You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
460 lines
20 KiB
460 lines
20 KiB
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
|
<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/extensions/activeqt/examples/dotnet/dotnet.doc:1 -->
|
|
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
|
<title>Walkthrough: Using Qt objects in Microsoft .NET</title>
|
|
<style type="text/css"><!--
|
|
fn { margin-left: 1cm; text-indent: -1cm; }
|
|
a:link { color: #004faf; text-decoration: none }
|
|
a:visited { color: #672967; text-decoration: none }
|
|
body { background: #ffffff; color: black; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
|
|
<table border="0" cellpadding="0" cellspacing="0" width="100%">
|
|
<tr bgcolor="#E5E5E5">
|
|
<td valign=center>
|
|
<a href="index.html">
|
|
<font color="#004faf">Home</font></a>
|
|
| <a href="classes.html">
|
|
<font color="#004faf">All Classes</font></a>
|
|
| <a href="mainclasses.html">
|
|
<font color="#004faf">Main Classes</font></a>
|
|
| <a href="annotated.html">
|
|
<font color="#004faf">Annotated</font></a>
|
|
| <a href="groups.html">
|
|
<font color="#004faf">Grouped Classes</font></a>
|
|
| <a href="functions.html">
|
|
<font color="#004faf">Functions</font></a>
|
|
</td>
|
|
<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Walkthrough: Using Qt objects in Microsoft .NET</h1>
|
|
|
|
|
|
|
|
|
|
<!-- toc -->
|
|
<ul>
|
|
<li><a href="#1"> Introduction
|
|
</a>
|
|
<ul>
|
|
<li><a href="#1-1"> Qt vs .NET
|
|
</a>
|
|
</ul>
|
|
<li><a href="#2"> Walkthrough: .NET interop with MC++ and IJW
|
|
</a>
|
|
<li><a href="#3"> Walkthrough: .NET/COM Interop with ActiveQt
|
|
</a>
|
|
<ul>
|
|
<li><a href="#3-1"> Starting a Project
|
|
</a>
|
|
<li><a href="#3-2"> Importing Qt Widgets
|
|
</a>
|
|
<li><a href="#3-3"> Using Qt Widgets
|
|
</a>
|
|
<li><a href="#3-4"> Handling Qt Signals
|
|
</a>
|
|
</ul>
|
|
<li><a href="#4"> Summary
|
|
</a>
|
|
<ul>
|
|
<li><a href="#4-1"> Limitations
|
|
</a>
|
|
<li><a href="#4-2"> Performance Considerations
|
|
</a>
|
|
</ul>
|
|
</ul>
|
|
<!-- endtoc -->
|
|
|
|
<p> <h2> Introduction
|
|
</h2>
|
|
<a name="1"></a><p> In the following walkthrough we will show how Qt objects can be used
|
|
in a .NET environment, and how .NET objects can be used in a Qt
|
|
environment.
|
|
<p> <h3> Qt vs .NET
|
|
</h3>
|
|
<a name="1-1"></a><p> Qt is a C++ library and is compiled into traditional, native
|
|
binaries that make full use of the performance provided by the
|
|
runtime environment.
|
|
<p> One of the key concepts of .NET is the idea of "intermediate language
|
|
code" - the source code is compiled into a bytecode format, and at
|
|
runtime, that bytecode is executed in a virtual machine - the <em>Common Language Runtime</em> (CLR).
|
|
<p> Another key concept is that of <em>managed code</em>. This is essentially
|
|
intermediate language code written in such a way that the CLR can take
|
|
care of the memory management, i.e. the CLR will do automatic garbage
|
|
collection, so the application code does not need to explicitly free
|
|
the memory for unused objects.
