将新对象分配给类属性 C# 表达式树

Question

如何使用表达式树分配以下语句

myFoo.myBar = new Bar((;

我的代码如下 -

    public static Action<TObject, TProperty>CreateNewObjectAndSet<TObject,TProperty>(string propertyName)
    {
        ParameterExpression paramExpression = Expression.Parameter(typeof(TObject));
        MemberExpression propertyGetterExpression = Expression.Property(paramExpression, propertyName);
        var newObject = Expression.New(typeof(TProperty));
        var x = Expression.Assign(propertyGetterExpression, newObject);
        var paramExpressions = new ParameterExpression[2];
        paramExpressions[0] = paramExpression;
        paramExpressions[1] = newObject;
        Action<TObject, TProperty> result = Expression.Lambda<Action<TObject, TProperty>>(x, paramExpressions).Compile();
        return result;
    }

语句处发生编译错误

paramExpression[1] = newObject;

Answer 1

由于目标表达式为：

myFoo.myBar = new Bar();

您不需要 2 个参数，只需要 1 个 myFoo 实例来设置属性。因此，请像这样更改代码：

public static Action<TObject> CreateNewObjectAndSet<TObject, TProperty>(string propertyName) where TProperty: new() {
    ParameterExpression paramExpression = Expression.Parameter(typeof(TObject));
    MemberExpression propertyGetterExpression = Expression.Property(paramExpression, propertyName);
    var newObject = Expression.New(typeof(TProperty));
    var x = Expression.Assign(propertyGetterExpression, newObject);
    var paramExpressions = new ParameterExpression[1];
    paramExpressions[0] = paramExpression;
    Action<TObject> result = Expression.Lambda<Action<TObject>>(x, paramExpressions).Compile();
    return result;
}

然后像这样打电话：

var setter = CreateNewObjectAndSet<Foo, Bar>("myBar");
setter(myFoo);