If I have a control, within a FormView, that is bound using a <% #Bind(...)%> expression. At run time, is there any way of retrieving the name of the field the control is bound to.
To be clear, if the expression is <% #Bind("UserName") %>
I want to return the string "UserName".
after messing around extensively in debug, I found this to work
((System.Web.UI.WebControls.AutoGeneratedField)((System.Web.UI.WebControls.DataControlFieldCell)(e.Row.Cells[0])).ContainingField).SortExpression
In debug use shift+F9 to open the quick watch window pain and explore your Event Argument visually
Related
As we know, ASP.NET WebForms will generate a Unique ID (as well as name) to a control to prevent collisions in the control heirarchy. Let's say we have a TextBox control with an assigned ID of "MyTextBox" in the markup. If this textbox is on a page with a Master Page then the TextBox control will be given a Unique ID of "ctl00$MainContent$MyTextBox" or something similar.
What I want to know is, for a given page, is it possible to know what the prefix WILL BE? In my above example I would like to know all controls I create on that page will be assigned with a prefix of "ctl00$MainContent$". I have examined the Page object and I cannot find an easy way to extract this information. Note: inspecting already existing controls on the page (like the TextBox) isn't an option. I simply need to know, at run time, what the prefix would be.
-- EDIT: Why do I need to do this? --
Ultimately I am trying to solve the problem that this post illustrates:
ASP.NET 4.5 TryUpdateModel not picking Form values in WebForm using Master-Page
I'm using the ModelBinding features introduced in ASP.NET 4.5. Problem is, as the above post points out, is that the name value collection found in the form will NOT match up with your model's properties. The built-in FormValueProvider expects a one-to-one match with the form key (name) and the model's properties. Unfortuantely, the form's keys will have the typical "ctl00$MainContent$" prefix to the names.
I have a semi-working solution where I created a custom IValueProvider that compares the end of the form key with the model's property. This works 95% of the time, but there's always a chance of multiple hits.
Ideally, and this is what I'm trying to figure out, if I could determine WHAT the prefix is I can then prefix that the IValueProvider's passed in key, look for that in the form and find the exact match.
So that is why I'm wondering if there's any way to know what the prefix should be for a given page.
The real answer is to simply code in such a way that you never have to know this information. that might not always be easy - but that's quite much what we do. You can certainly in code behind get/grab the "id" of the given button.
so for example, I become VERY tired of having to wire up a little toast message all over the place. So, I put in a little js routine (in the master page).
But I did need the client ID of a given control.
Well, the code behind needed (wants) to place the toast message next to whatever I clicked on.
So my server side "toast" message caller of course will after the server side code is done does the common "script" inject that will run when the page finally makes it final trip back down to the browser, displays the page, and then of course runs that script I injected.
So, my server side code does this:
MyToast2(Me, btnUpdate.ClientID.ToString, "Update ok!", "Settings changed")
So note how I get/grab/pass the "ID" of the control that the server is going to render. You can use ClientID to get the the final "ID" used for that control in code behind.
So, that btnUpdate is just a simple button placed on the web form. But who cares what super ugly "ID" the server assigns. i just need the "id" of the control so the JavaScript client side can pick up that control - and thus know/get/have the position of the control, and thus I get this result:
Or if I am some place else - again I can call that js routine - and that routine needs the current control. so might have this:
So, I can now just call a routine and pop up a message - not have to write any new js code for the gallzion notices and little pops I have all over the place.
so the little javaScript routine of course does this:
function toastcallm(cntrol, h, t, d) {
var cmd = $('#' + cntrol);
var mypos = cmd.position();
bla bla bla
But only important was that I get/determine and pass the used server "client" id to that routine - I don't really care what it is , or how to see, or how to list them out. I suppose a better jQuery selector or using wild card might work - but I really don't want to know the control ahead of time - but only that I can get the clientID used when I need it.
I simply write code that assumes somewhere along the way when I need such a client id, I simply get it and use it.
So, on the server side? Well, we always build and write code based on the control ID, but you want to get your hands on the actual id? Then you can use in the server code behind:
btnUpdate.ClientID.ToString
(ie: somecontrol.ClientID).
While going through some of the code, i found there is written like this:
ListViewDataItem dataItem = (ListViewDataItem)(((ImageButton)sender).Parent.Parent);
int noteId = Convert.ToInt32(((HiddenField)dataItem.FindControl("hidNoteId")).Value);
Please explain the meaning of these two line.
There is a control (typed to hidden field) that is being used to track the identity of item within a ListView (http://msdn.microsoft.com/en-us/library/bb398790.aspx)
And it's code that shouldn't be written, IMO. It's inefficient and brittle. Also, the identity of the item is stored in plain text in the source of the page.
This code appears to be getting the identity of a databound item when a button is clicked. A better way would be to simply set the command arguments of the button, like so:
<asp:ImageButton runat="server" CommandArgument="[Binding Expression]" />
In the event handler for the button, the CommandArgument can be retrieved and converted to an Int32. With this methodology, you shouldn't even need that hidden field.
