Tag: design

Take control of Delphi forms in your multimonitor application

The authors of the the VCL helpfully added multi monitor “support” a few versions back. Somewhat less helpfully, this support is very limited – it has no way to say “create form X on monitor 3”, which is a very useful thing to do in some kinds of applications – those intended to run on a multimon system in a specific configuration.

You can readily move forms around (with .Left, .Top, etc.) on to specific monitors after a Form is open, but not while it is opening (in OnShow or OnCreate), because a fine method TCustomForm.SetWindowToMonitor will jump in and undo your work.

Not surprisingly, most of the obvious methods to override to fix this, are not virtual. (An aside – I think the bias toward final methods in Delphi, C#, and some other languages, is a poor idea, and I think the guideline of “design for overriding, or prevent it” is even worse.) With some looking, I found a workaround, shown here somewhat mangled by WordPress:

private

FSetBoundsEnabled: boolean;

public

procedure SetBounds(ALeft, ATop, AWidth, AHeight: Integer); override;

…..

procedure TSomeForm.SetBounds(ALeft, ATop, AWidth, AHeight: Integer);

begin if FSetBoundsEnabled then inherited;

end;

FSetBoundsEnabled will be False by default. Sometime after your form is loaded (use a Timer or a windows message to signal this), set FSetBoundsEnabled := True then set your .Left and .Top to put your form whereever it needs to be.

Refactoring to Patterns? No, learn the primitives.

Last night at XPSTL, John Sextro gave a talk on the “Move Embellishment to Decorator” refactoring as described in Joshua Kerievsky’s Refactoring to Patterns book. I greatly enjoyed and benefitted from the original Design Patterns book (from the Gang of Four) which was already old (published 1994) when I heard about it and bought it in 1998. (By the way, when I looked it up on Amazon to put in the link above, Amazon reminded me that: “You purchased this item on February 18, 1998”.)

I enjoyed John’s talk, and I hope he does more of them.  He hit a few rough spots along the way (the usually excellent IntelliJ IDEA IDE failed mysteriously, for example), but worked through it and reached the target of composable decorators. The rough spots led to some interesting diversions also.
I’m not sold on the “refactoring to patterns” idea though; it seems like a distraction from a more important goal: to gain deep experience and understanding of how to use the underlying “primitives” (encapsulation, abstraction, polymorpism, low coupling, high cohesion, etc.). Once you grasp the primitives, the design patterns are useful mainly as a tool for talking about how something works – in other words, write good code, then perhaps notice that it follows one of the “patterns”, if you find that helpful in explaining how the code works.

Several times at XPSTL, we’ve had lengthy conversations about how to choose whether to use “Strategy” or “Command” or “Decorator” or …. I’m not convinced that these conversations are helpful. My answer is that it is silly to look for a list of rules in choosing which pattern to use. Read the patterns, use them to learn good ways to use and combine the primitives. Then do that in your code:

  • Notice that you can benefit from polymorphism, and use it.
  • Notice that you can split a class in to two separately cohesive parts, and do so.
  • Notice that you could get composability by replacing inheritance with aggregation, and so so.

You’ll end up with the right “Pattern” – and you probably won’t care.

Why I will also never deploy with Java Web Start again

Keith Lea pointed out that he will never deploy with Java Web Start again.

With Web Start in its current form, he’s be deploying with it long before I will use it again.  “Never” is much too soon.. here is why, echoing and expanding on Keith’s experiences. Some of these things are not Web Start’s fault per se. But they are unavoidable with Web Start.

A key piece of background: the most important point of Web Start for us is the notion of auto-update. We periodically put a application Jar up, update the JNLP to point to it, and our users get the new version running on their PC without a re-install process.

Java Web Start doesn’t work for a large number of users

We have the same trouble here. With a large number of users, inevitably Web Start does not work for all of them. For a few percent of users, it simply does not work. We don’t know why. Yes, we upgrade them all to the current Java, the current browser version, etc. Most of the time we get around this with a cycle or two of completely removing then reinstalling Java. In a few cases, the solution was to repave the machine entirely. Both of these are a considerable burden on our customers.

Users don’t like the experience

The part they hate most is this: the auto-update to the current application version is not optional. We upload a new version, and the next time a user runs the application (if Web Start’s update works… see below), they get the new version… even if the new version is a couple of megabytes of bloat… even if the user is on a slow, wireless link… even if the user only wanted to use the application for a minute or two.

Java/JWS detection in the browser is necessary, and unreliable

Mercifully, we have been able to avoid the problem by other means; our customers install Java on a machine right before they launch our application with Web Start.

