High Level Languages

1
High Level Languages

• Delphi
• Lecture 5

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Last Lecture

• Last Lecture we covered the following
• Memos
• Strings
• Dialog Boxes
• A Simple Word Processor

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This Lecture

• In Todays Lecture we will cover
• Menus in Delphi
• The menu designer
• Creating menus by hand
• Example menu item code
• Databases
• Borland Database
• SQL in Delphi

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1. Menus

• Almost all Windows applications use Menus.They
  are a quick way to make your apps look
  professional, and are preferable to buttons.
• Delphi makes creating menus easy with the Menu
  Designer.
• All the Menu Designers commands are accessed via
  the Menu Designer context menu or by interacting
  with the Object Inspector.

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2. Menu Designer
Simply Drag and Drop a Main Menu onto your Form.
Double-Clicking the icon that is now on your form
will bring up the Menu Designer.
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Menu Designer

• The Menu Designer has the following features
• It can create both main menus and context menus.
• It provides immediate access to the Code Editor
  to handle the OnClick events for menu items.
• It can insert menus from templates or from
  resource files and it can save custom menus as
  templates.

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Adding a Main Menu

• As we saw, to create a main menu on your form,
  the first thing you must do is add a MainMenu
  component to your form.
• The MainMenu component has very few properties
  and no events. All the menus work is done by the
  individual menu items.
• To display the Menu Designer, double-click on the
  MainMenu icon.

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Menu Designer

• The menu designer looks like a blank form without
  grid points.
• The menu designer can be sized in any way you
  want. The size is just for convenience and has no
  bearing on how the menu operates at runtime.
• You can create menus by hand or import menu
  templates.

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3. Creating a Menu by Hand

• The menu designer always has a blank menu item
  that acts as a placeholder for any new menu items
  you wish to create.
• When you first start the menu designer, the blank
  item is selected.
• If you want to create a File menu (as an example)
  you would click on the Caption property, type
  File and press enter.

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Use of Ampersand

• The ampersand () is used to create the
  underlined character for a menu item.
• The underlined character is the accelerator the
  user can type in combination with the Alt key to
  navigate a menu using a keyboard.
• For instance, the Exit menu item would be typed
  as Exit, so that x is the accelerator I.e.
  Alt-x will do the same as choosing Exit from the
  menu.

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Adding to your Menu

• When you have pressed enter, after typing File,
  the File Menu shows up in the menu designer.
• A new placeholder is added below the File menu,
  for sub-menu options.
• In addition, a new pop-up placeholder is created
  to the right of the File menu.
• You can then go on to add other menus and
  sub-menus in a similar way.

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Refining your Menu

• Standard File menu items are New, Open, Save,
  Save As, Print, Print Setup, Exit.
• A separator is the horizontal line on a menu that
  separates groups of menu items.
• To add a separator to a menu, just put in a
  hyphen (-) as a menu item.

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Inserting a Template Menu

• You can insert standard templates directly into
  the Menu Designer to save time - just right click
  on the Menu Designer and choose Insert From
  Template.
• A dialog box pops up showing a list of templates
  for you to choose from.
• You can delete unwanted menu items from an
  installed template simply by choosing an item and
  pressing delete.

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Template List
Just right click anywhere in the menu designer
and choose Insert from Template.
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4. Creating Menu Item Code

• Menus work in exactly the same way as buttons.
  If you double click an item the event code for
  that item will be created for you automatically.
• The following slides will give you an idea of how
  to program menu item event handler code.
• We will use the example of a Windows Notepad type
  application, where text is loaded from and saved
  to text files and text it cut and pasted etc.

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NewClick Event

• procedure TMainForm.NewClick(Sender TObject)
• var
• Res Integer
• begin
• Open a file. First check to see if the
• current file needs to be saved
• if Memo.Modified then begin
• Display a message box
• Res Application.MessageBox(
• The current file has changed. Save
  changes?,
• Notepad Message, MB_YESNOCANCEL)
• ...

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NewClick Event

• ...
• If Yes was clicked then save the current
  file
• if Res IDYES then
• FileSaveClick(Sender)
• If No was clicked then do nothing
• if Res IDCANCEL then
• Exit
• end
• ...

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NewClick Event

• ...
• Delete the strings in the memo, if any
• if Memo.Lines.Count gt 0 then
• Memo.Clear
• Set the FileName property of the Save Dialog
  to a
• blank string. This lets us know that the file
  has
• not yet been saved
• SaveDialog.FileName
• end

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OpenClick Event

• procedure TMainForm.OpenClick(Sender TObject)
• var
• Res Integer
• begin
• Open a file. First check to see if the
• current file needs to be saved
• if Memo.Modified then begin
• Display a message box
• Res Application.MessageBox(
• The current file has changed. Save
  changes?,
• Notepad Message, MB_YESNOCANCEL)
• If Yes was clicked then save the current
  file
• if Res IDYES then
• FileSaveClick(Sender)
• If No was clicked then do nothing
• if Res IDCANCEL then
• Exit
• end
• ...

