ASP.NET PDF Viewer using C#, VB/NET

Figure 11-4. The ASCII art is saved back as an ordinary image. The remaining part of the TextImageHandler is the canRead method shown in Listing 11-10. The nonstatic method calls the static method. The nonstatic method is really just a wrapper to provide the interface that Qt expects. The static method uses the peek method to see whether the file starts with the TEXT prefix. If the prefix is found, it is assumed that the rest of the file is okay, and true is returned to indicate that the handler can read the file.

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} } catch (Exception ex) { Console.WriteLine("Log message: " + ex.Message); // Rethrow throw;

}

}

The first thing to notice is that we caught the base Exception type, having just said that we almost never do that. We want to log every exception, and because we re rethrowing rather than eating it, we won t simply ignore exceptions we weren t expecting. After we execute our handler code (just writing the message to the console in this case), we use the throw keyword, without any object, to rethrow the exception we just caught. If you compile and run that, you ll see the following output:

When designing file formats it is a good idea to prefix your actual data with a unique header. Tip This makes it possible to see whether the file is a good candidate for reading without having to read the entire file.

This is a property on the behavior that overrides the base autocomplete behavior where a drop-down list appears on the parent control When set to true, the list is hidden, which is logical, because in this case you don t want to show it and instead want to display the friendlier, richer text including the formatting and hyperlinks shown in Figure 7-21 This example demonstrated the asynchronous updating of an area of the page using Atlas Script, custom behaviors, and back-end web services You can see how straightforward it was to implement using scripting, with more complex functionality implemented using a custom behavior It s recommended that you take a look at how the custom behavior was implemented to get a better understanding of how you can implement your own.

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. Log error: The PlatformWidth must be initialized to a value > 0.0 Error running turtle: The PlatformWidth must be initialized to a value > 0.0 Waiting in the finally block

Notice that we get the output from both of the exception handlers. That s not the only way to throw from a catch block: it is perfectly reasonable to throw any exception from our exception handler! We often do this to wrap up an exception that comes from our implementation in another exception type that is more appropriate for our context. The original exception is not thrown away, but stashed away in the InnerException property of the new one, as shown in Example 6-18.

// 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); } running in the same direction MotorState.Running && MotorState.Running) || MotorState.Reversed && MotorState.Reversed))

The string list takes a list and extends it with methods, making it easier to work with the contents The other types of special lists are made for putting new items in a specific part of the list and getting items from one specific part The classes are QStack and QQueue, in which the stack class can be classified as a LIFO (last in, first out) list, and the queue is classified as a FIFO (first in, first out) list Working with the stack, new items are added to or pushed onto it using push The top method is used to look at the current item The current item is returned and removed from the stack by calling pop This is called popping the stack Before trying to pop the stack, you can check whether there is something there to get by using the isEmpty method.

// The motors are running in opposite directions, // so we don't move, we just rotate about the // center of the rig

if ((LeftMotorState == RightMotorState == (LeftMotorState == RightMotorState == { Rotate(duration);

MotorState.Running && MotorState.Reversed) || MotorState.Reversed && MotorState.Running))