teaching machines

CS 330 Lecture 18 – XML Pull Parsing and GUI Abstraction

March 5, 2014 by Chris Johnson. Filed under cs330, lectures, spring 2014.

Agenda

• what ?s
• think about this
• languages for data (https://maps.googleapis.com/maps/api/geocode/json?sensor=false&address=)
• a GUI description language using XML
• XML pull parsing

TODO

• Read http://msdn.microsoft.com/en-us/magazine/cc500572.aspx. Read http://stackoverflow.com/questions/3536893/what-are-the-pros-and-cons-of-xml-and-json. Bonus 1/4 sheet.

Think About This

Code

gui.xml

<?xml version="1.0" encoding="UTF-8"?>
<panel orientation="vertical">
 <panel orientation="horizontal">
  <label text="To:" />
  <textbox name="toBox" />
 </panel>
 <panel orientation="horizontal">
  <label text="Subject:" />
  <textbox name="subjectBox" />
 </panel>
 <textarea name="bodyBox" />
 <button text="Send" />
</panel>

gui_madness.c

#include <stdio.h>
#include <stdlib.h>
#include <expat.h>
#include <string.h>

void open_handler(void *data,
          const char *tag,
          const char **attributes) {
  /* printf("open tag: %s\n", tag); */

  if (strcmp(tag, "panel") == 0) {
    int is_vertical = 1;
    for (int i = 0; attributes[i] != NULL; i += 2) {
      if (strcmp(attributes[i], "orientation") == 0) {
        if (strcmp(attributes[i + 1], "horizontal") == 0) {
          is_vertical = 0;
        }
      }
    }
    printf("JPanel panel = new JPanel(new BoxLayout(BoxLayout.%s));\n", is_vertical ? "PAGE_AXIS" : "LINE_AXIS");
  } else if (strcmp(tag, "button") == 0) {
    printf("new JButton(%s);\n", attributes[1]);
  }
}

void close_handler(void *data,
           const char *tag) {
  /* printf("close tag: %s\n", tag); */
}

int main(int argc, char **argv) {
  XML_Parser parser = XML_ParserCreate(NULL);
  XML_SetElementHandler(parser, open_handler, close_handler);

  const int BUFFER_SIZE = 8192;
  char buffer[BUFFER_SIZE];

  FILE *xml_file = fopen(argv[1], "r");
  int is_eof = 0;

  while (!is_eof) {
    int length = fread(buffer, sizeof(char), BUFFER_SIZE, xml_file);
    is_eof = feof(xml_file);
    XML_Parse(parser, buffer, length, is_eof);
  }

  fclose(xml_file);
  XML_ParserFree(parser);

  return 0;
}

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