|
|
<p> The MS compilers for C# and VB.NET will only produce managed
|
|
code. Such programs cannot directly call normal, native functions
|
|
or classes. <a href="#footnote1"><sup>(1)</sup></a><a name="footnote-call1"></a>
|
|
<p> The MS C++ compiler for .NET on the other hand, can produce both
|
|
normal and managed code. To write a C++ class that can be compiled
|
|
into managed code, the developer must flag the class as managed using
|
|
the <tt>__gc</tt> keyword, and restrict the code to only use the subset of
|
|
C++ known as "Managed Extensions for C++", or MC++ for short. The
|
|
advantage is that MC++ code can freely call and use normal C++
|
|
functions and classes. And it also works the other way around: normal
|
|
C++ code can call managed functions and use managed classes (e.g. the
|
|
entire .NET framework class library), including managed functions and
|
|
classes implemented in C# or VB.NET. This feature of mixing managed
|
|
and normal C++ code immensely eases the interoperability with .NET,
|
|
and is by Microsoft referred to as the "It Just Works" (IJW) feature.
|
|
<p> This document demonstrates two different ways of integrating normal
|
|
C++ code (that uses Qt) with managed .NET code. First, the manual way
|
|
is presented, which includes using a thin MC++ wrapper class around
|
|
the normal Qt/C++ class. Then, the automated way is presented, which
|
|
utilizes the <a href="activeqt.html#ActiveQt">ActiveQt</a> framework as a generic bridge. The advantage of
|
|
the first method is that it gives the application developer full
|
|
control, while the second method requires less coding and relieves the
|
|
developer of dealing with the conversion between managed and normal
|
|
data objects.
|
|
<p> The impatient reader, who right away wants to see a <a href="qpushbutton.html">QPushButton</a> and a
|
|
custom Qt widget (<a href="qaxserver-example-multiple.html">QAxWidget2</a>) run in a .NET GUI application is referred to the example
|
|
directory of ActiveQt. It contains the result of this walkthrough
|
|
using both C# and VB.NET, created with Visual Studio.NET (not 2003).
|
|
Load <tt>examples/dotnet/walkthrough/csharp.csproj</tt>,
|
|
<tt>examples/dotnet/walkthrough/vb.vbproj</tt>
|
|
<a href="#footnote2"><sup>(2)</sup></a><a name="footnote-call2"></a>
|
|
or <tt>examples/dotnet/wrapper/wrapper.sln</tt> into the IDE and run
|
|
the solution.
|
|
<p> <h2> Walkthrough: .NET interop with MC++ and IJW
|
|
</h2>
|
|
<a name="2"></a><p> Normal C++ classes and functions can be used from managed .NET code by
|
|
providing thin wrapper classes written in MC++. The wrapper class will
|
|
take care of forwarding the calls to the normal C++ functions or
|
|
methods, and converting parameter data as necessary. Since the wrapper
|
|
class is a managed class, it can be used without further ado in any
|
|
managed .NET application, whether written in C#, VB.NET, MC++ or other
|
|
managed programming language.
|
|
<p>
|
|
|
|
<pre> // native Qt/C++ class
|
|
class Worker : public <a href="qobject.html">QObject</a>
|
|
{
|
|
<a href="metaobjects.html#Q_OBJECT">Q_OBJECT</a>
|
|
Q_PROPERTY(QString statusString READ statusString WRITE setStatusString)
|
|
public:
|
|
Worker();
|
|
|
|
<a href="qstring.html">QString</a> statusString() const;
|
|
|
|
public slots:
|
|
void setStatusString(const <a href="qstring.html">QString</a> &string);
|
|
|
|
signals:
|
|
void statusStringChanged(const <a href="qstring.html">QString</a> &string);
|
|
|
|
private:
|
|
<a href="qstring.html">QString</a> status;
|
|
};
|
|
</pre>
|
|
<p> The Qt class has nothing unusual for Qt users, and as even the Qt
|
|
specialities like <tt>Q_PROPERTY</tt>, <tt>slots</tt> and <tt>signals</tt> are
|
|
implemented with straight C++ they don't cause any trouble when
|
|
compiling this class with any C++ compiler.