Users don’t know what JNLP files are

… and they unwittingly misuse them

There is only one right way to use a JNLP file with Web Start, if you want Web Start’s auto update capability to work: pass around / link to / email the URL that points it it. But in the Real World, user misuse JNLP file in many ways:

  • Email the JNLP to a group of users. The users then click on it in the email… so they get the old JNLP each time they click on it. From there the auto-update (based on the URL in side the JNLP) might or might not work.
  • Copy the JNLP file on to the desktop. They do this because the “feature” in web start to create desktop icons, appears to semi-randomly work or not work.
  • Put the JNLP file on a machine, then disable web browsing on that machine… thus disabling Web Start’s auto-update… invisibly.

You cannot make the user experience much better

Most of the unpleasantness happens outside of the application’s control.

Random Caching

Web Start has a cache. The browser has a cache. Between the two of these, sometimes it is not possible to persuade Web Start to update an application to the current code (in the current JNLP file on the server). There is no visibility in to where/when/how-long the old JNLP data is cached. Sometimes clearing the browser cache fixes this, sometimes it is necessary to remove and reinstall the Web Started application. This is enormously frustrating when a field user needs the current application version Right Now, which you deployed to your Web Start web server some weeks ago.

Wireless Hostillity

Wireless network connections are sometimes slow and unreliable. Web Start always downloads a whole file or fails, as far as we can tell; thus a user on a weak connection might repeatedly wait several minutes for a Web Start update, have it fail, then start again at the beginning. Of course they can’t cancel the update as noted above.

If Not Web Start, What?

Like Keith, I have concluded that a native, non-Web Start solution is the way to do. We’ve built this sort of this for several past applications, and while it takes some coding and testing to get it right (work we planned to avoid by using th off the shelf Web Start approach), it tends to work very well. Here are some key design points for auto-updating applications:

  • The user is in control. Tell the user you have a new version to offer. Perhaps start downloading it in the background. But don’t try to force them to update now.
  • Tell the user about the new version in the application, perhaps in the status bar; not only at application startup.
  • Keep the old version, and expose it to the user. The new version might not work, so if they user can click a button to run the old version instead, you have transformed an emergency in to an inconvenience. (It has been suggested that we should not update our JNLP files, rather put up a new JNLP and pass out its URL. This is totally unfeasible for our, since most users would update rarely or never.)
  • Download in the background. The user can keep getting their work done with version N while version N+1 is downloading.
  • No silent failures. If the application can’t access its update information, expose this fact clearly to users and support staff.
  • Dodge the browser cache. Do whatever you must do, to have as few layers of caching as possible; ideally just one layer, in the application auto update mechanism itself. One way to avoid the browser cache is to use a “raw” HTTP-over-TCP library in the application.
  • Incremental Download – if a new version download retrieves 1.9 megabytes of a 2.0 megabyte file, keep the 1.9 and start there next time.

Slider Control for Touch-Screen Applications

An improved version of this post is cross-posted on the Oasis Digital blog.

At Oasis Digital we are working on an application that will run on a touch-screen computer, and which will be used to (among other things) control an audio amplification system. There are some design considerations for touch-screen applications which are rather stark once you use the touch-screen for a few minutes:

  • A finger is rather less precise than a mouse pointer – hitting small targets is hard
  • Drag/drop operations (or grab-adjust operations) sometimes don’t start quite where you aimed
  • Your finger blocks the point on the screen where you are pressing
  • The concept of keyboard “focus” is moot on applications with no keyboard

To accomodate the first two of these, I’ve built a prototype/example of a slider control to use for audio adjustment in such an application. It has these key features:

  1. It does not matter if you click on the “handle” or on the rest of the bar – because with touch screen you won’t be able to reliably do one vs. the other.
  2. The adjustment is not immediate; there is a limit of the speed of the adjustment to produce smoother audio control. The slider handle will move down very quickly, but will move up slowly. This avoids the possibility of an accidental touch pushing the audio amplification in to feedback.

The prototype/example looks like the screenshot here:

Touchscreen Slider

… but ignore the static image, it doesn’t tell the story. To see it in action, take a look at the screencast (currently in a WMV file, easily viewable only on Windows) or download the example program and play with it. The source is also on github.

This example runs on Delphi 2007 (rather old… but I had it handy on the PC at hand), an enhanced version of it in us used in a production application for a touch-screen audio control system. My secondary goal was to use it as a target to create an AJAX control with the same behavior. Anyone want to write that?