I am trying to extend the ASP GridView control by adding some buttons above it. Such as Insert/Delete/Print etc. I must extend the GridView control because it is used at a lot of places in the project. The buttons and the control must be wrapped in an UpdatePanel so it can do partial updating. I am trying to do something like this:
UpdatePanel up = new UpdatePanel();
ImageButton newButton = new ImageButton();
newButton.ImageUrl = "../Images/new.gif";
up.ContentTemplateContainer.Controls.Add(newButton);
up.ContentTemplateContainer.Controls.Add(this);
Page.Form.Controls.Add(up);
The problem is I don't know where to put it, and I don't even know if this will work. If I put it at OnLoad/OnPreRender I get this:
"The control collection cannot be modified during DataBind, Init, Load, PreRender or Unload phases."
This error occures on the second add.
If I put it in CreateChildControls Page is not yet created.
Please give me some pointers.
In this situation, I'd probably build my own custom server control that inherits from GridView.
Here's a link to a MSDN article that should get you started: Walkthrough: Developing and Using a Custom Web Server Control
EDIT:
Since you're already creating the custom server control; I think this might be your problem line: Page.Form.Controls.Add(up)
Try using simply Controls.Add(up). What it looks like you're trying to do is add the update panel to the Page itself; when you should really be adding it to the controls collection of your extended GridView
Related
I have a Web User Control that I need to add to a page simply in order to add it to an HtmlForm so I can send an email with this User Control, however, I do not need this Control to appear on the page, I just need it to fill with data so I can send this email, and then be removed so it does not appear on the page.
Currently I have tried:
myControl c = new myControl();
c.InitializeAsUserControl(Page);
c.fillInfo(data);
//add to email form and send email
yet this adds the control to the current page on post back once the email has been sent and a confirmation message
I have also tried
myControl c = (myControl)Page.LoadControl("~/filename.ascx");
//send email
Page.Controls.Remove(c);
yet this also renders the control on the page and does not remove it. I have tried to add it to a panel and set Visible to false, but unfortunately this does not work either. If I simply create a new myControl() without rendering on page or calling LoadControl I get exceptions thrown when fillInfo is called when it tries to modify asp:labels in the User Control saying that the objects are null or not instantiated.
Which part of the page cycle are you loading and unloading the controls? To work properly it needs to be done in Page_Init. It's a common mistake to do it in Page_Load. If it is added anywhere else other than Page_Init it won't be added to the ViewState correctly and problems will ensue.
Rather than unload - I would add it to a Panel and set Visibility to false. Could be the reason that isn't working for you at the moment is that the control is being added at the wrong part of the page cycle and isn't being added to ViewState correctly.
Could that be your problem?
I suggest reading the entire TRULY UNDERSTANDING DYNAMIC CONTROLS series. To successfully use dynamic controls with postbacks, viewstate, bindings, and the other WebForms features, you really have to know the page and control lifecycles and their interactions inside out.
When you load and set ViewState depends on the cycle. ViewState is loaded between Page_Init and Page_Load, so the control has to be in Page_Init. However, any processing based on auto-loaded ViewState, needs to go in Page_Load. Where/when ViewState is enabled depending on the control hierarchy can also affect this. I suggest you read that guide above in depth if you really want it to work. Or, you'll have to post your entire control code and its use in a page for us to tell you which parts you are missing or have in the wrong part of the page lifecycle.
I've made dynamic controls work, but 99% of the time, unless the control is extremely trivial, it's easier to find a different solution than it is to make sure all the interactions work correctly with dynamic control creation.
I am building a custom master page type control i.e. sort of like a datagrid but should be easier to add custom functionality into it. It's going great but part of the desired functionality is to have a paging control that switches on and off and part of that control would be a textbox that displays the current page number and on TextChanged redirects to the new page of the dataset.
The problem I'm having is that technically the textbox which has its event fired is embedded in a control that is embedded in the control you actually put on the page sort of like
Page
|
Display Control
|
Paging Control
|
Textbox
Buried all the way down there the event is not firing. Worse the postback javascript isn't even being written onto the page (Nothing on the page posts back so far this is the only bit that really needs to).
I've been trawling around Google for quite a while now and picked up that I need to implement INamingContainer (done) and I need to add the control into the page's control tree (is Pre_Init too late for that? When's a good time to Add the Control to the page?) then the event should fire, apparently. But I've been unable to find an example of best practice on this there are quite a few near misses where people are having button angst but this isn't a button.
