visual-studio 非静态方法需要 PropertyInfo.SetValue 中的目标
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Non-static method requires a target in PropertyInfo.SetValue
提问by Victor Gil
Ok, so I'm learning about generics and I'm trying to make this thing run, but its keep saying me the same error. Here's the code:
好的，所以我正在学习泛型并且我正在尝试让这个东西运行，但它一直在告诉我同样的错误。这是代码：
public static T Test<T>(MyClass myClass) where T : MyClass2
{
var result = default(T);
var resultType = typeof(T);
var fromClass = myClass.GetType();
var toProperties = resultType.GetProperties();
foreach (var propertyInfo in toProperties)
{
var fromProperty = fromClass.GetProperty(propertyInfo.Name);
if (fromProperty != null)
propertyInfo.SetValue(result, fromProperty, null );
}
return result;
}
回答by Ronald Wildenberg
This happens because default(T)returns nullbecause Trepresents a reference type. Default values for reference types are null.
发生这种情况是因为default(T)返回null因为T表示引用类型。引用类型的默认值为null.
You could change your method to:
您可以将方法更改为：
public static T Test<T>(MyClass myClass) where T : MyClass2, new()
{
var result = new T();
...
}
and then it will work as you want it to. Of course, MyClass2and its descendants must have a parameterless constructor now.
然后它会像你想要的那样工作。当然，MyClass2它的后代现在必须有一个无参数的构造函数。
回答by JaredPar
The problem here is that Tderives from MyClassand is hence a reference type. So the expression default(T)will return the value null. The following call to SetValue is operating an a nullvalue but the property is an instance property hence you get the specified message.
这里的问题是它T源自MyClass引用类型，因此是引用类型。所以表达式default(T)将返回值null。以下对 SetValue 的调用正在操作一个null值，但该属性是一个实例属性，因此您将获得指定的消息。
You'll need to do one of the following
您需要执行以下操作之一
- Pass a real instance of
Tto the Test function to set the property values on - Only set the static properties on the type
- 将 的真实实例传递
T给 Test 函数以设置属性值 - 只在类型上设置静态属性
回答by user794791
Instead of
代替
propertyInfo.SetValue(result, fromProperty, null);
try:
尝试：
foreach (var propertyInfo in toProperties)
{
propertyInfo.GetSetMethod().Invoke(MyClass2, new object[]
{
MyClass.GetType().GetProperty(propertyInfo.Name).
GetGetMethod().Invoke(MyClass, null)
});
}
