WinForms: GUI Programming in .NET

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Goal

“.NET supports two types of form-based apps, WinForms and WebForms. WinForms are the traditional, desktop GUI apps. The great news is that Visual Studio .NET enables quick, drag-and-drop construction of form-based applications…”

• Event-drevet, code-behind programmering• Visual Studio .NET• WinForms• Controls

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Part 1

• Event-drevet, code-behind programing…

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Event-driven applications

• The idea is very simple:– “user actions” becomes “events”– events is transferred one by one to the application, which

processes the event in a eventhandler

– This is how most gui’s are made…

GUI App

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Eksamples on GUI-baserede events

• Mouse move• Mouse click• Mouse double-click• Key press• Button click• Menu selection• Change in focus• Window activation• etc.

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Code-behind

• Events are handled by methods (eventhandlers). These eventhandlers is placed “behind” the visiable GUI– In MS-terms known as "code-behind"– Our job is to program there methods…

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Call-backs

• Events is a call from an object back to us…• How is the connection made?

– Visual Studio establish the connection via autogenerated code.

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Part 2

• Visual Studio .NET…

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Visual Studio .NET (VS.NET)

• One IDE used for all forms of .NET development– From classlibraries over form-based apps to web services– You can use C#, VB, C++, J#, etc.

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Basis operation

• Visual Studio operates in 1 of 3 ways:

1) design

2) run

3) break

• See VS title bar if you are in doubt…

design run

break

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Example: a windows-application

• GUI apps based on forms and controls…– one form represents a window– One form has 0 or more controls– One control interacts with the user

• Let us implement a GUI app in a number of steps…

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Step 1

• Make a new project of type “Windows Application”– VS. will automatically make a form…

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Step 2 — GUI design

• Find the controls from the toolbox…– Place the mouse over the toolbox to see

controls– drag-and-drop on the form– Place and size your controls

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GUI design …

• A simple calculator:

• Place and configure controls– Click to chose– set properties viathe Properties-window

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Step 3 — codedesign

• Implement the forms “Code behind”…• Dobbelt-clik on the control you want to

implement – the eventhandler is generated

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Step 4 — run mode

• Run!

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Break mode?

• Is started in this appI for example by typing something wrong…

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Work with Visual Studio

• In Visual Studio we work with

source files, projects & solutions

• Source files holds code– extension .cs, .vb, etc.

• A project represents 1 assembly– Used by VS to keep track of source files– all source files must be written in the same – language– extension .csproj, .vbproj, etc.

• Solution (*.sln) files keeps track of projects– So you can work on more than one project

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Part 3

• WinForms…

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WinForms

• Another name for traditional, Windowslike GUI-applications– Unlike WebForms,

which is web-based

• Is implementer via FCL– Portable to any .NET platform

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Abstraction

• FCL works as an abstraction– parts WinForm app from the underlaying platform

System.Windows.Forms.Form

CLR

Windows OS

instance of

FCL classobject

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Form properties

• Form properties controls the forms visual apperance:

– AutoScroll– BackgroundImage– ControlBox– FormBorderStyle (sizable?)– Icon– Location– Size– StartPosition– Text (fx window's caption)– WindowState (minimized, maximized, normal)

Form1 form;form = new Form1();form.WindowState = FormWindowState.Maximized;form.Show();

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Form methods

• Actions which can be executed on a form:

– Activate: give this form focus– Close: close & free ressourcer– Hide: save, but keep resources for later use. – Refresh: redraw– Show: make the form visible on screen & activate

form.Hide(); . . .

form.Show();

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Form events

• Events you can react on:– find the propertieswindow– dubbleclik on the event-name

– Load: just before the form is shown for the first time– Closing: when the form is closing (cancel is possible)– Closed: when the form can be closed in a secure way– Resize: when the user changes the form-size– Click: when the user clicks on the forms background– KeyPress: when the user press some button on the

keyboard while the form has focus

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Example

• ASK THE USER BEFORE A FORM IS CLOSED:

private void Form1_Closing(object sender, System.ComponentModel.CancelEventArgs e){ DialogResult r;

r = MessageBox.Show("Do you really want to close?", "MyApp", MessageBoxButtons.YesNo, MessageBoxIcon.Question, MessageBoxDefaultButton.Button1); if (r == DialogResult.No) e.Cancel = true;}

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Part 4

• Controls…

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Controls

• Userinterfaceobjecter på formen:

– labels– buttons– text boxes– menus– list & combo boxes– option buttons– check boxes– etc.

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Abstraction

• Some forms, are controls based on classes in FCL:– System.Windows.Forms.Label– System.Windows.Forms.TextBox– System.Windows.Forms.Button– etc.

• Controls are objecter of these classes

object

object

object

object

object

object

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Who makes all these objecter?

