I'm just starting to get my hands dirty with silverlight and "value converter" keeps popping up. I don't remember reading about them in the ASP.NET web app world. Is this something special in Silverlight/WPF? What is its purpose?
Thanks!
From this excellent post:
When you’re binding data to controls there will be times when the data needs to be modified or tweaked some on the way into a control or as the data leaves a control and goes back to the source property (during a TwoWay binding for example). Sure, you can always write code to change a given value, but in many cases it’s much easier to write a simple value converter instead that can be re-used. In this post I’ll walk through creating a value converter and then show the code for a few of the value converters I find myself using fairly frequently.
There is stark contrast between the web platform and the Windows when it comes to data binding. Especially in WPF / Silverlight / Windows Phone 7. These technologies support databinding differently compared to Web which is stateless.
A very common example of a value convertor is when you want to hide or show a control in WPF / Silverlight. Controls like stack panel have visibility property which is an enum. We can assign values like Visible / Collapse / Hidden to show or hide the stack panel. In most cases the visibility is controlled by a boolean value. So you use a convertor to convert the boolean to visibility.
Another example of value convertor could be formatting of amount fields. Say you want to display 1000 which is stored in the database as $1,000.00 in an amount text box. You can use the value convertor to do so.
The possibilities are endless. You can think of value convertor as a visual representation of something. Another example I can think of is the completion progress of any task. You can show a nice colourful progressbar instead of showing values like 10%, 20%, 30% completed :)
Hope this helps.
Related
I have this textbox in asp.net webform page used to enter a city. On entering some text it provides suggestions just like facebook does of matching results.
I tried these two methods to implement this.
I first used onTextChanged event and AJAX and found out it only works when the textbox loses focus. I wanted a solution to work as you type. Advantage of using this was that I could use a database and it would be fast, because no xml files will be transferred in the process.
2.I used ajax, clientside using js. But the problem is the xml containing cities, there states, country is a massive 30MB file. So, it was impossible to use it, so thought of making 26 small xml files of each alphabet out of that big one but still they would be big enough to actually use. So, now I am planning to use 26*26 files containing the cities with same first two alphabets but I think its ineffective way to do what I want.
Is there any other efficient way of accomplishing it?
The best way would be to use a database, if I could.
You need to use onkeypress and/or onkeyup events instead.
Did you know that there are plug-and-play auto-complete components out there that are free? For example http://jqueryui.com/demos/autocomplete/
Use JSON! It's much more compact. You'll probably save 30-40% on the size of that data.
Did you know that you don't need to pass the whole data set for that to work? You can have it live on the server (e.g. in the database, or cached on the webserver for faster access and less db traffic), and have clients only pull small set of data at a time, based on characters that they type. That JQuery UI AutoComplete supports that feature.
If you cannot use JQuery and JQuery UI (not wanting would be an unacceptable answer), then I'm pretty sure there are other free alternatives, including this one: http://www.asp.net/ajaxLibrary/AjaxControlToolkitSampleSite/AutoComplete/AutoComplete.aspx
I'm sorry for maybe making such a basic question but in ASP.NET websites what does the __VIEWSTATE input field represent?
Also, is there any way to compute it's value (based on the values of other form fields)?
EDIT
I understand that __VIEWSTATE, as the name suggests, maintains the values of form field values in webpages however what I'm interested in knowing is how this state (the string) is generated. If I base64_decode any __VIEWSTATE string all I see is a bunch of cryptic HTML.
Is there any way to better understand what exactly is being encoded? I've searched on past questions and I've found some tools that can do this like this one, but unfortunately it doesn't seem to work.
The reason I'm asking this is because I've access to a web service API that gives me most of the values I need to work with. However I also need an additional field that is only available on the last stage of the form. I already contacted the web service provider but unfortunately and they're not going to update their API so soon. I was hoping I could prefill the form initial values using the web service data and then calculate the __VIEWSTATE to access the last field that shows up on the last stage of the form, it would make the whole process a lot faster.
Not sure if I made myself clear enough though...
