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

Now that the user script is installed, point your browser to the page with Ajax requests you want to debug. Immediately, the XMLHttpRequest Debugging window should open. Click the help link at the top of the window to display the script s help module (see Figure 7-1). You can move the XMLHttpRequest Debugging window around the page by clicking its header and dragging it to the desired place. Toggle the help contents off by clicking the help link again. With the XMLHttpRequest Debugging window now open, you can proceed by initiating an Ajax request. Upon initiating the request, the window will refresh itself with information pertaining to the Ajax request and the subsequent response. XMLHttpRequest Debugging relays information about both the request and the response. The first line in the information window indicates the method of the request, such as GET or POST. The next line details the URL along with the query string that made up the request. Inspect this line carefully if you re sending request parameters as part of the query string, as you ll easily notice any errors here.

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Figure 13-13. Low2High NXT-G Program The program reads the PCF8574 and moves the value of the 4 low bits up by multiplying by 16. This is the same thing as shifting the value up by 4 bits. If we wrote this shifted value to the PCF8574, the correct LEDs would light to correspond to whatever buttons were being pressed. However, we must also rewrite ones to the input pins so when we loop back around to the I2CbusR again, the pins can be read as inputs. That is why we add 15 to make the each of the low 4 bits one. The Low2High NXC program shown in Listing 13-3 does the same thing as the NXT-G program. However, it takes care of both the read and write with a single function called I2CBytes. This high-level function writes a 1 byte data (WriteBuf[1]), waits for the transmission to finish, and then reads 1 byte of data back from the device (ReadBuf[0]). Listing 13-3. low2high.nxc Program #define I2Cport S1 // NXT sensor port 1 #define I2CAddr8574 0x40 // 0x40 8574 or 0x70 for 8574A byte WriteBuf[] = {I2CAddr8574, 0xFF}; // Sent to 8574 byte ReadBuf[]; // Receive from PCF8574 int RdCnt=1; // Number of bytes to read task main (){ SetSensorLowspeed (I2Cport); // Configure NXT port while (true){ // write output data and read back port value I2CBytes(I2Cport, WriteBuf, RdCnt, ReadBuf); // shift left 4 bits and make lowest 4 bits 1 WriteBuf[1] = (ReadBuf[0] << 4) + 0x0f; } }

Although the structure of the data is the same and is represented by a float, the meanings are quite different Mixing up the meaning of data in an algorithm is a common cause of bugs in programs, and the volume type is in part an attempt to avoid this You define a union type using the type keyword, followed by the type name, followed by an equals sign just as all type definitions Then comes the definition of the different constructors, separated by vertical bars The first vertical bar is optional A constructor is composed of a name that must start with a capital letter; this is to stop the common bug of getting constructor names mixed up with identifier names The name can optionally be followed by the keyword of and then the types that make up that constructor.

XMLHttpRequest Debugging allows you to view the body of the request by clicking the body link. The body of the request is usually NULL unless a string or XML document was passed as a parameter to the XMLHttpRequest object s send() method. The bottom half of the request information window details the server response. Clicking the headers link shows all the response headers sent by the server. The entire contents of the server response are displayed when the response link is clicked. Finally, the text of the callback method called by XMLHttpRequest when the response completes is displayed by clicking the callback link. If that window is too small, the entire contents of both the request and response information sections can be exported to a larger browser window at any time by clicking the export link. Figure 7-2 shows the XMLHttpRequest Debugging window displaying the request and response values and the XMLHttpRequest object s callback function.