如何使用 "Expression.Parameter" 和 "Expression.Call" API 调用通用方法
How to Call a Generic Method using "Expression.Parameter" and "Expression.Call" APIs
使用 表达式树 API 我想生成如下所示的代码：
FieldInfo enumFieldInfo = enumFieldInfoSet.SingleOrDefault(fieldInfo => fieldInfo.Name == enumName);
我写了这段代码，但它不起作用：
var enumerableType = typeof(Enumerable);
var enumerableGenericType = typeof(IEnumerable<>).MakeGenericType(typeof(FieldInfo));
var predicateGenericType = typeof(Func<>).MakeGenericType(typeof(Func<FieldInfo, bool>));
ParameterExpression fieldInfoSource = Expression.Parameter(enumerableGenericType, "fieldInfoSource");
ParameterExpression predicateSource = Expression.Parameter(predicateGenericType, "funcPredicateOnFieldInfo");
var arrayOfTypes = new Type[] { enumerableGenericType, predicateGenericType };
MethodCallExpression SingleOrDefaultMethodCall = Expression.Call(enumerableType, "SingleOrDefault",arrayOfTypes, fieldInfoSource, predicateSource);
这是 运行时间错误：类型 'System.Linq.Enumerable' 上的泛型方法 'SingleOrDefault' 与提供的类型参数和参数不兼容。如果该方法是非泛型的，则不应提供类型参数。
我已经尝试了多种类型强制组合，但仍然没有找到正确的组合。我知道 SingleOrDefault 是 Enumerable class 上的扩展方法，它需要两个参数；我已经通过调试器查看了代码，并在 运行-time 编写代码检查其属性；我错过了什么。
问题是您正在使用带有类型的 Expression.Call 重载，对于静态方法，您需要使用 MethodInfo.
的重载
void Main()
{
Expression<Func<IEnumerable<FieldInfo>, Func<FieldInfo,bool>, FieldInfo>> singleOrDefaultExpr = (l,p) => l.SingleOrDefault(p);
var callSource = (MethodCallExpression)singleOrDefaultExpr.Body;
var method = callSource.Method;
var collectionParameter = Expression.Parameter(typeof(IEnumerable<FieldInfo>), "enumFieldInfoSet");
var enumNamePredicateParameter = Expression.Parameter(typeof(Func<FieldInfo,bool>), "enumNamePredicate");
var body = Expression.Call(method, collectionParameter, enumNamePredicateParameter);
var lambda = Expression.Lambda<Func<IEnumerable<FieldInfo>, Func<FieldInfo, bool>, FieldInfo>>(body, collectionParameter, enumNamePredicateParameter);
var f = lambda.Compile();
Console.WriteLine(f(typeof(Apple).GetFields(), fi => fi.Name == "color").Name);
}
class Apple
{
public string color;
}
另外，您可以使用另一种方法来查找所需的 MethodInfo：
var method = typeof(Enumerable)
.GetMethods()
.Single(m => m.Name == "SingleOrDefault" && m.GetParameters().Count() == 2)
.MakeGenericMethod(new[] {typeof(FieldInfo)});
更新：
其实有一个更简单的方法，你的方法是对的，但是你的代码出错了。
var collectionParameter = Expression.Parameter(typeof(IEnumerable<FieldInfo>), "enumFieldInfoSet");
var enumNamePredicateParameter = Expression.Parameter(typeof(Func<FieldInfo,bool>), "enumNamePredicate");
var body = Expression.Call(typeof(Enumerable), "SingleOrDefault", new[] { typeof(FieldInfo)}, collectionParameter, enumNamePredicateParameter);
var lambda = Expression.Lambda<Func<IEnumerable<FieldInfo>, Func<FieldInfo, bool>, FieldInfo>>(body, collectionParameter, enumNamePredicateParameter);
问题是 SingleOrDefault 只有一个 泛型类型参数：'FieldInfo' 在这种情况下：
SingleOrDefault<FieldInfo>(....
