Question

I have 2 classes: MyForm and Database

In MyForm I have a method to change a label text to show error:

public void printError(string text){
    label1.Text = text;
}

My Database class needs to access that method too, so I make it static:

public static void printError(MyForm form, string text){
    form.label1.Text = text;
}

Now the problem is, how do I call that method from Database class?

This question I found said that I need to pass MyForm into Database’s contructor like this:

class MyForm : Form{
    Database db;
    public Form(){
        db = new Database(this);
    }
}

class Database{
    MyForm form;
    public Database(MyForm f){
        form = f;
    }
    ...
    //then I can access the printError like this
    MyForm.printError(form, "You got error");
}

I tried that and it freezes the form. Any other solution?

Thanks

Answer 1

Here is a very simple example of how you can achieve this without your data layer knowing about your UI:

class MyForm : Form
{
    Database db;

    public Form()
    {
        db = new Database(this);
    }

    public void DoSomething()
    {
        var errors = db.Login("", "");
        if (errors.Any())
            label1.Text = errors.First(); // Or you can display all all of them
    }
}

class Database
{    
    public List<string> Login(string username, string password)
    {
        var errors = new List<string>();

        if (string.IsNullOrEmpty(username))
            errors.Add("Username is required");

        if (string.IsNullOrEmpty(password))
            errors.Add("Password is required");

        [...]

        return errors;
    }
}