.NET/ASP.NET/C#/VB.NET PDF Document SDK

Figure 8-5. Scribble: a simple drawing application implemented using events Events created this way can also be published on the form s interface so that code consuming the form can also take advantage of these events. Again, a big problem facing a programmer working with events in WinForms is the volume of events available, which can make choosing the right one difficult. Perhaps surprisingly, most events are defined on the class Control, with each specialization providing only a handful of extra events. This generally makes life a bit easier, because if you have used an event with a control, odds are it will also be available on another. To help beginners with the most common events on the Control class, I have provided a summary in Table 8-4. Table 8-4. A Summary of Events on the Control Class

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Figure 6-3. Plot of Raw values versus shaft angle The pot resistance value you buy depends on how many degrees of rotation your application requires. The 10k Raw values change almost linearly with angle, so if you were going to be marooned on a desert island, you d pack the 10k pot. However, picking the right resistance for your application greatly improves the angular resolution you ll get. The graph in Figure 6-4 shows the range of Raw values, given that you re only using the pots in their optimal range: 90 degrees for the 50k , 180 degrees for the 20k , and 270 degrees for the 10k .

catch(ParserConfigurationException e) { System.out.println("ParserConfigurationException: " + e); } catch(SAXException e) { System.out.println("SAXException: " + e); } /* Note how the Java implementation of the W3C DOM has the same methods * as the JavaScript implementation, such as getElementsByTagName and * getNodeValue. */ NodeList selectedPetTypes = xmlDoc.getElementsByTagName("type"); String type = null; String responseText = "Selected Pets: "; for(int i = 0; i < selectedPetTypes.getLength(); i++) { type = selectedPetTypes.item(i).getFirstChild().getNodeValue(); responseText = responseText + " " + type; } response.setContentType("text/xml"); response.getWriter().print(responseText); } private String readXMLFromRequestBody(HttpServletRequest request){ StringBuffer xml = new StringBuffer(); String line = null; try { BufferedReader reader = request.getReader(); while((line = reader.readLine()) != null) { xml.append(line); } } catch(Exception e) { System.out.println("Error reading XML: " + e.toString()); } return xml.toString(); } }

This event is caused by the user clicking the control. It is a high-level event, and although it is ordinarily caused by the user clicking with the mouse, it might also be caused by the user pressing Enter or the spacebar when on a control. There are a series of events called MouseDown, MouseClick, and MouseUp that provide more detailed information about the actions of the mouse, but because these events just provide information about the mouse actions, generally the Click should be handled instead of these events. Otherwise, this will lead to the control responding in ways users expect, because it will respond to keystrokes and mouse clicks. This is raised when the mouse is clicked twice in quick succession; the amount of time is determined by the user s operating system settings. Programmers should be careful when handling this event because every time this event is raised, a Click event will have been raised before it, so in general programmers should handle either this event or the Click event. continued

The Bourns 3310C or 3310Y potentiometers make excellent angle sensors for the NXT. The 3310C in Figure 6-5 has three terminals on one side, whereas the 3310Y has them coming out the back in a triangle pattern. You should definitely solder your connections to these pots, or else the wires will pull off too easily. (Both these potentiometers can be purchased from Digi-Key in a variety of resistance values.)

Now that you ve been working with JavaScript a little more, you may be thinking to yourself that you want to keep more model information on the browser. However, after seeing the previous example that uses XML to send complex data structures to the server, you may be less inclined to do so. Creating XML strings by string concatenation is not an appealing or robust technique for generating or modifying XML data structures.