ch05_Creating Forms.pdf

Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

Chapter 5

Creating Forms

In this chapter, we discuss forms, the basic element of a .NET Compact Framework GUI application,

examining their unique characteristics and their role in providing the user interface. [Comment 5cs.1]

What are Forms? .......................................................................................................................................... 1

Forms are Derived from Form ......................................................................................................... 2

Properties, Methods, and Events..................................................................................................... 2

An Event Capturing Application ....................................................................................................... 7

Manipulating Forms..................................................................................................................................... 10

Creating Forms .............................................................................................................................. 10

Displaying Forms ........................................................................................................................... 11

Closing Forms ................................................................................................................................ 13

Orphaned Forms ............................................................................................................................ 14

The Weather Sample Application ..................................................................................................15

Tracking Forms .............................................................................................................................. 18

The Controls Collection.................................................................................................................. 20

Multi-threading ............................................................................................................................... 21

Inheritance and Visual Inheritance.............................................................................................................. 22

Conclusion .................................................................................................................................................. 28

What are Forms?

.NET Compact Framework applications present information and receive input by displaying

one or more forms to the user. These forms have a set of characteristics that make them unique

among the object classes that you encounter in Compact Framework programming. These

characteristics also make Compact Framework forms somewhat different from desktop forms.

What makes forms unique is that they: [Comment 5cs.2]

•

Are derived, directly or indirectly, from System.Windows.Forms.Form [Comment 5cs.3]

•

All inherited events are supported [Comment 5cs.4]

•

On a Pocket PC, are displayed full-screen and are not resizable [Comment 5cs.5]

•

Can be displayed as modal or modeless forms [Comment 5cs.6]

•

On a Pocket PC, present the user with a mechanism for closing or minimizing the form, but

not both [Comment 5cs.7]

•

Can be closed but not opened [Comment 5cs.8]

•

Are indestructible until they have been closed [Comment 5cs.9]

•

Are worthless after they have been closed [Comment 5cs.10]

•

Are owned by a thread [Comment 5cs.11]

Chapter 5 – Creating Forms

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Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

Forms are Derived from Form

Like everything else in .NET that is not a value type, forms are objects. Normally you derive

your forms directly from the Form class that is defined in the System.Windows.Forms

namespace. This is the default derivation whenever you add a new form to the project. Listing 5-

1 shows the code file that resulted when adding a form named FormDemo to a project. [Comment

5cs.12]

Listing 5-1 – The code that defines a new form [Comment 5cs.13]

using System;

using System.Drawing;

using System.Collections;

using System.ComponentModel;

using System.Windows.Forms;

namespace MainPlusOthers

{

/// <summary>

/// Summary description for FormDemo.

/// </summary>

public class FormDemo : System.Windows.Forms.Form

{

The first few lines of code leave no doubt that you are defining an object class, one that

inherits from Form . [Comment 5cs.14]

Optionally, your form classes can be derived from other form classes, classes that were

themselves derived from Form . For further discussion of deriving forms from other forms, see

the Inheritance section later in this chapter. [Comment 5cs.15]

Properties, Methods, and Events

Because your forms are derived from the base class of Form , they inherit the properties,

methods, and events of the Form class. The Form class itself obtains most of its properties,

methods, and events through inheritance, with an inheritance chain that starts at Object and

descends through the following classes: MarshalByRefObject , Component , Control ,

ScrollableControl , and ContainerControl . Tables 5-1 through 5-3 list the properties,

methods, and events, respectively, of the Form class. Those that are form-specific, this is, ones

that are defined within the Form class rather than being inherited, are marked with an asterisk

“(*)”. For the reader convenience we have broken them down into categories of our own

choosing. Chapter 7, Inside Controls , provides additional information about the Control class,

which is the base class for all control classes which wrap around a native operating system

window. [Comment 5cs.16]

Table 5-1 - Form Propertie s [Comment 5cs.17]

Category

Property Name

Comments

Pocket PC-Specific Comments

Ownership

Parent

For dialog boxes, do not set a

parent.

Inherited from Control , Parent is

normally null because forms do not

have a parent. When a form is a dialog

box, however, its parent is the form that

spawned the dialog (the parent is

disabled).

Chapter 5 – Creating Forms

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Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

Category

Property Name

Comments

Pocket PC-Specific Comments

Controls

Collection containing the controls that

reside on the form

TopLevelControl Inherited from Control, provides

immediate access to the form which

contains a set of controls.

State

Capture

Boolean indicating whether form should

grab all mouse / stylus input.

A form automatically sets

mouse capture for a mouse

down event, and releases the

mouse capture for a mouse up

event.

Enabled

Indicates whether form can receive

keyboard and mouse input. When a form

is disabled, all controls contained in the

form are disabled (see chapter 6, Mouse

and Keyboard Input )

Focused

Boolean indicating whether keyboard

input is directed to the form.

Visible

Boolean indicating whether form and its

child controls are on the desktop, and

whether the top-level form appears on the

task list or not.

WindowState (*) Whether form is initially full-screen

(maximized) or not.

Ignored – forms run full-screen.

Appearance

BackColor

Color used to draw form surface

ControlBox (*) Presence of close button (when set to

false, prevents minimize-box and

maximize-box from appearing). When

run on desktop framework, controls

whether system menu appears (The

Windows CE user-interface does not

support a system menu.)

Whether a form has a close box

or Ok button. (Pocket PC

programs have no close button.)

FormBorderStyle

(*)

Sets type of border and whether form is

resizeable. (CF programs running under

the desktop framework vary slightly from

the same program running under CE.)

Ignored.

Icon (*)

Ignored on Pocket PC and Windows CE.

(Appears only running on the desktop.)

