vb,net my collection 属性 in my class 抛出错误
vb,net my collection property in my class is throwing an error
我正在学习 collections，我有一个人 class
Imports System
Imports System.Collections.Generic
Imports System.Text
Public Class Person
Public Sub New()
End Sub
Public Sub New(ByVal id As Integer, ByVal first_name As String, ByVal mid_name As String, ByVal last_name As String, ByVal age As Short, ByVal sex As Char)
Me.p_id = id
Me.first_name = first_name
Me.mid_name = mid_name
Me.last_name = last_name
Me.p_age = age
Me.p_sex = sex
End Sub
Private p_id As Integer = -1
Private first_name As String = String.Empty
Private mid_name As String = String.Empty
Private last_name As String = String.Empty
Private p_age As Short = 0
Private p_sex As Nullable(Of Char) = Nothing
Public Property ID() As Integer
Get
Return p_id
End Get
Set(ByVal value As Integer)
p_id = value
End Set
End Property
Public Property FirstName() As String
Get
Return first_name
End Get
Set(ByVal value As String)
first_name = value
End Set
End Property
Public Property MiddleName() As String
Get
Return mid_name
End Get
Set(ByVal value As String)
mid_name = value
End Set
End Property
Public Property LastName() As String
Get
Return last_name
End Get
Set(ByVal value As String)
last_name = value
End Set
End Property
Public Property Age() As Short
Get
Return p_age
End Get
Set(ByVal value As Short)
p_age = value
End Set
End Property
Public Property Sex() As Nullable(Of Char)
Get
Return p_sex
End Get
Set(ByVal value As Nullable(Of Char))
p_sex = value
End Set
End Property
End Class
和一个员工 Class 我定义了一个人 属性
Imports System
Imports System.Collections.Generic
Imports System.Text
Public Class Employee
Public Sub New()
End Sub
Public Sub New(ByVal id As Integer, ByVal companyName As String, ByVal office As String, colPerson As Person)
'Me._employeeid = id
'Me._companyName = companyName
'Me._office = office
End Sub
Private _employeeid As Integer = -1
Private _companyName As String = String.Empty
Private _office As String = String.Empty
Public Property Empoyee_ID() As Integer
Get
Return _employeeid
End Get
Set(ByVal value As Integer)
_employeeid = value
End Set
End Property
Public Property CompanyName() As String
Get
Return _companyName
End Get
Set(ByVal value As String)
_companyName = value
End Set
End Property
Public Property Office() As String
Get
Return _office
End Get
Set(ByVal value As String)
_office = value
End Set
End Property
Property colPerson As List(Of Person)
End Class
我如何填充这些人class
Sub Main()
Dim pList As List(Of Person) = New List(Of Person)()
Dim thePerson As New List(Of Person) From
{
New Person With {.Age = 29, .FirstName = "John", .LastName = "Shields", .MiddleName = "", .Sex = "M", .ID = 1},
New Person With {.Age = 34, .FirstName = "Mary", .LastName = "Matthew", .MiddleName = "L", .Sex = "F", .ID = 2},
New Person With {.Age = 55, .FirstName = "Amber", .LastName = "Carl", .MiddleName = "P", .Sex = "M", .ID = 3},
New Person With {.Age = 12, .FirstName = "Kathy", .LastName = "Berry", .MiddleName = "O", .Sex = "F", .ID = 4}
}
'pList.Add(New Person(1, "John", "", "Shields", 29, "M"c))
