I have a couple of controls that are set to runat="server", but are showing up as "not declared" in the vb code behind. They are not being setup in the designer.vb file at all, even if the design.vb is re-created.
The only thing that I can think might be causing this is that the controls are inside of a custom control. The code looks something like this (it has been modified because of NDA):
<abc:MyCustomControl>
<additionalItems>
<asp:CheckBox id="coolCheckboxOfPower" runat="server" Text="Triple Rainbow!">
</asp:CheckBox>
</additionalItems>
</abc:MyCustomControl>
So using the example above, if I try to use coolCheckboxOfPower in my vb page, it says it is not declared.
It has been suggested to me that asp controls cannot be nested. Is this true, and if so, how do I get around that?
Asp controls can certainly be nested. Just look at asp:Panel, asp:ListView etc. You have to do some extra work when creating your control to enable this to happen. Namely you have to make have an ITemplate property on your control. Check out the following Building Templated Custom ASP.NET Server Controls to get you started
Related
Climbing the learning curve for creating asp.net webform pages with Visual Studio 2010 (VB).
I had written a fairly complicated .aspx page with form controls, including textboxes and buttons, etc. I never thought to place the form controls inside a <form> block. Instead, all the controls include the "runat" directive; for example, <asp:textbox id="txtUserName" runat="server"> etc. In the codebehind I access the data with strUserName = txtUserName.text. This seems to work just fine.
Now, though, I received some form pages from our contracted "professional" web developer wherein the form code is all enclosed in a <form runat="server">block, and none of the controls include the runat directive. Accessing the data from these controls is a little different: It uses the <input type="text name="txtUserName" id="txtUserName" /> method, and accessing the data in the codebehind
is strUserName = Request.Form("txtUserName").ToString.
My method seems to work fine, but I am wondering if there is a difference in behavior or reliability between my method and his. Even though my way works, am I doing it wrong?
Mine is based on online research I have done to learn this stuff, and I don't remember seeing anything that looked like his. However, just today I see places that are saying that on .aspx pages, form controls MUST be enclosed in a <form> block (i.e., this page at w3schools.com).
Can anyone clarify this for me?
Thanks for your help!
You're not doing it incorrectly (you're using my preferred approach) but your inputs should still be in an enclosing Form tag.
He's using HtmlControls (System.Web.UI.HtmlControls namespace) and you're using web controls (System.Web.UI.WebControls.) Your controls provide better functionality on the server (viewstate and accessing via server code) and his approach is lighter weight.
Situation: I have been creating webpages in HTML5/CSS3 & Javascript using Sublime 2 text editor for a year, however a college course now requires me to use Asp.Net and Visual Studio 2010. I do not use the designer because I am proficient at doing things by hand, however I find that writing asp: inside every element is time consuming and causes syntax errors when applied to some HTML 5 tags and not others.
Example HTML 5: <button id="btn" type="submit" value="Button"/>
Example Asp.net: <asp:Button ID="Button1" runat="server" Text="Button" />
Question: Can the asp: portion be omitted without effecting anything or is it required for IIS or the C# back-end functionality? What about runat="server" can that be omitted?
Google has come up dry regarding my inquiry, so any help is appreciated.
you simply cannot remove either of the two
but hear me out why, because I have a feeling you are not familiar with ASP and therefor are mistaking the meaning of the asp: and the runat="server" syntax.
first: runat="server"
this property on an element, tells the the compiler that this is actually a server side control
so a <button/> is not the same as an <button runat="server"/>
the first one is pure html, while the second one is a control, which can be bound to on the server side. .Net will give it a clientID (not to be mistaken by the ID you have to give it yourself).
second: asp:
this is a prefix, on certain elements, that tells the compiler these are ASP controls (the default controls given by the ASP.net framework). These include Buttons, TextBoxes, DropDownLists, ...
do not mistake 1 of these with a html element.
an <asp:Button id="myAspButton" runat="server"/>
is not the same as a <button id="myHtmlButton"/>
the first, is a server side control, which can be bound to (see it's runat="server" attribute), and this control renders to the browser as a <input type="submit"/> for example.
you could alter the rendering of the asp.net button class to make it return something entirely differnt if you wish.
and you are also not limited to using asp.net classes.
you can create your own controls, and put them in a custom created library
you could give those your own prefix.
if I created such a custom control, I could register a prefix for it in the web.config file,
and thus I could create a custom button extending from the original one (but with a default label in front...
<myc:CustomButton ID="myButton" Text="myButton" Label="myLabel" runat="server"/>
which could render into:
<label>myLabel</label>
<button ID="*******">myButton</button>
the asterisks are symbolizing the Unique ID it will get from the .net framework
if you want to know more on custom controls, or extending default controls
here is a step by step explanation to create custom controls, or extend from a TextBox control.
it also shows how you add a custom prefix for your controls (in the this case 'cc')
you can find more info here
The runat="server" part is required to tell .NET that it will have to render a button there (which will contain .NET specific ID for processing upon POST). Not too familiar with web forms (I started with MVC), but I would assume that the asp: part is to help distinguish between server controls and standard HTML markup.
Why not try removing it and if it breaks something, then you know it's needed. For instance if the button doesn't show up after removing it, then obviously the .NET markup parser needs it to be there in order to know that it is a place holder for a server control.
I'm a newbie in asp.net.
When using FormView, there is a big amount of code in ItemTemplate, EditItemTemplate and InsertItemTemplate which is almost identical.
