從另一個類別調用函數時出現錯誤：字段初始值設定項無法引用非靜態字段，方法或屬性

Question

我在調用類的類USBDriveSerialNumber的公共方法getSerialNumberFromDriveLetter時出現此錯誤。

錯誤：字段初始值設定項無法引用非靜態字段，方法或屬性。

我的代碼

using System.Data; 
using System.Drawing; 
using System.Linq; 
using System.Text; 
using System.Windows.Forms; 
using System.Diagnostics; 

namespace WindowsFormsApplication2 
{ 
    public partial class Form1 : Form 
    { 
     public Form1() 
     { 
      InitializeComponent(); 
     } 
     USBDriveSerialNumber usb = new USBDriveSerialNumber(); 
     string serial = usb.getSerialNumberFromDriveLetter("f:\\"); 
     // Debug.WriteLine(serial); 
    } 

} 

//USBDriveSerialNumber Class 

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Management; 

namespace WindowsFormsApplication2 
{ 
    class USBDriveSerialNumber 
    { 
     string _serialNumber; 
     string _driveLetter; 

     public string getSerialNumberFromDriveLetter(string driveLetter) 
     { 
      this._driveLetter = driveLetter.ToUpper(); 

      if (!this._driveLetter.Contains(":")) 
      { 
       this._driveLetter += ":"; 
      } 

      matchDriveLetterWithSerial(); 

      return this._serialNumber; 
     } 

     public void matchDriveLetterWithSerial() 
     { 

      string[] diskArray; 
      string driveNumber; 
      string driveLetter; 

      ManagementObjectSearcher searcher1 = new ManagementObjectSearcher("SELECT * FROM Win32_LogicalDiskToPartition"); 
      foreach (ManagementObject dm in searcher1.Get()) 
      { 
       diskArray = null; 
       driveLetter = getValueInQuotes(dm["Dependent"].ToString()); 
       diskArray = getValueInQuotes(dm["Antecedent"].ToString()).Split(','); 
       driveNumber = diskArray[0].Remove(0, 6).Trim(); 
       if (driveLetter == this._driveLetter) 
       { 
        /* This is where we get the drive serial */ 
        ManagementObjectSearcher disks = new ManagementObjectSearcher("SELECT * FROM Win32_DiskDrive"); 
        foreach (ManagementObject disk in disks.Get()) 
        { 

         if (disk["Name"].ToString() == ("\\\\.\\PHYSICALDRIVE" + driveNumber) & disk["InterfaceType"].ToString() == "USB") 
         { 
          this._serialNumber = parseSerialFromDeviceID(disk["PNPDeviceID"].ToString()); 
         } 
        } 
       } 
      } 
     } 

     private string parseSerialFromDeviceID(string deviceId) 
     { 
      string[] splitDeviceId = deviceId.Split('\\'); 
      string[] serialArray; 
      string serial; 
      int arrayLen = splitDeviceId.Length - 1; 

      serialArray = splitDeviceId[arrayLen].Split('&'); 
      serial = serialArray[0]; 

      return serial; 
     } 

     private string getValueInQuotes(string inValue) 
     { 
      string parsedValue = ""; 

      int posFoundStart = 0; 
      int posFoundEnd = 0; 

      posFoundStart = inValue.IndexOf("\""); 
      posFoundEnd = inValue.IndexOf("\"", posFoundStart + 1); 

      parsedValue = inValue.Substring(posFoundStart + 1, (posFoundEnd - posFoundStart) - 1); 

      return parsedValue; 
     } 
    } 
} 

Answer 1

你應該叫getSerialNumberFromDriveLetter方法內部構造或創建一個新的方法

 public Form1() 
     { 
     InitializeComponent(); 
     USBDriveSerialNumber usb = new USBDriveSerialNumber(); 
     string serial = usb.getSerialNumberFromDriveLetter("f:\\"); 
     } 

Answer 2

不能使用實例變量初始化另一個實例變量，因爲編譯器重新排列這些變量。

將其更改爲

string serial = new USBDriveSerialNumber().getSerialNumberFromDriveLetter("f:\\"); 

或使USB靜態

static USBDriveSerialNumber usb = new USBDriveSerialNumber(); 
string serial = usb.getSerialNumberFromDriveLetter("f:\\"); 

或移動設置串行構造器

string serial; 
public Form1() 
{ 
     InitializeComponent(); 
     serial = usb.getSerialNumberFromDriveLetter("f:\\"); 
}