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使用C中的反射从字符串获取属性值#

reflection c#

756

pedrofernandes · 技术社区 · 15 年前

我正在尝试实现 Data transformation using Reflection ^一我的代码中的示例。

这个 GetSourceValue 函数有一个比较各种类型的开关,但我想删除这些类型和属性,并 获取源程序 仅使用单个字符串作为参数获取属性的值。我想在字符串中传递一个类和属性,并解析该属性的值。

这有可能吗?

^一 _{Web Archive version of original blog post}

21 回复 | 直到 5 年前

1492

Ed Swangren 11 年前

 public static object GetPropValue(object src, string propName)
 {
     return src.GetType().GetProperty(propName).GetValue(src, null);
 }

当然,您需要添加验证和其他内容,但这就是其中的要点。

188

jheddings 12 年前

像这样的怎么样:

public static Object GetPropValue(this Object obj, String name) {
    foreach (String part in name.Split('.')) {
        if (obj == null) { return null; }

        Type type = obj.GetType();
        PropertyInfo info = type.GetProperty(part);
        if (info == null) { return null; }

        obj = info.GetValue(obj, null);
    }
    return obj;
}

public static T GetPropValue<T>(this Object obj, String name) {
    Object retval = GetPropValue(obj, name);
    if (retval == null) { return default(T); }

    // throws InvalidCastException if types are incompatible
    return (T) retval;
}

这将允许您使用单个字符串下降到属性中,如下所示:

DateTime now = DateTime.Now;
int min = GetPropValue<int>(now, "TimeOfDay.Minutes");
int hrs = now.GetPropValue<int>("TimeOfDay.Hours");

您可以将这些方法用作静态方法或扩展。

Eduardo Cuomo Sajjad Ali Khan 10 年前

添加到任何 Class :

public class Foo
{
    public object this[string propertyName]
    {
        get { return this.GetType().GetProperty(propertyName).GetValue(this, null); }
        set { this.GetType().GetProperty(propertyName).SetValue(this, value, null); }
    }

    public string Bar { get; set; }
}

然后,您可以将其用作:

Foo f = new Foo();
// Set
f["Bar"] = "asdf";
// Get
string s = (string)f["Bar"];

J0e3gan 10 年前

用这个怎么样 CallByName 的 Microsoft.VisualBasic 命名空间(命名空间) Microsoft.VisualBasic.dll )?它使用反射来获取普通对象、COM对象甚至动态对象的属性、字段和方法。

using Microsoft.VisualBasic;
using Microsoft.VisualBasic.CompilerServices;

然后

Versioned.CallByName(this, "method/function/prop name", CallType.Get).ToString();

Devsined 10 年前

杰丁斯的回答很好。我希望改进它,允许引用聚合数组或对象集合,以便propertyname可以是property1.property2[x].property3:

    public static object GetPropertyValue(object srcobj, string propertyName)
    {
        if (srcobj == null)
            return null;

        object obj = srcobj;

        // Split property name to parts (propertyName could be hierarchical, like obj.subobj.subobj.property
        string[] propertyNameParts = propertyName.Split('.');

        foreach (string propertyNamePart in propertyNameParts)
        {
            if (obj == null)    return null;

            // propertyNamePart could contain reference to specific 
            // element (by index) inside a collection
            if (!propertyNamePart.Contains("["))
            {
                PropertyInfo pi = obj.GetType().GetProperty(propertyNamePart);
                if (pi == null) return null;
                obj = pi.GetValue(obj, null);
            }
            else
            {   // propertyNamePart is areference to specific element 
                // (by index) inside a collection
                // like AggregatedCollection[123]
                //   get collection name and element index
                int indexStart = propertyNamePart.IndexOf("[")+1;
                string collectionPropertyName = propertyNamePart.Substring(0, indexStart-1);
                int collectionElementIndex = Int32.Parse(propertyNamePart.Substring(indexStart, propertyNamePart.Length-indexStart-1));
                //   get collection object
                PropertyInfo pi = obj.GetType().GetProperty(collectionPropertyName);
                if (pi == null) return null;
                object unknownCollection = pi.GetValue(obj, null);
                //   try to process the collection as array
                if (unknownCollection.GetType().IsArray)
                {
                    object[] collectionAsArray = unknownCollection as Array[];
                    obj = collectionAsArray[collectionElementIndex];
                }
                else
                {
                    //   try to process the collection as IList
                    System.Collections.IList collectionAsList = unknownCollection as System.Collections.IList;
                    if (collectionAsList != null)
                    {
                        obj = collectionAsList[collectionElementIndex];
                    }
                    else
                    {
                        // ??? Unsupported collection type
                    }
                }
            }
        }

