I have a dropdown list that is populated when the page loads, like this:
protected void Page_Load(object sender, EventArgs e)
{
ddlCars.Items.Add("Ford");
ddlCars.Items.Add("Chevy");
ddlCars.Items.Add("BMW");
ddlCars.Items.Add("Jeep");
ddlCars.Items.Add("Nissan");
}
It works fine, but when a user changes the selection of the dropdown list, the list is repopulated and I see the same items twice, because the page is reloading and these values are being re-added.
What would be the best way to stop this from happening? It is important that AutoPostBack stays enabled, so that I change information based on user selection.
Thanks
You need to put that code in a !Page.IsPostBack block.
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
ddlCars.Items.Add("Ford");
ddlCars.Items.Add("Chevy");
ddlCars.Items.Add("BMW");
ddlCars.Items.Add("Jeep");
ddlCars.Items.Add("Nissan");
}
}
This will allow that code to run once (when the page loads the first time), and then be ignored whenever the page is posting back to the server due to user interaction, etc.
For more information, see Page.IsPostBack on MSDN.
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack) {
ddlCars.Items.Add("Ford");
ddlCars.Items.Add("Chevy");
ddlCars.Items.Add("BMW");
ddlCars.Items.Add("Jeep");
ddlCars.Items.Add("Nissan");
//ddlCars.datasource=?
//ddlCars.databind();
}
}
Related
I am making a web page with asp.net, the problem has to be with a asp:datagrid and its page index changing event. The records are displaying and paging correctly but after making a filter and reduce its grid content and trigger the page index again, the grid refreshes and came back all the other records.
This is my PageLoad()
if (!IsPostBack)
{
txtDate1.Attributes.Add("placeholder", "Enter Start Date DD//MM//YY");
txtDate2.Attributes.Add("placeholder", "Enter End Date DD//MM//YY");
this.bindgrid();
}
else
this.bindgridfilter(txtDate1.Text, txtDate2.Text);
My bindGridsmethods()
private void bindgrid()
{
ds = Classes.DBMethods.ShowRecords();
grdRecords.DataSource = ds.Tables[0];
grdRecords.DataBind();
}
private void bindgridfilter(string date1, string date2)
{
dsf = Classes.DBMethods.SearchBetweenDates(date1,date2);
grdRecords.DataSource = dsf.Tables[0];
grdRecords.DataBind();
}
My PageIndexChanging Event
protected void grdRecords_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
grdRecords.PageIndex = e.NewPageIndex;
grdRecords.DataBind();
}
And my FilterButton Click()
protected void Filter_Click(object sender, EventArgs e)
{
grdRecords.DataSource = null;
bindgridfilter(txtDate1.Text, txtDate2.Text);
}
Now it does the opposite it disappear the grid after making a change of page without a filter, and if it applies a filter now the pagination works correctly
In most web pages, just setting up a drop down list, a grid view, or whatever?
You ONLY want to bind and load the drop down list, or gridview ONE time.
If you re-beind, and re-load the control AGAIN with data, then you will lose your settings.
So, 99% of the time, you want to do such loading ONLY one time,and ONLY on the first page load. Hence, your page load event needs to be this:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
txtDate1.Attributes.Add("placeholder", "Enter Start Date DD//MM//YY");
txtDate2.Attributes.Add("placeholder", "Enter End Date DD//MM//YY");
bindgrid();
}
}
So, now when a button is clicked, or say gv selected index changes, or whatever? Then the information can be used.
If you rebind on each post back, then a gv, or even a simple drop down list will lose its values - hence ONLY load and bind your controls on first "real" page load as per above.
Page load fires EACH time and for each post back. So, any button click or whatever? The page load event will run again. Hence, your general setup code, startup code, and code to load up things like a drop down list, or gridview?
You need to have a if (!IsPostBack) code stub. The last 200 web pages I have created - everyone has such a code stub, and you really for all purposes can't build a working web page without this "setup" or "first load" code stub. If you re-load or re-setup your controls each time, then anything the user enters or does with such controls will be lost.
Of course YOUR buttons etc. and code can and will re-load the grid, but since the page load fires every time with all and any button click (any post-back), then that re-load code will also re-fire, and you don't want that to occur.
