通用集合和继承 [英] Generic collections and inheritance
问题描述
我有一个基类，它包含一个通用列表，需要由基类及其子类访问
。 />
对此最好的解决办法是什么？
我对仿制药相当新，但我知道这个事实
如果你有一个继承自A的B类，然后是
List< Bdoes NOT不继承自List< A>。所以我理解
为什么下面的例子没有编译，但我没有
看看如何解决上述问题...例如，
我需要能够从下面的LeaseContract类返回BindingList< LeaseContractLine>
。
//样本：
使用系统;
使用System.Collections.Generic;
使用System.ComponentModel;
使用System.Windows.Forms;
命名空间GenericInheritanceTest
{
公共部分类Form1：表格
{
/ /一个只有一个DataGridView的简单表单：
public Form1（）
{
InitializeComponent（）;
}
private void Form1_Load（object sender，EventArgs e）
{
LeaseContract leaseContract = new LeaseContract（）;
//在DataGridView中显示合约行：
uxLeaseContractGrid.DataSource = leaseContract.GetLines（）;
}
}
公共类合同
{
protected BindingList< ContractLine_lines = new
BindingList< ContractLine>（）;
public Contract（）{}
//
//提供功能的方法适用于所有类型的合同......
//
}
公共类LeaseContract：合同
{
public LeaseContract（）{}
public BindingList< LeaseContractLineGetLines（）
{
//无法编译（因为演员表无效）：
return（BindingList< LeaseContractLine>）_行;
}
//
//特定的LeaseContract方法等
//
}
public class ContractLine
{
public ContractLine（）{}
}
公共类LeaseContractLine：ContractLine
{
public LeaseContractLine（）{}
}
}
任何帮助都会有很大帮助！
谢谢，
Lars
我会尝试使合约本身成为通用类：
这样的东西：
公共类合同< Twhere T：ContractLine
{
protected BindingList< T_lines = new BindingList< T>（）;
}
公共类LeaseContract：Contract< LeaseContractLine>
{
....
}
-
Adam Clauss
" Lars" < no ***** @ dev.nullwrote in message
news：zK ************************* *****@megapath.net ...
我有一个持有通用的基类需要
的列表才能被基类及其子类访问。
最佳解决方案是什么？
我对仿制药相当新，但我知道这个事实
如果你有一个B类继承自A，那么
List< Bdoes NOT inherit来自List< A>。所以我理解
为什么下面的例子没有编译，但我没有
看看如何解决上述问题...例如，
我需要能够从下面的LeaseContract类返回一个BindingList< LeaseContractLine>
。
//样本：
使用System;
使用System.Collections.Generic;
使用System.ComponentModel;
使用System.Windows.Forms;
命名空间GenericInheritanceTest
{
公共部分类Form1：表格
{
//一个只有一个DataGridView的简单表单：
public Form1（）
{
InitializeComponent（）;
}
private void Form1_Load（对象发件人，EventArgs e）
{
LeaseContract leaseContract = new LeaseContract（）;
//显示DataGridV中的合同行iew：
uxLeaseContractGrid.DataSource = leaseContract.GetLines（）;
}
}
公共类合同
{
protected BindingList< ContractLine_lines = new
BindingList< ContractLine>（）;
public合同（）{}
//
//为所有类型的合同提供功能的方法......
//
}
公共类LeaseContract：合同
{
public LeaseContract（）{}
public BindingList< LeaseContractLineGetLines（）
{
//无法编译（因为演员表无效）：
return（BindingList< LeaseContractLine>）_ lines;
}
//
//特定的LeaseContract方法等
//
}
public c ContractLine
{
public ContractLine（）{}
}
公共类LeaseContractLine： ContractLine
{
public LeaseContractLine（）{}
}
}
任何帮助都会有很大的帮助！
谢谢，
Lars
" Adam Clauss" < ca ***** @ tamu.eduwrote in message
news：12 ************* @ corp.supernews.com ...
>我会尝试使合约本身成为通用类：
这样的东西：
public class Contract< Twhere T：ContractLine
{
protected BindingList< T_lines = new BindingList< T>（）;
}
公共类LeaseContract：合约< LeaseContractLine>
{
...
