码并删除所有if语句：

    enum Conversions
    {
        Inches = 1,
        Feet = 12,
        Yards = 36,
    }
    double DoConversion(string from, string to, double quantity)
    {
        Conversions convertFrom = Conversions.Inches;
        Conversions convertTo = Conversions.Inches;
        if (Enum.TryParse<Conversions>(from, out convertFrom) && Enum.TryParse<Conversions>(to, out convertTo))
        {
            return quantity * ((double)convertFrom / (double)convertTo);
        }
        else 
        {
            return 0;
        }

    }

此函数将From / To单位作为字符串，将double作为数量并进行转换。它不是用于乘法或除法的不同算法，而是乘以2个转换值的除法

Answer 2

问题是您已将FromList和ToList作为字符串，并且您正尝试从FromList / ToList中选择SelectedItem属性，但是在FromList / ToList中不存在这样的属性，因为您已将它们作为代码中的字符串。可能是您需要使用在设计中定义的Listcontrol而不是在代码中使用字符串对象。

private void btnCalc_Click(object sender, EventArgs e)
    {
        string Fromlist; // this is string so will not work for you
        string ToList;  // this is string so will not work for you
        string Inches;
        string Feet;
        string Yards;
        double Entered, Output;
//as FromList and ToList are string defined above below logic will not work as there is no property like SelectedItem in string.
 if (FromList.SelectedItem = "Inches" && ToList.SelectedItem = "Inches")
        {
}

Answer 3

好的，所以我使用switch和parse重新编码它，它现在按预期工作。感谢大家的帮助！以下是工作代码：

    public Form1()
    {
        InitializeComponent();
    }
    private void btnClear_Click(object sender, EventArgs e)
    {
        txtEntered.Text = "";
        lblOutput.Text = "";
    }
    private void btnExit_Click(object sender, EventArgs e)
    {
        this.Close();
    }
    private void btnCalc_Click(object sender, EventArgs e)
    {

        string From;
        string To;
        double Entered, Output;

        Entered = double.Parse(txtEntered.Text);

        if (FromList.SelectedIndex != -1)
        {
            From = FromList.SelectedItem.ToString();
            To = ToList.SelectedItem.ToString();
            switch (From)
            {
                case "Inches":
                    switch (To)
                    {
                        case "Inches":
                            Output = Entered;
                            lblOutput.Text = Output.ToString("N2") + " Inches";
                            break;
                        case "Feet":
                            Output = Entered / 12;
                            lblOutput.Text = Output.ToString("N2") + " Feet";
                            break;
                        case "Yards":
                            Output = Entered / 36;
                            lblOutput.Text = Output.ToString("N2") + " Yards";
                            break;
                    }
                    break;
                    case "Feet":
                    switch (To)
                    {
                        case "Inches":
                            Output = Entered * 12;
                            lblOutput.Text = Output.ToString("N2") + " Inches";
                            break;
                        case "Feet":
                            Output = Entered;
                            lblOutput.Text = Output.ToString("N2") + " Feet";
                            break;
                        case "Yards":
                            Output = Entered / 3;
                            lblOutput.Text = Output.ToString("N2") + " Yards";
                            break;
                    }
                    break;
                    case "Yards":
                    switch (To)
                    {
                        case "Inches":
                            Output = Entered * 36;
                            lblOutput.Text = Output.ToString("N2") + " Inches";
                            break;
                        case "Feet":
                            Output = Entered * 3;
                            lblOutput.Text = Output.ToString("N2") + " Feet";
                            break;
                        case "Yards":
                            Output = Entered;
                            lblOutput.Text = Output.ToString("N2") + " Yards";
                            break;
                    }
                    break;
            }
        }

        }
    }
}

尝试在选择每个列表框时进行输出

3 个答案: