[英]How can you instantiate an object with a string and send a parameter in C#?
下面的代碼生成此輸出正常:
This is page one.
This is page two.
但是如何更改它以便從List<string>
動態實例化PageItem對象?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace TestInstant
{
class Program
{
static void Main(string[] args)
{
List<string> pageItemsIdCodes = new List<string>() { "PageItem1", "PageItem2" };
PageItemManager pageItemManager = new PageItemManager(pageItemsIdCodes);
pageItemManager.DisplayMenu();
Console.ReadLine();
}
}
class PageItemManager
{
private Dictionary<string, BasePageItem> PageItemRecords = new Dictionary<string, BasePageItem>();
public PageItemManager(List<string> pageItemsIdCodes)
{
//manually
PageItemRecords.Add("PageItem1", new PageItem1(this));
PageItemRecords.Add("PageItem2", new PageItem2(this));
//HOW DO i DO THIS DYNAMICALLY:
//PSEUDO-CODE:
//foreach (string pageItemIdCode in pageItemsIdCodes)
//{
// Type t = Type.GetType(pageItemIdCode);
// //ERROR: Cannot implicitly convert type 'TestInstant.PageItemManager' to 'TestInstant.BasePageItem'
// BasePageItem pageItem = Activator.CreateInstance(t, new BasePageItem[] { this });
// PageItemRecords.Add(pageItemIdCode, pageItem);
//}
//Type t = Type.GetType(pageItemIdCode);
//ERROR: Cannot implicitly convert type 'object' to 'TestInstant.BasePageItem'.
//BasePageItem pageItem = Activator.CreateInstance(t); // Change constructor
//pageItem.PageItemManager = this; // Add SetMananger call to BasePageItem
//PageItemRecords.Add(pageItemIdCode, pageItem);
}
public void DisplayMenu()
{
foreach (var pageItemRecord in PageItemRecords)
{
Console.WriteLine(pageItemRecord.Value.Title);
}
}
}
class BasePageItem
{
public string Title { get; set; }
protected PageItemManager pageItemManager;
public BasePageItem(PageItemManager pageItemManager)
{
this.pageItemManager = pageItemManager;
}
}
class PageItem1 : BasePageItem
{
public PageItem1(PageItemManager pageItemManager)
: base(pageItemManager)
{
Title = "This is page one.";
}
}
class PageItem2 : BasePageItem
{
public PageItem2(PageItemManager pageItemManager)
: base(pageItemManager)
{
Title = "This is page two.";
}
}
}
我相信你可以使用Activator.CreateInstance來獲取輸入參數。
foreach (string pageItemIdCode in pageItemsIdCodes)
{
Type t = Type.GetTypeFromProgID(pageItemIdCode);
Object pageItem = Activator.CreateInstance(t, new object[]{this});
PageItemRecords.Add(pageItemIdCode, pageItem);
}
或者正如groo所說,只是投下它:
foreach (string pageItemIdCode in pageItemsIdCodes)
{
Type t = Type.GetTypeFromProgID(pageItemIdCode);
BasePageItem pageItem = (BasePageItem)Activator.CreateInstance(t, new object[]{this});
PageItemRecords.Add(pageItemIdCode, pageItem);
}
如果要返回實際類型,還可以執行以下操作:
foreach (string pageItemIdCode in pageItemsIdCodes)
{
Type t = Type.GetTypeFromProgID(pageItemIdCode);
BasePageItem pageItem = Activator.CreateInstance(t); // Change constructor
pageItem.SetMananger(this); // Add SetMananger call to BasePageItem
PageItemRecords.Add(pageItemIdCode, pageItem);
}
這是完整的工作示例:
using System;
using System.Collections.Generic;
using System.Text;
namespace TestInstant
{
class Program
{
static void Main(string[] args)
{
List<string> pageItemsIdCodes = new List<string>();
pageItemsIdCodes.Add("PageItem1");
pageItemsIdCodes.Add("PageItem2");
PageItemManager pageItemManager = new PageItemManager(pageItemsIdCodes);
pageItemManager.DisplayMenu();
Console.ReadLine();
}
}
class PageItemManager
{
private Dictionary<string, BasePageItem> PageItemRecords = new Dictionary<string, BasePageItem>();
public PageItemManager(List<string> pageItemsIdCodes)
{
//manually
//PageItemRecords.Add("PageItem1", new PageItem1(this));
//PageItemRecords.Add("PageItem2", new PageItem2(this));
foreach (string pageItemIdCode in pageItemsIdCodes)
{
Type t = Type.GetType("TestInstant."+pageItemIdCode);
BasePageItem pageItem = (BasePageItem)Activator.CreateInstance(t, new Object[] { this });
PageItemRecords.Add(pageItemIdCode, pageItem);
}
}
public void DisplayMenu()
{
foreach (BasePageItem pageItemRecord in PageItemRecords.Values)
{
Console.WriteLine(pageItemRecord.Title);
}
}
}
class BasePageItem
{
private string mTitle;
public string Title { get { return mTitle; } set { mTitle = value; } }
protected PageItemManager pageItemManager;
public BasePageItem(PageItemManager pageItemManager)
{
this.pageItemManager = pageItemManager;
}
}
class PageItem1 : BasePageItem
{
public PageItem1(PageItemManager pageItemManager)
: base(pageItemManager)
{
Title = "This is page one.";
}
}
class PageItem2 : BasePageItem
{
public PageItem2(PageItemManager pageItemManager)
: base(pageItemManager)
{
Title = "This is page two.";
}
}
}
這成功編譯。 我剛嘗試過。
foreach(string pageItemIdCode in pageItemsIdCodes) {
Type t = Type.GetType(pageItemIdCode);
BasePageItem pageItem = (BasePageItem) Activator.CreateInstance(t, new object[] { this });
PageItemRecords.Add(pageItemIdCode, pageItem);
}
然后它在運行時失敗,因為pageItemIdCode
值不正確。 更改如下:
List<string> pageItemsIdCodes = new List<string>() { "TestInstant.PageItem1", "TestInstant.PageItem2" };
使代碼成功運行。
您需要記住,當Reflection方法無法找到某些內容時,它總是返回null
,而不是引發異常。 如果您的代碼期望Type.GetType
始終成功,那么您需要檢查空值並引發自己的異常,否則您將獲得級聯故障,因為空值通過其余代碼傳播。
查看Activator.CreateInstance的重載。 您可以將對象數組中的構造函數傳遞給它們一個。
我可以建議Assembly.CreateInstance()您可以使用此函數來創建指定程序集的實例。
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