|
|
<p>
|
|
|
|
<pre> class Worker;
|
|
|
|
// .NET class
|
|
public __gc class netWorker
|
|
{
|
|
public:
|
|
netWorker();
|
|
~netWorker();
|
|
|
|
__property String *get_StatusString();
|
|
__property void set_StatusString(String *string);
|
|
|
|
__event void statusStringChanged(String *args);
|
|
|
|
private:
|
|
Worker *workerObject;
|
|
};
|
|
</pre>
|
|
<p> The .NET wrapper class uses keywords that are part of MC++ to indicate
|
|
that the class is managed/garbage collected (<tt>__gc</tt>), and that <tt>StatusString</tt> should be accessible as a property in languages that
|
|
support this concept (<tt>__property</tt>). We also declare an event
|
|
function <tt>statusStringChanged(String*)</tt> (<tt>__event</tt>), the
|
|
equivalent of the respective signal in the Qt class.
|
|
<p> Before we can start implementing the wrapper class we need a way to
|
|
convert Qt's datatypes (and potentionally your own) into .NET
|
|
datatypes, e.g. <a href="qstring.html">QString</a> objects need to be converted into objects
|
|
of type <tt>String*</tt>.
|
|
<p> When operating on managed objects in normal C++ code, a little extra
|
|
care must be taken because of the CLR's garbage collection. A normal
|
|
pointer variable should not <a href="#footnote3"><sup>(3)</sup></a><a name="footnote-call3"></a> be used to refer to a managed
|
|
object. The reason is that the garbage collection can kick in at any
|
|
time and move the object to another place on the heap, leaving you
|
|
with an invalid pointer.
|
|
<p> However, two methods are provided that solves this problem easily. The
|
|
first is to use a <em>pinned</em> pointer, i.e. declare the pointer variable
|
|
with the <tt>__pin</tt> keyword. This guarantees that the object pointed to
|
|
will not be moved by the garbage collector. It is recommended that
|
|
this method not be used to keep a references to managed objects for a
|
|
long time, since it will decrease the efficiency of the garbage
|
|
collector. The second way is to use the <tt>gcroot</tt> smartpointer
|
|
template type. This lets you create safe pointers to managed
|
|
objects. E.g. a variable of type <tt>gcroot<String></tt> will always point
|
|
to the String object, even if it has been moved by the garbage
|
|
collector, and it can be used just like a normal pointer.
|
|
<p>
|
|
|
|
<pre> #include <<a href="qstring-h.html">qstring.h</a>>
|
|
|
|
#using <mscorlib.dll>
|
|
#include <vcclr.h>
|
|
|
|
using namespace System;
|
|
|
|
String *QStringToString(const <a href="qstring.html">QString</a> &qstring)
|
|
{
|
|
<a name="x2467"></a> return new String(qstring.<a href="qstring.html#ucs2">ucs2</a>());
|
|
}
|
|
</pre>
|
|
<p> <pre> QString StringToQString(String *string)
|
|
{
|
|
wchar_t __pin *chars = PtrToStringChars(string);
|
|
return QString::fromUcs2(chars);
|
|
}
|
|
</pre>
|
|
<p> The convertor functions can then be used in the wrapper class
|
|
implementation to call the functions in the native C++ class.
|
|
<p>
|
|
|
|
<pre> #include "networker.h"
|
|
#include "worker.h"
|
|
#include "tools.h"
|
|
|
|
netWorker::netWorker()
|
|
{
|
|
workerObject = new Worker();
|
|
}
|
|
</pre>
|
|
<p> <pre> netWorker::~netWorker()
|
|
{
|
|
delete workerObject;
|
|
}
|
|
</pre>
|
|
<p> The constructor and destructor simply create and destroy the Qt
|
|
object wrapped using the C++ operators <tt>new</tt> and <tt>delete</tt>.
|
|
<p> <pre> String *netWorker::get_StatusString()
|
|
{
|
|
return QStringToString(workerObject->statusString());
|
|
}
|
|
</pre>
|
|
<p> The netWorker class delegates calls from the .NET code to the native
|
|
code. Although the transition between those two worlds implies a small
|
|
performance hit for each function call, and for the type conversion,
|
|
this should be negligible since we are anyway going to run within the
|
|
CLR.
|
|
<p> <pre> void netWorker::set_StatusString(String *string)
|
|
{
|
|
workerObject->setStatusString(StringToQString(string));
|
|
__raise statusStringChanged(string);
|
|
}
|
|
</pre>
|
|
<p> The property setter calls the native Qt class before firing the
|
|
event using the <tt>__raise</tt> keyword.
|
|
<p> This wrapper class can now be used in .NET code, e.g. using C++, C#,
|
|
Visual Basic or any other programming language available for .NET.
|
|
<p>
|
|
|
|
<pre> using System;
|
|
|
|
namespace WrapperApp
|
|
{
|
|
class App
|
|
{
|
|
void Run()
|
|
{
|
|
netWorker worker = new netWorker();
|
|
|
|
worker.statusStringChanged += new netWorker.__Delegate_statusStringChanged(onStatusStringChanged);
|
|
|
|
System.Console.Out.WriteLine(worker.StatusString);
|
|
|
|
System.Console.Out.WriteLine("Working cycle begins...");
|
|
worker.StatusString = "Working";
|
|
worker.StatusString = "Lunch Break";
|
|
worker.StatusString = "Working";
|
|
worker.StatusString = "Idle";
|
|
System.Console.Out.WriteLine("Working cycle ends...");
|
|
}
|
|
|
|
private void onStatusStringChanged(string str)
|
|
{
|
|
System.Console.Out.WriteLine(str);
|
|
}
|
|
|
|
[STAThread]
|
|
static void Main(string[] args)
|
|
{
|
|
App app = new App();
|
|
app.Run();
|
|
}
|
|
}
|
|
}
|
|
</pre>
|
|
<p> <h2> Walkthrough: .NET/COM Interop with ActiveQt
|
|
</h2>
|
|
<a name="3"></a><p> Fortunately .NET provides a generic wrapper for COM objects, the
|
|
<em>Runtime Callable Wrapper</em> (RCW). This RCW is a proxy for the
|
|
COM object and is generated by the CLR when a .NET Framework client
|
|
activates a COM object. This provides a generic way to reuse COM
|
|
objects in a .NET Framework project.
|
|
<p> Making a <a href="qobject.html">QObject</a> class into a COM object is easily achieved with
|
|
ActiveQt and demonstrated in the <a href="qaxserver-examples.html">examples</a>. The walkthrough will use the Qt classes implemented
|
|
in those examples, so the first thing to do is to make sure that those
|
|
examples have been built correctly, e.g. by opening the <a href="qaxserver-demo-multiple.html">demonstration pages</a> in Internet
|
|
Explorer to verify that the controls are functional.
|
|
<p> <h3> Starting a Project
|
|
</h3>
|
|
<a name="3-1"></a><p> Start Visual Studio.NET, and create a new C# project for writing a
|
|
Windows application. This will present you with an empty form in
|
|
Visual Studio's dialog editor. You should see the toolbox, which
|
|
presents you with a number of available controls and objects in
|
|
different categories. If you right-click on the toolbox it allows
|
|
you to add new tabs. We will add the tab "Qt".
|
|
<p> <h3> Importing Qt Widgets
|
|
</h3>
|
|
<a name="3-2"></a><p> The category only has a pointer tool by default, and we have to add
|
|
the Qt objects we want to use in our form. Right-click on the empty
|
|
space, and select "Customize". This opens a dialog that has two
|
|
tabs, "COM Components" and ".NET Framework Components". We used
|
|
ActiveQt to wrap QWidgets into COM objects, so we select the "COM
|
|
Components" page, and look for the classes we want to use, e.g.
|
|
"QPushButton" and "QAxWidget2".
|
|
<p> When we select those widgets and close the dialog the two widgets
|
|
will now be available from the toolbox as grey squares with their
|
|
name next to it <a href="#footnote4"><sup>(4)</sup></a><a name="footnote-call4"></a> .
|
|
<p> <h3> Using Qt Widgets
|
|
</h3>
|
|
<a name="3-3"></a><p> We can now add an instance of QAxWidget2 and a <a href="qpushbutton.html">QPushButton</a> to
|
|
the form. Visual Studio will automatically generate the RCW for the
|
|
object servers. The QAxWidget2 instance takes most of the upper
|
|
part of the form, with the QPushButton in the lower right corner.
|
|
<p> In the property editor of Visual Studio we can modify the properties
|
|
of our controls - QPushButton exposes the <a href="qwidget.html">QWidget</a> API and has many
|
|
properties, while QAxWidget2 has only the Visual Studio standard
|
|
properties in addition to its own property "lineWidth" in the
|
|
"Miscellaneous" category. The objects are named "axQPushButton1" and
|
|
"axQAxWidget21", and since especially the last name is a bit
|
|
confusing we rename the objects to "resetButton" and "circleWidget".
|
|
<p> We can also change the Qt properties, e.g. set the "text" property
|
|
of the <tt>resetButton</tt> to "Reset", and the "lineWidth" property of the
|
|
<tt>circleWidget</tt> to 5. We can also put those objects into the layout
|
|
system that Visual Studio's dialog editor provides, e.g. by setting
|
|
the anchors of the <tt>circleWidget</tt> to "Left, Top, Right, Bottom", and
|
|
the anchors of the <tt>resetButton</tt> to "Bottom, Right".
|
|
<p> Now we can compile and start the project, which will open a user
|
|
interface with our two Qt widgets. If we can resize the dialog,
|
|
the widgets will resize appropriately.
|
|
<p> <h3> Handling Qt Signals
|
|
</h3>
|
|
<a name="3-4"></a><p> We will now implement event handlers for the widgets. Select the
|
|
<tt>circleWidget</tt> and select the "Events" page in the property
|
|
editor. The widget exposes events because the QAxWidget2 class has
|
|
the "StockEvents" attribute set in its class definition. We implement
|
|
the event handler <tt>circleClicked</tt> for the <tt>ClickEvent</tt> to increase
|
|
the line width by one for every click:
|
|
<p>
|
|
|
|
<pre> private void circleClicked(object sender, System.EventArgs e)
|
|
{
|
|
this.circleWidget.lineWidth++;
|
|
}
|
|
</pre>
|
|
<p> In general we can implement a default event handler by double
|
|
clicking on the widget in the form, but the default events for
|
|
our widgets are right now not defined.
|
|
<p> We will also implement an event handler for the <tt>clicked</tt> signal
|
|
emitted by <a href="qpushbutton.html">QPushButton</a>. Add the event handler <tt>resetLineWidth</tt> to
|
|
the <tt>clicked</tt> event, and implement the generated function:
|
|
<p> <pre> private void resetLineWidth(object sender, System.EventArgs e)
|
|
{
|
|
this.circleWidget.lineWidth = 1;
|
|
this.resetButton.setFocus();
|
|
}
|
|
</pre>
|
|
<p> We reset the property to 1, and also call the <tt>setFocus()</tt> slot
|
|
to simulate the user style on Windows, where a button grabs focus
|
|
when you click it (so that you can click it again with the spacebar).
|
|
<p> If we now compile and run the project we can click on the circle
|
|
widget to increase its line width, and press the reset button to
|
|
set the line width back to 1.
|
|
<p> <h2> Summary
|
|
</h2>
|
|
<a name="4"></a><p> Using ActiveQt as a universal interoperability bridge between the
|
|
.NET world and the native world of Qt is very easy, and makes it
|
|
often unnecessary to implement a lot of handwritten wrapper classes.