不要将它与方法参数混淆，它们有两个：
SingleOrDefault<GenericParameter>(
this IEnumerable<GenericParameter> firstMethodParameter,
Func<GenericParameter, bool> secondMethodParameter
)
George 很好地帮助我走上了正确的轨道，并为我提供了部分答案；我重新设计了我的代码，这样我就很清楚了。这是我想在测试我们的元编程运行时时机器生成的代码示例。我提供的代码多于特定问题所需的代码，但我希望其他人能看到更大的上下文。
// Code to Generate Enum Field Metadata ...
string enumName = Enum.GetName(theEnumType, theOrdinalEnumValue);
Array enumValues = Enum.GetValues(theEnumType);
object enumValue = enumValues.GetValue(theOrdinalEnumValue);
object enumObject = Enum.ToObject(theEnumType, theOrdinalEnumValue);
// Create Local variables of the types targeted for assignment expressions that we will make in the generated code
var enumVariables = Expression.RuntimeVariables(Expression.Variable(typeof(string), "gcEnumName"),
Expression.Variable(typeof(Array), "gcEnumValues"),
Expression.Variable(typeof(object), "gcEnumValue"),
Expression.Variable(theEnumType, "gcEnumObject"),
Expression.Variable(typeof(FieldInfo), "gcFieldInfoOnEnum"));
// Setup the Input Parameters for calls into Enum and Array Types in preperation for Assignments
ParameterExpression theInputOfEnumType = Expression.Variable(typeof(Type), "theInputOfEnumType");
ParameterExpression theEnumFieldNameValue = Expression.Variable(typeof(string), "theEnumFieldNameValue");
ParameterExpression aEnumObjectIndexValue = Expression.Variable(typeof(int), "aEnumObjectIndexValue");
ParameterExpression anArrayOfEnumObjects = Expression.Variable(typeof(Array), "anArrayOfEnumObjects");
ParameterExpression anEnumerableObject = Expression.Variable(typeof(Enumerable), "anEnumerableObject");
ParameterExpression directEnumTypeResolved = Expression.Variable(theEnumType, "directEnumTypeResolved");
ParameterExpression fieldInfoOnEnum = Expression.Variable(typeof(FieldInfo), "fieldInfoOnEnum");
var fieldInfoEnumerableRepresentation = typeof(Enumerable);
在调用 "Expression.Call" 的过程中，我们需要获取一些 MethodInfo 数据
// We need to generate MethodInfo on the Methods we want to call in the generated code. This is metadata
// we need to call the Expression.Call API.
MethodInfo enumGetNameMethodInfo = enumMetadata.GetMethods().FirstOrDefault(info => info.Name == "GetName");
MethodInfo enumGetValuesMethodInfo = enumMetadata.GetMethods().FirstOrDefault(info => info.Name == "GetValues");
MethodInfo enumGetValueMethodInfo = arraryMetadata.GetMethods()
.FirstOrDefault(methodInfo => (methodInfo.Name == "GetValue") && methodInfo.GetParameters().Any(param =>param.ParameterType == typeof(int)));
MethodInfo enumToObjectMethodInfo = enumMetadata.GetMethods()
.FirstOrDefault(info => info.Name == "ToObject");
// We know that there exist a number of polymorphic instances of the "SingleOrDefault" Extension method
// so we use the name of the parameter named "predicate" to locate our method. **FYI Can't use the MethodInfo data in a call to Expression.Call - It's a generic definition**.
MethodInfo enumerableSingleOrDefaultInfo = fieldInfoEnumerableRepresentation.GetMethods()
.FirstOrDefault(methodInfo => (methodInfo.Name == "SingleOrDefault") &&
methodInfo.GetParameters()
.Any(param => param.Name == "predicate"));
下面是调用通用方法的最终代码：
// An approach to setup a Generic method call that will be used in an Expression.Assign call
// I decompose this code so for debugging purposes
// I create the "inputOfTSourceType" as a Generic Type because in the Definition of "SingleOrDefault" method there is only one Generic Parameter;
// also, take special note that in the assemblage of Expression.Call methods any of the methods that take a MethodInfo instance you can't pass in
// a "Generic" method definition. If you take a look at the code that is called it will throw and exception if it detects the IsGenericMethodDefinition
// flag is true.
var inputOfTSourceType = typeof(IEnumerable<>).MakeGenericType(typeof(FieldInfo)); // This is the type on the "source" TSource parameter
var predicateOfFuncType = typeof(Func<FieldInfo, bool>); // This is the type on the "predicate" parameter
// Take note there that we only define one(1) type here ("inputParameterType"); this is the type we wish apply to the Generic Type TSource
// declaration: public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate);
var inputParameterType = new[] {typeof(FieldInfo)}; // This is the type we must match to "source" parameter
// The "SingleOrDefault" method can take two parameters and in this case I need to pass in a lambda expression as the predicate.
// Se we need two parameters.
