Simple .NET/ASP.NET PDF document editor web control SDK

Unexpected data type Unexpected data format Unexpected result Unexpected method call Unavailable resource Contended resource

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To build a plugin and install it so that Qt can find it takes more than just running qmake project. You can use it to create a starting point, but you have to modify the project file extensively. Listing 11-11 shows the project file for the ASCII art image format plugin. The HEADERS and SOURCES lines are just the same as for all Qt projects. The lines above them specify that you are building a template, while the lines below indicate where the plugin will be installed. Starting from the top, you set the TEMPLATE to lib, which tells QMake that you are building a library, not an application. The next line tells QMake the name of the plugin: textimage. Following is the CONFIG line, in which you specify that the lib will be used as a plugin and that it should be built in release mode (without debugging information). The last line in the top section is the VERSION line, which is used to tell different plugin versions apart. In this case, the resulting file is named textimage1. The last two lines set up an installation target, which configures the actions that are performed when you run make install. The first line of this section sets the path of the target to $$[QT_INSTALL_PLUGINS]/imageformats that is, the plugins/imageformats directory inside the Qt installation directory. The second line of this section and the last line of the project file tell Qt to install target when make install is run. It will copy the plugin file to the appropriate directory, making it possible for Qt to find it. Listing 11-11. The project file for the TextImagePlugin and TextImageHandler TEMPLATE = lib TARGET = textimage CONFIG += plugin release VERSION = 1.0.0

A client passes data to a method that is not of the expected type. A client passes data to a method in a format that is not recognized. A client receives information from a method that it did not expect for the given input (e.g., null). The class wasn t expecting you to call a particular method at that time; you hadn t performed some required initialization, for example. A method tried to access a resource of some kind and it failed to respond in a timely fashion; a hardware device was not plugged in, for instance. A method tried to access a scarce resource of some kind (memory or a hardware device that cannot be shared) and it was not available because someone else was using it.

Obviously, that s a much abbreviated list, but it contains some of the most common exceptions you ll see in real applications. One of the most useful that you ll throw yourself is the ArgumentException. You can use that when parameters passed to your methods fail to validate. Let s make use of that in our RunFor method. Say that a feature of our turtle hardware is that it crashes and becomes unresponsive if we try to run it for zero seconds. We can work around this in our software by checking for this condition in the RunFor method, and throwing an exception if clients try this, as shown in Example 6-21.

Understanding how this technology all hangs together is best shown using a simple example. In this case, say you have a client application that uses JavaScript and an XMLHttpRequest object that calls a server to perform the simple addition of two integers. As the user types the values into the text boxes on the client, the page calls the server to have it to add the two values and return a result that it displays in a third text box. You can see the application in action in Figure 1-9.

public void RunFor(double duration) { if (duration <= double.Epsilon) { throw new ArgumentException( "Must provide a duration greater than 0", "duration"); } try { // ... } catch (InvalidOperationException iox)

{

HEADERS += textimagehandler.h textimageplugin.h SOURCES += textimagehandler.cpp textimageplugin.cpp target.path += $$[QT_INSTALL_PLUGINS]/imageformats INSTALLS += target To build and make this project, you must run qmake, followed by make. If it completes without any problems, you can run make install to make the plugin available to Qt.

}

throw new Exception("Some problem with the turtle has occurred", iox); } catch (Exception ex) { // Log here Console.WriteLine("Log error: " + ex.Message); // Rethrow throw; } finally { Console.WriteLine("In the Turtle finally block"); }

The second parameter in this constructor should match the name of the parameter that is in error. The first represents the exception message.