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.
Related
the website I'm currently developing can display dynamically-built forms.
A form is composed of fields, which are created directly by the users and can be displayed as one of multiple types that we support (text box, list box, tickbox, radiobuttonlist etc.). The rendering logic uses a repeater that iterates over a collection of all the fields defined by the user.
Inside the repeater (directly in the aspx page), one instance of each of the types we support is defined.
<asp:Repeater ID="fieldRepeater" runat="server">
<ItemTemplate>
<asp:TextBox ID="textBox" runat="server" />
<asp:DropDownList ID="dropDownList" runat="server" />
<asp:CheckBox ID="checkBox" runat="server" />
<asp:RadioButtonList ID="radioButtonList" runat="server" />
[...]
</ItemTemplate>
</asp:Repeater>
During the loading, we figure out which control is required and actively hide all the other ones.
Being still new to the web based development world, this approach seems very odd to me. My guts would prefer keeping the UI clean and instanciate exactly the controls that are required in CodeBehind and not start "playing" with visibility... but the current approach has some obvious benefits as well.
Is it really how one would do it in a web app?
Are there some best practices here?
Thanks!
I have no idea what the best practice is here, but I have done something similar before in a previous project and tried both approaches. Both will work.
Creating the controls in code-behind can be fiddly, especially if you are having to deal with post-backs. The controls have to be created in OnInit, as otherwise they won't get the posted form values and viewstate populated. This will cause complications if any of the control creation is based on the values of other controls, as you won't known the values without manually delving into the posted form values.
The only practical disadvantage with your current approach that I can think of is that all four controls (TextBox, DropDownList etc.) have to be instantiated and processed server-side by ASP.Net, which is a bit of a waste of resources. But it's probably not too significant; maybe do some profiling to see. I do agree that it seems a bit odd though, it doesn't feel very "clean".
As you said you're new to web development, then I would recommend continuing with your current approach of including all the controls and hiding the irrelevant ones. I just found it simpler when I did, even though it may not seem as nice.
Good luck!
I'm creating an UserControl and I'm passing a variable to it.
It works fine if I do it this way:
<uc:TestControl ID="testControl" runat="server" Variable="test"></uc:TestControl>
However I want to pass a dynamic variable to the control like this:
<uc:TestControl ID="testControl" runat="server" Variable="<%=dynamicVariable%>"></uc:TestControl>
But unfortunately that doesn't work and I know I could assign it on Page_Load but I don't like that way.
So I'm wondering if it's possible at all. Is there any way to assign a dynamic variable to an attribute like I wanted above? Or am I required to do it in Page_Load?
Any feedback would be appreciated!
Thanks!
<%= syntax doesn't work with controls marked as runat="server" .Try using the databind syntax
Variable="<%#dynamicVariable%>"
Then calling databind on the user control as per this SO question
EDIT
To database i think it's a straight
testControl.DataBind()
supported in ASP.Net 3.5 and greater.
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).
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
I'm kinda new to ASP.NET and I have much more experience with windows forms.
I need to show a table with some result data in a page
Now, with winforms I would do something like this
ResultForm myForm = new ResultForm();
myForm.ResultDataTable = dataTable;
myForm.Show();
Any tip on how could I do something similar with Asp.Net?
tks
You can redirect to a page using Server.Transfer method and in that page use a databound control. You can databind any data controls in ASP.Net, like gridview, datalist etc.
Set the datasource and then databind the control.
Try using the DataGrid ASP.NET control:
In the .ASPX file
<asp:DataGrid runat="server" id="dgData" AutoGenerateColumns="true" />
In the .ASPX.CS file
dgData.DataSource = dataTable;
dgDate.DataBind();
The code that you did work well for "windows-forms", but does not work in ASP.NET.
My suggestion, as well as other users too, is that you study a little about web development.
There are huge differences between "web-forms" and "windows-forms", starting with the types of objects and their behavior in the UI.
This code can not be applied to "web-forms" directly.