        return obj;
    }

testing 6 年前

如果我使用的代码来自 Ed S. 我得到

“ReflectionExtensions.GetProperty(Type,String)”由于其保护级别而不可访问

似乎 GetProperty() 在xamarin.forms中不可用。 TargetFrameworkProfile 是 Profile7 在我的可移植类库(.NET Framework 4.5、Windows 8、ASP.NET Core 1.0、Xamarin.android、Xamarin.ios、Xamarin.ios classic)中。

现在我找到了一个可行的解决方案:

using System.Linq;
using System.Reflection;

public static object GetPropValue(object source, string propertyName)
{
    var property = source.GetType().GetRuntimeProperties().FirstOrDefault(p => string.Equals(p.Name, propertyName, StringComparison.OrdinalIgnoreCase));
    return property?.GetValue(source);
}

Source

Rubens Farias 9 年前

关于嵌套属性讨论,如果使用 DataBinder.Eval Method (Object, String) 如下:

var value = DataBinder.Eval(DateTime.Now, "TimeOfDay.Hours");

当然,您需要在 System.Web 装配,但这可能不是什么大问题。

Matt Frear 7 年前

.NET标准中要调用的方法已更改(从1.6开始)。我们还可以使用C 6的空条件运算符。

using System.Reflection; 
public static object GetPropValue(object src, string propName)
{
    return src.GetType().GetRuntimeProperty(propName)?.GetValue(src);
}

tom redfern 9 年前

使用的属性信息 系统反射 命名空间。无论我们尝试访问什么属性,反射编译都很好。运行时出错。

    public static object GetObjProperty(object obj, string property)
    {
        Type t = obj.GetType();
        PropertyInfo p = t.GetProperty("Location");
        Point location = (Point)p.GetValue(obj, null);
        return location;
    }

它可以很好地获取对象的位置属性

Label1.Text = GetObjProperty(button1, "Location").ToString();

我们会得到位置:x=71,y=27 我们也可以用同样的方法返回location.x或location.y。

Boncho Valkov 9 年前

public static List<KeyValuePair<string, string>> GetProperties(object item) //where T : class
    {
        var result = new List<KeyValuePair<string, string>>();
        if (item != null)
        {
            var type = item.GetType();
            var properties = type.GetProperties(BindingFlags.Public | BindingFlags.Instance);
            foreach (var pi in properties)
            {
                var selfValue = type.GetProperty(pi.Name).GetValue(item, null);
                if (selfValue != null)
                {
                    result.Add(new KeyValuePair<string, string>(pi.Name, selfValue.ToString()));
                }
                else
                {
                    result.Add(new KeyValuePair<string, string>(pi.Name, null));
                }
            }
        }
        return result;
    }

这是一种在列表中获取所有属性及其值的方法。

Recursor 10 年前

这是另一种查找嵌套属性的方法,不需要字符串来告诉您嵌套路径。对于单属性方法,请归功于Ed S.。

    public static T FindNestedPropertyValue<T, N>(N model, string propName) {
        T retVal = default(T);
        bool found = false;

        PropertyInfo[] properties = typeof(N).GetProperties();

        foreach (PropertyInfo property in properties) {
            var currentProperty = property.GetValue(model, null);

            if (!found) {
                try {
                    retVal = GetPropValue<T>(currentProperty, propName);
                    found = true;
                } catch { }
            }
        }

        if (!found) {
            throw new Exception("Unable to find property: " + propName);
        }

        return retVal;
    }

        public static T GetPropValue<T>(object srcObject, string propName) {
        return (T)srcObject.GetType().GetProperty(propName).GetValue(srcObject, null);
    }

Irshad Kredns 9 年前

你从来没有提到你要检查的对象,而且由于你拒绝了引用一个给定对象的对象,我假设你是指一个静态对象。

using System.Reflection;
public object GetPropValue(string prop)
{
    int splitPoint = prop.LastIndexOf('.');
    Type type = Assembly.GetEntryAssembly().GetType(prop.Substring(0, splitPoint));
    object obj = null;
    return type.GetProperty(prop.Substring(splitPoint + 1)).GetValue(obj, null);
}

