I'm currently analyzing the code behind for a web application. The Default page contains a GridView with several bound DataFields that are supposed to be populated, when the page loads and reloads, with data based on a URL parameter that's passed on initial load. The way it works in summary is this:
-I have a GridView1_Init method that is called when the page loads, this retrieves data using an OldDbConnection and a URL parameter appended as part of the OleDbCommand SQL statement.
-The data is read and stored in the Web.config file. At this point, when debugging, I can see and verify the there is data being retrieved.
-Now I'm calling a GridView1_RowDataBound method to populate each row. I have it in the Default.aspx page within the GirdView parameters as OnRowDataBound="GridView1_RowDataBound"
My problem is that this method never gets called for one of the URL parameters I'm passing and as a result the Databound rows in the GridView don't get populated and the page displays nothing. I have another URL parameter I use to test and it works perfectly with that one, i.e. the page loads with the Gridview displaying all the data as expected. I'm not sure why the method GridView1_RowDataBound is getting called for one URL parameter, but not for the other. I've debugged using both and also ran the query in SQL Server Management Studio and I am getting data back for both. Thanks in advance for your help.
I'm not sure.. but try these 1-on the page load define a GridView1.datasource=....;
GridView1.Databind();
2-check the html tags are formed correctly.
Ok, I did a little more digging using Visual Studio and SQL Server Management Studio and first determined that the gridview was using a different stored procedure, than the one I was referencing, to populate the grid. Second, after rummaging through the database, I discovered that the table being referenced for data to populate the grid was empty. After inserting some test data, I went back and reran the application and finally had some data being displayed in the grid. Always the little things.
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).
I have a treelist and I populate it with data in the load event of the form, it works.
In another form, I can add new values to the underlying data source. Then, I show the form again, which contains the treelist. In the load event, I perform the new query, also the data is the newest and I set the datasource to this new data. But the treelist is showing incorrect data. Why?
What am I missing?
Since there is no example of the code you are using, I'd suggest to use BeginUpdate() and EndUpdate() like this:
treeList.BeginUpdate();
treeList.DataSource = your data;
treeList.EndUpdate();
EndUpdate(): Unlocks the TreeList object after a call to the BeginUpdate method and causes an immediate visual update
I am totally new to classes and OOP, so please bear with me.
I am creating a large scale web app which I'm trying to keep tidy by creating my own classes.
For instance I have a Public Class Product which has several properties. One way I am using it is on page load a product ID is assigned to the ID property which in turn gets the details for that product and assigns the various data to the other properties. So within my code I can used for example product.price or product.description and get the appropriate values. This has worked fine, but I found that because the class was initiated on page load it was getting the data from the DB each time that the page refreshed. I stopped this by using an If Not IsPostback to initiate the class. This meant that the data was pulled in only on the initial page load. So far so good.
I then needed to compare a value in a textbox with a property of the product. I have a textchanged event with
If textbox1.Text <> product.description Then....
but here I get a wavy line under product.description and VS2010 is saying that the object is not defined. Its Dim'd in the page.load so I moved the Dim statement outside the page class so that it will be accessible to all events on the page.
The dim statement is Dim product as New product
In my not ispostback chunk of code I have for example product.ID = 1 which will get all the product properties for product 1
The wavy line has gone but when I run the page all works fine on page load. Data is displayed so my product class is working fine. As soon as I make a change in textbox1 and the event triggers product.description is nothing. It got reinitalised.
How do I stop this from happening...
Your "Product" is not persisted between postbacks.
Only control objects in aspx page are persisted/restored automatically.
To remedy this there are multiple approaches.
If Product is loaded via setting "Product.id=1" then what I woudl do is have a hiddenfield that receives the value of the product.id during prerender event (to save it in the page) and in an init event I would restore the "Product.id=hiddenfield.value" but only when it is a postback to reload your object.
EDIT
Thanks for picking my answer. I'll elaborate a little on the various ways to deal with this and why I suggested my answer.
Store Key in HiddenField Reload from DB:
PROS: Product is always Fresh/Correct/Current values. Corresponding to the database. Databases are very efficient to return a record based on a primary key. Very little data is sent to and posted back from the client browser. Low complexity. Each page opened by the client is safely isolated.