ParameterExpression fieldInfoSource = Expression.Parameter(inputOfTSourceType, "fieldInfoSource"); // This is: this IEnumerable<TSource>
ParameterExpression predicateSource = Expression.Parameter(predicateOfFuncType, "funcPredicateOnFieldInfo"); // This is: Func<TSource, bool> predicate
MethodCallExpression SingleOrDefaultMethodCall =
Expression.Call(fieldInfoEnumerableRepresentation, // This is the Object Instance for which the
"SingleOrDefault", // The Name of the Generic Method
inputParameterType, // The Generic Type
fieldInfoSource, // this is the "this" source parameter
predicateSource); // this the "predicate" parameter
Expression localEnumNameAssignment =
Expression.Assign(enumVariables.Variables[0], EnumGetNameMethodCall);
Expression localEnumObjectsAssignment =
Expression.Assign(enumVariables.Variables[1], EnumGetValauesMethodCall);
Expression localEnumObjectAssignment =
Expression.Assign(enumVariables.Variables[2], ArrayGetValueMethodCall);
Expression localEnumTypeAssignment =
Expression.Assign(enumVariables.Variables[3], Expression.Convert(EnumToObjectMethodCall, theEnumType));
Expression localFieldInfoAssignment =
Expression.Assign(enumVariables.Variables[4], Expression.Convert(SingleOrDefaultMethodCall, typeof(FieldInfo)));
BlockExpression blockExpression =
Expression.Block(enumVariables,
localEnumNameAssignment,
localEnumObjectsAssignment,
localEnumObjectAssignment,
localEnumTypeAssignment,
localFieldInfoAssignment,
enumTypeToReturn);
这是生成的代码：
$gcEnumName = .Call System.Enum.GetName(
$theInputOfEnumType, $gcEnumName = (System.String)$theEnumFieldNameValue)
$gcEnumValues = .Call System.Enum.GetValues($theInputOfEnumType)
$gcEnumValue = .Call $anArrayOfEnumObjects.GetValue((System.Int32) $theOrdinalEnumValue)
$gcEnumObject = (WorkflowMessagingCommands).Call System.Enum.ToObject(
$theInputOfEnumType,
(System.Object)$theEnumInstance)
// Here is the generated code to call "SignleOrDefault"
$gcFieldInfoOnEnum = .Call System.Linq.Enumerable.SingleOrDefault(
$thisSourceType,
$predciateType)
使用 表达式树 API 我想生成如下所示的代码：
FieldInfo enumFieldInfo = enumFieldInfoSet.SingleOrDefault(fieldInfo => fieldInfo.Name == enumName);
我写了这段代码，但它不起作用：
var enumerableType = typeof(Enumerable);
var enumerableGenericType = typeof(IEnumerable<>).MakeGenericType(typeof(FieldInfo));
var predicateGenericType = typeof(Func<>).MakeGenericType(typeof(Func<FieldInfo, bool>));
ParameterExpression fieldInfoSource = Expression.Parameter(enumerableGenericType, "fieldInfoSource");
ParameterExpression predicateSource = Expression.Parameter(predicateGenericType, "funcPredicateOnFieldInfo");
var arrayOfTypes = new Type[] { enumerableGenericType, predicateGenericType };
MethodCallExpression SingleOrDefaultMethodCall = Expression.Call(enumerableType, "SingleOrDefault",arrayOfTypes, fieldInfoSource, predicateSource);
这是 运行时间错误：类型 'System.Linq.Enumerable' 上的泛型方法 'SingleOrDefault' 与提供的类型参数和参数不兼容。如果该方法是非泛型的，则不应提供类型参数。
我已经尝试了多种类型强制组合，但仍然没有找到正确的组合。我知道 SingleOrDefault 是 Enumerable class 上的扩展方法，它需要两个参数；我已经通过调试器查看了代码，并在 运行-time 编写代码检查其属性；我错过了什么。
问题是您正在使用带有类型的 Expression.Call 重载，对于静态方法，您需要使用 MethodInfo.