'pList.Add(New Person(2, "Mary", "Matthew", "Jacobs", 35, "F"c))
'pList.Add(New Person(3, "Amber", "Carl", "Agar", 25, "M"c))
'pList.Add(New Person(4, "Kathy", "", "Berry", 21, "F"c))
'pList.Add(New Person(5, "Lena", "Ashco", "Bilton", 33, "F"c))
'pList.Add(New Person(6, "Susanne", "", "Buck", 45, "F"c))
'pList.Add(New Person(7, "Jim", "", "Brown", 38, "M"c))
'pList.Add(New Person(8, "Jane", "G", "Hooks", 32, "F"c))
'pList.Add(New Person(9, "Robert", "", "", 31, "M"c))
'pList.Add(New Person(10, "Cindy", "Preston", "Fox", 25, "F"c))
'pList.Add(New Person(11, "Gina", "", "Austin", 27, "F"c))
'pList.Add(New Person(12, "Joel", "David", "Benson", 33, "M"c))
'pList.Add(New Person(13, "George", "R", "Douglas", 55, "M"c))
'pList.Add(New Person(14, "Richard", "", "Banks", 22, "M"c))
'pList.Add(New Person(15, "Mary", "C", "Shaw", 39, "F"c))
'
'loop through the list
' PrintOnConsole(pList, "1. --- Looping through all items in the List<T> ---")
'
'Filtering List(T) using a single condition - (Age > 35)
'Dim filterOne As List(Of Person) = pList.FindAll(Function(p As Person) p.Age > 35)
'PrintOnConsole(filterOne, "2. --- Filtering List<T> on single condition (Age > 35) ---")
''
'' Filtering List(T) on multiple conditions (Age > 35 and Sex is Female)
'Dim filterMultiple As List(Of Person) = pList.FindAll(Function(p As Person) p.Age > 35 AndAlso p.Sex = "F"c)
'PrintOnConsole(filterMultiple, "3. --- Filtering List<T> on multiple conditions (Age > 35 and Sex is Female) ---")
''
''Sorting List(T) (Sort on FirstName)
'Dim sortFName As List(Of Person) = pList
'sortFName.Sort(Function(p1 As Person, p2 As Person) p1.FirstName.CompareTo(p2.FirstName))
'PrintOnConsole(sortFName, "4. --- Sort List<T> (Sort on FirstName) ---")
'
'Sorting List(T) descending (Sort on LastName descending)
'Dim sortLNameDesc As List(Of Person) = pList
'sortLNameDesc.Sort(Function(p1 As Person, p2 As Person) p2.LastName.CompareTo(p1.LastName))
'PrintOnConsole(sortLNameDesc, "5. --- Sort List<T> descending (Sort on LastName descending) ---")
''Add new List(T) to existing List(T)
'Dim newList As List(Of Person) = New List(Of Person)()
'newList.Add(New Person(16, "Geoff", "", "Fisher", 29, "M"c))
'newList.Add(New Person(17, "Samantha", "Carl", "Baxer", 32, "F"c))
'pList.AddRange(newList)
'PrintOnConsole(pList, "6. --- Add new List<T> to existing List<> ---")
''Remove multiple items from List(T) based on condition (remove male employees)
'Dim removeList As List(Of Person) = pList
'removeList.RemoveAll(Function(p As Person) p.Sex = "M"c)
'PrintOnConsole(removeList, "7. --- Remove multiple items from List<> based on condition ---")
'' Create Read Only List(T)
'Console.WriteLine("Create Read Only List<>")
'Dim personReadOnly As IList(Of Person) = pList
'Console.WriteLine("Before - Is List Read Only? True or False : " & personReadOnly.IsReadOnly)
'personReadOnly = pList.AsReadOnly()
'Console.WriteLine("After - Is List Read Only? True or False : " & personReadOnly.IsReadOnly & "</br>")
'
'Dim pList1 As New Person
Dim emp As New List(Of Employee)
Dim r As New Employee
