.NET/Java PDF, Tiff, Barcode SDK Library

You should consider very carefully whether you want to catch instances of the base Exception type. When you do that you are saying something bad happened, but I don t really know what it was. That degree of uncertainty tends to imply that the app has lost control of its own internal consistency. It is a common practice to catch Exception in your top-level exception handlers (e.g., in Main or, as we ll see later, in threading worker functions); and when you do, you normally need to terminate the application (or at least restart some subsystem). Of course, you might know perfectly well what might go wrong, and you re catching Exception because you can t be bothered to list the half dozen exception types you intend to handle in the same way. (Maybe F1 wasn t working so well that day and you couldn t inspect the docs; and someone was pressing you to check in your changes.) Beware! What happens if an implementation detail changes in another class on which you depend, such that a new exception is thrown Your handler will swallow it up and carry on. That might be OK, and your game of tic-tac-toe will continue happily. Or it might have unintended consequences, such as data loss or the start of WWIII. You just can t know in advance.

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When the flow of control leaves the try block successfully, or the flow of control exits the last catch block if an exception occurred in the try block, the code in the finally block is executed. In other words, the code in the finally block is always executed, regardless of whether there was an exception. If you designed your exception-handling code nicely, you ll almost certainly use far more finally blocks than you do catch blocks. The finally block is a good place for cleaning up your resources, or winding back internal state if an error occurs, to ensure that your pre- and post conditions are still valid, whereas a catch block allows you to deal with an error condition you, as a client, understand in some way even if it is only to present a message to the user (as in this case). If we compile and run our code again, we ll see the following output:

line = stream.readLine(); if( line.length() != width ) return false; for( int x=0; x<width; ++x ) { switch( QString(map).indexOf(line[x]) { case 0: result.setPixel( x, y, 0xffffffff break; case 1: result.setPixel( x, y, 0xffdfdfdf break; case 2: result.setPixel( x, y, 0xffbfbfbf break; case 3: result.setPixel( x, y, 0xff9f9f9f break; case 4: result.setPixel( x, y, 0xff7f7f7f break; case 5: result.setPixel( x, y, 0xff5f5f5f break; case 6: result.setPixel( x, y, 0xff3f3f3f break; case 7: result.setPixel( x, y, 0xff000000 break; default: return false; } } } if( stream.status() != QTextStream::Ok ) return false; *image = result; return true; }

Arthur is at (0,0) and is pointing at angle 0.00 radians. Arthur is at (0,10) and is pointing at angle 0.00 radians. Error running turtle: The PlatformWidth must be initialized to a value > 0.0 Waiting in the finally block...

Notice how the error-handling code is now consolidated neatly into clearly defined blocks, rather than scattered throughout our code, and we ve been able to cut down substantially on the number of points of return from our method.

At the moment, we re not handling any exceptions in our Turtle itself. Let s imagine that our Turtle is being provided to clients in a library, and we (as the leading vendors of turtle simulators) want the library to do some internal logging when errors occur: maybe we have an opt-in customer experience program that sends telemetry back to our team. We still want the errors to propagate up to the client for them to deal with; we just want to see them on the way past. C# gives us the ability to catch, and then transparently rethrow, an exception, as shown in Example 6-17.

Saving an image as ASCII art and then reading it back results in some losses. The color-togray-scale conversion and back is far from perfect. Taking the ASCII art image from Figure 11-3 and saving back to an ordinary pixel-based image results in the image shown in Figure 11-4.

The next parameter is serviceMethod, which as you can guess is the name of the service method to call Now, you may remember that typing three letters into the text box triggered this behavior, so these letters should somehow be passed to the web service to determine the correct list of articles to return, but this isn t happening in any of these parameters, so how does the web service get them The answer is in the behavior definition itself If you take a look at the this_onTimerTick definition in the implementation code, you ll see that it pulls the text from the parent control of the behavior In this case, the parent control for the behavior is the text box, so it gets the text from there and passes it to the service to get the related articles Finally, the autoHideCompletionListElementParent attribute is set to True.

// Run the turtle for the specified duration public void RunFor(double duration) { try { if (LeftMotorState == MotorState.Stopped && RightMotorState == MotorState.Stopped) { // If we are at a full stop, nothing will happen return; } // The motors are both // then we just drive if ((LeftMotorState == RightMotorState == (LeftMotorState == RightMotorState == { Drive(duration); } // // // if running in the same direction MotorState.Running && MotorState.Running) || MotorState.Reversed && MotorState.Reversed))

{

The motors are running in opposite directions, so we don't move, we just rotate about the center of the rig ((LeftMotorState == MotorState.Running && RightMotorState == MotorState.Reversed) || (LeftMotorState == MotorState.Reversed && RightMotorState == MotorState.Running)) Rotate(duration);