Data overriding onClick command

Question

Data overriding onClick command

Asked 10 years ago

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3

Guys, I have a little problem in Asp.net webforms. And I made a nice pie.

I know the solution to this might be a little simple, but I’m confused.

Follows the code:

public partial class Default : System.Web.UI.Page
{
    List<Pessoa> lista; 

    protected void Page_Load(object sender, EventArgs e) {
        if (!IsPostBack) return;

        if (lista == null)
            lista = new List<Pessoa>();
    }

    protected void btnEnviar_Click(object sender, EventArgs e) {
        Pessoa p = new Pessoa();
        p.Id = lista.Count + 1;
        p.Nome = "João";
        p.Sobrenome = "Silva";
        p.Idade = 20;

        lista.Add(p);
        CarregarGrid();
    }

    private void CarregarGrid() {
        gvDados.DataSource = lista;
        gvDados.DataBind();
    }
}

When I click on the button, I want to add a new person in the Grid, but it is overwritten, always in the pageload of the page the list is as 'null'. Always he adds:

1 - Joao - silva.

How can I do this keeping the information current? Whenever you click on the button I want you to always add one more, as an example below:

1 - Joao - silva. 2 - Joao - silva. 3 - John - John....

I don’t quite understand your question. When Gridview is loaded it displays the correct data, but when you click add it loads all the data? I think for your case it might be best to iterate over the list and add one to one. If your problem is with regard to loss of user provided data.

– Richard Dias

2014/10/28 at 18:37
@Richarddias Um, right, so the problem is that when I click the button, the page of the 'Reload', and with that I lose the information from the list. That is, it will always be a new one. The first time I click, Gridview displays the data correctly, but it ALWAYS displays the first data.

– Erico Souza

2014/10/28 at 18:43
Have you used debug mode to see if your list is being filled in correctly? I think to accomplish this action maybe you could use ajax, avoid reloading the whole page. I don’t use Web Forms, but I know a little bit about Windows Forms and MVC, so I don’t really know what the implications of that might be.

– Richard Dias

2014/10/28 at 18:52
Right, I will perform the test with ajax, I think that really the problem is in the page Reload that it loses the information. I’ve used debug, and the list is filled in correctly yes.

– Erico Souza

2014/10/28 at 18:53
1

Unless he stores the list in a session. Here’s what’s best for his case.

– Richard Dias

2014/10/28 at 19:20
1

@Tiagosilva thanks for the tip from Viewstate. :)

– Erico Souza

2014/10/29 at 09:44

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by Filipe Oliveira • **2,655** points · Answer 1 · 2014-10-28T19:25:34+00:00

You can solve this using ViewState[].

Viewstate is the mechanism that ASP.NET uses to maintain the state of controls and objects when a Postback occurs on the page. The information is stored in a html control of type Hidden called _VIEWSTATE.

Source

Do it this way

    public List<Pessoa> lista  { 
        get { return ViewState["Pessoas"] as List<Pessoa>; } 
        set{ lista = value; } 
    }
    protected void Page_Load(object sender, EventArgs e) {
        if (!IsPostBack) {
            ViewState["Pessoas"] = new List<Pessoa>();
            return;
        }
        if (lista == null) {
            lista = new List<Pessoa>();
        }
    }
    protected void btnEnviar_Click(object sender, EventArgs e) {
        Pessoa p = new Pessoa();
        p.Id = lista.Count + 1;
        p.Nome = "João";
        p.Sobrenome = "Silva";
        p.Idade = 20;

        lista.Add(p);
        CarregarGrid();
    }
    private void CarregarGrid() {
        gvDados.DataSource = lista;
        gvDados.DataBind();
    }