CONS: Multiple database transactions. If the DB is already strained or extremely massive you may need to consider even the smallest efficiency gain, but this is not common or likely on a primary key based record
Session State (store entire object):
PROS: Lowest time to "load" object since it's available in memory already once loaded. Less DB Transactions. No data piggy backed to the client and back again.
CONS: Object can become "out-of-date" if altered in the DB. Users who open multiple pages of your application can end up getting the wrong object if both require a different "Product", so instead to be totally safe you need a more complex structure in place to store more then one product or store them based on some kind of key (such as the product ID). Server Memory is used, if serving thousands of users or your product data is large it can become an issue, especially if you do this in many pages with many objects.
Serialization (store the entire object in the page in a field, similar to event state):
PROS: Once loaded, the Database is accessed only once for a specific product, then the product is held, in it's entirety inside the page, it is recreated by the server from the data in the field or via viewstate. Each page opened by the client is safely isolated. Is fairly easy to implement storing in ViewState of the Page.
CONS: Object can become "out-of-date" if altered in the DB. ALLOT more data is added to your page responce and the users next page request. Is more complex to implement because the object needs to be designed to be serialized correctly. Complex objects require allot of manual code to be serialized successfully.
again, there are many other ways to deal with this, such as storing items in a synclocked dictionary style object global to the application, but is considerablby more and more complex as you go.
This is likely the standard ASP.NET page life cycle problem.
After you initialize the page, it gets sent to the user's browser. When the user clicks on something, the browser sends a postback request back to your application. The view state allows the textbox1 object to remember what was in its Text property. However, your Page_Load ran from scratch, and, yes, everything including your product object got recreated from scratch.
If you want your product object to "remember" what it knew before the postback, you'll have to remind it. One way would be to store the initialized value in Session state, and then refresh your product object during the postback section of the Page_Load method.
Every time you do a postback, you're working with a new instance of your page class. The prior copy of your class was thrown away and probably disposed before your browser even rendered the page to the screen.
If you want to persist a value across http requests (of which postbacks are just one type), then you need to put it somewhere like the Session.
I am trying to generate a report by passing parameters selected using two drop down menus which are in page1.aspx and sending them to page2.aspx which is the page for my report viewer (and the report i want to generate).
I tried to use the response.redirect command and server.transfer command with the help of click_button event from my code behind page for page1.aspx but it didn't work.
Can any body help me how to do this, i am trying to figure this out since a really long time and i am new to ASP.NET, i also tried to google it but couldn't find any information regarding the same. Any help would be really appreciated. Thank you
I repeat the question:
What is the way to transfer parameters from page1.aspx to a report viewer in page2.aspx such that the parameters are selected using two dropdown menus in page1.aspx and are used as a criteria to generate report in page2.aspx?
You could create an object class where you save the state of parameters.
Inside that object you create 2 variables par1 and par2.
In page1.aspx when you define what the parameters are, assuming this is not directly a report parameter, but still has to be passed into a report that you will load, you could create a new instance of the class object, store the variables within, and reference that object in page2.aspx when calling the report url into the reportviewer.
In case you are loading parameters inside the report, i think you need a dataset in report1 that uses a stored procedure that includes saving the parameters in a database table. That way, in your second report you can call for this stored data directly in the database.
Those 2 solutions i think should do. If you need more help let me know.
Hello friends I have a list box control in my asp.net project.
I want to know how to get selected index to set currently updated item in database.
Please help me with this. Do i need to perform some data base operation to find the key for currently updated data and then i'll have to set it or there exist some property to deal with this? thanks in adavance
One thing to watch out for, which I have come accross more than once is that if you call your CompanyListBox() method in your Page_Load method, you will lose the selected index unless it is only called on the first page load. To make sure of this, place your call to CompanyListBox() within the following block:
if(!Page.IsPostBack)
{
CompanyListBox();
}
You can access the selected index in your postback by using the following code:
var id = (Int32)listCompany.SelectedItem.Value
Then it is up to you to use that in your data access to update the record in the database. Looks to me that you are using some kind of framework or manager class for your database access. The companyManager should have methods for saving your updated item to the database. Good luck.