注意,我用局部变量标记了正在检查的对象 obj . null 表示静态,否则将其设置为您想要的。还要注意, GetEntryAssembly() 是获取“正在运行”程序集的几种可用方法之一,如果在加载类型时遇到困难,您可能会希望使用它。

Irshad Kredns 9 年前

下面的代码是一个递归方法,用于显示对象实例中包含的所有属性名和值的整个层次结构。此方法使用了Alexd的简化版本 GetPropertyValue() 回答上面的这个问题。多亏了这条讨论线,我才知道该怎么做!

例如,我使用此方法显示 WebService 通过调用以下方法进行响应:

PropertyValues_byRecursion("Response", response, false);

public static object GetPropertyValue(object srcObj, string propertyName)
{
  if (srcObj == null) 
  {
    return null; 
  }
  PropertyInfo pi = srcObj.GetType().GetProperty(propertyName.Replace("[]", ""));
  if (pi == null)
  {
    return null;
  }
  return pi.GetValue(srcObj);
}

public static void PropertyValues_byRecursion(string parentPath, object parentObj, bool showNullValues)
{
  /// Processes all of the objects contained in the parent object.
  ///   If an object has a Property Value, then the value is written to the Console
  ///   Else if the object is a container, then this method is called recursively
  ///       using the current path and current object as parameters

  // Note:  If you do not want to see null values, set showNullValues = false

  foreach (PropertyInfo pi in parentObj.GetType().GetTypeInfo().GetProperties())
  {
    // Build the current object property's namespace path.  
    // Recursion extends this to be the property's full namespace path.
    string currentPath = parentPath + "." + pi.Name;

    // Get the selected property's value as an object
    object myPropertyValue = GetPropertyValue(parentObj, pi.Name);
    if (myPropertyValue == null)
    {
      // Instance of Property does not exist
      if (showNullValues)
      {
        Console.WriteLine(currentPath + " = null");
        // Note: If you are replacing these Console.Write... methods callback methods,
        //       consider passing DBNull.Value instead of null in any method object parameters.
      }
    }
    else if (myPropertyValue.GetType().IsArray)
    {
      // myPropertyValue is an object instance of an Array of business objects.
      // Initialize an array index variable so we can show NamespacePath[idx] in the results.
      int idx = 0;
      foreach (object business in (Array)myPropertyValue)
      {
        if (business == null)
        {
          // Instance of Property does not exist
          // Not sure if this is possible in this context.
          if (showNullValues)
          {
            Console.WriteLine(currentPath  + "[" + idx.ToString() + "]" + " = null");
          }
        }
        else if (business.GetType().IsArray)
        {
          // myPropertyValue[idx] is another Array!
          // Let recursion process it.
          PropertyValues_byRecursion(currentPath + "[" + idx.ToString() + "]", business, showNullValues);
        }
        else if (business.GetType().IsSealed)
        {
          // Display the Full Property Path and its Value
          Console.WriteLine(currentPath + "[" + idx.ToString() + "] = " + business.ToString());
        }
        else
        {
          // Unsealed Type Properties can contain child objects.
          // Recurse into my property value object to process its properties and child objects.
          PropertyValues_byRecursion(currentPath + "[" + idx.ToString() + "]", business, showNullValues);
        }
        idx++;
      }
    }
    else if (myPropertyValue.GetType().IsSealed)
    {
      // myPropertyValue is a simple value
      Console.WriteLine(currentPath + " = " + myPropertyValue.ToString());
    }
    else
    {
      // Unsealed Type Properties can contain child objects.
      // Recurse into my property value object to process its properties and child objects.
      PropertyValues_byRecursion(currentPath, myPropertyValue, showNullValues);
    }
  }
}

Rahma Samaroon 7 年前

public static TValue GetFieldValue<TValue>(this object instance, string name)
{
    var type = instance.GetType(); 
    var field = type.GetFields(BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance).FirstOrDefault(e => typeof(TValue).IsAssignableFrom(e.FieldType) && e.Name == name);
    return (TValue)field?.GetValue(instance);
}

public static TValue GetPropertyValue<TValue>(this object instance, string name)
{
    var type = instance.GetType();
    var field = type.GetProperties(BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance).FirstOrDefault(e => typeof(TValue).IsAssignableFrom(e.PropertyType) && e.Name == name);
    return (TValue)field?.GetValue(instance);
}