Paul Wilson has a very good article: ViewState: All You Wanted to Know
VIEWSTATE can be deserialized with the LosFormatter class.
A quick Google search answers the question:
http://msdn.microsoft.com/en-us/library/ms972976.aspx
First sentence:
Microsoft® ASP.NET view state, in a
nutshell, is the technique used by an
ASP.NET Web page to persist changes to
the state of a Web Form across
postbacks.
If you really want to understand it well, see Dave Reed's article about ViewState.
Do take a look at the biter script posted at http://forums.techarena.in/windows-software/1329157.htm.
That script shows how to set up and use __ViewState and other .NET variables.
That script logs into a .NET site, and gets stock values, without going thru a browser. Instead of user doing it manually, the script does it programmatically.
What do you mean by compute it's value?
Assume that it is a compressed (actually Base64 encoded) pair of your form fields/values in text form, which gets serialized into server side objects for you to work with.
The easiest way of doing this in Razor is putting this on a view:
#{
throw new Exception();
}
I've received a project for internal use. My application has to store about 100 rows of meta data of a game and each row has about 15 fields maximum. Fields can be game name, game category, maker, source code path, etc. I will most likely have to join about 5-10 tables for each row of record. Only a few people are using it and will receive very little hits. Speed performance is not a much of an issue. The rows of data I have to present must be sortable and searchable
My current solution is to use ASP.NET's GridView control with ASP.NET's AJAX UpdatePanel to give it that ajax feel. I'm thinking of using LINQ-to-SQL as my data access layer. I'm thinking of building my own custom search engine but if there's an existing control that has this feature already, i would prefer to use that; anyone know of such control exist? Anyways what do you guys think?
Update #1:
I'm looking into creating a DynamicData website. Any have thoughts on that?
Use ext.js!
Look at the Grid Samples, its a very shallow learning curve and provides you with amazing results in little to no time.
http://extjs.com/products/extjs/
Basically, you expose your data via a web service (asmx or WCF, your choice), throw the Ext.Js grid onto your html/aspx page and point it at your webservice. Configure the control for things like sorting/searching/expanding/grouping/paging etc (use the api reference http://extjs.com/deploy/dev/docs/).
ASP.NET Dynamic Data looks really cool, particularly for sites where you've got:
lots of data
not a lot of worries about performance
no / little desire to skin / design the site
no / little desire to extend existing / write new functionality.
So I'd say that's a good match for your project.
Gridview is your best bet. It's so powerful if you know how to use it correctly. It does automatic sorting and if you can code pretty well you can get the data to be filterable(if that's a word). It also makes the Connection to the database for you....so in my opinion, you can't beat the gridview when it comes to reports like that.
We have an ASP.NET application that uses the Infragistics WebSchedule control to display appointments etc in the same manner as Outlook. The problem we have is that the customer wants to be able to print the page as it appears on the screen - which the control itself does not appear to support directly.
We have developed a Crystal Report that does a fair job but it is pretty complicated and just a little bit flaky (it does not stretch to accommodate all of the appointments for a particular day so if there are too many then they spill over). Bascially we have bullied Crystal to doing something it is not really meant to do - render a graphical representation of a diary rather than list the data in a tabular manner.
Does anyone have a better alternative to this?
Thanks in advance
DayPilot Pro (our product) supports PNG export that allows easy calendar/schedule printing (almost a pixel-by-pixel copy of the HTML control).
It's working for both the Calendar (traditional Outlook-like day/week view):
http://www.daypilot.org/demo/Calendar/
and for the Scheduler (showing a time line for multiple resources):
http://www.daypilot.org/demo/Scheduler/
Try "Print/export" button below the controls.
Well in the end I decided to junk the Crystal Report in this instance. It's fine for tabular data and graph data but not really suitable for a graphical representation of a diary/scheduler.
I opted for an XML/XSLT solution which has turned out better than I expected - especially in terms of speed.
I was able to generate an XML stream and depending on the date range feed it to a suitable XSL template which produced a Weekly or Monthly view of the report. A colleague sprinkled some CSS over it and we're sorted.