}
感谢您的回复 - 这似乎解决了这个问题。当
试图在实际应用程序中实现这个时，我来了另一个问题
但是：ContractLine类持有
a对父母的引用（合同类）。尝试分配给此引用的
在下面的AddLine（）中给出了编译错误：
无法将类型''Contract< T>''转换为''Contract< ContractLine>''"
（缩写信息）。
这是更新的示例代码：
使用System;
使用System.Collections.Generic;
使用System.ComponentModel;
使用System.Windows.Forms;
命名空间GenericInheritanceTst
{
公共部分类Form2：表格
{
public Form2（）
{
InitializeComponent（）;
}
}
//合同& ContractLine类：
公共类合同< Twhere T：ContractLine，new（）
{
protected BindingList< T_lines = new BindingList< T> （）;
公共合同（）{}
public void AddLine（）
{
T contractLine = new T（）;
//不能编译（不能将类型''合同< T>''转换为
''合同< ; ContractLine>''"）：
contractLine.Parent = this;
_lines.Add（contractLine）;
}
}
公共类ContractLine
{
公共合同< ContractLineParent;
public ContractLine（）{}
}
// LeaseContract& LeaseContractLine类：
公共类LeaseContract：Contract< LeaseContractLine>
{
public LeaseContract（）{}
public BindingList< LeaseContractLineGetLines（）
{
return _lines;
}
}
公共类LeaseContractLine：ContractLine
{
public LeaseContractLine（）{}
}
}
我缺少什么？
谢谢，
Lars
"拉斯" < no ***** @ dev.nullwrote in message
news：b9 ************************* *****@megapath.net ...
感谢您的回复 - 这似乎解决了这个问题。当
试图在实际应用程序中实现这个时，我来了另一个问题
但是：ContractLine类持有
a对父母的引用（合同类）。尝试分配给此引用的
在下面的AddLine（）中给出了编译错误：
无法将类型''Contract< T>''转换为''Contract< ContractLine>''"
（缩写信息）。
嘿......其他人正在尝试做一些非常相似的事情。
见Kris Jennings的帖子（日期为07/21） / 2006 8:51 pm） - 更具体地说
见Barry Kelly的回复（9:28 pm）。
无论如何，ContractLine可能也需要是通用的。
命名空间GenericInheritanceTst
{
公共部分类Form2：表格
{
public Form2（）
{
InitializeComponent（）;
}
}
//合同& ContractLine类：
公共类合同< Twhere T：ContractLine< T>，new（）
{
protected BindingList< T_lines = new BindingList< ; T>（）;
public Contract（）{}
public void AddLine（）
{
T contractLine = new T（）;
contractLine.Parent = this;
_lines.Add（contractLine）;
}
}
公共类ContractLine< LineBasewhere LineBase：
ContractLine< LineBase>，new（）
{
公共合同< ContractLineParent;
公共ContractLine（）{}
}
// LeaseContract& LeaseContractLine类：
公共类LeaseContract：Contract< LeaseContractLine>
{
public LeaseContract（）{}
public BindingList< LeaseContractLineGetLines（）
{
return _lines;
}
}
公共类LeaseContractLine：ContractLine< LeaseContractLine>
{
public LeaseContractLine（）{}
}
}
泛型非常好...通用代码。但是他们很难有时候把你的思绪包裹起来。
-
Adam Clauss
Hi,
I have a base class holding a generic list that needs
to be accessed by both the base class and its subclasses.
What is the best solution to this?
I am fairly new to generics, but I am aware of that fact
that if you have a class B, that inherits from A, then
List<Bdoes NOT inherit from List<A>. So I understand
why the example below does not compile, but I fail to
see how to solve the problem stated above... For example,
I need to be able to return a BindingList<LeaseContractLine>
from the LeaseContract class below.
// Sample:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Forms;
namespace GenericInheritanceTest
{
public partial class Form1 : Form
{
// A simple form with only a DataGridView on it:
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
LeaseContract leaseContract = new LeaseContract();
// Display the contract lines in a DataGridView:
uxLeaseContractGrid.DataSource = leaseContract.GetLines();
}
}
public class Contract
{
protected BindingList<ContractLine_lines = new
BindingList<ContractLine>();
public Contract() { }
//
// methods providing functionality for all types of contracts...
//
}
public class LeaseContract : Contract
{
public LeaseContract() { }
public BindingList<LeaseContractLineGetLines()
{
// Will not compile (since the cast is not valid):
return (BindingList<LeaseContractLine>)_lines;
}
//
// specific LeaseContract methods, etc.
//
}
public class ContractLine
{
public ContractLine() { }
}
public class LeaseContractLine : ContractLine
{
public LeaseContractLine() { }
}
}
Any help would be greatly appreicated!
Thanks,
Lars
I would try making Contract itself a generic class:
Something like this:
public class Contract<Twhere T : ContractLine
{
protected BindingList<T_lines = new BindingList<T>();
}
public class LeaseContract : Contract<LeaseContractLine>
{
....
}
--
Adam Clauss
"Lars" <no*****@dev.nullwrote in message
news:zK******************************@megapath.net ...Hi,
I have a base class holding a generic list that needs
to be accessed by both the base class and its subclasses.