void Main()
{
Expression<Func<IEnumerable<FieldInfo>, Func<FieldInfo,bool>, FieldInfo>> singleOrDefaultExpr = (l,p) => l.SingleOrDefault(p);
var callSource = (MethodCallExpression)singleOrDefaultExpr.Body;
var method = callSource.Method;
var collectionParameter = Expression.Parameter(typeof(IEnumerable<FieldInfo>), "enumFieldInfoSet");
var enumNamePredicateParameter = Expression.Parameter(typeof(Func<FieldInfo,bool>), "enumNamePredicate");
var body = Expression.Call(method, collectionParameter, enumNamePredicateParameter);
var lambda = Expression.Lambda<Func<IEnumerable<FieldInfo>, Func<FieldInfo, bool>, FieldInfo>>(body, collectionParameter, enumNamePredicateParameter);
var f = lambda.Compile();
Console.WriteLine(f(typeof(Apple).GetFields(), fi => fi.Name == "color").Name);
}
class Apple
{
public string color;
}
另外，您可以使用另一种方法来查找所需的 MethodInfo：
var method = typeof(Enumerable)
.GetMethods()
.Single(m => m.Name == "SingleOrDefault" && m.GetParameters().Count() == 2)
.MakeGenericMethod(new[] {typeof(FieldInfo)});
更新：
其实有一个更简单的方法，你的方法是对的，但是你的代码出错了。
var collectionParameter = Expression.Parameter(typeof(IEnumerable<FieldInfo>), "enumFieldInfoSet");
var enumNamePredicateParameter = Expression.Parameter(typeof(Func<FieldInfo,bool>), "enumNamePredicate");
var body = Expression.Call(typeof(Enumerable), "SingleOrDefault", new[] { typeof(FieldInfo)}, collectionParameter, enumNamePredicateParameter);
var lambda = Expression.Lambda<Func<IEnumerable<FieldInfo>, Func<FieldInfo, bool>, FieldInfo>>(body, collectionParameter, enumNamePredicateParameter);
问题是 SingleOrDefault 只有一个 泛型类型参数：'FieldInfo' 在这种情况下：
SingleOrDefault<FieldInfo>(....
不要将它与方法参数混淆，它们有两个：
SingleOrDefault<GenericParameter>(
this IEnumerable<GenericParameter> firstMethodParameter,
Func<GenericParameter, bool> secondMethodParameter
)
George 很好地帮助我走上了正确的轨道，并为我提供了部分答案；我重新设计了我的代码，这样我就很清楚了。这是我想在测试我们的元编程运行时时机器生成的代码示例。我提供的代码多于特定问题所需的代码，但我希望其他人能看到更大的上下文。
// Code to Generate Enum Field Metadata ...
string enumName = Enum.GetName(theEnumType, theOrdinalEnumValue);
Array enumValues = Enum.GetValues(theEnumType);
object enumValue = enumValues.GetValue(theOrdinalEnumValue);
object enumObject = Enum.ToObject(theEnumType, theOrdinalEnumValue);
// Create Local variables of the types targeted for assignment expressions that we will make in the generated code
var enumVariables = Expression.RuntimeVariables(Expression.Variable(typeof(string), "gcEnumName"),
Expression.Variable(typeof(Array), "gcEnumValues"),
Expression.Variable(typeof(object), "gcEnumValue"),
Expression.Variable(theEnumType, "gcEnumObject"),
Expression.Variable(typeof(FieldInfo), "gcFieldInfoOnEnum"));
// Setup the Input Parameters for calls into Enum and Array Types in preperation for Assignments
ParameterExpression theInputOfEnumType = Expression.Variable(typeof(Type), "theInputOfEnumType");
ParameterExpression theEnumFieldNameValue = Expression.Variable(typeof(string), "theEnumFieldNameValue");
ParameterExpression aEnumObjectIndexValue = Expression.Variable(typeof(int), "aEnumObjectIndexValue");
ParameterExpression anArrayOfEnumObjects = Expression.Variable(typeof(Array), "anArrayOfEnumObjects");
ParameterExpression anEnumerableObject = Expression.Variable(typeof(Enumerable), "anEnumerableObject");
ParameterExpression directEnumTypeResolved = Expression.Variable(theEnumType, "directEnumTypeResolved");
ParameterExpression fieldInfoOnEnum = Expression.Variable(typeof(FieldInfo), "fieldInfoOnEnum");
var fieldInfoEnumerableRepresentation = typeof(Enumerable);
在调用 "Expression.Call" 的过程中，我们需要获取一些 MethodInfo 数据
// We need to generate MethodInfo on the Methods we want to call in the generated code. This is metadata
// we need to call the Expression.Call API.