Komal Narang 6 年前

public class YourClass
{
    //Add below line in your class
    public object this[string propertyName] => GetType().GetProperty(propertyName)?.GetValue(this, null);
    public string SampleProperty { get; set; }
}

//And you can get value of any property like this.
var value = YourClass["SampleProperty"];

Glory Raj 13 年前

Dim NewHandle As YourType = CType(Microsoft.VisualBasic.CallByName(ObjectThatContainsYourVariable, "YourVariableName", CallType), YourType)

andrewsi Laxman Battini 10 年前

更短的路……

var a = new Test { Id = 1 , Name = "A" , date = DateTime.Now};
var b = new Test { Id = 1 , Name = "AXXX", date = DateTime.Now };

var compare = string.Join("",a.GetType().GetProperties().Select(x => x.GetValue(a)).ToArray())==
              string.Join("",b.GetType().GetProperties().Select(x => x.GetValue(b)).ToArray());

Community kavare 7 年前

jheddings 和 AlexD 他们都写了关于如何解析属性字符串的很好的答案。我想把我的混合,因为我写了一个专门的图书馆正是为了这个目的。

Pather.CSharp 的主要类是 Resolver . 默认情况下,它可以解析属性、数组和字典条目。

例如,如果有这样的对象

var o = new { Property1 = new { Property2 = "value" } };

想要得到 Property2 ,您可以这样做:

IResolver resolver = new Resolver();
var path = "Property1.Property2";
object result = r.Resolve(o, path); 
//=> "value"

这是最基本的路径示例。如果你想看看它还能做什么,或者你能怎么延伸它,就去看看它。 Github page .

user3175253 6 年前

这是我的解决方案。它还与COM对象一起工作,并允许从COM对象访问集合/数组项。

public static object GetPropValue(this object obj, string name)
{
    foreach (string part in name.Split('.'))
    {
        if (obj == null) { return null; }

        Type type = obj.GetType();
        if (type.Name == "__ComObject")
        {
            if (part.Contains('['))
            {
                string partWithoundIndex = part;
                int index = ParseIndexFromPropertyName(ref partWithoundIndex);
                obj = Versioned.CallByName(obj, partWithoundIndex, CallType.Get, index);
            }
            else
            {
                obj = Versioned.CallByName(obj, part, CallType.Get);
            }
        }
        else
        {
            PropertyInfo info = type.GetProperty(part);
            if (info == null) { return null; }
            obj = info.GetValue(obj, null);
        }
    }
    return obj;
}

private static int ParseIndexFromPropertyName(ref string name)
{
    int index = -1;
    int s = name.IndexOf('[') + 1;
    int e = name.IndexOf(']');
    if (e < s)
    {
        throw new ArgumentException();
    }
    string tmp = name.Substring(s, e - s);
    index = Convert.ToInt32(tmp);
    name = name.Substring(0, s - 1);
    return index;
}

Hennadii 6 年前

看看 Heleonix.Reflection 图书馆。您可以通过路径获取/设置/调用成员,或者创建一个比反射更快的getter/setter(编译为委托的lambda)。例如:

var success = Reflector.Get(DateTime.Now, null, "Date.Year", out int value);

或者创建一次getter并缓存以供重用(这更具性能,但如果中间成员为空,则可能引发NullReferenceException):

var getter = Reflector.CreateGetter<DateTime, int>("Date.Year", typeof(DateTime));
getter(DateTime.Now);

或者如果你想创建一个 List<Action<object, object>> 对于不同的getter,只需为已编译的委托指定基类型(类型转换将添加到已编译的lambda中):

var getter = Reflector.CreateGetter<object, object>("Date.Year", typeof(DateTime));
getter(DateTime.Now);

OneCricketeer Gabriele Mariotti 5 年前

以下方法非常适合我:

class MyClass {
    public string prop1 { set; get; }

    public object this[string propertyName]
    {
        get { return this.GetType().GetProperty(propertyName).GetValue(this, null); }
        set { this.GetType().GetProperty(propertyName).SetValue(this, value, null); }
    }
}

要获取属性值:

MyClass t1 = new MyClass();
...
string value = t1["prop1"].ToString();

要设置属性值:

t1["prop1"] = value;