We Keep Coding

Saving data into files and reload them later

I am working on a WPF project with C#.
There is a MainWindow and some other windows showing some data. I have also three XML files, where data from lists can be saved. The code is all written and works perfect.
Now my question is, how to save the whole file. I want to have the capability to, for example, save all the data into files, and user can open these files later and load the data into lists, and commence working, where they left the application before.
Can anybody help me?

If I understand your question correctly, you need to do it with following steps:
Save your XML files with a specific extension name.
you can achieve this by many ways: e.g. you can save your actual XML files into a location, and then just create a link file that contents links to these files. Or you can ZIP all the XML files into one single file.
link the default extension name to your application (so it will be opened by your application by default)
Open/read the file with XML content from your application.
Check this
Deserialize XML into items and display them in your list.

How do I open a PDF file List in a new Window in ASP.NET?

How do I open a PDF file List in dialog box in a new Window in an ASP.NET application ?
I want list of pdf file which is stored in folder in my application and then select any of pdf and save in logged user's particular folder.

Since you want to display a list of pdf files stored in a folder on the server side you will need to render the list to a page in some format that makes sense. You may open that up as a dialog (perhaps using something like jquery ui) but it wouldn't be necessary.
Next to each file you could have a button that indicates the action you are after, say 'Copy'.
This would then send the id/name of the relevant file to the server and the server code could copy the file to some other location on the server that you refer to as the users folder.
However, if you want to download the file to the user's machine that is something else and you will find many answer here on SO about that.

How can I read an xml file from the users computer on an ASP.NET MVC2 site?

I am writing a website to consolidate a bunch of XML files with data into one MySQL database. I need to have a way to allow users to select a directory on their computer that contains a bunch of xml files. The site then reads each of those files and takes care of consolidating the information.
Is there a simple way (like the default open file dialog for win forms and wpf) to bring up a file dialog on a users computer, let the user pick a directory, and then be able to read the xml files in the selected directory? Would I have to upload them to the site temporarily first? Or could I just access them on the users computer?
Thanks!!

You can't access files from a webserver directly. You would need to write an ActiveX Control if you really don't find another way.
The standard conform way it just uploading one or more files with the browser fileupload:
http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.fileupload.aspx
I would suggest that the user should zip the files and just upload the zip file.
There are some hacks - but I don't think it fits:
http://the-stickman.com/web-development/javascript/upload-multiple-files-with-a-single-file-element/
http://dotnetslackers.com/articles/aspnet/Upload_multiple_files_using_the_HtmlInputFile_control.aspx

I think you have to have a web dialog to upload the files to a temp location like you already mentioned and do the consolidation there before committing to your database. Or, maybe you can do the consolidation in JavaScript in the user's browser instance.

How to start application from C# application?

how can i start any application from C#
i mean for example, if i have an openfiledialog and the user opened it and selected any file and opened it, i need this file to opened in its application whatever its extension and its default start application.
i have googled and found that Process.Start takes the file name and its application but i don't know what is the type of the file the user is going o open
thanks in advance for any replies.

Process.Start has several overloads; you want the one that takes only a string. From MSDN:
It can be of any file type for which the extension has been associated with an application installed on the system. For example the file name can have a .txt extension if you have associated text files with an editor, such as Notepad, or it can have a .doc if you have associated .doc files with a word processing tool, such as Microsoft Word.
Example:
Process.Start(myOpenFileDialog.FileName);

You can call Process.Start with any filename and the file will open in its default program.

how to create a custom file extension in C#?

I need help in how to create a custom file extension in my C# app. I created a basic notes management app. Right now I'm saving my notes as .rtf (note1.rtf). I want to be able to create a file extension that only my app understands (like, note.not, maybe)

As a deployment point, you should note that ClickOnce supports file extensions (as long as it isn't in "online only" mode). This makes it a breeze to configure the system to recognise new file extensions.
You can find this in project properties -> Publish -> Options -> File Associations in VS2008. If you don't have VS2008 you can also do it manually, but it isn't fun.

File extensions are an arbitrary choice for your formats, and it's only really dependent on your application registering a certain file extension as a file of a certain type in Windows, upon installation.
Coming up with your own file format usually means you save that format using a format that only your application can parse. It can either be in plain text or binary, and it can even use XML or whatever format, the point is your app should be able to parse it easily.

There are two possible interpretations of your question:
What should be the file format of my documents?
You are saving currently your notes in the RTF format. No matter what file name extension you choose to save them as, any application that understands the RTF format will be able to open your notes, as long as the user knows that it's in RTF and points that app to that file.
If you want to save your documents in a custom file format, so that other applications cannot read them. you need to come up with code that takes the RTF stream produced by the Rich Edit control (I assume that's what you use as editor in your app) and serializes it in a binary stream using your own format.
I personally would not consider this worth the effort...
What is the file name extension of my documents
You are currently saving your documents in RTF format with .rtf file name extension. Other applications are associated with that file extension, so double-clicking on such file in Windows Explorer opens that application instead of your.
If you want to be able to double click your file in Windows Explorer and open your app, you need to change the file name extension you are using AND create the proper association for that extension.
The file extension associations are defined by entries in the registry. You can create these per-machine (in HKLM\Software\Classes) or per-user (in HKCU\Software\Classes), though per-machine is the most common case. For more details about the actual registry entries and links to MSDN documentation and samples, check my answer to this SO question on Vista document icon associations.

I think it's a matter of create the right registry values,
or check this codeproject's article

You can save file with whatever extension you want, just put it in file name when saving file.
I sense that your problem is "How I can save file in something other than RTF?". You'll have to invent your own format, but you actually do not want that. You still can save RTF into file named mynote.not.
I would advise you to keep using format which is readable from other programs. Your users will be thankful once they want to do something with their notes which is not supported by your program.