获取文本框的先前值asp.net vb.net

Question

I am working on a project and people are allowed to "update" categories, like changing the name of the category. With that I have the following message This is called after clicking on the update button with the SQL statement :

    Dim cs As ClientScriptManager = Page.ClientScript
            cs.RegisterStartupScript(Me.GetType(), "Message", "alert
(' The category has been changed to:" + TextBoxCategorie.Text + "')", True)

Which display: The category has been changed to: [Value of the textbox]

But is it possible to store the previous value, so you get something like:

"Sand" has been succesfully updated to "Mud"

Thanks in advance

Answer 1

Create a HiddenField to go along with the TextBox. When the page initially loads, fill the HiddenField with the initial value. On the PostBack, compare the TextBox value to the HiddenField value. You'll have access to both the old and the new.

Just make sure you're not refilling the HiddenField on PostBack - though if you're filling from the database it probably wouldn't matter. But if you fill only on (Not Me.IsPostBack), then on the PostBack, it should be delivering you the value it had when the page was first loaded.

Answer 2

element.defaultValue gives you the original value on clientside.

Dim script As String = "var txt=document.getElementById('" & TextBoxCategorie.ClientID & "');if(txt!=null)alert(txt.defaultValue + ' has been changed to: " + TextBoxCategorie.Text + "')"
cs.RegisterStartupScript(Me.GetType(), "Message", script, True)

However, that'll work only if it was changed in this request. If it was already changed before the page was sent to the client(as RegisterStartupScript suggests) you have to store the old value somewhere else or load it from database.

Answer 3

Take a look at the Page Life Cycle Overview and you can grab the value from the TextBox before it is overwritten. There is an event named OnTextChanged that would seem to be useful but the issue is that the old value is overwritten by this time (the Page_Load already fires by this point). I would look into simply using the Page_Init and assigning the TextBox value to a variable prior to overwriting it.

protected void Page_Init(object sender, EventArgs e)
{
     String oldValue = TextBox.Text;
}