when I have controls on a page and I want to data bind them I usually do this in the Page_Load event.
However I have some controls to be databound within a user control. In the code behind for the user control is there a similiar event to Page_Load I could use to databinding?
The DataBindChildren sounds appropriate for what you are trying to do
protected override void DataBindChildren()
{
// Bind a data source to the server control's child controls.
}
If you have created a user control using an ascx it has a Page_Load event that can be accessed exactly like a page.
http://msdn.microsoft.com/en-us/library/fb3w5b53.aspx
Related
I'm using asp.net user control in my web page. I used asp.net repeater control on the user control & created one property of user control.And depending on the value of the propery i loaded the datasource property of repeater control on user control at page load event.
Then i used the userc ontrol on the another asp.net web page & set the property on the page load event. after that it is loading the datasource of repeater control of the user control.
Again I have set the user control property on the text changed event of the text box which is placed on the another web page. I want to again load the datasource of repeater control of the user control depending on the value entered in the text box. How to handle this?
Use OnTextChanged event to bind you repeater, after event fire use __doPostback event and pass some value to it, so that when its postback you can find that value and identify that this post back is done from textchange in IsPostBack event or even you can pass the page event in __doPostBack which will fire automatically then that event for example public void BindRepeaterOnTextChange(){}
check this link for more information
http://wiki.asp.net/page.aspx/1082/dopostback-function/
Working on an ASP.NET 4.0 project, which uses user controls to dynamically generate a form based on definitions stored in the database. One form field would look like this:
<usc:RefControl ID="ctrlUser1"
ReferenceFieldId='product.user1'
ValidationFormat="^\d+\.?\d{0,2}$"
runat="server"/>
Behind the scenes the control emits a RegularExpressionValidator based on the RefControl.ValidationFormat property.
This works fine, however the problem is that this architecture only allows us to validate with regexes. Now I need to add date format validation, based on the user's preferences (which aren't dependent on their UICulture).
Reluctant to refactor the entire user control setup, I need to be able to pass a on-the-fly regex pattern to the ValidationFormat property. Currently I'm using a data binding expression to bind the property to a page instance method:
<usc:RefControl ID="ctrlUser2"
ReferenceFieldId='product.user2'
ValidationFormat="<%# GetUserDateValidationFormat()%>"
runat="server"/>
Code behind:
/// <summary>
/// Returns a regular expression that validates the current user's date format
/// </summary>
public string GetUserDateValidationFormat()
{
//...
}
Works okay on first page load, but on subsequent postbacks the validation doesn't work. I think the issue is that the data binding expression doesn't evaluate at all, but I'm not sure I understand why. I'm calling Page.DataBind() in Page_Init whether Page.IsPostBack or not, so shouldn't this work?
If you see I'm barking up the wrong tree, any alternative solutions to the same problem are also welcome.
EDIT
Managed to solve this problem. The issue was with the way ASP.NET page life cycle invokes the user control's events before the page's own events. The control values were being initialized before the data binding on the page could happen.
Because I still need to do the control initialization before Page_Load to subscribe the controls to viewstate, I simply moved the initialization logic to the Page.InitComplete event so the call to Page.DataBind() could get called first.
protected void Page_Init(object sender, EventArgs e)
{
Page.InitComplete += new EventHandler(Page_InitComplete);
}
So the event tree becomes
User Control Page_Init => Hook InitComplete handler
Page (aspx) Page_Init => Bind data
User Control Page_InitComplete => Initialize the control
Couldn't you just set the property in Page_Load()?
public void Page_Load(...)
{
ctrlUser1.ValidationFormat = GetUserDateValidationFormat();
// do whatever stuff you do
}
I'm currently building a user control that displays a message when a Repeater is empty.
The idea is simple, provide the user control with the ID of the Repeater. When the user control is rendered look up the Repeater and check Items.Count. If it's zero then display the message.
I would like to add one more feature though. I want to be able to hide the Repeater if there are no Items.
Obviously I can't do this in protected override void Render(HtmlTextWriter writer) because the Repeater has (possibly) already been rendered. I also can't do this when the the Repeater ID is assigned to the user control, as the databinding hasn't happened yet.
So my question is.. what event can I override in my user control where databinding has occurred, but rendering has not.
