转换泛型类型然后使用Ref

本文关键字：Ref 然后 泛型类型 转换 | 更新日期: 2023-09-27 17:50:36

我需要弄清楚我的问题。

我有这样一个方法:

public static void SetEntityValue<TEntity>(ref TEntity entityToTransform, PropertyHelper entityProperty)
{
   // create type from entity
   Type t = entityToTransform.GetType();
   // get the property to set
   var prop = t.GetProperty(entityProperty.Name);
   // set the property value to the one parsed
   prop.SetValue(entityToTransform, entityProperty.Value, null);
}

PropertyHelper只包含两个属性，Name和Value。

所以，我有一个方法，它接受一个泛型类型，然后需要初始化一个新的，并填充它的属性值，这个方法会这样做吗:

TEntity ReadIntoEntity<TEntity>(TEntity entity, XElement node)
{
    if (!node.HasElements)
        throw new IllFormedDocumentException("Entity found but contains no properties");
    var xmlProps = node.Elements();
    Type t1 = entity.GetType();
    // the line which initialises a new TEntity same as string myString = new string();
    TEntity newEntity = Activator.CreateInstance<TEntity>();
    var props = t1.GetProperties();
    var readableProps = props.Select(x => new PropertyHelper(GenericHelper.GetEntityProperty(x), GenericHelper.GetEntityValueAsObject<TEntity>(entity, x)));
    List<string> foundAProp = new List<string>();
    foreach (var el in xmlProps)
    {
        // iterate through all xml elements
        foreach (var prop in readableProps)
        {
            // check the prop exists in the xml set
            // We found a prop that exists!
            if (el.Name.ToString() == prop.Name.ToString())
            {
                foundAProp.Add(prop.Name.ToString());
                GenericHelper.SetEntityValue<TEntity>(ref newEntity, prop);
            }
        }
    }
}

会像非泛型那样工作吗? 

MyEntity ReadIntoEntity(XElement node)
{
    if (!node.HasElements)
        throw new IllFormedDocumentException("Entity found but contains no properties");
    var xmlProps = node.Elements();
    MyEntity newEntity = new MyEntity();
    var props = typeof(MyEntity).GetProperties();
    var readableProps = props.Select(x => new PropertyHelper(GenericHelper.GetEntityProperty(x), GenericHelper.GetEntityValueAsObject<TEntity>(entity, x)));
    List<string> foundAProp = new List<string>();
    foreach (var el in xmlProps)
    {
        // iterate through all xml elements
        foreach (var prop in readableProps)
        {
            // check the prop exists in the xml set
            // We found a prop that exists!
            if (el.Name.ToString() == prop.Name.ToString())
            {
                foundAProp.Add(prop.Name.ToString());
                GenericHelper.SetEntityValue<MyEntity>(ref newEntity, prop);
            }
        }
    }
}

So effective is:

TEntity newEntity = Activator.CreateInstance<TEntity>();

等价于:

MyEntity newEntity = new MyEntity();

谢谢

转换泛型类型然后使用Ref

这个方法会做这件事吗?

然而:

TEntity newEntity = Activator.CreateInstance<TEntity>();

应替换为

TEntity newEntity = new TEntity();

在为参数添加new()泛型约束后。这将添加编译时检查，以确保实体具有有效的无参数构造函数。例如:

TEntity ReadIntoEntity<TEntity>(TEntity entity, XElement node)
    where TEntity : class, new()
{
    // ...

你不需要ref在你的第一个方法中，假设你所有的实体都是class类型。

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