C#: INTRODUCTION

FOR DEVELOPERS

Neal Stublen

nstublen@jccc.edu

Open/Close Connections

ADO.NET uses “connection pooling” to optimize opening and closing connections to the database

cxn.Open() and cxn.Close() are using connections from the connection pool that share the same connection string

ADO.NET manages the actual connection to the database

http://msdn.microsoft.com/en-us/library/8xx3tyca(v=vs.110).aspx

Think of it like this…class SqlConnectionPool{ public SqlConnection Open(string cxnStr) { if (mPool.Contains(cxnString)) { return mPool[cxnString]; } // Create a new connection ... }}

And…class SqlConnectionPool{ public void CheckIdle() { foreach (cxn in mPool) { if (cxn.IsIdle()) { cxn.ReallyClose(); mPool.Remove(cxn); } } }}

DataSets in Class Libraries Create a DataSet in the class libraries Select “Referenced DataSets” when

adding a DataSet control to a form Add a BindingSource Add form controls and bind them to the

BindingSource

MENUS, TOOL BARS, AND STATUS BARS

Designer Walkthrough

Summary

MenuStrip w/ defaults ToolStrip w/ defaults StatusStrip View Menu Toggles PerformClick() ToolStripContainer w/ docking ContextMenuStrip SplitContainer ErrorProvider

FILES AND DATA STREAMS

File System Static Classes System.IO namespace Directory

CreateDirectory, Exists, Delete File

Exists, Delete, Copy, Move Path

Combine, GetDirectoryName, GetFileName, GetExtension, GetTempFileName

DirectorySeparatorChar, VolumeSeparatorChar

File System Instance Classes

DirectoryInfoEnumeratorDirectories(), EnumerateFiles()

FileInfoName, Length, Open(), OpenText()

File System Exceptions

FileNotFoundException DirectoryNotFoundException EndOfStreamException IOException

Stream Classes

FileStream StreamReader StreamWriter BinaryReader BinaryWriter

Code Practice

Browse for a text file Place the filename in a TextBox Read each line from the file and insert

into a ListView Use two columns in the ListView

Line numberContent

Review

OpenFileDialog ImageList ListView, DetailsView

XML FILES

What’s XML?

Structured data file Tags identify each data element Tags can have attributes and child tags

<Books> <Book Code=“BK0001”> <Name>Having Fun in Kansas City</Name> <Price>19.95</Price> </Book> </Books>

XML Tags

Elements are identified by start tags, <tag_name>, and end tags, </tag_name>

Content can be placed between tags in the form of text or additional elements

Elements can be described using a single tag, <tag_name />

Comments are tags in the form,

<!-– my comment -->

Tag Attributes

In addition to content, each tag can also contain zero, one, or more attributes instead of child elements:

<Book ISBN=“978-1-890774-59-2”></Book>

<Book> <ISBN>978-1-890774-59-2</ISBN></Book>

Working with XML Files

Any text editor can be used to create XML files

Visual Studio helps create and edit XML filesCreates XML declarationColor coded tagsAutomatic indentation and closing tagsExpanding and collapsing tags

XmlReader/XmlWriter

System.XML is the namespace that contains XML classes

Useful for exporting and importing data in a common format

Writing XML FilesXmlWriter w = XmlWriter.Create(path, settings);w.WriteStartDocument();

// A start tagw.WriteStartElement(root_name);// A nested start tagw.WriteStartElement(parent_name);// An attribute on the parent_name tagw.WriteAttributeString(name, value);// A complete elementw.WriteElementString(child_name, value);// End tags for parent_name and rootw.WriteEndElement();w.WriteEndElement();

w.Close();

Using XMLWriterSettings

Define indentation

XmlWriterSettings settings = new XmlWriterSettings();settings.Indent = true;settings.IndentChars = " ";

Code Practice

Create a new project called CustomerExport

Export the rows from the Customers table to Customers.xml

Consider how you would use SqlConnection, SqlCommand, and SqlReader

Save the XML file on the Desktop as…

XML Format<Customers> <Customer id="157"> <Name>Abeyatunge, Derek</Name> <Address>1414 S. Dairy Ashford</Address> <City>North Chili</City> <State>NY</State> <ZipCode>14514 </ZipCode> </Customer> ...</Customers>

Review

MemoryStream XmlWriter SqlDataReader “inspection” System.Environment.GetFolderPath FileStream Debugging visualizers