Expression.ArrayAccess()在IDictionary<string上，object>按键名

Question

如何创建表达式树，通过数组访问来读取IDictionary<string,object>的值

我想代表：

((IDictionary<string,object>)T)["KeyName"]

我找不到用字符串名访问ArrayAccess的任何例子。我想要这样的东西：

var parameterExpression = Expression.Parameter(typeof(IDictionary<string, object>));

var paramIndex = Expression.Constant("KeyName");

var arrayAccess = Expression.ArrayAccess(parameterExpression, paramIndex);

我在声明它不是数组时出错。怎样做才是正确的呢？

Answer 1

*想要访问属性Item：

var dic = new Dictionary<string, object> {
    {"KeyName", 1}
};
var parameterExpression = Expression.Parameter(typeof (IDictionary<string, object>), "d");
var constant = Expression.Constant("KeyName");
var propertyGetter = Expression.Property(parameterExpression, "Item", constant);

var expr = Expression.Lambda<Func<IDictionary<string, object>, object>>(propertyGetter, parameterExpression).Compile();

Console.WriteLine(expr(dic));

如果您在带有索引器的类上弹出遮罩，则有一个Item属性。考虑一下这个例子：

class HasIndexer {
    public object this[int index] {
        get { return null; }
    }
}

有以下(与索引者相关) IL：

.property instance object Item(
    int32 index
)
{
    .get instance object ConsoleApplication8.HasIndexer::get_Item(int32)
}

.method public hidebysig specialname 
    instance object get_Item (
        int32 index
    ) cil managed 
{
    // Method begins at RVA 0x2050
    // Code size 2 (0x2)
    .maxstack 8

    IL_0000: ldnull
    IL_0001: ret
} // end of method HasIndexer::get_Item