如何从()=> foo.Title表达式获取对象实例

Question

我有一个带有属性的简单类

class Foo 
{ 
    string Title { get; set; } 
}

我试图通过调用函数来简化数据绑定

BindToText(titleTextBox, ()=>foo.Title );

这被宣称为

void BindToText<T>(Control control, Expression<Func<T>> property)
{
    var mex = property.Body as MemberExpression;
    string name = mex.Member.Name;

    control.DataBindings.Add("Text", ??? , name);
}

那么我应该???为我的Foo班级实例投入什么呢.如何foo从lambda表达式中获取对调用实例的引用？

编辑: 实例应该在某处,因为我可以调用property.Compile()并创建一个使用foo我的BindToText函数中的实例的委托.所以我的问题是,如果可以在不添加函数参数中实例的引用的情况下完成此操作.我呼吁Occum的Razor提供最简单的解决方案.

编辑2: 许多人没有注意到的是在我的函数内部访问实例时存在的闭包foo,如果我编译lambda.为什么编译器知道在哪里找到实例,我不知道？我坚持认为必须有一个答案,而不必通过额外的论证.

---

解

感谢VirtualBlackFox解决方案是这样的:

void BindText<T>(TextBoxBase text, Expression<Func<T>> property)
{
    var mex = property.Body as MemberExpression;
    string name = mex.Member.Name;
    var fex = mex.Expression as MemberExpression;
    var cex = fex.Expression as ConstantExpression;            
    var fld = fex.Member as FieldInfo;
    var x = fld.GetValue(cex.Value);
    text.DataBindings.Add("Text", x, name);            
}

这让我只需输入BindText(titleText, () => foo.Title);.

Answer 1

您想要的小LINQPad样本:

void Foo<T>(Expression<Func<T>> prop)
{
    var propertyGetExpression = prop.Body as MemberExpression;

    // Display the property you are accessing, here "Height"
    propertyGetExpression.Member.Name.Dump();

    // "s" is replaced by a field access on a compiler-generated class from the closure
    var fieldOnClosureExpression = propertyGetExpression.Expression as MemberExpression;

    // Find the compiler-generated class
    var closureClassExpression = fieldOnClosureExpression.Expression as ConstantExpression;
    var closureClassInstance = closureClassExpression.Value;

    // Find the field value, in this case it's a reference to the "s" variable
    var closureFieldInfo = fieldOnClosureExpression.Member as FieldInfo;
    var closureFieldValue = closureFieldInfo.GetValue(closureClassInstance);

    closureFieldValue.Dump();

    // We know that the Expression is a property access so we get the PropertyInfo instance
    // And even access the value (yes compiling the expression would have been simpler :D)
    var propertyInfo = propertyGetExpression.Member as PropertyInfo;
    var propertyValue = propertyInfo.GetValue(closureFieldValue, null);
    propertyValue.Dump();
}

void Main()
{
    string s = "Hello world";
    Foo(() => s.Length);
}