I had been having a great deal of issues trying to put a server control button and event handler onto a master page. Every time I clicked the button from one of the content pages, the postback would take me not back to the content page, but to the site.master URL, so naturally that would crash my application. I scoured the internet for a solution, but I couldn't get any to work for me. I finally figured out a very easy fix and so I thought I'd share it in case anyone else runs into similar troubles.
On the Master Page's Page_Init() method, I assigned the PostBackUrl attribute of the server control to the current page Uri using HttpContext.Current.Request.Url.AbsoluteUri;
(UserLogin is my button control name)
protected void Page_Init(object sender, EventArgs e)
{
UserLogin.PostBackUrl = HttpContext.Current.Request.Url.AbsoluteUri;
}
Related
I am working on web application. I have a grid that shows data to the user. When user click on the any row of the grid, it redirects user to another page, as we have a asp link control on the a column.
Issues
My code is like
if (!Page.IsPostBack)
{
//CODE
}
When user click on the BROWSER BACK button, it does not execute the CODE. Simply show the data from CACHE.
How can I execute the CODE , on browser back button click ?
It's a global problem with ASP.Net. Most of developers thinks like Windows developer. It ends with a postback for mostly any action, including navigation actions.
To solve such problems:
Avoid using button to change page. Generate an hyperlink with the target url.
Wrap parts of the page within an update panel. The benefits is that the browser won't see a page change after each postback. Then you will be able to "refresh" the page without warning dialog
When populating a grid, instead of "selecting" a row from codebehin, generate a link to the same page with "?ID=42" in the url, and bind this value to the grid as the selectedvalue
The root cause of this "evil" behavior, is that postback are issued using HTTP Post request. Then, the browser requires to repost the page to rebuild it.
Using the technics mentionned above, you are issuing GET request. This kind of request doesn't require to resubmit anything.
Try Disabling browser cache for the page that you don't want to cache.
protected void Page_Load(object sender, EventArgs e)
{
Response.Cache.SetExpires(DateTime.UtcNow.AddDays(-1));
Response.Cache.SetValidUntilExpires(false);
Response.Cache.SetRevalidation(HttpCacheRevalidation.AllCaches);
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Cache.SetNoStore();
if (!Page.IsPostBack)
{
//CODE
}
}
I find this as a funny little problem. I think the reason lies behind the life-cycle of page-object/events-generation, but the question is how I come around the problem?
In Default.aspx there exist some funny controls but also a
<asp:PlaceHolder runat="server" id="phUserContent"></asp:PlaceHolder>
This placeholder is empty until runtime. Code behind are, in some circumstances, loading UserControls into it. Like this
Control ctr = LoadControl("~/UserControl/Note.ascx");
phUserContent.Controls.Add(ctr);
This Note.ascx contains some interesting controls and finally a LinkButton that fires an event. The LinkButton-code are very easy and gramatically correct,
<asp:LinkButton runat="server" ID="lbUpdate" OnClick="lbUpdate_Click" Text="Update"></asp:LinkButton>
In the Code behind for the ascx I have the code for the event,
protected void lbUpdate_Click(object sender, EventArgs e)
{ ... }
As I wroted, the postback occurs, the page are regenerated as I would suspect - but without the lbUpdate_Click event to be executed. A break-point is of course tried.
I'm looking for two possible scenarios. One is that I missed something really easy (you know, like wroted in wrong code behind file) or that I missed an important part of the Page Generation Cycle.
I'm mostly into the second, like this (i just think here..)
1. Page (ascx) got it's changes
2. Submit was clicked
3. Ascx was re-generated
4. Events was cleared but was exist and doesnt cast error.
5. After reload, initial content was reloaded
The effect would be that the compiler can't see the breakpoint and the values was never saved due to a "execution of an empty event". But this is just a amateours guess, please advice me.
[UPDATE AS PER ANSWER]
This is how I was solved it, based on the acepted answer below.
List<Control> ctr;
public User()
{
ctr = new List<Control>();
}
protected void Page_PreInit(object sender, EventArgs e)
{
ctr.Add(LoadControl("~/UserControl/Note.ascx"));
}
protected void Page_Load(object sender, EventArgs e)
{
ctr.ForEach(d => phUserContent.Controls.Add(d));
}
Shortly..
1. The class got a list of Controls
2. In Page_PreInit (before creation) add UC (u can have X of them here)
3. In Page_Load (where all ctr are created) add each UC to the PH.
Which also make the events in the UC also working, no magic and no dumb complications :-)
It's a lifecycle issue.
Remember, every page request creates a new Page object, and new instances of all the controls on it. If you are dynamically creating a control, then it has to be done in the exact same manner on every postback. If you want the new control to fire an event, then it has to have the same id as the old one, and have the event hooked up to it before control events are processed in the lifecycle.
If you're creating the control dynamically at a point in the page lifecycle that occurs after ViewState is handled, then you'll have to manage your own state as well. In other words, if you're not dynamically creating the control during the PreInit phase, then you'll have to manually deal with restoring state.
In an effort to speed up my site, I am trying to disable the viewstate as I don't think I am using it everywhere. I have a master page setup with user controls loaded (using LoadControl) in default.aspx. My typical page setup would be:
Main.master -> Default.aspx -> ControlWrapper.ascx -> MyControl.ascx
I have put EnableViewState="false" in my Default.aspx page. Now when I try and read a value from a DropDownList in MyControl.ascx it comes back blank when the form is posted. First all, why is this? I thought I should still be able to read the value from the drop down list?