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OpenClick Event

• ...
• Execute the File Open dialog. If OK was
  pressed then
• open the file using the LoadFromFile method.
  First
• clear the FileName property
• OpenDialog.FileName
• if OpenDialog.Execute then begin
• if Memo.Lines.Count gt 0 then
• Memo.Clear
• Memo.Lines.LoadFromFile(OpenDialog.FileName)
• SaveDialog.FileName OpenDialog.FileName
• end
• end

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SaveClick Event

• procedure TMainForm.SaveClick(Sender TObject)
• begin
• If a filename has already been provided then
  there is
• no need to bring up the File Save dialog.
  Just save the
• file using SaveToFile
• if SaveDialog.FileName ltgt then begin
• Memo.Lines.SaveToFile(SaveDialog.FileName)
• Set Modified to False since weve just
  saved
• Memo.Modified False
• if no filename was set then do a SaveAs
• end else FileSaveAsClick(Sender)
• end

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SaveAsClick Event

• procedure TMainForm.SaveAsClick(Sender Tobject)
• begin
• Display the File Save dialog to save the file
  
• Set modified to False since we just saved
  
• SaveDialog.Title Save As
• if SaveDialog.Execute then begin
• Memo.Lines.SaveToFile(SaveDialog.FileName)
• Memo.Modified False
• end
• end

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FileExitClick Event

• Delphi handles the File Exit routine in a single
  function Close
• This function does all the background stuff
  needed to close the form. It is the same as
  clicking on the X in the top-right corner of a
  form.
• procedure TMainForm.ExitClick(Sender
  TObject)
• begin
• close
• end

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Pop Up Menus

• Everything that you can do with a normal menu can
  be done with a Pop Up Menu.
• Simply add a Pop Up Menu VCL component to your
  form, right click it and your off.
• Note that the Pop Up Menu has a few more
  properties, such as Animation, Alignment and
  TrackButton.

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5. Databases

• Databases boring as sin (but useful).
• Database programming has its own set of
  buzzwords BDE, client, server, ODBC, alias, SQL,
  query, stored procedure, etc. At its simplest a
  database consists of data stored in one or more
  tables.
• A table probably contains fields such as
  FirstName, LastName, PhoneNumber, BraSize, etc.
• These fields are filled with data to create
  individual records in a database file.

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Database Basics
z
z
z

• The term database is used to describe an
  all-encompassing data creation and maintenance
  system.
• A complete client/server SQL database solution
  can also contain numerous queries and stored
  procedures.
• Therefore, a database (or Database Management
  System DBMS) is more than just a table with
  data.

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Database Example
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Cursor

• The pointer to the current record within a
  database is called the cursor.
• The cursor points to the record that will be read
  if data is requested and the record that will be
  updated if any edits are made.
• The cursor is moved when a user browses the
  database, inserts records, deletes records and so
  on.

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Database Basics - Dataset

• A collection of data returned by a database is
  called a dataset.
• A dataset can be the results of a query
  containing data acquired from one or more tables.
• Although data may come to you from several
  different sources, it is presented to you as a
  single dataset.

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Local Databases

• The simplest type of database is the local
  database.
• A local database is a database that resides on a
  single machine.
• Generally, the local database is only accessed by
  your program no one else has access to it.
• Paradox, dBASE and Access databases are usually
  local databases.

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Client/Server Databases

• With a client/server database, the database
  itself is stored and maintained on a file server.
• One or more users (the clients) have access to
  the database across a network of some sort.
• More than one user may try to access the database
  at the same time. The server knows how to handle
  simultaneous accesses.
• Users access the database through client
  applications that ensure correct usage.

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Database Architecture

• A single-tier database is a database in which
  changes happen immediately (local).
• In a two-tier database, the client application
  talks to the database server through database
  drivers.
• In a multitier client/server architecture, the
  client application talks to one or more
  application servers that, in turn, talk to the
  database server.

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6. Borland Database Engine

• To enable access to local databases and to
  client/server databases, Delphi provides the
  Borland Database Engine (BDE).
• The BDE is a collection of DLLs and utilities
  that enables access to a variety of databases.
• To talk to client/server databases, you must have
  the Client/Server version of Delphi.

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Borland Database Engine (DBE)

• The diagram below shows the relationship between
  your application, the BDE and the DB.

