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Pedro Ávila
Asked: 2020-06-03 16:58:31 +0800 CST 2020-06-03 16:58:31 +0800 CST

Initialize string variable

  • 772

How can I initialize an empty string whose value is "" but in this line of code:

Presenter.OnRazonSocialChanged(txtRazonSocial.Text);

I had solved it in the constructor of the Presenter in the following way:

public ProveedorPresenter(Proveedor model, ProveedorView view)
    {
        _model = model;
        _view = view;


        _model.RazonSocial = "";
        _model.DocumentoIdentidad = "";
        _model.Direccion = "";
        _model.Fijo = "";
        _model.Celular = "";
        _model.Representante = "";
        _model.Email = "";

        _view.Presenter = this;
    }

It must work like this

Without initializing the variables as empty, it gives me the following error: Mistake

As you will see I depend on the TextChanged event, what would be the solution?

Thank you all for answering, I promise to improve the quality of my questions and spend more time preparing them. Thanks to all of you I managed to solve it this way.

Create a method in the Presenter called Initialize Model

public void InicializarNodelo()
    {
        _model.RazonSocial = string.Empty;
        _model.DocumentoIdentidad = string.Empty;
        _model.Direccion = string.Empty;
        _model.Fijo = string.Empty;
        _model.Celular = string.Empty;
        _model.Representante = string.Empty;
        _model.Email = string.Empty;
    }

And I call it in the load of my View(form)

private void ProveedorView_Load(object sender, EventArgs e)
    {
        Presenter.InicializarNodelo();
    }
c#

4 Answers

  1. You can use null coalescing operator ??

    Presenter.OnRazonSocialChanged(txtRazonSocial.Text ?? "");

    In case the property Textis nullthe empty string will be used "".

    • 5

  2. It seems to me that what you want is to validate the content of the TextBox:

            if (string.IsNullOrWhiteSpace(txtRazonSocial.Text)) {
            // contenido del TextBox Vacio !
        }else{
Presenter.OnRazonSocialChanged(txtRazonSocial.Text);
        }
    • 2
  3. Best Answer

    Your question seems to be related to Implementing the MVP Design Pattern so I'll answer it with that context in mind.

    It seems that what you are trying to do is assign the empty string to txtRazonSocial.Textand at the same time pass it to the Presenter.OnRazonSocialChanged(). You can easily achieve this with the following expression:

    Presenter.OnRazonSocialChanged(txtRazonSocial.Text = "");

    either

    Presenter.OnRazonSocialChanged(txtRazonSocial.Text = String.Empty);

    However according to the following code from the other question.

    public class ProveedorPresente
{
    private Proveedor _model;
    private ProveedorView _view;

    ...

    public void OnRazonSocialChanged(string razonSocial)
    {
        _model.RazonSocial = razonSocial;
    }

    ...
}

    and its use here

    public partial class ProveedorView : Form
{
    public ProveedorPresente Presenter { get; set; }
    public ProveedorView()
    {
        InitializeComponent();
    }

    ...

    private void txtRazonSocial_TextChanged(object sender, EventArgs e)
    {
        Presenter.OnRazonSocialChanged(txtRazonSocial.Text);
    }

    ...
}

    It is not clear to me why you want to pass the empty string in the handler every time the Company Name is modified, the objective of the method txtRazonSocial_TextChangedis to notify the Presentercontrol that the value has changed and pass the new value so that it in turn can set it in the Model.

    In any case, if you want to initialize the control as an empty string, you should set it to Proveedor(model) before initializing the controls with the model values.

    • 2

  4. Here is my answer, based on the other answers ( enrique7mc and Carlos ) (I can't see the image)

    I understand that you want to prevent the stringone you send as a parameter to the function from OnRazonSocialChanged(string)being null.

    Let's start by saying you have this:

    public ProveedorPresenter(Proveedor model, ProveedorView view)
{
    _model = model;
    _view = view;


    _model.RazonSocial = "";
    _model.DocumentoIdentidad = "";
    _model.Direccion = "";
    _model.Fijo = "";
    _model.Celular = "";
    _model.Representante = "";
    _model.Email = "";

    _view.Presenter = this;
}

    Where you are assigning your modeltype parameter Proveedorto the internal field _modelof the class ProveedorPresenterand then you assign all the values ​​to "" Which practically does not make sense (at least for me) , the most correct thing would be to create a constructor in the following way:

    public ProveedorPresenter(ProveedorView view, Proveedor model = null)
{
    _model = (model != null) ? model : new Proveedor();
    // ...
}

    Where you assign a parameter modelwith a default value nullso that if you do not specify it in the constructor call, it will assign _modelthe value of a new provider to the field, so that the values ​​will be initialized to "" (If you specified it in the empty constructor of Proveedor)

    Then in your method OnRazonSocialChanged(string)you do this:

    public void OnRazonSocialChanged(string s)
{
    _model.RazonSocial = (string.IsNullOrEmpty(s) || string.IsNullOrWhiteSpace(s)) ? "" : s;
}

    And you will have what you need so that the how does not leave stringyou null.

    • 1