Firstly, both the lines seem a bit crazy in their use of brackets and casting. There's probably a better way to do what they're doing, but without more code it's difficult to offer any suggestions.
Anyway, the first line is going to be in an event handler for an event raised by an ImageButton. The event handler method will have a sender argument; this is being cast to an ImageButton. Then Parent.Parent is called on this ImageButton; this will give the object two levels up in the control heirarchy. The developer is obviously quite sure this is a ListViewDataItem, so it's being cast to one of these. Therefore the variable dataItem now contains an instance of a ListViewDataItem.
In the second line, the FindControl method is being called on dataItem. There is presumably a control under this ListViewDataItem with an ID of "hidNoteId". FindControl returns a Control; but the developer knows this control is actually a HiddenField, so there's a cast. The Value property of this hidden field is then passed into the Convert.ToInt32 method to give an integer - this is then stored in the noteId variable.
So at the end of it all, there's a ListView, in which each data item contains a hidden field that contains the value of some ID. This code is getting the ID.
dataItem is a bound control, which when clicked is being used to represent a placeholder. This is used to identify which line is being executed within in the control.
By looking for a parent's parent of this control, it's giving the code a starting point to navigate to the correct row to extract a value from.
After the row is found, the noteId is being assigned a hidden value and cast into an integer.
When items are bound to a grid/repeater, with a button as the post-back control, a way is needed to identify which row is being executed. All the code is doing above is navigating the control and extracting a value from a set of values within the row.
This seems really simple, but for some reason Im stumped..
Im dynamically generating an HTML Select Box, lets call it myselect. Im creating this select box based on some database values Im generating an HTML Select Box.. almost like a string that Im just spitting out to the page. So it's never a control in the codebehind, just part of a string thats rendered as HTML by the browser. If I submit my form, and in my codebehind I perform:
Dim myVal as String = Request.Form("myselect")
That code will give me the VALUE of the myselect select box. How can I refer to this control to cast it as a System.Web.UI.HtmlControls.HtmlSelect control? Request.Form seems to give me the value, but I want to reference the object itself..
If this select box isn't declared statically on your page (that is, you're adding it to the Control Collection), you'll have to do something like this: Dim MySelect as HtmlSelect = Page.FindControl("MySelect") as HtmlSelect
You'll have to forgive me if my casting syntax is a bit off -- I'm used to casting in C#.
If your dynamically generating the control in your code file, then it will not be available to you on post back. As long as you generate it again before the viewstate is processed (you can do it in your oninit), then you can access it as you would anything else.
MySelect.SelectedValue
In response to the comments above (thanks for your help), I found what Gabriel McAdams and jwiscarson had to say were true. In browsing the Request object, I found that its nothing more than a collection of key\value pairs. Performing Request.Form("myformobj") will return a value, because thats all thats available to the application. If necessary, I suppose I can whip up some nifty javascript to track form object types, but it's certainly not necessary in my case.
Thanks for the help
alt text http://img3.imageshack.us/img3/1488/advancedsearch.png
I'm building an "Advanced Search" interface in an ASP.NET application. I don't need SO to write this thing for me, but I'm stuck on a specific problem regarding dynamic controls and ViewState. I would like some direction for how to approach this. Here's my situation:
Ingredients:
A serviceable set of API objects representing entities, fields, and searches, which handles constructing a search, generating SQL, and returning the results. So that's all taken care of.
ASP.NET 3.5
Desired Interface Functionality:
(1) On initial page load, the interface gets a preconfigured Search object with a set of SearchCriterion objects. It binds them into a set of controls (see image above.)
Some search items are simpler, like:
Field (DropDownList) | Operator (DropDownList) | Value (TextBox)
Search Criterion controls for some field types have important information stored in viewstate, like:
Field (DropDownList) | Operator (DropDownList) | Value (DropDownList) where the "Value" dropdownlist is populated by a database query.
Some fields are lookups to other Entities, which causes a chain of field selectors, like:
Field (DropDownList) Field (DropDownList) | Operator (DropDownList) | Value
(2) The user modifies the search by:
Adding and Removing search criteria by clicking respective buttons
Configuring existing criteria by changing the Field, Operator, or Value. Changes to Field or Operator will require the control to reconfigure itself by changing the available operators, changing the "Value" input control to a different type, or adding/removing DropDownLists from the "Fields" section if Lookup-type fields are selected/unselected.
(3) Finally, the user hits "Search" to see their results.
The Problem:
As you probably already know if you're answering this question, controls added dynamically to the page disappear on postback. I've created a UserControl that manipulates the control collection and neatly accomplishes step (1) above as you can see in the attached image. (I'm not concerned about style at this point, obviously.)
However on Postback, the controls are all gone, and my Search API object is gone. If I could get the dynamically generated control collection to just play nice and stick in ViewState, I could examine the controls on postback, rebuild the Search object, then handle control events neatly.
Possible Solutions
I could make the Search object serializable and store it in viewstate. Then on page load I could grab it and reconstruct the control collection at page load time. However I'm not sure if this would play nicely with controls raising events, and what happens to the viewstate of Drop-down lists that contain data from the database - could I get it back? It's highly undesirable for me to have to re-query the database on every postback.
