通过自定义类实现接口ICustomFormatter和IFormatProvider来实现输出格式化

使用格式自定义类让表格数据自动根据配置的计量单位来处理数据的计量单位转化和显示：

Public Function Format(format1 As String, arg As Object, formatProvider As System.IFormatProvider) As String Implements System.ICustomFormatter.Format
        If (String.IsNullOrEmpty(format1)) Then
            If (arg Is GetType(IFormattable)) Then
                Return CType(arg, IFormattable).ToString(format1, formatProvider)
            ElseIf (arg Is Nothing) Then
                Return String.Empty
            Else
                Return arg.ToString()
            End If
        Else
            If (arg Is Nothing) Then
                Return String.Empty
            ElseIf (IsNumeric(arg)) Then
                If ([Enum].IsDefined(GetType(EMUnitClass), format1)) Then
                    Dim pUnitClass As EMUnitClass
                    pUnitClass = CType([Enum].Parse(GetType(EMUnitClass), format1), EMUnitClass)
                    Return Me.formatByUnitClass(pUnitClass, Convert.ToDouble(arg))
                Else
                    If (arg Is GetType(IFormattable)) Then
                        Return CType(arg, IFormattable).ToString(format1, formatProvider)
                    Else
                        Return arg.ToString()
                    End If
                End If
            Else
                Return arg.ToString()
            End If
        End If
    End Function

    Public Function GetFormat(formatType As System.Type) As Object Implements System.IFormatProvider.GetFormat
        If (formatType Is GetType(ICustomFormatter)) Then    'OrElse formatType Is GetType(NumberFormatInfo)
            Return Me
        Else
            Return Nothing
        End If
    End Function

显示指定DataGridViewRow的Column的FormatPrivider

pColumn.DefaultCellStyle.FormatProvider = MyHub.mModuleMain.mUnitManager ‘自定义的类

如果以为这样子就可以实现自定义格式化，那就大错特错了，还需要指定CellFormatting事件才能真正启用自定义格式化功能

    Private Sub xDataGridView1_CellFormatting(sender As Object, e As System.Windows.Forms.DataGridViewCellFormattingEventArgs) Handles xDataGridView1.CellFormatting
        If (TypeOf e.CellStyle.FormatProvider Is ICustomFormatter AndAlso (Not String.IsNullOrEmpty(e.CellStyle.Format))) Then
            e.Value = CType(e.CellStyle.FormatProvider.GetFormat(GetType(ICustomFormatter)), ICustomFormatter).Format(e.CellStyle.Format, e.Value, e.CellStyle.FormatProvider)
            e.FormattingApplied = True
        End If
    End Sub

参考的C#实现例子

public class MyEnumFormatter : IFormatProvider, ICustomFormatter {

    public object GetFormat(Type formatType) {
        if (formatType == typeof(ICustomFormatter))
            return this;
        else
            return null;
    }

    public string Format(string format, object arg, IFormatProvider formatProvider) {
        return ((NameOfEnumType)Convert.ToInt32(arg)).ToString();
    }

}

void dataGridView_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e) {
    if (e.CellStyle.FormatProvider is ICustomFormatter) {
        e.Value = (e.CellStyle.FormatProvider.GetFormat(typeof(ICustomFormatter)) as ICustomFormatter).Format(e.CellStyle.Format, e.Value, e.CellStyle.FormatProvider);
        e.FormattingApplied = true;
    }
}

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