So can anyone point me in the direction of getting a control embedded in a control embedded in a control added to a page to behave properly?
You need INamingContainer only if you plan to add more than one instance of your custom control to the same page. What it does is enabling unique id generation so you don't end up with controls with the same ID. I recommend you inherit from CompositeControl when creating your custom control.
Pre_Init is not too late. Actually it is pretty early considering the lifecycle. You can instantiate custom controls and add them to the live controls collection in a lot of places. I would recommend you do it in Page_Init (before viewstate is loaded) or Page_Load(after view state is loaded). Even if you add it later in the page lifecycle the control will catch up in events.
To subscribe to events of child controls you can use the FindControl method:
MyControl myControl = Page.FindControl("MyControl1");
TextBox textBox = myControl.FindControl("TextBox1") as TextBox;
The answer was a combination of the above answer and the comment on the original question. The vital thing to get the event to happen is to make sure that your controls (parent and child) inherit from CompositeControl and INamingContainer e.g.
public partial myControl:CompositeControl,INamingContainer
etc...
Then you override your composite control's CreateChildControls() method and create your controls and do the wire up there. This will ensure correct bubbling. and mean that the event handling takes place within your comoposite control...
I am writing a survey generating system in asp.net. i asked an ealier question about the best way to create controls that can be passed about as variables. This was problematic with user controls so i was advised to use custom controls and a quick way to do this was to inherit from the panel control and just add a bunch of standard controls the the controls collection by overriding the CreateChildControls method. This way i could create my "survey" controls,which are basically Questions in the survey. THe question controls are then dynamically added to the page. This all works well but know i have come to the point that i want to try and retrieve the values from these controls and i seem to be lost in a nether world of of viewstates and page lifecycles. I can ensure that the dynamically added text boxes have a known ID, however even if i add the parent control in the page init handler the CreateChildControls method does not run until after until after the viewstate is loaded. I cannot work out how to retreive the values from these text boxes.
You can call the EnsureChildControls method on the init handler of your control to ensure CreateChildControls is called before the ViewState is loaded.
You certainly seem to be doing this the hard way. TextBox values are not saved in the Viewstate, they are posted in the request.
Why aren't you using a UserControl here? So you can "pass" it somewhere? what exactly are you trying to do?
I have a composite server control that does quiet a number of things; one of which is to display a ModalPopup OnClick of a dynamically generated HtmlAnchor control.
I need to create this ModalPopupExtender control dynamically in my server control and trigger it from within.
I have been able to create it and trigger it from a button created at design time but not at runtime. This is as a result of the ID assign to the link is always not found by the ModalPopupExtender control.
I have tried assigning a static ID but no success. Can anyone help?
I figured it out. All i needed to do was recreate the HtmlAnchor control in the overridden CreateChildControls method on postback.
Thanks David for you concern.
I want to make use of "complex" usercontrols with more than one control element within. It's the same control I will reuse in the list, and I have a PlaceHolder control for it already.
I can add the control with LoadControl(path to .ascx) - no problem.
I can through my custom properties get/set access the embedded Labels, too, so I can initialize each control perfectly.
But when adding LinkButtons, I get into trouble/problems.
When I click the button, I do get a "submit" of the page rendering the controls; but the control's own button event does not seem to fire (or at least PageLoad on the parent page seems to fire first?) - I can't figure out where my event goes or where to look for a name/ID or parameter for this button.
How come or what am I doing wrong here?
I've made a "fake button" now by using a label more with a "hardcoded A HREF" with an ID in the URL, but I would like to learn what event I need to catch and where or how to init the button, because I want to be able to use "default ASP.NET" controls for these usercontrols (hopefully without too much patchwork-coding)...
The only reason that events get "lost" is because your controls are not being recreated in such a manner that ASP.Net can associate the event with the control after the postback. It does so through the use of the ID property.
In other words, you're doing one of three things wrong:
1) You're assigning the ID's of your linkbuttons differently during the creating phase in Init after the postback
2) You're creating your linkbuttons dynamically using code, but you're doing it after the Init phase of the page lifecycle, so that your controls do not participate in ViewState.
3) You're re-binding the datasource of the parent control containing the linkbuttons on every postback. Use if (!IsPostBack) to prevent rebinding it every time.
Without seeing your code I can't give anything more specific than that unfortunately.