• Who is responsible for creating control-objects?-generated by Visual Studio– After the form-object is created the control-objects are

made…

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Naming conventions

• Set named the names of your controls via Name property

• The Microsoft Naming Convention:– cmdOK referes to a command-button– lstNames refers to a List Box Control– txtFirstName refers to a Textbox Control

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Labels

• Used for static text– Used as labels on other things in the

form– Or for visualising read-only results

• Interesting properties:– Text: what the user sees– Font: how the user sees

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Command-knapper

• For clicking and thereby initiate some

action

• Interesting properties:– Text: buttontext– Font: How the button is shown– Enabled: possible to click?

– AcceptButton: Click on ENTER– CancelButton: Click on ESC

• Interesting events:– Click: When the button is pushed

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Text boxes

• Most normal control!– Show test– data from for example databases

• Lots of features…

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Text box properties

• Basic properties:– Text: what is in the box (string)– Modified: is the text modified by the user? (boolean)– ReadOnly: if the user should not be able to modify

• Multi-line text boxes?– MultiLine: True makes multiple lines possible– Lines: array of strings, one for each line in the

textbox– ScrollBars: none, horizontal, vertical or both horiz. & vert.

– AcceptsReturn & AcceptsTab: sould the user be able to use

tabulator and return

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Text box methods

• Interesting methoder:– Clear: remove content– Cut, Copy, Paste: interaction with clipboard– Undo: undo last change in textbox– Select, SelectAll: chose some of the content

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Text box events

• Intereresting events:– Enter, Leave: appears when focus changes– KeyPress: appears when some ascii button is

activated– KeyDown, KeyUp: appears with keyboard combinations– TextChanged: appears when text changes

– Validating and Validated• Validating makes it possible to reject invalid input

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private void txtName_Validating(object sender, System.ComponentModel.CancelEventArgs e){ if (this.textBox1.Text.Trim() == "") { // invalid input! MessageBox.Show("Please enter name or id..."); e.Cancel = true; // cancel returns focus back to text box }}

Example: input invalidation

• Text boxe often demands validation– .NET offers the Validating event– Triged when a box looses focus

cmdOk.CausesValidation = True

cmdCancel.CausesValidation = False

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Caveats• The Validating event has some “points"…• Error:

- If the cancel button is triggeret by ESC, it is still validated– If the user click x to close form, it is still validated

• If the vox can have focus:– What if the user trigger OK via enter(default)??– What if th user clicks OK before it gets focus?

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Work-arounds…

• Hide the box• Don’t set the box’ CancelButton property• Asure validation in OK button:

private void cmdOK_Click(object sender, System.EventArgs e) { foreach (Control c in this.Controls) if (c is TextBox) { // check for valid input... c.Focus(); // give control focus, then validate if (!this.Validate()) return; }}

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Radio buttons and Check boxes

• Makes it possible for the user to choose one

or more options

• Radio buttons:

– The user can only choose one(mutually-exclusive)

• Check boxes:– The user can choose more than one (independent)

• Properties & events:– Checked: True if choosen, False if not– CheckedChanged appears when "Checked“ is changed

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Group boxes

• Visual grupping of controls• Make iteration over the groupmembers• possible…

foreach (RadioButton rb in this.groupBox1.Controls) if (rb.Checked) MessageBox.Show(rb.Name);

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Customer[] customers; . . // create & fill array with objects... .

// display customers in list box foreach (Customer c in customers) this.listBox1.Items.Add(c);

List Boxes

• Good for visualising lists of data– Lists of strings– Lists of object (list box will call ToString())

// display name of selected customer (if any)Customer c;c = (Customer) this.listBox1.SelectedItem;if (c == null) return;else MessageBox.Show(c.Name);

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Warnings

1. Don’t write code where the order of events matters…– The orders is never garantied– Every event is independent from others

2. Some kode trigger events behimd the code…– A natural sideeffect of event-drevet programmering

this.textBox1.Text = "new value" // triggers TextChanged

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Only a small part of it all…

• Menuer, dialoger, toolbars, etc.

• Tousend of other controls– .NET and ActiveX– Rightclick onToolbox– "Customize Toolbox"

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Summing up

• Event-driven programming is very intuitive with GUI apps

• Forms are the first step in GUI design– every form represents a window on the screen– Construction of GUI with drag-and-drop

• The user interacts primary with the forms control-objekter– labels, text boxes, buttons, etc.– GUI programming is control programming!!!

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References

• Books:– S. Lippman, "C# Primer"– R. Grimes, "Developing Applications with Visual Studio .NET"

• De bedste bøger om GUI er pt VB-baserede:– J. Savage, "The VB.NET Coach" (introductory)– F. Balena, "Programming Microsoft VB .NET (Core

Reference)" (broad coverage, intermediate level)