protected override Expression VisitMember(MemberExpression node)
{
// Member expression could be in form of simple fields or
// properties
if (node.Expression is ConstantExpression)
{
var ci = (ConstantExpression)node.Expression;
var mi = (FieldInfo)node.Member;
Value = mi.GetValue(ci.Value);
}
else if (node.Member is PropertyInfo)
{
var pi = (PropertyInfo)node.Member;
// Visiting subexpression recursivly to obtain
// property objects value (for example, for expression () => foo.X
// pi will contain "X" and value - "foo"
var visitor = new CustomVisitor();
visitor.Visit(node.Expression);
var value = visitor.Value;
if (visitor.Processed)
{
Value = pi.GetValue(value);
}
}
return(node);
}
public static void Main()
{
Expression <Func <Parent, int> > expression = s => s.Application.ID;
var val = new CustomVisitor().ConvertToString(expression);
Console.WriteLine("expression is " + val);
}
public static string Query <T>(this T obj, Expression <Func <T, bool> > filter)
{
CustomVisitor visitor = new CustomVisitor();
Expression epress = visitor.Visit(filter);
return(visitor.ToSqlCommand());
}
protected override Expression VisitMethodCall(MethodCallExpression node)
{
var methodInfo = node.Method;
var visitor = new CustomVisitor();
visitor.Visit(node.Object);
if (visitor.Processed)
{
Value = methodInfo.Invoke(visitor.Value, null);
}
else
{
Value = Expression.Lambda(node).Compile().DynamicInvoke();
}
return(node);
}
private static object ProcessExpression(Expression expression)
{
var visitor = new CustomVisitor();
visitor.Visit(expression);
if (visitor.Processed)
{
return(visitor.Value);
}
// Can't process this expression with our custom visitor.
// Using heavy-weight compilation
var argAsObj = Expression.Convert(expression, typeof(object));
return(Expression.Lambda <Func <object> >(argAsObj, null).Compile()());
}
static void Main(string[] args)
{
//如果想执行新增加的操作
ShapeVisitor visitor = new CustomVisitor();
AppStructure app = new AppStructure(visitor);
Shape shape = new Rectangle();
shape.Draw(); //执行自己的操作
app.Process(shape); //执行新的操作
shape = new Circle();
shape.Draw(); //执行自己的操作
app.Process(shape); //执行新的操作
shape = new Line();
shape.Draw(); //执行自己的操作
app.Process(shape); //执行新的操作
Console.ReadLine();
}
