从我的项目中检索所有表格

Question

I know this question has been asked before. I have the code to do this but i am getting an error and I think I know why but I am just really getting into .Net Reflection so I wish to get confirmation on whether I am correct or not.

Here is the code. I want to retrieve all the forms from my project that have a basetype of "BaseEditForm" and then all of those that end with "EditForm" I want to put in a List to populate a ListBox.

public void LoadAllEditForms()
        {
            formsList = new List<string>();

            try
            {
                Assembly project = Assembly.Load("UnionAdministrator");

                foreach (Type t in project.GetTypes())
                {
                    if (t.BaseType == typeof (BaseEditForm))
                    {
                        var emptyCtor = t.GetConstructor(Type.EmptyTypes);
                        if (emptyCtor != null)
                        {
                            var f = (Form) emptyCtor.Invoke(new object[] {});
                            if (f.Name.EndsWith("EditForm"))
                                formsList.Add(f.Name);
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

I am getting the error message "Object reference not set to an instance of an object." on the line

var f = (Form) emptyCtor.Invoke(new object[] {});

emptyCtor is not null and besides there is no way for emptyCtor to get to this point if it is null. So I am confused about the error message. So here is my question. For this to work properly do all my forms have to have a default constructor? Almost all my forms have a constructor that takes one or more parameters. Is that my problem?

Answer 1

Your code works fine.
It must be one of your constructors that throw the exception.

Check all of your derived Forms to see if any of them (those that does not take any ctor parameters) could throw a NullReferenceException if invoked.

Answer 2

I'm not sure why you're going through the trouble of trying to execute the constructor of every form. You could simplify your code (and avoid the whole issue) by just looking at the type names.

public void LoadAllEditForms()
{
    Assembly project = Assembly.Load("UnionAdministrator");

    var formsList = project.GetTypes()
        .Where (t => t.BaseType == typeof(BaseEditForm) && t.Name.EndsWith("EditForm"))
        .ToList();
}