我正在尝试为(在运行时)为所有类型的委托创建包装器创建一个方法.这样可以创建一种灵活的注入额外日志记录的方法(在本例中).在第一步中,我尝试围绕给定的input-argument 创建try-catch包装.
try
{
Console.WriteLine(....);
// Here the original call
Console.WriteLine(....);
}
catch(Exception ex)
{
Console.WriteLine(.....);
}
我正在使用泛型方法调用CreateWrapper2(见下文)
private static readonly MethodInfo ConsoleWriteLine = typeof(Console).GetMethod("WriteLine", new[] { typeof(string), typeof(object[]) });
private static MethodCallExpression WriteLinExpression(string format, params object[] args)
{
Expression[] expressionArguments = new Expression[2];
expressionArguments[0] = Expression.Constant(format, typeof(string));
expressionArguments[1] = Expression.Constant(args, typeof(object[]));
return Expression.Call(ConsoleWriteLine, expressionArguments);
}
public T CreateWrapper2(T input)
{
Type type = typeof(T);
if (!typeof(Delegate).IsAssignableFrom(type))
{
return input;
}
PropertyInfo methodProperty = type.GetProperty("Method");
MethodInfo inputMethod = methodProperty != null ? (MethodInfo)methodProperty.GetValue(input) : null;
if (inputMethod == null)
{
return input;
}
string methodName = inputMethod.Name;
ParameterInfo[] parameters = inputMethod.GetParameters();
ParameterExpression[] parameterExpressions = new ParameterExpression[parameters.Length];
// TODO: Validate/test parameters, by-ref /out with attributes etc.
for (int idx = 0; idx < parameters.Length; idx++)
{
ParameterInfo parameter = parameters[idx];
parameterExpressions[idx] = Expression.Parameter(parameter.ParameterType, parameter.Name);
}
bool handleReturnValue = inputMethod.ReturnType != typeof(void);
ParameterExpression variableExpression = handleReturnValue ? Expression.Variable(inputMethod.ReturnType) : null;
MethodCallExpression start = WriteLinExpression("Starting '{0}'.", methodName);
MethodCallExpression completed = WriteLinExpression("Completed '{0}'.", methodName);
MethodCallExpression failed = WriteLinExpression("Failed '{0}'.", methodName);
Expression innerCall = Expression.Call(inputMethod, parameterExpressions);
LabelTarget returnTarget = Expression.Label(inputMethod.ReturnType);
LabelExpression returnLabel = Expression.Label(returnTarget, Expression.Default(returnTarget.Type)); ;
GotoExpression returnExpression = null;
if (inputMethod.ReturnType != typeof(void))
{
// Handle return value.
innerCall = Expression.Assign(variableExpression, innerCall);
returnExpression = Expression.Return(returnTarget, variableExpression, returnTarget.Type);
}
else
{
returnExpression = Expression.Return(returnTarget);
}
List tryBodyElements = new List();
tryBodyElements.Add(start);
tryBodyElements.Add(innerCall);
tryBodyElements.Add(completed);
if (returnExpression != null)
{
tryBodyElements.Add(returnExpression);
}
BlockExpression tryBody = Expression.Block(tryBodyElements);
BlockExpression catchBody = Expression.Block(tryBody.Type, new Expression[] { failed, Expression.Rethrow(tryBody.Type) });
CatchBlock catchBlock = Expression.Catch(typeof(Exception), catchBody);
TryExpression tryBlock = Expression.TryCatch(tryBody, catchBlock);
List methodBodyElements = new List();
if(variableExpression != null) methodBodyElements.Add(variableExpression);
methodBodyElements.Add(tryBlock);
methodBodyElements.Add(returnLabel);
Expression wrapperLambda = Expression.Lambda(Expression.Block(methodBodyElements), parameterExpressions);
Console.WriteLine("lambda:");
Console.WriteLine(wrapperLambda.GetDebugView());
return wrapperLambda.Compile();
}
对于void-methods(比如Action<>),这段代码可以满足我的需求.但是当有一个返回值时,我得到了从范围''引用的'System.Boolean'类型的异常" 变量",但它没有被定义 "
许多其他帖子谈论Expression.Parameter不止一次为参数调用; 对我来说,这里看起来像是其他错误,但我找不到它.一切顺利,直到.Compile它崩溃.
对于Func下面是生成的表达式的DebugView.
.Lambda #Lambda1(System.Int32 $i) {
.Block() {
$var1;
.Try {
.Block() {
.Call System.Console.WriteLine(
"Starting '{0}'.",
.Constant(System.Object[]));
$var1 = .Call LDAP.LdapProgram.b__0($i);
.Call System.Console.WriteLine(
"Completed '{0}'.",
.Constant(System.Object[]));
.Return #Label1 { $var1 }
}
} .Catch (System.Exception) {
.Block() {
.Call System.Console.WriteLine(
"Failed '{0}'.",
.Constant(System.Object[]));
.Rethrow
}
};
.Label
.Default(System.Boolean)
.LabelTarget #Label1:
}
}
我错过了什么？(在调试期间我试过:
Expression.Variable从try-body内部移动到顶层.
通过typed-给catch块提供了与try-block相同的Body.Type Expression.Return.
)
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