|
|
Instead, the <a href="qaxfactory.html">QAxFactory</a> implementation in the otherwise completely
|
|
cross-platform Qt project provides the glue that .NET needs to to
|
|
generate the RCW.
|
|
<p> If this is not sufficient we can implement our own wrapper classes
|
|
thanks to the C++ extensions provided by Microsoft.
|
|
<p> <h3> Limitations
|
|
</h3>
|
|
<a name="4-1"></a><p> All the limitations when using ActiveQt are implied when using this
|
|
technique to interoperate with .NET, e.g. the datatypes we can use
|
|
in the APIs can only be those supported by ActiveQt and COM. However,
|
|
since this includes subclasses of <a href="qobject.html">QObject</a> and <a href="qwidget.html">QWidget</a> we can wrap
|
|
any of our datatypes into a QObject subclass to make its API
|
|
available to .NET. This has the positive side effect that the same
|
|
API is automatically available in <a href="http://www.trolltech.com/products/qsa">QSA</a>, the cross platform
|
|
scripting solution for Qt applications, and to COM clients in general.
|
|
<p> When using the "IJW" method, in priciple the only limitation is the
|
|
time required to write the wrapper classes and data type conversion
|
|
functions.
|
|
<p> <h3> Performance Considerations
|
|
</h3>
|
|
<a name="4-2"></a><p> Every call from CLR bytecode to native code implies a small
|
|
performance hit, and necessary type conversions introduce an
|
|
additional delay with every layer that exists between the two
|
|
frameworks. Consequently every approach to mix .NET and native
|
|
code should try to minimize the communication necessary between
|
|
the different worlds.
|
|
<p> As ActiveQt introduces three layers at once - the RCW, COM and finally
|
|
ActiveQt itself - the performance penalty when using the generic
|
|
Qt/ActiveQt/COM/RCW/.NET bridge is larger than when using a
|
|
hand-crafted IJW-wrapper class. The execution speed however is still
|
|
sufficient for connecting to and modifying interactive elements in a
|
|
user interface, and as soon as the benefit of using Qt and C++ to
|
|
implement and compile performance critical algorithms into native code
|
|
kicks in, ActiveQt becomes a valid choice for making even non-visual
|
|
parts of your application accessible to .NET.
|
|
<p>
|
|
<hr>
|
|
<ol> <li><a name="footnote1"></a>
|
|
The .NET framework provides Platform Invocation
|
|
Services - P/Invoke - that enable managed code to call native C (not
|
|
C++) functions located in DLLs directly. The resulting application
|
|
then becomes partially unmanaged. <a href="#footnote-call1">Back...</a> <li><a name="footnote2"></a>
|
|
|
|
You will notice that in the generated code the following line is
|
|
commented out: <pre>
|
|
' VB is case insensitive, but our C++ controls are not.
|
|
' Me.resetButton.enabled = True
|
|
</pre>
|
|
|
|
This line is regenerated without comment whenever you change the
|
|
dialog, in which case you have to comment it out again to be able
|
|
to run the project. This is a bug in the original version of
|
|
Visual Studio.NET, and is fixed in the 2003 edition.
|
|
<a href="#footnote-call2">Back...</a> <li><a name="footnote3"></a>
|
|
Indeed, the compiler will in
|
|
many cases disallow it. <a href="#footnote-call3">Back...</a> <li><a name="footnote4"></a>
|
|
Icons could be added by modifying the
|
|
way the controls register themselves. <a href="#footnote-call4">Back...</a></ol>
|
|
</hr><p>See also <a href="qaxserver-examples.html">The QAxServer Examples</a>.
|
|
|
|
<!-- eof -->
|
|
<p><address><hr><div align=center>
|
|
<table width=100% cellspacing=0 border=0><tr>
|
|
<td>Copyright © 2007
|
|
<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
|
|
<td align=right><div align=right>Qt 3.3.8</div>
|
|
</table></div></address></body>
|
|
</html>
|