IDictionary< string,object>上的Expression.ArrayAccess()按键名 [英] Expression.ArrayAccess() on IDictionary<string,object> by key name
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问题描述
如何创建表达式树以通过数组访问IDictionary<string,object>
来读取值?
How do I create expression tree for reading a value by array access for an IDictionary<string,object>
?
我想代表:
((IDictionary<string,object>)T)["KeyName"]
我找不到用于以字符串名称访问的ArrayAccess的任何示例.我想要类似的东西:
I can't find any example of ArrayAccess being used to access with string name. I want something like:
var parameterExpression = Expression.Parameter(typeof(IDictionary<string, object>));
var paramIndex = Expression.Constant("KeyName");
var arrayAccess = Expression.ArrayAccess(parameterExpression, paramIndex);
我收到错误消息,指出它不是数组.正确的方法是什么?
I get error stating it is not an array. What is correct way to do this?
推荐答案
您可能* 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));
如果使用索引器在类上打开引擎盖,则会有一个Item
属性.考虑以下示例:
If you pop the hood on a class with an indexer, there is an Item
property. Consider this example:
class HasIndexer {
public object this[int index] {
get { return null; }
}
}
具有以下(与索引器有关)IL:
has the following (relevant to indexers) 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
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