移动信息有困难

Question

我似乎在我尝试为学校做的一个程序中遇到了一点障碍。我想让一个新班级接收数据并让总数发送到新的屏幕。我在课上做了同样的事情，但不同之处在于它来自文本框，而且这次我不需要移动数据的文本框，所以我尝试的方式给了我一个错误。以下是我走到这一步：

public StudentSelection() 
    { 
     InitializeComponent(); 
    } 
    public decimal firstCounter; 
    public decimal secondCounter; 
    public decimal finalCounter; 

    struct StudentScores 
    { 
     public string StuId; 
     public decimal TestOne; 
     public decimal TestTwo; 
     public decimal Final; 
    } 
    StudentScores[] allStudentScores = new StudentScores[10]; 
    // class level array to hold 10 products - read in from a file 

    private void StudentSelection_Load(object sender, EventArgs e) 
    { 
     // read products file into products structure array 
     try 
     { 


      // ALWAYS initialize a structure array before using the array 
      // before adding, changing, etc. 
      for (int x = 0; x < 10; x++) 
      { 
       allStudentScores[x].StuId = ""; 
       allStudentScores[x].TestOne = 0; 
       allStudentScores[x].TestTwo = 0; 
       allStudentScores[x].Final = 0; 
      } 

      int arrayIndex = 0; // needed for incrementing index value of the array 
      // when reading file into array 

      // now read file into the array after initialization 
      StreamReader inputFile; 

      string lineofdata; // used to hold each line of data read in from the file 
      string[] ProductStringArray = new string[4]; // 6 element string array to hold 
      // each "field" read from every line in file 

      inputFile = File.OpenText("StudentScores.txt"); // open for reading 

      while (!inputFile.EndOfStream) //keep reading until end of file 
      { 
       lineofdata = inputFile.ReadLine(); // ReadLine() reads an entire row of data from file 
       ProductStringArray = lineofdata.Split(','); //each field is separated by ';' 
       allStudentScores[arrayIndex].StuId = ProductStringArray[0]; // add first element of array to first column of allProducts 
       allStudentScores[arrayIndex].TestOne = decimal.Parse(ProductStringArray[1]); 
       firstCounter += allStudentScores[arrayIndex].TestOne; 
       allStudentScores[arrayIndex].TestTwo = decimal.Parse(ProductStringArray[2]); 
       secondCounter += allStudentScores[arrayIndex].TestTwo; 
       allStudentScores[arrayIndex].Final = decimal.Parse(ProductStringArray[3]); 
       finalCounter += allStudentScores[arrayIndex].Final; 
       StudentListView.Items.Add(ProductStringArray[0]); 
       arrayIndex++; // increment so NEXT row is updated with next read 

      } 

      //close the file 
      inputFile.Close(); 
     } 
     catch (Exception anError) 
     { 
      MessageBox.Show(anError.Message); 

     } 
    } 
    private void NextButton_Click(object sender, EventArgs e) 
    { 
     decimal firstResult, secondResult, finalResult, stuOne, stuTwo, stuThree; 
     string stuName; 

     // call the method in our datatier class 
     decimal.TryParse(firstCounter, out firstResult); 
     decimal.TryParse(secondCounter, out secondResult); 
     decimal.TryParse(finalCounter, out finalResult); 

     DataTier.AddOurNumbers(firstResult, secondResult, finalResult); 
     DataTier.StudentData(stuName, stuOne, stuTwo, stuThree); 

     // now hide this window and display a third window with the total 
     this.Hide(); 
     // display third window 
     ScoreScreen aScoreScreen = new ScoreScreen(); 
     aScoreScreen.Show(); 
    } 


} 

和我的新类

class DataTier 
{ 
    // public static variable available to all windows 
    public static decimal firstTotal, secondTotal, finalTotal, stuTestOne, stuTestTwo, stuTestThree; 
    // static is not associated with any object 

    public static string stuIDCode; 

    // create a public method to access from all windows 
    public static void AddOurNumbers(decimal NumOne, decimal NumTwo, decimal numThree) 
    { 
     // devide to get an average 
     firstTotal = NumOne/10; 
     secondTotal = NumTwo/10; 
     finalTotal = numThree/10; 
    } 

    public static void StudentData(string name, decimal testOne, decimal testTwo, decimal testThree) 
    { 
     stuIDCode = name; 
     stuTestOne = testOne; 
     stuTestTwo = testTwo; 
     stuTestThree = testThree; 
    } 
} 

的错误是在三个decimal.TryParse部分，我不知道为什么它不工作，除了错误说“不能从十进制转换为字符串”。任何帮助将不胜感激。

Answer 1

更改它：

decimal.TryParse(firstCounter, out firstResult); 
    decimal.TryParse(secondCounter, out secondResult); 
    decimal.TryParse(finalCounter, out finalResult); 

    DataTier.AddOurNumbers(firstResult, secondResult, finalResult); 

要：

DataTier.AddOurNumbers(firstCounter, secondCounter, finalCounter); 

的问题是，你要叫decimal.TryParse(string s, out decimal result)为decimal.TryParse（十进制S，出小数结果）。

您的输入已经是decimal并且不需要任何转换。

---

补充说明的是，该代码

decimal.TryParse(someString, out someOutputDecimal); 

没有一个适当的if语句围绕它会悄悄地失败（不通知有关失败的任何东西）。事实上，输出值被设置为0，并且就好像没有收到错误的输入一样。如果输入始终有效，则应该使用decimal.Parse(someString)。但是，在某些情况下，如果输入无效，则默认为0，可能是所需的行为。

Answer 2

decimal.TryParse()方法接受一个字符串作为其第一个参数并尝试将其转换为decimal值。在你的情况下，你传递给TryParse()的变量已经是decimal变量，并且不需要解析它们。如果你只想类变量复制到局部变量，所有你需要做的是：

firstResult = firstCounter; 
secondResult = secondCounter; 
finalResult = finalCounter; 

或在这种特殊情况下，你可以通过类变量直接进入AddOurNumbers：

DataTier.AddOurNumbers(firstCounter, secondCounter, finalCounter); 

这里需要注意的一点是，只要您将值从一个值分配到另一个值，或者将它们传递给方法，就可以复制C＃中的值类型，例如decimals和其他基元。这意味着即使在调用DataTier.AddOurNumbers()后firstCounter,secondCounter或thirdCounter的值发生了更改，您的数据层已收到的值也不会更改。