Question

有时需要使用一些辅助值初始化单例类。但我们不能“发布”它的构造函数。解决方法是什么？

注意！重载GetInstance或设置颜色不是我的想法。颜色应仅设置一次。我想确保MyPainter使用初始化颜色绘制 ONLY 。 应该使用任何默认颜色。

为了更加清晰，我提供了一个示例：

''' <summary>
''' Singleton class MyPainter
''' </summary>
Public Class MyPainter
  Private Shared _pen As Pen
  Private Shared _instance As MyPainter = Nothing

  Private Sub New()
  End Sub

  ''' <summary>
  ''' This method should be called only once, like a constructor!
  ''' </summary>
  Public Shared Sub InitializeMyPainter(ByVal defaultPenColor As Color)
    _pen = New Pen(defaultPenColor)
  End Sub


  Public Shared Function GetInstance() As MyPainter
    If _instance Is Nothing Then
      _instance = New MyPainter
    End If

    Return _instance
  End Function

  Public Sub DrawLine(ByVal g As Graphics, ByVal pointA As Point, ByVal pointB As Point)
    g.DrawLine(_pen, pointA, pointB)
  End Sub

End Class

感谢。

Answer 1

如果你想在创建时只初始化一次，为什么不在构造函数中通过调用某个方法来完成它，这会从某个地方提取参数？如果多次调用此初始化 - 将其转换为单独的方法，如setOptions。

Answer 2

你能不能只重载你的GetInstance方法吗？

Dim _IsInitialized as boolean = false    
Public Shared ReadOnly Property IsInitialized() As Boolean
        Get
            Return _IsInitialized
        End Get
    End Property


Public Shared Function GetInstance() As MyPainter
        If _instance Is Nothing Then
            _instance = New MyPainter
        End If

        _IsInitialized = True
        Return _instance
    End Function

    Public Overloads Shared Function GetInstance(ByVal DefaultPenColor As Color) As MyPainter
        If _instance Is Nothing Then
            _instance = New MyPainter
            InitializeMyPainter(DefaultPenColor)
        End If

        _IsInitialized = True
        Return _instance
    End Function

在调用GetInstance方法之前，请检查它是否已初始化。如果没有给它笔颜色。

If MyPainter.IsInitialized then
     Dim Painter as MyPainter = MyPainter.GetInstance
Else
     Dim Painter as MyPainter - MyPainter.GetInstance(System.Drawing.Color.Red)
EndIf

Answer 3

您可以声明共享构造函数，但它们必须是无参数的：

Public Class MyPainter
    Private Shared _pen As Pen

    Shared Sub New()
        _pen = New Pen(Color.White)
    End Sub

    ....

End Class

您可以在构造函数中将颜色设置为合理的默认值，然后添加辅助方法以根据需要更改颜色，就像您在样本中一样：

Public Shared Sub SetColor(ByVal defaultPenColor As Color)
    _pen = New Pen(defaultPenColor)
End Sub

Answer 4

您可以在GetInstance中使用可选参数

Public Shared Function GetInstance(Optional ByVal defaultPenColor As Color = Colors.Red) As MyPainter
    If _instance Is Nothing Then
      If defaultPenColor is nothing then
          defaultPenColor = Colors.Red
      end if
      _pen = New Pen(defaultPenColor)
      _instance = New MyPainter
    End If

    Return _instance
End Function

Answer 5

创建一个采用所需参数的CreateInstance方法。并从GetInstance中删除创建功能。那不完全是单身，但至少你知道事情会被正确地初始化。

Answer 6

你可以使用一个Init方法:(这是一个C＃的例子，我刚刚遇到了与可初始化的单例相同的问题）

public sealed class XSingleton
{
    private static XSingleton instance = null;
    int value = -1;

    private XSingleton(int v)
    {
        value = v;
    }

    public static void Init(int v)
    {
        if (instance != null) throw new Exception("Init() must be called only once!");
        instance = new XSingleton(v);
    }

    public static XSingleton Instance
    {
        get
        {
            if (instance == null) throw new Exception("Call Init() before!");
            return instance;
        }
    }

    public int Value { get { return value; } }
}

如果您尝试使用XSingleton unitinialized或尝试初始化多次，则会出现异常。

所以你用

初始化单例

XSingleton.Init(123);

现在您可以使用已初始化的值：

Console.WriteLine(XSingleton.Instance.Value);

如何初始化Singleton？

6 个答案: