Windows CE Programming Intro

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Compact Framework Interop
Douglas Boling President Boling Consulting
Inc. dboling_at_bolingconsulting.com
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About Me

• Independent Windows CE consultant
• Microsoft Embedded MVP
• Writer
• Author of Programming Windows CE
• Various articles
• Windows CE Instruction
• Windows CE Application Development
• Windows CE OAL and Drivers
• .NET Compact Framework
• www.bolingconsulting.com

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Agenda

• Quick intro to the Compact Framework
• What is Interop?
• P/Invoke Basics
• Marshalling
• Calling native DLLs
• Notifications from outside
• Whats coming in Version 2.0

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Integration Imperative
Web Applications
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Integration Imperative
Screen Scrape
6
Windows Embedded Platforms
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.NET on Embedded Devices

• Windows XP Embedded
• Full v1.0 .NET runtime
• 1.1 in SP2
• Total compatibility
• Windows CE .NET
• Specially designed runtime
• Smaller foot print
• Tuned for low memory, low power devices
• Limited to two languages
• C, Visual Basic .NET

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.NET Compact Framework

• In short .NET runtime for small devices
• CLR subset of FCL
• 1.0 supports
• Pocket PC 2000, 2002
• Windows Mobile 2003
• Pocket PC and Smartphone
• Windows CE .NET 4.1 and later
• 2.0 supports
• Windows Mobile 2003 for Pocket PC only
• Windows CE 5.0 and later

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Get the Latest Stuff!

• Two service packs have been released
• Service Pack 1
• Bug fixes
• Service Pack 2
• Minor class library additions
• Performance improvements
• Bug fixes
• Version 2.0 in Whidbey beta

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CF Similarities

• Same type safe execution
• No uninitialized variables
• No unsafe casts
• No bad array indexing
• No bad pointer math
• Similar garbage collection
• No ref counting
• No leaks
• JIT compilation
• Compiled code kept in memory
• Pitched in low memory situations

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CF Similarities

• Exceptions for error handling
• Language neutral type system
• Common scheme across all managed code
• Use of assemblies
• PE file format
• Mutithread support
• Windows Forms support
• Can consume web services

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CF Difference Strategy

• V1 support for client processing
• Little support for devices as servers
• Reduced resources on embedded devices
• Less CPU power/system memory renders some .NET
  features impractical
• CF Development schedule
• They had to ship!

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CF Differences

• No COM interop support
• Use P/Invoke to call unmanaged functions
• Manually create managed class that P/Invokes to
  DLL that then calls COM interfaces
• No remoting
• Client web services supported
• No ASP .NET
• No generic serialization
• No install time compilation
• No nGen

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CF Differences

• No reflection emit
• Domain neutral code areas not supported
• Asynchronous delegates not supported
• File change notifications not supported
• No XML schema validation
• No XML xpath queries
• FCL Subset

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Other Changes

• .NET CF Class library about 25 of desktop class
  library
• Runtime tuned for embedded systems
• Low memory devices
• Low power CPUs
• Extra classes added
• IrDA classes
• SQLCE classes
• Pocket PC control support
• MessageWindow class

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.NET CF Size

• Approximately 1.3 Mbytes on Pocket PC (ARM)
• Needs approximately 1 Meg of RAM
• Application sizes quite small
• 5 100k

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.NET Framework
System.Web
System.Windows.Forms

• Services
• Description
• Discovery
• Protocols

• UI
• HTML Controls
• Web Controls

Design
Component Model
System.Drawing
Security
Cache
Drawing 2D
Printing
Session State
Configuration
Imaging
Text
System.XML
System.Data
SQL Client
ADO.NET
XML Document
Serialization
SQL ServerCE
Design
Xslt/XPath
Reader/Writers
System
IO
Collections
Configuration

• Runtime
• Interop Services
• Remoting
• Serialization

Net
Security
Service Process
Reflection
Text
Diagnostics
Resources
Globalization
Threading
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.NET Compact Framework
System.Web
System.Windows.Forms

• Services
• Description
• Discovery
• Protocols

• UI
• HTML Controls
• Web Controls

Design
Component Model
System.Drawing
Security
Cache
Drawing 2D
Printing
Session State
Configuration
Imaging
Text
System.XML
System.Data
SQL Client
ADO.NET
XML Document
Serialization
SQL ServerCE
Design
Xslt/XPath
Reader/Writers
System
IO
Collections
Configuration

• Runtime
• Interop Services
• Remoting
• Serialization

Net
Security
Service Process
Reflection
Text
Diagnostics
Resources
Globalization
Threading
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.NET CF Interop

• Why important?
• The v1 release of .NET Compact Framework will not
  support everything necessary for a Windows CE
  application
• Even if it did, embedded devices frequently need
  to be closer to the hardware than PC applications

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General Strategy

• Enable developers to provide their own solutions
• Decent P/Invoke support
• COM ready managed threads
• Basic support for notifying managed code of
  external events
• Somewhat of an afterthought

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General Architecture

• Managed applications are managed as Windows CE
  processes
• Subject to the same limitations of a Windows CE
  process
• 32/64 Meg memory space
• DLL issues in Pocket PC 2002
• Native DLLs are loaded into the process space of
  the managed application
• Unmanaged DLLs not loaded until called
• Call your unmanaged DLLs early

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What is Supported

• Supported
• Calling unmanaged functions in DLLs
• P/Invoke support
• Unsupported
• Directly calling COM interfaces
• Only by calling unmanaged DLLs that deal with COM
  objects
• ActiveX controls
• Third party solution available

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Steps for Calling Native Code

• Decide what you need to do
• Look for a managed way
• Always choose the managed way before P/Invoke
• Look in the SDK for the unmanaged call
• Yes, youll still need to know the API

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Steps for Calling Native Code

• Create managed class to wrap P/Invoke calls
• Declare an static, extern function with matching
  call parameters
• Declare function as external
• C Mark with the DllImport attribute
• VB .NET Use Lib keyword
• Create public methods that call P/Invoke methods

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Two General Possibilities

• Call Win32 API directly
• Simplest
• Doesnt require native DLL
• Limited marshalling support
• Calling native DLL
• Enables custom marshalling
• Native DLL can
• Call APIs with complex arguments
• Call COM interfaces

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Calling Win32 Functions

• Finding the API
• Declaring the API
• Calling the API

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Finding the Win32 Function

• Understand the difference between the Pocket PC
  and an embedded Windows CE device
• Pocket PCs are based on Windows CE
• Contain some unique APIs
• Dont support every single Windows CE API
• Embedded Windows CE devices can have different
  APIs
• Check the specific SDK for that device

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Declaring External Functions

• Function to call should be declared with matching
  parameters
• Function must be marked
• static and extern in C
• DllImport attribute

DllImport(coredll.dll") public static extern
unsigned int GetTickCount ()
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External Functions in VB

• VB .NET function declaration
• Use Lib keyword to declare external function

Declare Function GetTickCount Lib "coredll.dll"
() _ As Integer
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External Function Prototypes

• Check documentation
• Pocket PC 2000 and 2002
• Need Embedded Visual C 3.0
• Windows Mobile 2003
• Need Embedded Visual C 4.0
• Look in .h files in SDK
• SDKs available on Microsofts web site

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Which DLL?

• Windows CE API DLL is COREDLL.DLL
• Almost everything is here
• Some other DLLs are used
• AYGShell.dll Pocket PC shell functions
• CommCtrl.dll Common control lib
• WinSock.dll Windows Sockets
• Phone.dll High level phone control
• SMS.dll SMS messaging API

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Using DllImport

• DllImport attribute class parameters
• EntryPoint Specifies different native function
  name
• SetLastError Maintains last error value

DllImport ("\\windows\\UnManaged.dll",
EntryPoint"TestProcW",
SetLastErrortrue) public static extern int
TestProc (int a, byte b)
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At Runtime

• Calling function causes the CLR
• Load the DLL using LoadLibrary
• Use GetProcAddress to get entry point
• Call the function
• Problems resolving the function results in
  MissingMethodException in managed application
• Unhandled exceptions in the unmanaged code
  results in app termination

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Tips for using P/Invoke

• Isolate P/Invoke calls to custom classes
• Make P/Invoke functions private
• Public functions call P/Invoke functions in try /
  catch wrapper
• This also allows parameter checking and necessary
  marshaling

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Data Marshaling

• Simple Types
• Direct Translation
• Simple Objects and ValueTypes
• Objects that contain simple types
• Execution engine points at the data of the object
• Some exceptions
• Complex Objects and Value Types
• Objects containing other objects need to manually
  marshal data

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Marshaling Differences

• Objects marshaled only one level deep
• Objects that contain objects must be manually
  marshaled
• Datatypes are marshaled according to type
• MarshalAs attribute is not supported

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Marshaling Differences 2

• Object data is always laid out sequentially
• StructLayout attribute is not used
• Packing always set to 4
• Floating point and 64-bit integer parameters need
  to be passed in as binary data
• Cannot use delegates with native code

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Marshaling Of Simple Types

• The execution engine marshaling of simple data
  types

bool and Boolean do NOT always convert to a
Win32 BOOL
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Marshaling Simple Objects
Execution Engine will resize managed strings
after native function call
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Marshaling Simple Objects

• Classes are laid out sequentially
• Packing always set to 4
• Only classes containing simple types will be
  automatically marshaled

public class Rect int left int top int
right int bottom
typedef struct _RECT LONG left LONG top
LONG right LONG bottom RECT
C
Native Code - C
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Marshaling Complex Objects

• Marshal class
• Located in System.Runtime.InteropServices
• Provides advanced functionality to customize
  marshaling
• Allows you to get copy managed objects into
  native code
• Allows you to read and write raw memory if needed
• When all else fails use byte array

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Classic P/Invoke Areas

• The registry API
• Interprocess communication
• Managing very large memory blocks
• Anything hardware related
• Anything with a COM Interface
• Obex, Pocket Outlook (POOM),

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Writing Native DLLs

• Standard Windows CE dll
• Created with Embedded Visual C
• CPU specific
• Need a version for each CPU supported
• Beware C name mangling
• Callable functions must be exported

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Tips for Writing Native DLLs

• Use Extern C
• Simplifies your exported function name
• Depends.exe and Dumpbin /Exports are your friend
• Test with a simple native application
• Make sure the DLL loads properly
• Make sure the function is exposed as you expected

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Limitations

• Functions in DLLs should not block for long
  periods of time
• DLLs cant call into managed code
• Events must be signaled using window messages

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Code Example
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External Events

• How can a .NET CF application be notified of
  external events?
• MessageWindow class
• CF unique class for external event reporting
• Basically, its a window that exposes its WndProc
  to the managed code
• Helper methods to send/post messages to other
  windows

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MessageWindow Class

• Apps can send and receive window messages
• Messages have two 32 bit parameters
• No support for marshaling data pointed to by
  window parameters

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MessageWindow Class

• SendMessage Sends a message
• PostMessage Posts a message
• Hwnd Handle to native window
• WndProc Override to receive messages sent
  to window

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Using MessageWindow

• Derive class from MessageWindow
• Override the WndProc method
• Interpret window messages as necessary events
• Use WM_USERx

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Using MessageWindow

• Pass window handle of MessageWindow class to
  native DLL
• When native DLL detects event, use SendMessage to
  send WM_USERx message to MessageWindow class
• When MessageWindow derived class receives
  message, fire event to signal other managed
  code.

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Compact Framework 2.0
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V2 .NET CF Improvements

• Performance improvements
• Better JITer
• Often used paths optimized
• XML Serialization
• Schema ? XSD ? C Classes
• XML Schemas
• XPath
• SQL CE Result Set
• Typed direct access to SQL CE database
• Works with DataBinder

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V2 .NET CF Improvements

• Improved support for COM interop
• Runtime Callable wrappers
• Improved marshalling support
• More types
• Embedded arrays
• MarshalAs attribute
• Additional controls supported
• Web Browser Doc List
• Date/Time Picker Rich Ink
• Month Calendar Splitter
• Link Label Data Container
• Notification Bubble
• Controls window handle exposed

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V2 Language Improvements

• Compact Framework picks up the improvements to
  the C compiler scheduled for Visual Studio 2005
• Generics
• Anonymous methods
• Partial Classes
• VB developers get the My namespace

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V2 Base Class Library Improvements

• Serial Port Class
• Registry Class
• Cryptology Classes
• Clipboard
• Messaging

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New XML/Database Support

• XML Serialization
• Schema ? XSD ? C Classes
• XML Schemas
• XPath
• SQL CE Result Set
• Typed direct access to SQL CE database
• Works with DataBinder

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Summary

• Try to avoid interop
• Calling native code is fairly straightforward
• Use eVC help and Where defined
• Export unmangled DLL functions
• Remember youre still on Windows CE
• 2.0 looks cool

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Suggested Reading And Resources
The tools you need to put technology to work!
TITLE
Available
Price
Programming Microsoft Windows CE .NET
Today
59.99

• Visit the Microsoft Press Kiosk today to receive
  40 off books purchased from Amazon.com
• Microsoft Press books are available at the TechEd
  Bookstore and also at the Ask the Experts area in
  the Expo Hall

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Questions
dboling_at_bolingconsulting.com www.bolingconsulting.
com