r.CompanyName = "zac"
r.Office = "home"
r.Empoyee_ID = 1
'Dim pList1 = New Person(1, "John", "", "Shields", 29, "M"c)
r.colPerson.Add(New Person(1, "John", "", "Shields", 29, "M"c))---> Gives error
emp.Add(r)
'
Dim i As New Employee
i.CompanyName = "zac1"
i.Office = "home1"
i.Empoyee_ID = 2
i.colPerson.Add(New Person(3, "Amber", "Carl", "Agar", 25, "M"c))
pList.Add(New Person(4, "Kathy", "", "Berry", 21, "F"c))
emp.Add(i)
'
Dim t As New Employee
t.CompanyName = "zac2"
t.Office = "home2"
t.Empoyee_ID = 2
pList.Add(New Person(5, "Lena", "Ashco", "Bilton", 33, "F"c))
pList.Add(New Person(6, "Susanne", "", "Buck", 45, "F"c))
emp.Add(t)
For Each item In emp
'item.CompanyName = "zac"
'item.Office = "home"
'item.colperson.Where(Function(x) x.ID = 17)
'Console.WriteLine("employee with person collection: " & item.CompanyName & " " & item.Office & " " & item.colperson.Where(Function(x) x.ID = 17).ToString & "</br>")
Console.WriteLine("employee with person collection: " & item.CompanyName & " " & item.Office & "</br>")
Next
End Sub
r.colPerson.Add(New Person(1, "John", "", "Shields", 29, "M"c))---> Gives error
它给出了一个错误，因为即使 colPerson 被声明为能够获取一个人的列表，它实际上并没有被设置为 be 一个人的列表，所以它目前是 Nothing，你不能调用 Nothing 的方法
Property colPerson As New List(Of Person)
^^^
添加 New 指令以确保它被声明并初始化为 List
的实例
另外，请：
- 不要在名字中加入“col”
List(Of Thing) 使用复数名称 - 这是一个人的列表，因此它至少应该被称为人，但也可能说明他们是什么样的人。例如，如果此 Employee 被少数人推荐，则称其为 RcommendedByPeople- 如果您正在编写 是 集合的 class，则仅在名称中使用 Collection，例如 Microsoft 在编写 MatchCollection 时所做的 - 常规集合表达式
Matches
- 确定 属性 是否为 public、私有等
即
Public Property RcommendedByPeople As New List(Of Person)
我正在学习 collections，我有一个人 class
Imports System
Imports System.Collections.Generic
Imports System.Text
Public Class Person
Public Sub New()
End Sub
Public Sub New(ByVal id As Integer, ByVal first_name As String, ByVal mid_name As String, ByVal last_name As String, ByVal age As Short, ByVal sex As Char)
Me.p_id = id
Me.first_name = first_name
Me.mid_name = mid_name
Me.last_name = last_name
Me.p_age = age
Me.p_sex = sex
End Sub
Private p_id As Integer = -1
Private first_name As String = String.Empty
Private mid_name As String = String.Empty
Private last_name As String = String.Empty
Private p_age As Short = 0
Private p_sex As Nullable(Of Char) = Nothing
Public Property ID() As Integer
Get
Return p_id
End Get
Set(ByVal value As Integer)
p_id = value
End Set
End Property
Public Property FirstName() As String
Get
Return first_name
End Get
Set(ByVal value As String)
first_name = value
End Set
End Property
Public Property MiddleName() As String
Get
Return mid_name
End Get
Set(ByVal value As String)
mid_name = value
End Set
End Property
Public Property LastName() As String
Get
Return last_name
End Get
Set(ByVal value As String)
last_name = value
End Set
End Property
Public Property Age() As Short
Get
Return p_age
End Get
Set(ByVal value As Short)
p_age = value
End Set
End Property
Public Property Sex() As Nullable(Of Char)
Get
Return p_sex
End Get
Set(ByVal value As Nullable(Of Char))
p_sex = value
End Set
End Property
End Class
和一个员工 Class 我定义了一个人 属性
Imports System