I could develop a custom server control (see this link) for this kind of thing... but that is a new topic for me and would involve some learning, plus I'm not totally sure if a custom server control would work any more nicely with non-fixed control collections. Anybody know about that?
I was thinking that I might be able to accomplish this using databound controls - for example I could bind my criterion collection to a repeater which has a fixed control collection (maybe hide the non-used "value" controls, use an inner repeater for the "Field" drop-down lists). Then all the information would stay in ViewState... right?
Any new ideas would be greatly appreciated.
thanks for your help.
b.Fandango
I've been coding for about a day and I got this working beautifully using the third option I suggested in my question - old-school databound controls. Actually I only thought of the idea when I was forced to write out the question in detail - doesn't that just happen to you all the time?
I put my SearchCriterionControl into an asp:Repeater and bound it to my object collection. For the Field Chooser I put an asp:DropDownList inside a nested asp:Repeater and bound the Field array to that. Everything works beautifully, keeps state, actually required very little code. So I never had to dynamically add controls to the page, thank goodness.
Thanks for your suggestions, Ender, Matt and andrewWinn.
Since no one else has taken a stab at this for 2 hours, I'll throw my hat in the ring with a solution that does not rely on viewstate at all (or the ASP.NET model of postbacks).
What if you grabbed all the input values with jQuery and instead of doing a post-back did a post against the page (or a new results.aspx page)? Or, you could make the entire thing asyncrhonous and do an Ajax request against a web method, get fed the results, and populate on the client side as needed?
The unfortunate thing here is you have to reconstruct which type of controls were used to figure construct your search query since that data wont be passed with the viewstate. But I imagine you were already going to have to do some kind of translation of your input data into a query form anyway.
Read here for more information about using jQuery to hit an ASP.NET page method. Remember - page methods must be static (it's an easy oversight).
I'm not sure what you're doing server side to construct your query - but I would highly recommend LINQ. I did a similar "advanced search" function previously, and after a few different attempts found that LINQ was a wonderful tool for this problem, regardless of whether I was hitting SQL with LINQtoSQL or just hitting an in-memory collection of objects.
This worked so well because 1) LINQ is deferred execution and 2) A LINQ query returns another queryable object. The implication here is that you can chain your LINQ queries together as you construct them from your input, instead of having to do a single massive clause translation to SQL or whatever backstore you are using (one of my attempts was constructing SQL clauses with strings, but still passing input data via SQLParameters for SQL injection protection - it was messy and complicated when hand crafted LINQ was orders of magnitude easier to understand and implement).
For example:
List<string> data; // or perhaps your a DB Context for LINQtoSQL?
var query = data.Where(item => item.contains("foo"));
if( {user supplies length search option} )
query = query.Where(item => item.Length < 5);
// etc, etc.
// LINQ doesn't do anything until the query is iterated, at which point
// it will construct the SQL statement without you worrying about details or parameter binding
foreach(string value in query)
; // do something with the results
Because of deferred execution and the queryable return type, you can concatenate LINQ queries to this expression all day long and let it worry about the implementation details (such as converting to a SQL query) at execution time.
I can't provide you with the exact steps that you will need to do, but I HIGHLY suggest looking into asp.net page life cycle. I created a user control as a DLL one time. I had to capture postback data at specific steps in the lifecycle and recreate and rebind the data at other steps. Additionally thinkgs like viewstate are only available at certain points also. I know that I had to override On_init, On_prerender and some other methods.
Sorry I couldn't be more help, but I don't have the code with me (its with an old employer). I hope this helps.
If you are adding controls to the controls tree dynamically, you need to add them on postpack as well. Just call the method that builds the control on Page_Load or Page_Init and the controls should stay on the page on postback.
I'm playing with Silverlight 3 at the mo. I'm trying to get the current user ID into the Silverlight 3 page. I've done a bit of research and initParams seems to be the right way to go. Trouble is, they seemed to use the asp:Silverlight control and that's gone in SL3. I'm stuck trying to get a variable into the initParams list, assuming this is the right way to go.
I've started with a new Silverlight 3 application called "MyFirstSilverlightApp". I've added a code-behind page to the "MyFirstSilverlightAppTestPage.aspx" to allow me to do any clever bits.
I've managed to hard-code an initParam by adding this to the params of the object defenition:
<param name="initParams" value="userID=id42" />
In App.xaml.cs, I've added the following to Application_Startup:
string userID = e.InitParams["userID"];
and I've passed that into my page in a parameter in the constructor and then used that in a control. That all works.
What I can't work out is how to get the value from the variable I created in the code-behind into the param name value definition. Any help would be gratefully received.
One quick a dirty approach would be to use <% %> in the param:-
<param name="intiParams" value="userID=<%=myUserID%>" />
My prefered solution is to create my own Silverlight Web Control that can render the object tag and its contents in manner taylored to my application.
Add it to your resources collection.
Try something like.
For Each item As KeyValuePair(Of String, String) In e.InitParams
Resources.Add(item.Key, item.Value)
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