如何创建泛型类型的类新实例 [英] How do I create new instance of Generic Type Class

问题描述

问题：

1. 如何创建，设置，返回和实例类型为T的对象？
2. 我将如何访问子类型（标签：数据库）？在静态函数

我想创建一个通用的GetAsClass功能，它会返回一个子类的初始化实例。我无法弄清楚如何创造我想要返回，返回子​​类类型的类的新实例。

I'm trying to create a generic "GetAsClass" function which would return an initialized instance of the subclass. I can't figure out how to create a new instance of the class I want to return and return the subclass type.

说我有两个类：

1. 标签
2. 用户

我要创建这将让任何类型它的基类的单一功能。在另一方面，我想，使其静态以及（但我没有获得这个，我不知道如何让子类类型。

I want to create a single function in the base class which will get whatever type it is. On another note, I'd like to make it static as well (but then I don't have access to "this" and I'm not sure how to get the subclass type.

    private async Task<T> GetAsClass<T>(string objectId) {

        Type classType = this.GetType();
        string className = classType.Name; 

        // This needs to be of type "T" (Tag myTag = new Tag();) How would I accomplish something like this?
        object toReturnObject = new object();
        ParseObject myParseObject = ParseObject.GetAsParseObject(objectId);

        foreach (PropertyInfo field in classType.GetRuntimeProperties()) {
            if (field.CanRead) {
                string propertyName = StringHelper.ToLowerCamelCase(field.Name);
                if (field.PropertyType == typeof(string)) {
                    string propertyValue = myParseObject.Get<string>(propertyName);
                    field.SetValue(toReturnObject , propertyValue);
                }
                if (field.PropertyType == typeof(int)) {
                    int propertyValue = myParseObject.Get<int>(propertyName);
                    field.SetValue(toReturnObject, propertyValue);
                }
            }
        }

        return toReturnObject;
    }

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推荐答案

您可能会发现此页面上的泛型类型约束的是有帮助的。 基本上，你会改变你的类的签名/方法是：

You may find this page on generic type constraints to be helpful. Basically, you would change the signature of your class/method to be:

private async Task<T> GetAsClass<T>(string objectId)
    where T: new()
{
    ...
}

和它将接受类型的T，只有当它提供了一个默认的构造函数不带参数。一旦条件得到保证，那么你的类可以调用新T（）

And it will accept types of T only if it provides a default constructor with no arguments. Once that condition is guaranteed, then your class can invoke new T()

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