Imports System.Collections.Generic
Imports System.Text
Public Class Employee
Public Sub New()
End Sub
Public Sub New(ByVal id As Integer, ByVal companyName As String, ByVal office As String, colPerson As Person)
'Me._employeeid = id
'Me._companyName = companyName
'Me._office = office
End Sub
Private _employeeid As Integer = -1
Private _companyName As String = String.Empty
Private _office As String = String.Empty
Public Property Empoyee_ID() As Integer
Get
Return _employeeid
End Get
Set(ByVal value As Integer)
_employeeid = value
End Set
End Property
Public Property CompanyName() As String
Get
Return _companyName
End Get
Set(ByVal value As String)
_companyName = value
End Set
End Property
Public Property Office() As String
Get
Return _office
End Get
Set(ByVal value As String)
_office = value
End Set
End Property
Property colPerson As List(Of Person)
End Class
我如何填充这些人class
Sub Main()
Dim pList As List(Of Person) = New List(Of Person)()
Dim thePerson As New List(Of Person) From
{
New Person With {.Age = 29, .FirstName = "John", .LastName = "Shields", .MiddleName = "", .Sex = "M", .ID = 1},
New Person With {.Age = 34, .FirstName = "Mary", .LastName = "Matthew", .MiddleName = "L", .Sex = "F", .ID = 2},
New Person With {.Age = 55, .FirstName = "Amber", .LastName = "Carl", .MiddleName = "P", .Sex = "M", .ID = 3},
New Person With {.Age = 12, .FirstName = "Kathy", .LastName = "Berry", .MiddleName = "O", .Sex = "F", .ID = 4}
}
'pList.Add(New Person(1, "John", "", "Shields", 29, "M"c))
'pList.Add(New Person(2, "Mary", "Matthew", "Jacobs", 35, "F"c))
'pList.Add(New Person(3, "Amber", "Carl", "Agar", 25, "M"c))
'pList.Add(New Person(4, "Kathy", "", "Berry", 21, "F"c))
'pList.Add(New Person(5, "Lena", "Ashco", "Bilton", 33, "F"c))
'pList.Add(New Person(6, "Susanne", "", "Buck", 45, "F"c))
'pList.Add(New Person(7, "Jim", "", "Brown", 38, "M"c))
'pList.Add(New Person(8, "Jane", "G", "Hooks", 32, "F"c))
'pList.Add(New Person(9, "Robert", "", "", 31, "M"c))
'pList.Add(New Person(10, "Cindy", "Preston", "Fox", 25, "F"c))
'pList.Add(New Person(11, "Gina", "", "Austin", 27, "F"c))
'pList.Add(New Person(12, "Joel", "David", "Benson", 33, "M"c))
'pList.Add(New Person(13, "George", "R", "Douglas", 55, "M"c))
'pList.Add(New Person(14, "Richard", "", "Banks", 22, "M"c))
'pList.Add(New Person(15, "Mary", "C", "Shaw", 39, "F"c))
'
'loop through the list
' PrintOnConsole(pList, "1. --- Looping through all items in the List<T> ---")
'
'Filtering List(T) using a single condition - (Age > 35)
'Dim filterOne As List(Of Person) = pList.FindAll(Function(p As Person) p.Age > 35)
'PrintOnConsole(filterOne, "2. --- Filtering List<T> on single condition (Age > 35) ---")
''
'' Filtering List(T) on multiple conditions (Age > 35 and Sex is Female)
'Dim filterMultiple As List(Of Person) = pList.FindAll(Function(p As Person) p.Age > 35 AndAlso p.Sex = "F"c)
'PrintOnConsole(filterMultiple, "3. --- Filtering List<T> on multiple conditions (Age > 35 and Sex is Female) ---")
''
''Sorting List(T) (Sort on FirstName)
'Dim sortFName As List(Of Person) = pList