MethodInfo enumGetNameMethodInfo = enumMetadata.GetMethods().FirstOrDefault(info => info.Name == "GetName");
MethodInfo enumGetValuesMethodInfo = enumMetadata.GetMethods().FirstOrDefault(info => info.Name == "GetValues");
MethodInfo enumGetValueMethodInfo = arraryMetadata.GetMethods()
.FirstOrDefault(methodInfo => (methodInfo.Name == "GetValue") && methodInfo.GetParameters().Any(param =>param.ParameterType == typeof(int)));
MethodInfo enumToObjectMethodInfo = enumMetadata.GetMethods()
.FirstOrDefault(info => info.Name == "ToObject");
// We know that there exist a number of polymorphic instances of the "SingleOrDefault" Extension method
// so we use the name of the parameter named "predicate" to locate our method. **FYI Can't use the MethodInfo data in a call to Expression.Call - It's a generic definition**.
MethodInfo enumerableSingleOrDefaultInfo = fieldInfoEnumerableRepresentation.GetMethods()
.FirstOrDefault(methodInfo => (methodInfo.Name == "SingleOrDefault") &&
methodInfo.GetParameters()
.Any(param => param.Name == "predicate"));
下面是调用通用方法的最终代码：
// An approach to setup a Generic method call that will be used in an Expression.Assign call
// I decompose this code so for debugging purposes
// I create the "inputOfTSourceType" as a Generic Type because in the Definition of "SingleOrDefault" method there is only one Generic Parameter;
// also, take special note that in the assemblage of Expression.Call methods any of the methods that take a MethodInfo instance you can't pass in
// a "Generic" method definition. If you take a look at the code that is called it will throw and exception if it detects the IsGenericMethodDefinition
// flag is true.
var inputOfTSourceType = typeof(IEnumerable<>).MakeGenericType(typeof(FieldInfo)); // This is the type on the "source" TSource parameter
var predicateOfFuncType = typeof(Func<FieldInfo, bool>); // This is the type on the "predicate" parameter
// Take note there that we only define one(1) type here ("inputParameterType"); this is the type we wish apply to the Generic Type TSource
// declaration: public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate);
var inputParameterType = new[] {typeof(FieldInfo)}; // This is the type we must match to "source" parameter
// The "SingleOrDefault" method can take two parameters and in this case I need to pass in a lambda expression as the predicate.
// Se we need two parameters.
ParameterExpression fieldInfoSource = Expression.Parameter(inputOfTSourceType, "fieldInfoSource"); // This is: this IEnumerable<TSource>
ParameterExpression predicateSource = Expression.Parameter(predicateOfFuncType, "funcPredicateOnFieldInfo"); // This is: Func<TSource, bool> predicate
MethodCallExpression SingleOrDefaultMethodCall =
Expression.Call(fieldInfoEnumerableRepresentation, // This is the Object Instance for which the
"SingleOrDefault", // The Name of the Generic Method
inputParameterType, // The Generic Type
fieldInfoSource, // this is the "this" source parameter
predicateSource); // this the "predicate" parameter
Expression localEnumNameAssignment =
Expression.Assign(enumVariables.Variables[0], EnumGetNameMethodCall);
Expression localEnumObjectsAssignment =
Expression.Assign(enumVariables.Variables[1], EnumGetValauesMethodCall);
Expression localEnumObjectAssignment =
Expression.Assign(enumVariables.Variables[2], ArrayGetValueMethodCall);
Expression localEnumTypeAssignment =
Expression.Assign(enumVariables.Variables[3], Expression.Convert(EnumToObjectMethodCall, theEnumType));
Expression localFieldInfoAssignment =
Expression.Assign(enumVariables.Variables[4], Expression.Convert(SingleOrDefaultMethodCall, typeof(FieldInfo)));
BlockExpression blockExpression =
Expression.Block(enumVariables,
localEnumNameAssignment,
localEnumObjectsAssignment,
localEnumObjectAssignment,
localEnumTypeAssignment,
localFieldInfoAssignment,
enumTypeToReturn);
这是生成的代码：
$gcEnumName = .Call System.Enum.GetName(
$theInputOfEnumType, $gcEnumName = (System.String)$theEnumFieldNameValue)
$gcEnumValues = .Call System.Enum.GetValues($theInputOfEnumType)
$gcEnumValue = .Call $anArrayOfEnumObjects.GetValue((System.Int32) $theOrdinalEnumValue)
$gcEnumObject = (WorkflowMessagingCommands).Call System.Enum.ToObject(
$theInputOfEnumType,
(System.Object)$theEnumInstance)
// Here is the generated code to call "SignleOrDefault"
$gcFieldInfoOnEnum = .Call System.Linq.Enumerable.SingleOrDefault(
$thisSourceType,
$predciateType)