For example:
<asp:ListBox ID="ListBox2" runat="server" Rows="1" CssClass="field"
DataSourceID="StatusList" DataTextField="DESCRIPTION"
DataValueField="STAT_ID" SelectedValue='<%# Bind("STAT_ID") %>'>
</asp:ListBox>
(Note: at the exception that Eval() would be used instead of Bind() in ItemTemplate)
I've been trying to avoid repeating this code but without the expecting result:
ListView allows the use of LayoutTemplate - but I didn't see any examples that insert this kind of code in LayoutTemplate. And inserting this code in LayoutTemplate would result in an error.
DetailView allows to produce code automatically but I'd like to use a specific design (for ex. using "fieldset" that encompasses some fields).
What would be the best way to avoid repeating this kind of code ?
You don't have to much choice about seperately specifying the Bind/Eval part, but you do have some control over the other pieces. You can make a custom UserControl that contains your layout.
Usually I include a property on this usercontrol called "Mode" which I either set to Edit or View, then based off of this property I change enabled/visible properties on the controls. You'll also need to include a property for each value you want bound/displayed in the usercontrol.
Put some labels, textboxes, etc... in your designer and hook them up to properties in your code behind, put the usercontrol on your page in your item/edit template and eval/bind to your data to the various properties (make sure to set the mode so it displays right).
In my own server control, I would like to implement something similar to the ListView:
<asp:ListView runat="server">
<LayoutTemplate>
<asp:PlaceHolder runat="server" id="itemPlaceholder" />
</LayoutTemplate>
</asp:ListView>
I have created an ITemplate property, I can set the layout in the aspx page, and I am doing ITemplate.InstantiateIn(myControl).
But I can't figure out how to insert controls at the placeholder. I'm guessing it would be something like MyTemplate.FindControl("itemPlaceholder").Controls.Add(myControl). I tried casting to the type of my ITemplate, but I get the error:
Unable to cast object of type 'System.Web.UI.CompiledTemplateBuilder' to type 'MyNamespace.MyLayoutTemplate'
What am I missing?
Edit: I just found this: http://www.nikhilk.net/SingleInstanceTemplates.aspx Control developers can define templates to be single instance using metadata which causes the ID'd controls within the template contents to be promoted to the page level... The parser and code-generator together work behind the scenes to add member fields, and initialize them at the right time.. It seems to be only for user controls? I tried Page.FindControl() after doing this but it didn't find anything.
Ok, this was simply a matter of user error. I instantiated the ITemplate in a Panel, so obviously Page.FindControl() (which is not recursive) wouldn't work. Once I did Panel.FindControl(), everything worked.
In the past I have used this library with sucess
http://www.denisbauer.com/ASPNETControls/DynamicControlsPlaceholder.aspx
So I haven't used ASP.NET for three years or so and I'm really rusty on it. My old code isn't available to me for review (at an old company). This question should be pretty basic, but I can't find any good or reliable or not-super-old resources on the issue, so I'm asking here.
Can I get a general overview of databinding again? I remember it being really useful for select boxes, etc., but I don't really remember how it works. Maybe a good ASP.NET tutorial in general, because I don't remember how it handles POST requests or anything like that really either. Should I just try ASP.NET MVC?
Relatedly, suppose I have a public variable in my codebehind page. Right now I am accessing it by saying Page.DataBind() at the end of the page load function and then running <%# variable %> in the ASPX, but that's not how I remember doing it before and I reckon that it's not very good practice. What's the best way to display variables from codebehind?
Databinding in general (at least in the WebForms model) is mostly a case of assigning fields to be displayed, setting the DataSource property to a suitable object that contains those fields e.g. a DataReader, DataTable, a Collection, and calling the DataBind method. So for your select case, you'd put an <asp:dropdownlist runat="server" id="MyDropDownList"> in the markup for the page, and then in the code
DataSet myDataSet;
myDataSet = someDataMethod();
MyDropDownList.DataTextField = fieldname;
MyDropDownList.DataValueField = fieldname;
MyDropDownList.DataSource = myDataSet;
MyDropDownList.DataBind();
Or you can avoid writing that kind of code and do it in the markup if you use a DataSource control e.g. <asp:SqlDataSource>, <asp:ObjectDataSource>
<asp:SqlDataSource runat="server" id="MySqlDataSource" ConnectionString="aConnectionString" SelectCommand="MyStoredProcName" SelectCommandType="StoredProcedure" />
<asp:dropdownlist runat="server" id="MyDropDownList" DataSourceId="MySqlDataSource" DataTextField="fieldname" DataValueField="fieldname">
For putting your variable on a page, the way you might have done it before is to have a label or textbox on the page, that in your code-behind you assign your variable to the Text property e.g.
<asp:label runat="server" id="MyLabel" />
MyLabel.Text = myVariable.ToString();
Postbacks: you can test the IsPostback property of a page in code-behind to determine if it's a postback or not. After the Page_Load method, other methods will fire if you've defined them e.g. SelectedIndexChanged for a DropDownList.
I really wanted to answer this question with examples and code etc.. but I would just be rehashing information that has been on the web for years and been explained in blogs and articles countless times. You can start with this article
which explains almost everything you need to know.
I have bolded the ones that I think are important to note that some my skim over.
<%# %> Syntax
Page.DataBind() versus Control.DataBind()
Data-bound list controls
Repeater control
DataList control
DataGrid control
Accessing data
DataSet class
DataReader class
Binding in list control templates
DataBinder.Eval method
Explicit casting
ItemDataBound event
As for learning MVC over webforms, that is whole different story. They both have pluses and minuses depending on your time, what you NEED to know and what portions of the project are important. Both techs can accomplish the same thing as they are all ASP.NET at their core, just different approaches so you will be fine either way.