'sortFName.Sort(Function(p1 As Person, p2 As Person) p1.FirstName.CompareTo(p2.FirstName))
'PrintOnConsole(sortFName, "4. --- Sort List<T> (Sort on FirstName) ---")
'
'Sorting List(T) descending (Sort on LastName descending)
'Dim sortLNameDesc As List(Of Person) = pList
'sortLNameDesc.Sort(Function(p1 As Person, p2 As Person) p2.LastName.CompareTo(p1.LastName))
'PrintOnConsole(sortLNameDesc, "5. --- Sort List<T> descending (Sort on LastName descending) ---")
''Add new List(T) to existing List(T)
'Dim newList As List(Of Person) = New List(Of Person)()
'newList.Add(New Person(16, "Geoff", "", "Fisher", 29, "M"c))
'newList.Add(New Person(17, "Samantha", "Carl", "Baxer", 32, "F"c))
'pList.AddRange(newList)
'PrintOnConsole(pList, "6. --- Add new List<T> to existing List<> ---")
''Remove multiple items from List(T) based on condition (remove male employees)
'Dim removeList As List(Of Person) = pList
'removeList.RemoveAll(Function(p As Person) p.Sex = "M"c)
'PrintOnConsole(removeList, "7. --- Remove multiple items from List<> based on condition ---")
'' Create Read Only List(T)
'Console.WriteLine("Create Read Only List<>")
'Dim personReadOnly As IList(Of Person) = pList
'Console.WriteLine("Before - Is List Read Only? True or False : " & personReadOnly.IsReadOnly)
'personReadOnly = pList.AsReadOnly()
'Console.WriteLine("After - Is List Read Only? True or False : " & personReadOnly.IsReadOnly & "</br>")
'
'Dim pList1 As New Person
Dim emp As New List(Of Employee)
Dim r As New Employee
r.CompanyName = "zac"
r.Office = "home"
r.Empoyee_ID = 1
'Dim pList1 = New Person(1, "John", "", "Shields", 29, "M"c)
r.colPerson.Add(New Person(1, "John", "", "Shields", 29, "M"c))---> Gives error
emp.Add(r)
'
Dim i As New Employee
i.CompanyName = "zac1"
i.Office = "home1"
i.Empoyee_ID = 2
i.colPerson.Add(New Person(3, "Amber", "Carl", "Agar", 25, "M"c))
pList.Add(New Person(4, "Kathy", "", "Berry", 21, "F"c))
emp.Add(i)
'
Dim t As New Employee
t.CompanyName = "zac2"
t.Office = "home2"
t.Empoyee_ID = 2
pList.Add(New Person(5, "Lena", "Ashco", "Bilton", 33, "F"c))
pList.Add(New Person(6, "Susanne", "", "Buck", 45, "F"c))
emp.Add(t)
For Each item In emp
'item.CompanyName = "zac"
'item.Office = "home"
'item.colperson.Where(Function(x) x.ID = 17)
'Console.WriteLine("employee with person collection: " & item.CompanyName & " " & item.Office & " " & item.colperson.Where(Function(x) x.ID = 17).ToString & "</br>")
Console.WriteLine("employee with person collection: " & item.CompanyName & " " & item.Office & "</br>")
Next
End Sub
r.colPerson.Add(New Person(1, "John", "", "Shields", 29, "M"c))---> Gives error
它给出了一个错误，因为即使 colPerson 被声明为能够获取一个人的列表，它实际上并没有被设置为 be 一个人的列表，所以它目前是 Nothing，你不能调用 Nothing 的方法
Property colPerson As New List(Of Person)
^^^
添加 New 指令以确保它被声明并初始化为 List
另外，请：
- 不要在名字中加入“col”
List(Of Thing)使用复数名称 - 这是一个人的列表，因此它至少应该被称为人，但也可能说明他们是什么样的人。例如，如果此 Employee 被少数人推荐，则称其为 RcommendedByPeople- 如果您正在编写 是 集合的 class，则仅在名称中使用 Collection，例如 Microsoft 在编写 MatchCollection 时所做的 - 常规集合表达式
Matches - 确定 属性 是否为 public、私有等
即
Public Property RcommendedByPeople As New List(Of Person)