Consider the Page's PreRender event. That way binding has happened but nothing has yet been rendered although they are just about to.
I am calling my user control in a web page dynamically.
For the first time when I click the button on user control, the event is not firing. When I click the same for a second time, the events are firing..
Can anyone help me?
Sounds like the hookup to the button OnClick event is not occurring on every page load, which is required.
Can you guarantee that the hookup is being performed when you add the control and after a poastback to the page? I always put my event hooks in the Page_Init or Page_Load event handlers and outside of any Postback check. Try putting a breakpoint on the Handler hook up and see if the breakpoint gets "hit" twice.
An event hookup for a button would look similar to:
protected void Page_Load(object sender, EventArgs e)
{
btnSearch.Click += new EventHandler(btnSearch_Click); // breakpoint on this line
}
The client id of the control is derived from the ID of all containing controls that are marked with the INamingContainer interface. So, make sure that ALL controls in the hierarchy have a fixed ID.
For example if you have a Button control inside a Repeater, the ID of the button and the repeater are concatenated to make the client ID for the button. So both the repeater and the button should have the same ID across postbacks.
You can compare the HTML for the first request with the HTML of the second request to quickly determine if this is the problem.
Assign an ID for your dynamically created control -- otherwise no events will be fired.
Are you waiting for the download of full page before pressing the button?
The events are javascript functions hidden by ASP.Net in the page, that maybe not present at the time of your clicking.
I have an ASP.NET web form which I am adding a variable number User Controls to. I have two problems:
The User Controls are added to a PlaceHolder on the form in the first PageLoad event (I only add them when "(!this.IsPostback)", but then when the form is posted back, the controls are gone. Is this normal? Since other controls on the form keep their state, I would expect these dynamically added ones to stay on the form as well. Do I have to add them for every postback?
I also have a button and an event handler for the button click event, but this event handler is never called when I click on the button. Is there something special I have to do to catch events on dynamically added controls?
Yes, you need to add them in every postback.
Yes... the control needs to be in the control hierarchy before asp.net dispatches the event (i.e. create the dynamic controls as early in the page lifecycle as possible).
1) You should add the controls on the Pre-init (Page life cycle)
2) You have to attach the event handler to the event of the created button.(events might occur much later in the page life cycle than the same events for controls created declaratively)
To achieve this, add your controls at page init instead of page load. (re-add at postback)
You'll need to know the id of the buttons added to bind them to the event.
I ran into a similar problem. I had a page that displayed a collection of custom web controls. My solution was to add an additional invisible web control so that when I clicked a button to add another control that I would just use the invisible one. Then on post back my load function would add another invisible control to the collection.
I figured out yesterday that you can actually make your app work like normal by loading the control tree right after the loadviewstateevent is fired. if you override the loadviewstate event, call mybase.loadviewstate and then put your own code to regenerate the controls right after it, the values for those controls will be available on page load. In one of my apps I use a viewstate field to hold the ID or the array info that can be used to recreate those controls.
Protected Overrides Sub LoadViewState(ByVal savedState As Object)
MyBase.LoadViewState(savedState)
If IsPostBack Then
CreateMyControls()
End If
End Sub
I ran into the exact same problem and struggled through like 5-6 hours.
I'm posting this maybe someone like me could get help.
1) You should initialize your controls at Page.PreInit event. (In my case I had to add my controls to a place holder so I extended PreInit to load those controls before but you don't need to do that. It depends on your scenario.)
2) You should bind those exact methods to your controls after you initialize them in your Page.PreInit event.
Here is my sample code:
protected override void OnPreInit(EventArgs e)
{
// Loading controls...
this.PrepareChildControlsDuringPreInit();
// Getting ddl container from session and creating them...
if (GetDDLSession().Count != 0)
{
foreach (DropDownList ddl in GetDDLSession())
{
ddl.SelectedIndexChanged += SelectedIndexChanged;
phDropDowns.Controls.Add(ddl);
}
}
base.OnPreInit(e);
}
public static void PrepareChildControlsDuringPreInit(this Page page)
{
// Walk up the master page chain and tickle the getter on each one
MasterPage master = page.Master;
while (master != null) master = master.Master;
}