C# 泛型类型转换 FROM 字符串
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原文地址: http://stackoverflow.com/questions/8625/
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Generic type conversion FROM string
提问by Rob Cooper
I have a class that I want to use to store "properties" for another class. These properties simply have a name and a value. Ideally, what I would like is to be able to add typedproperties, so that the "value" returned is always of the type that I want it to be.
我有一个类，我想用它来存储另一个类的“属性”。这些属性只有一个名称和一个值。理想情况下，我希望能够添加类型化属性，以便返回的“值”始终是我想要的类型。
The type should always be a primitive. This class subclasses an abstract class which basically stores the name and value as string. The idea being that this subclass will add some type-safety to the base class (as well as saving me on some conversion).
类型应该始终是原始类型。这个类是一个抽象类的子类，它基本上将名称和值存储为字符串。这个想法是这个子类将为基类添加一些类型安全（以及节省我的一些转换）。
So, I have created a class which is (roughly) this:
所以，我创建了一个类，它（大致）是这样的：
public class TypedProperty<DataType> : Property
{
public DataType TypedValue
{
get { // Having problems here! }
set { base.Value = value.ToString();}
}
}
So the question is:
所以问题是：
Is there a "generic" way to convert from string back to a primitive?
有没有一种“通用”的方法可以将字符串转换回原语？
I can't seem to find any generic interface that links the conversion across the board (something like ITryParsablewould have been ideal!).
我似乎找不到任何可以全面链接转换的通用接口（像ItryParsable这样的东西本来是理想的！）。
采纳答案by lubos hasko
I am not sure whether I understood your intentions correctly, but let's see if this one helps.
我不确定我是否正确理解了您的意图，但让我们看看这是否有帮助。
public class TypedProperty<T> : Property where T : IConvertible
{
public T TypedValue
{
get { return (T)Convert.ChangeType(base.Value, typeof(T)); }
set { base.Value = value.ToString();}
}
}
回答by Greg Hewgill
You could possibly use a construct such as a traits class. In this way, you would have a parameterised helper class that knows how to convert a string to a value of its own type. Then your getter might look like this:
您可能会使用诸如traits class 之类的构造。通过这种方式，您将拥有一个参数化的辅助类，该类知道如何将字符串转换为其自身类型的值。那么你的 getter 可能看起来像这样：
get { return StringConverter<DataType>.FromString(base.Value); }
Now, I must point out that my experience with parameterised types is limited to C++ and its templates, but I imagine there is some way to do the same sort of thing using C# generics.
现在，我必须指出，我对参数化类型的经验仅限于 C++ 及其模板，但我想有一些方法可以使用 C# 泛型来做同样的事情。
回答by dbkk
For many types (integer, double, DateTime etc), there is a static Parse method. You can invoke it using reflection:
对于许多类型（整数、双精度、日期时间等），有一个静态 Parse 方法。您可以使用反射调用它：
MethodInfo m = typeof(T).GetMethod("Parse", new Type[] { typeof(string) } );
if (m != null)
{
return m.Invoke(null, new object[] { base.Value });
}
回答by Tim Coker
lubos hasko's method fails for nullables. The method below will work for nullables. I didn't come up with it, though. I found it via Google: http://web.archive.org/web/20101214042641/http://dogaoztuzun.com/post/C-Generic-Type-Conversion.aspxCredit to "Tuna Toksoz"
lubos hasko 的方法对于 nullables 失败。下面的方法适用于可空值。不过我没有想出来。我是通过谷歌找到的：http: //web.archive.org/web/20101214042641/http://dogaoztuzun.com/post/C-Generic-Type-Conversion.aspx 感谢“Tuna Toksoz”
Usage first:
先用：
TConverter.ChangeType<T>(StringValue);
The class is below.
课程如下。
public static class TConverter
{
public static T ChangeType<T>(object value)
{
return (T)ChangeType(typeof(T), value);
}
public static object ChangeType(Type t, object value)
{
TypeConverter tc = TypeDescriptor.GetConverter(t);
return tc.ConvertFrom(value);
}
public static void RegisterTypeConverter<T, TC>() where TC : TypeConverter
{
TypeDescriptor.AddAttributes(typeof(T), new TypeConverterAttribute(typeof(TC)));
}
}
回答by Mastahh
public class TypedProperty<T> : Property
{
public T TypedValue
{
get { return (T)(object)base.Value; }
set { base.Value = value.ToString();}
}
}
I using converting via an object. It is a little bit simpler.
我使用通过对象进行转换。它稍微简单一点。
回答by Dinesh Rathee
TypeDescriptor.GetConverter(PropertyObject).ConvertFrom(Value)
TypeDescriptoris class having method GetConvertorwhich accept a Typeobject and then you can call ConvertFrommethod to convert the valuefor that specified object.
TypeDescriptor是具有GetConvertor接受Type对象的方法的类，然后您可以调用ConvertFrom方法来转换该value指定对象的方法。
回答by anhoppe
I used lobos answer and it works. But I had a problem with the conversion of doublesbecause of the culture settings. So I added
我使用了 lobos 答案并且它有效。但是由于文化设置，我在转换双打时遇到了问题。所以我加了
return (T)Convert.ChangeType(base.Value, typeof(T), CultureInfo.InvariantCulture);
回答by Bob C
Check the static Nullable.GetUnderlyingType.
- If the underlying type is null, then the template parameter is not Nullable, and we can use that type directly
- If the underlying type is not null, then use the underlying type in the conversion.
检查静态Nullable.GetUnderlyingType。- 如果底层类型为 null，则模板参数不是Nullable，我们可以直接使用该类型 - 如果底层类型不为 null，则在转换中使用底层类型。
Seems to work for me:
似乎对我有用：
public object Get( string _toparse, Type _t )
{
// Test for Nullable<T> and return the base type instead:
Type undertype = Nullable.GetUnderlyingType(_t);
Type basetype = undertype == null ? _t : undertype;
return Convert.ChangeType(_toparse, basetype);
}
public T Get<T>(string _key)
{
return (T)Get(_key, typeof(T));
}
public void test()
{
int x = Get<int>("14");
int? nx = Get<Nullable<int>>("14");
}
回答by Todd Menier
Yet another variation. Handles Nullables, as well as situations where the string is null and T is notnullable.
又一个变种。处理空值，以及字符串为空且 T不可空的情况。
public class TypedProperty<T> : Property where T : IConvertible
{
public T TypedValue
{
get
{
if (base.Value == null) return default(T);
var type = Nullable.GetUnderlyingType(typeof(T)) ?? typeof(T);
return (T)Convert.ChangeType(base.Value, type);
}
set { base.Value = value.ToString(); }
}
}
回答by Ghominejad
With inspiration from the Bob's answer, these extensions also support null value conversion and all primitive conversion back and fourth.
受Bob回答的启发，这些扩展还支持空值转换和所有原语来回转换。
public static class ConversionExtensions
{
public static object Convert(this object value, Type t)
{
Type underlyingType = Nullable.GetUnderlyingType(t);
if (underlyingType != null && value == null)
{
return null;
}
Type basetype = underlyingType == null ? t : underlyingType;
return System.Convert.ChangeType(value, basetype);
}
public static T Convert<T>(this object value)
{
return (T)value.Convert(typeof(T));
}
}
Examples
例子
string stringValue = null;
int? intResult = stringValue.Convert<int?>();
int? intValue = null;
var strResult = intValue.Convert<string>();