I've got a person object with a name and age property that implements INotifyPropertyChanged. I want to hook this object up to an ASP.NET form so that the 'name' and 'age' properties bind to textboxes in a way that, when changes happen in either place (in the control or in the object) the other will get updated.
Do I create an intermediary class that listens to each textbox change events and the objects change events and handle the updates between them? What's the best way to do this?
I'm unclear on how to get business objects and the UI talking to each other.
I've stressed over this exact problem a lot.
The short answer is, yes, an intermediate item.
The trick is to NOT write ANY code per control. You should be able to place a GUI control on the screen (That may or may not take code), and then bind your business logic to it through a generic binding mechanism.
I have defined the bindings through XML, through properties files, and through constant arrays--there are a million ways...
You probably have to write code per TYPE of object bound (a listbox binds differently than a text control) and you may have to write validators (but specifying the parameters to the validators and which control the validators bind to should also be done in data)
Now all that said, I'd be really surprised if some data-driven auto-binding mechanism didn't already exist, Microsoft has been into that since VB first came out (although their implementations used to be pretty inflexible, I'm sure they do a better job now).
I'm very insistent about the 0 lines of code per control because my job has typically involved configuring complex devices with dozens of pages of controls. A typical client/server system will have 7(!) lines of code PER CONTROL just to transport data from the DB, to the server, to the client, to the screen and back (this is a minimum for plain ole "dumb" code with no smart binding tricks).
0LOC/control may not be a requirement for everyone, but it's a good goal.
Comment response:
I've done most of my stuff manually in Java, so I'm not sure I can be too much help with the specifics.
Searching for C# and binding gave me this which looks promising, although it may be binding straight to a database which is too much IMO, it should bind to a business object, but the concepts should be the same.
One way to create the bindings at first is to manually instantiate binding objects... (Please excuse my Java)
TextControl textCtrl1=new TextControl("Name Goes Here");
new TextBinder(textCtrl1, personObject, nameField);
In Java, that second line gets tricky. When you are binding to a particular field, you HAVE to use reflection to find the setter and getter for that field of the personObject. In C# I think it should be easier.
Anyway, the binder should add itself as a listener to the control and the object, then forward changes back and forth.
Does that help any?
Edit2:
As you noticed, the hard part is noticing when your property is updated. Luckily, that is optional. More often than not, you don't need to update the component once the object is set (I had to deal with this a few times when I had distributed UIs that could update each other).
So, if you assume your object won't change, the "Binding" has to do the following:
get the value from the property and set it in the component.
add itself as a listener to the component.
store the property/object (if you can manipulate properties, you're set here. If not, you need to store the object and property name, and use reflection)
bail and wait for an "updated" event from your component.
When you get the update from your component:
- store the value in the property.
- You may want to set an "Updated" flag or store the original so that if you iterate through all the binding components, you can tell if any updates need to be saved/enable the "ok" button.
Your object should always be pretty much up-to-date now.
As you build a form, you may want to put all your binding controls into a collection so that you can do a few other operations...
A "Save" operation could call each binding control and tell it to copy from the control to the property, that way you don't need to use a listener.
A "Reset" operation can reset all the controls to their original value.
A "Test" operation can ask each control if it's been updated.
. etc
The neat thing about doing it this way is that every "Operation" you wish to add is pretty trivial to add, but automatically affects the entire UI.
You probably also want a little object hierarchy of controls with an abstract base "bind" class, then a specific binder for each type of control (text field, number field, date, spinner, table, pulldown)--I think that's about it.
This can be very simple, but gains complexity rapidly. Try it with a text field and see what you can do. A simple text binding object should just be like 5 lines of code if you can pass "properties" around in C#...
Okay, totally separate answer. As I told you, I'm not very up-to-date with C# technologies, but from what I've heard, LINQ may do this entire job for you.
In fact, LINQ may be made to do exactly what you are trying to do. It doesn't exist in Java, so that's why I gave you the "Manual" version in the other answer.
The comment at the bottom of this page: http://msdn.microsoft.com/en-us/library/z919e8tw.aspx alludes to a better way.