嘗試從每個列表框中選擇一個輸出時執行輸出

Question

我試圖從2個不同列表框中選擇具有相同測量單詞的3個選項中的一個。

用戶在文本框中輸入一個數字，然後從FromList列表框中選擇3個單位中的一個（單位是英寸，英尺和碼），然後從ToList列表框中選擇3個單位中的一個單位也是英寸，英尺和碼）。

當計算按鈕被點擊時，它會將測量英寸轉換爲英寸（不要數學，只是吐出他們輸入的標籤）或英寸到英尺或英寸到碼（如果FromList已選擇英寸）將輸出顯示到標籤。它也可以做腳到英寸，腳到腳（不做數學），腳到碼。最後，它會做到碼數，碼到碼，碼到碼（不算數）。

兩個列表框都將SelectionMode設置爲1，因此用戶只能從每個列表框中選取1個項目。我可以使用SelectedItem將第一個列表框設置爲一個值，但是它突出顯示的代碼中的9個錯誤是如果我嘗試設置它，如果第二個列表框中的項目被選中。以下是我試過到目前爲止：

你的問題

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

一個是你正在使用的賦值運算符，=，而不是平等的經營者，==，在你的if語句。

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

另外Entered永遠不會被賦予一個值。

有些事情，你可能要考慮，用枚舉來簡化你的代碼，並擺脫所有這些if聲明：

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; 
     } 

    } 

這個函數的自/至單位字符串和雙爲數量並進行轉換。而不是乘法或除法不同的算法，它只是乘以2轉換值的劃分

Answer 2

問題是你已經採取FromList和ToList作爲字符串，你試圖從FromList/ToList的SelectedItem屬性，但存在FromList/ToList中不存在此類屬性，因爲您已將它們作爲代碼中的字符串。可能你需要使用你在定義中定義的Listcontrol而不是在代碼中使用字符串對象。

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，所以我使用開關和解析重新編碼它，它現在按預期工作。感謝大家的幫助！這裏是工作代碼：

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; 
      } 
     } 

     } 
    } 
}