Set an application icon from the Visual

Studio project properties page.

Ignored.

MaximizeBox (*) Whether maximize box appears (requires

ControlBox = true)

Ignored.

MinimizeBox (*) Whether minimize box appears (requires

ControlBox = true)

When true , close box appears,

which when clicked causes form

to continue running.

When false , Ok box appears,

which when clicked causes form

to close and program to

terminate.

Text

Text for form's caption bar.

Menus

Menu (*)

A form's main menu.

Access to input panel (SIP)

requires a menu or a toolbar.

(There is no dedicated toolbar

property, but toolbars are added

to a form's control collection.)

Chapter 5 – Creating Forms

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Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

Category

Property Name

Comments

Pocket PC-Specific Comments

ContextMenu

A form's context menu.

Dialogs

DialogResult

(*)

Return value for dialog boxes.

Position & Size

Bottom

(read-only) X-coordinate for bottom of

window in parent's client area (or in

screen coordinates for top-level

windows).

Bounds

A Rectangle equal to ( Left , Top ,

Right , Bottom ) in parent's client area

coordinates for contained controls, and in

screen-coordinates for top-level forms.

ClientRectangle (read-only) A Rectangle equal to ( 0 ,

0 , ClientSize.Width ,

ClientSize.Height )

ClientSize

Size minus non-client elements.

Form height (including non-client

elements).

Height

Left

Y-axis location in parent (or screen)

coordinates.

Location

A Point equal to ( Left , Top )

Read-only

Right

Size

A Size equal to ( Width , Height )

Top

X-axis location in parent (or screen)

coordinates.

Width

Form width (including non-client

elements).

DataBinding

DataBindings

Collection of data binding objects.

(*) Specific to

Form class

Several of the properties are related to size and position, and you want to leave them as is.

On the Pocket PC, forms are displayed full-screen. But if you accidentally change the size, the

layout of controls in the forms designer might not be the same as what the user will see on a

Pocket PC. To ensure that you do not accidentally modify the size properties, use the Lock

Controls option. Right click on the form in Design View and select Lock Controls from the

context menu. [Comment 5cs.18]

The value of the form’s MinimizeBox property determines whether the form displays a

minimize box or a close box to the user. The impact of this choice is discussed in the Orphaned

Forms section of this chapter. [Comment 5cs.19]

The value of the form’s ControlBox property determines whether the form displays a control

box in the upper left corner of the form. The presence of a control box allows the user to display

the system menu. [Comment 5cs.20]

The Data Bindings collection is covered in Chapter 8, Data Binding , and is revisited in the

next chapter. [Comment 5cs.21]

The DialogResult property is most applicable to forms that are displayed as dialogs, and is

addressed in chapter 9, Inside More Controls . [Comment 5cs.22]

Chapter 5 – Creating Forms

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Programming the .NET Compact Framework in C#

By Paul Yao & David Durant

In the current version of the Compact Framework 1 , the icon property is not used. This

property accepts an icon created from a managed resource (in a .resx file). Such an icon can

only be loaded as a managed System.Drawing.Icon object. However, the user-interface shell

of both Pocket PC and Windows CE devices require a native (unmanaged) icon resource. Add a

native icon to a program in the Property Pages for a project by specifying the application icon.

[Comment 5cs.23]

The icon (*.ico) file format can accommodate more than one icon. When creating an icon for

a Compact Framework program, be sure that your icon supports two icons: a 16x16 image as

well as a 32x32 image. The smaller image appears on the Start menu; the larger image appears

in the program window. [Comment 5cs.24]

Table 5-2 - Form Method s [Comment 5cs.25]

Category

Method Name

Comments

Dialog Box Support

ShowDialog (*)

Displays a form as a dialog box, disabling the form's parent.

CreateGraphics

Fetches a Graphic object for drawing on the surface of the form.

Drawing

Invalidate

Mark a portion of a form for lazy redrawing (through Paint event).

Refresh

Immediate redraw of form and its controls (like call to Invalidate

and Update on form and on all contained controls)

Update

Immediate redraw of invalid portions.

PointToClient

Convert a point from screen coordinates to client coordinates.

Coordinate Conversion

PointToScreen

Convert a point from client coordinates to screen coordinates.

RectangleToClient

Convert a rectangle from screen coordinates to client coordinates.

RectangleToScreen

Convert a rectangle from client coordinates to screen coordinates.

Inherited Type Support

Equals

Checks a form for equality with another form.

GetType

Returns System.Windows.Forms.Form

ToString

Returns a string with the fully-qualified name of a form class

Invoke

Thread-safe access

Calls a delegate in a form (or other Control -derived class) in a

thread-safe manner. Thread-safe, by the way, does not mean the call

must be made on a separate thread, a point of confusion with

programmers new to Windows thread programming.

State

Close (*)

Requests that a form be closed.

Dispose

Requests that resources associated with a form be reclaimed.

Focus

Sets keyboard focus to a form.

Hide

Makes the form, and all contained controls, invisible.

Show

Allows a form and all contained controls to be visible.

Z-Order

BringToFront

Moves a form to the top of the local-input Z-order. The Compact

Framework does not support setting a form at the top of the global Z-

order; that requires calling the native SetForegroundWindow

function.

SendToBack

Moves a form to the bottom of the local-input Z-order.

(*) Specific to

Form class

The Show and Hide methods are equivalent to setting the Visible property to True or

False , respectively. Calling BringToFront or SendToBack results in a form being placed at the

top or bottom of the Z-order, respectively. [Comment 5cs.26]

1 Just before this book went to press, we tested this on the Compact Framework, version 1.0, SP-2.

Chapter 5 – Creating Forms

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