Is it correct? PageLoad()
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
txtDate1.Attributes.Add("placeholder", "Enter Start Date DD//MM//YY");
txtDate2.Attributes.Add("placeholder", "Enter End Date DD//MM//YY");
this.bindgrid();
}
}
PageIndex Event
protected void grdRecords_PageIndexChanging1(object sender, GridViewPageEventArgs e)
{
grdRecords.PageIndex = e.NewPageIndex;
if (txtDate1.Text == "" & txtDate2.Text == "")
{
bindgrid();
}
else
this.bindgridfilter(txtDate1.Text, txtDate2.Text);
}
Clarification: I am chilean, so my english is not perfect, sorry for the misspellings.
Hi, I am working with an image in c#.
I try to put an example image when the page open the first time, I used the post back for this, but when I press a button, execute the code in the post back section (which is right), after that it execute the Button code, but then, it pass again for the Page_Load method, and execute the "not post back" section, and i dont know why.
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
//Is post back
}
else // Is not post back
{
//Make things only when the page is open for the first time
}
}
I usually only use (!IsPostBack) on PageLoad for doing initial data loads or validations(like settings for users).
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
if (userIsAdmin)
{
button1.Enabled = true;
}
}
}
You could refer to the link for the explanation for PostBack https://learn.microsoft.com/en-us/dotnet/api/system.web.ui.page.ispostback?view=netframework-4.8
How can I make this piece of code work? I am dealing with a bigger issue but if I can make this work then I will know what to do.
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
Response.Write(ViewState["Value"].ToString());
}
}
protected void Button1_Click(object sender, EventArgs e)
{
ViewState["Value"] = "Button clicked";
}
Page_Load event happens before Button1_Click and hence you wont be able to access a value that is not already set.
You will need to use an event that happens after Button1_Click like Page_PreRender as you have used in the answer.
Please go through this link to understand Page Life Cycle, which is invaluable in Asp.Net Webforms development.
I was able to solve my problem by putting my logic in pageLoad method in the page_PreRender method like this:
protected void Page_PreRender(object sender,EventArgs e)
{
if (IsPostBack)
{
Response.Write(ViewState["Value"].ToString());
}
}
I have an .aspx page that has a page_load as follows:
protected void Page_Load(object sender, EventArgs e)
{
if (HttpContext.Current.User.Identity.Name != "")
{
....
}
else
{
FormsAuthentication.RedirectToLoginPage();
return;
}
}
protected void btnSubmit_Click(object sender, EventArgs e)
{
....
}
The issue I am noticing is that when the user clicks the submit button it goes though the Page_Load (goes though the else) and then tries to run though the protected void btnSubmit_Click(object sender, EventArgs e).
Is there a way to make it redirect to the login page and not continue to the next void?
This is NOT an issue. This is the normal ASP.NET Page Life Cycle.
Controls events fire right after the Page_Load event.
Note that the FormsAuthentication.RedirectToLoginPage method does not end the request by calling HttpResponse.End. This means that code that follows the RedirectToLoginPage method call will run.
Assuming you want to stop further processing from within the Page_Load (which I believe is your intention with return):
protected void Page_Load(Object sender, EventArgs e)
{
if (/*I want to kill processing*/)
{
// Method one:
Response.End(); // Though admittedly ugly
// Method two:
this.Context.ApplicationInstance.CompleteRequest();
return; // return as normal (short-circuit)
}
}
New to asp.net, I am having a problem on a website I am creating, I am using a master page to build my pages. I am trying to change the css class of a li tag using the onclick event in linkbuttons:
<asp:LinkButton runat="server" id="AboutButton" OnClick="about_click" PostBackUrl="about.aspx"><span>About</span></asp:LinkButton>
This linkbutton calls a function in the master page's code behind:
protected void about_click(object sender, EventArgs e)
{
if(Page.IsPostBack)
{
about.Attributes.Add`enter code here`("class", "current");
}
}
This only works when the page is loaded and the button is clicked again. Any help would be greatly appreciated.
By adding: if(Page.IsPostBack) you're specifically telling it not to execute that code the first time the page is loaded, but you want it to happen when the page is first loaded, by the sounds of the question.
Why did you add if(Page.IsPostBack). Try this
protected void Page_Load(object sender, EventArgs e)
{
if(!Page.IsPostBack)
{
about.Attributes.Add("class", "current"); //initial setting here
}
}
protected void about_click(object sender, EventArgs e)
{
about.Attributes.Add("class", "current");
}