Monday, September 18, 2006

Wt in-place-edit widget.

As promised, and following up on my previous post, a Wt implementation of the in-place-edit widget.

The code, starting with the class definition of the new widget:

class WInPlaceEdit : public WCompositeWidget
WInPlaceEdit(const std::string text, WContainerWidget *parent = 0);

const std::string text() const;

public signals:
Wt::Signal<std::string> valueChanged;

private slots:
void save();

WContainerWidget *impl_;
WText *text_;
WLineEdit *edit_;
WPushButton *save_;
WPushButton *cancel_;

and the implementation of the constructor, and the two methods:

WInPlaceEdit::WInPlaceEdit(const std::string text, WContainerWidget *parent)
setImplementation(impl_ = new WContainerWidget());

text_ = new WText(text, impl_);

edit_ = new WLineEdit(text, impl_);
save_ = new WPushButton("Save", impl_);
cancel_ = new WPushButton("Cancel", impl_);

text_->clicked.connect(SLOT(text_, WWidget::hide));
text_->clicked.connect(SLOT(edit_, WWidget::show));
text_->clicked.connect(SLOT(save_, WWidget::show));
text_->clicked.connect(SLOT(cancel_, WWidget::show));

save_->clicked.connect(SLOT(save_, WWidget::hide));
save_->clicked.connect(SLOT(cancel_, WWidget::hide));
save_->clicked.connect(SLOT(edit_, WFormWidget::disable));
save_->clicked.connect(SLOT(this, WInPlaceEdit::save));

cancel_->clicked.connect(SLOT(save_, WWidget::hide));
cancel_->clicked.connect(SLOT(cancel_, WWidget::hide));
cancel_->clicked.connect(SLOT(edit_, WWidget::hide));
cancel_->clicked.connect(SLOT(text_, WWidget::show));

const std::string WInPlaceEdit::text() const
return text_->text();

void WInPlaceEdit::save()


And this is what it does (sorry, no demo online yet since the current CVS is not release-ready) :
  • Client-side event handling (JavaScript), for all functionality but save().
  • Server-side event handling for the save() method, using AJAX.
  • Works also without JavaScript, but then all event-handling happens server-side and requires a complete page refresh.
  • Fast load time since invisible widgets (the edit buttons) or transmitted only after the visible widgets are displayed.
  • Small bandwidth footprint: the demo application loads in 11Kb spread over 4 HTTP requests. Note that no effort has been done to compress the JavaScript. The save() button triggers generates about 200 bytes.
Looking forward to see how this compares to the echo2 + GWT implementation !

Wednesday, September 13, 2006

Wt versus echo2+GWT

At the Agile AJAX blog, Dietrich Kappe is going to look at how GWT may be merged into Echo2.

Echo2 is comparable to Wt in the sense that it is a server-side library (although they call it a framework) to build web applications. On the other hand, GWT is comparable to Wt in the sense that it allows creating client-side event handling in the Java language. Wt provides this functionality using stateless slot learning, but then naturally starting from C++ code.

Combining Echo2 and GWT thus is a compelling idea, since they are two java-based complementary toolkits for web development.

Interestingly, the choice for a widget to create (which is in the framework world a component), fell on an edit-in-place field. Competitive as we are, and of course determined to show off the nice stuff in Wt, it will be nice to compare their implementation(s) to a Wt-based implementation.

Before comparing different implementations, we need to consider whether we have a comparable feature set, with respect to:
  • Does it work when JavaScript is disabled, or on browser that do not support JavaScript ?
  • Is the server state synchronized with client (does a 'reload' give the same page ?)
And then we will want to look at:
  • Code size and elegance
  • API -- how easy it is to use the widget/component ?
  • Were we really using only one language (C++ or Java) ? Is there any chance of runtime syntax errors (caused by faulty JavaScript or XML) ?
  • Does client-side or server-side event handling look similar ? Can we easily switch ?
  • Bandwidth usage and number of round trips
Of course, I am kind of setting the rules while both competing, rendering the comparision fairly biased.

But as this is a blog, you are welcome to add additional test criteria you might be interested in !

Good luck to the Java camp!

Thursday, July 13, 2006

i18n in Wt

I've been working on the i18n feature of Wt for the past few months though all my work still remains on the drawing board. I haven't integrated a single line of code yet to the repository. Wt is theoretically capable of displaying utf-8 but libxml++ seems not up to the job yet.The reason why Wt is not rendering unicode text from resources properly is that libxml++ throws a Glib::ConvertError exception if it encounters unicode characters. I think the libxml++ folks haven't resolved this issue yet even in the latest versions. The best solution? Switch to Xerces-C! More on that later.

Saturday, May 20, 2006

Wt AJAX C++ Toolkit

The Web Toolkit a.k.a. Wt (pronounced "witty") allows C++ programs to achieve write-once run-anywhere status through the functionality introduced by highly interactive AJAX web apps. Although, web applications has traditionally been the domain of interpreted and semi-interpreted languages, C++ access to this field is very limited. I state here the reasons why C++ still matters as a web application programming language.

Critics of native code point out that C/C++ programs allow programmers to shoot themselves on the foot. Although, this is still true today, the methodology that permits such actions is old-school C/C++ programming. Modern C++ design methods such as the ones offered by libraries like STL, Boost, and Qt, already address critical faults such as strings and pointer-memory management while at the same time retaining the performance aspects of running native code. For example, Wt in closely following Qt's object-tree model, allows objects to be allocated from the heap without the programmer worrying about deleting it later.

In addition, the availability of thousands of high-performance native libraries means that Wt is able to leverage those existing libraries directly without resorting to wrappers or RPC code. Though quite far-fetched at this point, it is quite possible to use Wt in writing a simulation program with a networked front-end GUI utilizing the best cross-platform solution: the plain web browser.

Lastly, I would like to point out my latest experience in working with a Java5-based web toolkit. Java is an excellent platform offering garbage collection and automatic memory management. But I was still plagued by memory leaks, crashing my whole web-app after four days of running straight. Someone pointed out that this was caused by registering a static class to an event listener or something like that. I did not find any on my code though. The leaks could be caused by a design error on my part. But my point is that if I were to spend my precious hours hunting for leaks in a tracing tool, I might as well do that in C++ (minus the verboseness and the performance snags)! So much for the vaunted claim about Java programmers never having to worry about memory management again.

You can now read more about, sample, and download Wt.