存储变量类型并在运行时使用它来创建集合 [英] Storing variable type and using it to create collections at runtime

问题描述

我有一个项目，它在 SQL 中存储值，然后检索它们进行分析.为了跟踪可能存储的值类型，我创建了一个大致如下所示的类:

I have a project which stores values in SQL and later retrieves them for analysis. To keep track of what kinds of values might be stored, I created a class roughly like this:

private class DataField
{
    public string FieldName;
    public string FieldType;
}

当读取值进行分析时，switch 语句的使用如下(简化):

When values are being read for analysis, a switch statement is used as follows (simplified):

switch (DataField.FieldType)
{
    case "int":
        List<int> InputData = new List<int>();
        // Populate list from DB
    break;
    case "bool":
        List<bool> InputData = new List<bool>();
        // Populate list from DB
    break;
}

我不是在多个地方维护代码，而是在寻找一种摆脱 switch 语句的方法，但这意味着我需要根据类型动态创建集合.当前该类型是(天真地?)一个字符串，但我认为我可以通过更改类来改进这一点:

Rather than maintain code in multiple places, I am looking for a way to get rid of the switch statement, but that means I need to dynamically create collections based on the type. Current that type is (naively?) a string, but I think I could improve this by changing the class:

private class ImprovedDataField
{
    public string FieldName;
    public Type FieldType;
}

然后以某种方式动态创建集合:

And then dynamically create collections somehow:

Type DataType = typeof(DataField.FieldType);
List<DataType> InputData = new List<DataType>();
// Populate list from DB

这当然不起作用，导致预期的类型或命名空间名称错误.

This of course does not work, resulting in a Type or namespace name expected error.

不幸的是，在我寻找解决方案时，我对使用 Type 类、泛型或匿名类型不太熟悉(似乎没有什么合适的).

Unfortunately I'm not very familiar with working with the Type class, nor generics nor anonymous types as I search for a solution (nothing seems to be appropriate).

如何减少代码重复，其中每个 switch 语句分支的唯一区别是生成的变量集合的类型?

How can I reduce duplication of code where the only difference in each switch statement branch is the type of variable collection being produced?

推荐答案

如果您想创建在运行时已知类型的对象的静态类型集合，您需要使用反射.请参阅即 此博客条目 - 这是创建 列表:

If you want to create statically-typed collection of objects of type known at runtime, you need to use reflection. See i.e. this blog entry - that's the solution for creating List<T>:

public static IList CreateGenericList(Type collectionType)
{
    var listType = typeof(List<>).MakeGenericType(new[] { collectionType});
    return (IList) Activator.CreateInstance(listType);
}

所以在你的例子中:

Type dataType = DataField.FieldType;
IList inputData = CreateGenericList(dataType);
// Populate list from DB

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