public static bool TryConvert(Expression parameter, Type sourceType, Type destType, out Action <List <Expression>, ParameterExpression, PropertyInfo, Func <Expression, Expression> > act, out ParameterExpression variable)
{
Expression expression = null;
variable = null;
act = null;
var typeCode = Type.GetTypeCode(sourceType);
if (typeCode == TypeCode.Empty || typeCode == TypeCode.DBNull)
{
return(false);
}
MethodInfo method = null;
//判断是否可以显式转换
if (destType.GetMethod("op_Explicit", new Type[] { sourceType }) != null)
{
expression = Expression.Convert(parameter, destType);
}
//判断是否可以隐式转换
else if (destType.GetMethod("op_Implicit", new Type[] { sourceType }) != null)
{
expression = parameter;
}
//判断是否存在继承关系
//Base base=Derive
else if (destType.IsAssignableFrom(sourceType))
{
expression = parameter;
}
//判断是否存在Convert.ToXX方法
else if (typeCode != TypeCode.String && typeCode != TypeCode.Object && Type.GetTypeCode(destType) != TypeCode.Object)
{
method = typeof(Convert).GetMethod("To" + destType.Name, BindingFlags.Static | BindingFlags.Public, null, new Type[] { sourceType }, new ParameterModifier[0]);
if (method != null)
{
expression = Expression.Call(null, method, parameter);
}
}
if (expression != null)
{
act = (list, p1, srcPropertyInfo, func) =>
{
list.Add(Expression.Assign(Expression.MakeMemberAccess(p1, srcPropertyInfo), func == null ? expression : func(expression)));
};
return(true);
}
bool skipChangeType = false;
// 目标类型是否存在TryParse方法————————否——————————ChangeType
// | |
// |是 |
// | 否 否 |
// 源类型是否为string———————————是否存在ToString方法—————
// | |
// |是 |是
// |——————————————————————
// |
// |
// 调用目标类型上的TryParse方法
if ((method = _tryParseDic.GetOrAdd(destType, t => t.GetMethod("TryParse", BindingFlags.Static | BindingFlags.Public, null, new Type[] { typeof(string), t.MakeByRefType() }, new ParameterModifier[0]))) != null)
{
skipChangeType = true;
MethodInfo toStringMethod = null;
//首先判断sourceType是不是string
var r = typeCode != TypeCode.String;
if (r)
{
//如果类型不是string，就需要看该类是否定义了自己的ToString方法
//BindingFlags.DeclaredOnly 标识只获取该类定义的方法，屏蔽继承的方法
if ((toStringMethod = _toStringDic.GetOrAdd(sourceType, t => t.GetMethod("ToString", BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly, null, Type.EmptyTypes, new ParameterModifier[0]))) == null)
{
skipChangeType = false;
}
}
if (skipChangeType)
{
Expression temp = parameter;
//如果sourceType不是string
if (r)
{
temp = Expression.Call(parameter, toStringMethod);
}
ParameterExpression p = VariableGenerator.Generate(destType);
expression = Expression.Call(null, method, temp, p);
act = (list, p1, srcPropertyInfo, func) =>
{
expression = Expression.IfThen(expression, Expression.Assign(Expression.MakeMemberAccess(p1, srcPropertyInfo), p));
list.Add(expression);
};
variable = p;
}
}
if (!skipChangeType)
{
expression = Expression.Convert(Expression.Call(null, ChangeTypeMethod, Expression.Convert(parameter, typeof(object)), Expression.Constant(Type.GetTypeCode(destType), typeof(TypeCode))), destType);
act = (list, p1, srcPropertyInfo, func) =>
{
list.Add(Expression.Assign(Expression.MakeMemberAccess(p1, srcPropertyInfo), func == null ? expression : func(expression)));
};
}
return(true);
}