I then tried enabling the ViewState on that control and it didn't work.
I also tried enabling the viewstate on the Page_Init event of MyControl.ascx using Page.EnableViewState = True; but that didn't help either.
I guess I am misunderstanding the viewstate somewhat, can someone point me in the right direction please?
p.s I don't know if this information is relevant but I am adding the contents of the DropDownList dynamically in the Page_Load event. (Thinking about it, could this be the issues - Will test this now).
Thanks.
With viewstate turned off, the values you are loading in Page_Load are no longer in the list when you post back (until you reload them obviously). If you want to work without viewstate, you will need to set the selected item from the value in Request.Form.
protected void Page_Load(object sender, System.EventArgs e)
{
ddlItems.Items.Add(new ListItem("test1", "test1"));
ddlItems.Items.Add(new ListItem("test2", "test2"));
ddlItems.Items.Add(new ListItem("test3", "test3"));
if (Page.IsPostBack)
ddlItems.SelectedValue = Request.Form["ddlItems"];
}
When you've set ViewState to false the dropdown needs to get populated before page load - which means you probably should do it at page init. Something like this:
protected void Page_Init(object sender, System.EventArgs e)
{
ddlItems.Items.Add(new ListItem("test1", "test1"));
ddlItems.Items.Add(new ListItem("test2", "test2"));
ddlItems.Items.Add(new ListItem("test3", "test3"));
}
Then you should be able to read the value at load:
protected void Page_Load(object sender, System.EventArgs e)
{
someTextBox = ddlItems.SelectedValue;
}
A bit of background:
On this page: Microsofts page cycle
At the image with the page cycle there is the methods "ProcessPostData" and "LoadPostData" firing in between Init and Load. The post data for the drop down contains the selected value - but not the possible values, so when it loads the post data it is essential that the possible values are already there (or it won't be able to set the selected value). Also before the post data has been loaded the selected value has not been set.
If viewstate is enabled it saves and retrieves the possible values in between postbacks.
I will assume you're using .NET 4. View State is the method that the ASP.NET page framework uses to preserve page and control values between round trips.
The reason it didn't work for you when View State was turned off is because that control was rendered again when you performed a PostBack to the server, meaning you lost your selected value.
The reason it didn't work for you when View State was off for the page, but on for the control is because in order for that to work, the following conditions must be met:
The EnableViewState property for the page is set to true.
The EnableViewState property for the control is set to true.
The ViewStateMode property for the control is set to Enabled or inherits the Enabled setting.
ASP .NET View State Overview
When you did EnableViewState = false; on a page then you should not expect DropdownList.SelectedValue after postback.
It will be good if you Enable/Disable ViewState on particular controls rather than disabling whole view state by specifying it on page directive.
When an asynchronous postback happened inside update panel, another postback happens also for MasterPage not only update panel embedded page .
I want to prevent this MasterPage postback .
is this possible ?
think like i have a MasterPage
and another page which is test.aspx which is content page of MasterPage
i have update panel at test.aspx
when asynchronous postback happens at this test.aspx update panel it also loads MasterPage Page_Load
i want to prevent this (it should not also load MasterPage Page_Load)
Thank you
ASP.NET's UpdatePanel (as well as any normal asp.net page)'s postback does postback the master page as well.
Normally, to properly deal with postbacks, programmers check for it and program accordingly :
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
dataBindAndSetUpControls();
}
}
So, my answer here is that I don't know if it is possible (and if it is, it certainly isn't easy), and that your request is not a normal thing to do, and programmers handle PostBacks via the blurb above.
I have command button added in my asp.net grids. After performing an action using that button, we refresh the grid to reflect the new data. (basically this action duplicates the grid row).
Now when user refresh the page using F5, an alert message is displayed (to resend the information to server) if we select "retry", the action is repeated automatically.
I know this is a common problem in asp.net, how can we best handle this?
Search for GET after POST - http://en.wikipedia.org/wiki/Post/Redirect/Get - basically, redirect to the current page after you're finished processing your event.
Something like:
Response.Redirect(Request.RawUrl)
If you think you don't need postback paradigm, you might want to look at ASP.NET MVC.
The problem is that asp.net buttons perform form posts when you push a button. If you replace the button with a link your problem should go away. You can also use a button that performs a javascript function that sets the document.location to the address of your page.
If I well understood, you simply have to check if you are in a post-back situation before populating your grid.
Assuming you do that on Page_Load, simply surround the operation with post-back test like this:
private void Page_Load(object sender, EventArgs e)
{
if(!this.IsPostBack)
{
// populate grid
}
}
You need to call response.Redirect(Request.Url.ToString());
or you can wrap the grid with updatepanel and after every command bind the datasource to grid
Inside your <asp:Repeater> tag put this:
EnableViewState="false"
This will cause your control to refresh every time the page loads, no matter if it's a postback or not.
for example:
if you click on 'button' system will catch the event 'button_click'.
if you refresh the page, system will re execute again the same event.
to don t have this problem, in your event insert :
on your event
private void button_click(object sender, System.EventArgs e)
{
button.Enabled =false;
button.Enabled =true;
}
is what you meant?