What is the best solution to this?
I am fairly new to generics, but I am aware of that fact
that if you have a class B, that inherits from A, then
List<Bdoes NOT inherit from List<A>. So I understand
why the example below does not compile, but I fail to
see how to solve the problem stated above... For example,
I need to be able to return a BindingList<LeaseContractLine>
from the LeaseContract class below.
// Sample:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Forms;
namespace GenericInheritanceTest
{
public partial class Form1 : Form
{
// A simple form with only a DataGridView on it:
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
LeaseContract leaseContract = new LeaseContract();
// Display the contract lines in a DataGridView:
uxLeaseContractGrid.DataSource = leaseContract.GetLines();
}
}
public class Contract
{
protected BindingList<ContractLine_lines = new
BindingList<ContractLine>();
public Contract() { }
//
// methods providing functionality for all types of contracts...
//
}
public class LeaseContract : Contract
{
public LeaseContract() { }
public BindingList<LeaseContractLineGetLines()
{
// Will not compile (since the cast is not valid):
return (BindingList<LeaseContractLine>)_lines;
}
//
// specific LeaseContract methods, etc.
//
}
public class ContractLine
{
public ContractLine() { }
}
public class LeaseContractLine : ContractLine
{
public LeaseContractLine() { }
}
}
Any help would be greatly appreicated!
Thanks,
Lars
"Adam Clauss" <ca*****@tamu.eduwrote in message
news:12*************@corp.supernews.com...>I would try making Contract itself a generic class:
Something like this:
public class Contract<Twhere T : ContractLine
{
protected BindingList<T_lines = new BindingList<T>();
}
public class LeaseContract : Contract<LeaseContractLine>
{
...
}Thanks for the reply - that seems to solve that problem. When
trying to implement this in the actual application, I come
across another problem, though: The ContractLine class holds
a reference to the parent (the Contract class). Trying to
assign to this reference gives a compile error in AddLine() below:
"Cannot convert type ''Contract<T>'' to ''Contract<ContractLine>''"
(abbreviated message).
Here is the updated sample code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Forms;
namespace GenericInheritanceTst
{
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}
}
// Contract & ContractLine class:
public class Contract<Twhere T : ContractLine, new()
{
protected BindingList<T_lines = new BindingList<T>();
public Contract() { }
public void AddLine()
{
T contractLine = new T();
// Won''t compile ("Cannot convert type ''Contract<T>'' to
''Contract<ContractLine>''"):
contractLine.Parent = this;
_lines.Add(contractLine);
}
}
public class ContractLine
{
public Contract<ContractLineParent;
public ContractLine() { }
}
// LeaseContract & LeaseContractLine class:
public class LeaseContract : Contract<LeaseContractLine>
{
public LeaseContract() { }
public BindingList<LeaseContractLineGetLines()
{
return _lines;
}
}
public class LeaseContractLine : ContractLine
{
public LeaseContractLine() { }
}
}
What am I missing?
Thanks,
Lars
"Lars" <no*****@dev.nullwrote in message
news:b9******************************@megapath.net ...Thanks for the reply - that seems to solve that problem. When
trying to implement this in the actual application, I come
across another problem, though: The ContractLine class holds
a reference to the parent (the Contract class). Trying to
assign to this reference gives a compile error in AddLine() below:
"Cannot convert type ''Contract<T>'' to ''Contract<ContractLine>''"
(abbreviated message).Heh... incidentally someone else is trying to do something very similar.
See the post by Kris Jennings (dated 07/21/2006 8:51pm) - more specifically
see the reply to that by Barry Kelly (9:28pm).
In any event, the ContractLine probably also needs to be generic.
namespace GenericInheritanceTst
{
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}
}
// Contract & ContractLine class:
public class Contract<Twhere T : ContractLine<T>, new()
{
protected BindingList<T_lines = new BindingList<T>();
public Contract() { }
public void AddLine()
{
T contractLine = new T();
contractLine.Parent = this;
_lines.Add(contractLine);
}
}
public class ContractLine<LineBasewhere LineBase :
ContractLine<LineBase>, new()
{
public Contract<ContractLineParent;
public ContractLine() { }
}
// LeaseContract & LeaseContractLine class:
public class LeaseContract : Contract<LeaseContractLine>
{
public LeaseContract() { }
public BindingList<LeaseContractLineGetLines()
{
return _lines;
}
}
public class LeaseContractLine : ContractLine<LeaseContractLine>
{
public LeaseContractLine() { }
}
}
Generics make for very good... generic code. But they can be difficult to
wrap your mind around at times.
--
Adam Clauss
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