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BDE Drivers

• Database formats can be very different.
• Delphi comes with a set of drivers that enable
  your application to talk to several different
  types of databases.
• These drivers translate high-level database
  commands (such as open or post) into commands
  specific to a particular database type (specifics
  not needed).

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BDE Aliases

• A BDE alias is a set of parameters that describes
  a database connection
• It tells the BDE which type of driver to use and
  the location of the database files on disk and
  maybe the users username.
• After you create an alias for your database, you
  can use that alias to select the database in your
  Delphi programs.

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Delphi Database Components

• With a basic introduction to how databases are
  pieced together, we can now go on to consider the
  various database components, provided by the VCL.
• The VCL database components fall into two
  categories
• Non-visual data access components
• Visual data-aware components

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Delphi Database Components

• The non-visual data access components provide the
  mechanism that enables you to get at the data.
• The visual data-aware components enable you to
  view and edit the data.
• Again VCL components can be simply drag dropped.

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Delphi Database Components

• The data access components are derived from the
  TDataSet class and include TTable, TQuery and
  TStoredProc.
• The visual data-aware components include TDBEdit,
  TDBListBox, TDBGrid, TDBNavigator and more.
• The visual components act like TEdit, TListBox
  etc. except that they are linked to a specific
  database table.

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VCL Database Components
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The Query Component

• The Query component provides a way of accessing a
  database table using Structured Query Language
  (SQL).
• SQL is a powerful way of accessing tables.
• The Query component is the preferred method of
  accessing data in client/server databases.
• We will end our discussion on databases by
  describing the primary properties and methods of
  the TQuery class.

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7. SQL Property

• The SQL property is a TStringList that contains
  the SQL statements to execute.
• You can set the SQL propertys value via the
  Object Inspector at design time or through code
  at runtime.
• Remember the SQL property is a string list, not a
  string. Make sure you clear the previous contents
  before adding lines to it, e.g.
• Query1.SQL.Clear
• Query1.SQL.Add(select from country)

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SQL Commands

• SQL is a reasonably powerful query language.
• Refer to the DBS Lectures from last semester for
  a more in depth discussion.
• The following slides, which are for reference
  only, describe the following fundamental SQL
  commands
• SELECT
• INSERT
• DELETE
• UPDATE

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Executing SQL Statements

• The statements in the SQL query property will be
  executed when either the Open method or the
  ExecSQL method is called.
• The Open method is used for SQL statements that
  include SELECT.
• The ExecSQL method is used for SQL statements
  that include INSERT, UPDATE or DELETE.

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Executing SQL Statements

• The SQL SELECT statement retrieves certain
  columns from a database, e.g.
• Query1.SQL.Clear
• Query1.SQL.Add(select Name, Capital
• from country)
• Query1.Open

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Executing SQL Statements

• The SQL DELETE statement deletes records from a
  dataset.
• Query1.SQL.Clear
• Query1.SQL.Add(delete from country
• where name Jimland)
• Query1.ExecSQL

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Executing SQL Statements

• The SQL INSERT command inserts a record into a
  dataset.
• Query1.SQL.Clear
• Query1.SQL.Add(insert into country)
• Query1.SQL.Add((Name, Capital))
• Query1.SQL.Add(values (Jimland,
• Jimville))
• Query1.ExecSQL

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Executing SQL Statements

• The SQL UPDATE command will update a dataset.
• Query1.SQL.Clear
• Query1.SQL.Add(update country)
• Query1.SQL.Add(set Capital
• Royburg)
• Query1.SQL.Add(where Name
• Royland)
• Query1.SQL.ExecSQL

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Executing SQL Statements

• To make your SQL statements more flexible, you
  can use parameters.
• A parameter is similar to a variable.
• Query1.SQL.Add(select from country where Name
  Param1)
• Query1.SQL.ParamByName(Param1).AsString
  Brazil
• Query1.Open
• The value of Param1 in the Params property is
  substituted for the parameter name.

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Executing SQL Statements

• Another way to set the parameters value is to
  use the Params array
• Query1.Params0.AsString Brazil
• Using the Params array is more error prone to
  using ParamByName as you would have to remember
  the order (the index) of each parameter.

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Databases in Delphi

• The previous slides intended to give you a brief
  (so you might stay awake) introduction to
  database access through Delphi.
• Delphi makes the development of Database Client
  Applications very easy with its various VCL
  components.
• For more information refer to Part II of the
  Delphi Developers Guide on the course Web site
  chapters 12 to 27.

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Next Lecture

• DELPHI MULTIMEDIA PROGRAMMING
• The coursework is announced, so probably worth
  coming to. I will also answer any questions about
  the coursework then.
• The Coursework deadline March 21st 5pm.