问题
I am currently using FieldInfo.GetValue
and FieldInfo.SetValue
quite a lot in my programm, which is significantly slowing up my programm.
For PropertyInfo
I use the GetValueGetter
and GetValueSetter
methods so I only use reflection once for a given type. For the FieldInfo
, the methods don't exist.
What is the suggested approach for FieldInfo
?
EDIT: I followed this useful link from CodeCaster's reply. This is a great search direction.
Now the "only" point that I don't get in this answer is how I can cache the getters / setters and re-use them in a generic way, using only the field's name - which is basically what the SetValue
is doing
// generate the cache
Dictionary<string, object> setters = new Dictionary<string, object>();
Type t = this.GetType();
foreach (FieldInfo fld in t.GetFields()) {
MethodInfo method = t.GetMethod("CreateSetter");
MethodInfo genericMethod = method.MakeGenericMethod( new Type[] {this.GetType(), fld.FieldType});
setters.Add(fld.Name, genericMethod.Invoke(null, new[] {fld}));
}
// now how would I use these setters?
setters[fld.Name].Invoke(this, new object[] {newValue}); // => doesn't work without cast....
回答1:
You could use Expression
s to generate faster field accessors. If you want them to work on Object
rather than the field's concrete type, you'd have to add casts (Convert
) in the expression.
using System.Linq.Expressions;
class FieldAccessor
{
private static readonly ParameterExpression fieldParameter = Expression.Parameter(typeof(object));
private static readonly ParameterExpression ownerParameter = Expression.Parameter(typeof(object));
public FieldAccessor(Type type, string fieldName)
{
var field = type.GetField(fieldName,
BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
if (field == null) throw new ArgumentException();
var fieldExpression = Expression.Field(
Expression.Convert(ownerParameter, type), field);
Get = Expression.Lambda<Func<object, object>>(
Expression.Convert(fieldExpression, typeof(object)),
ownerParameter).Compile();
Set = Expression.Lambda<Action<object, object>>(
Expression.Assign(fieldExpression,
Expression.Convert(fieldParameter, field.FieldType)),
ownerParameter, fieldParameter).Compile();
}
public Func<object, object> Get { get; }
public Action<object, object> Set { get; }
}
Usage:
class M
{
private string s;
}
var accessors = new Dictionary<string, FieldAccessor>();
// expensive - you should do this only once
accessors.Add("s", new FieldAccessor(typeof(M), "s"));
var m = new M();
accessors["s"].Set(m, "Foo");
var value = accessors["s"].Get(m);
来源:https://stackoverflow.com/questions/38528620/c-sharp-fieldinfo-reflection-alternatives