Developing Portable Mobile Web Applications
The first four lines of the file initialize jQTouch and assign an instance to the variable jQT. The parameter “.icon” is one of many that can be defined for jQTouch. It points to a 57x57 pixel icon for the application (Figure 4).
Short name for the database.
Database version number.
Display name for the database.
Maximum size of the database.
SQLite creates the database if it does not exist. The anonymous function executes an SQLite transaction that creates or opens a table called “notes”. Each row of that table represents a note with the following columns:
INTEGER id KEY: unique identifier auto-incremented by SQLite.
DATE lastedit: date the note was last edited.
TEXT title: title of the note.
TEXT note: contents of the note.
Once the table is opened, we call a function, refreshNotes(), described below, that will update the list displayed on the “home” screen.
SQL string: template for the SQL to be executed.
Array of parameters whose values replace the ? marks in the SQL template.
Function that executes if the operation was successful—in this case, an anonymous function.
Function that executes if there was an error—in this case, errorHandler().
If successful, we clear out the values in the input elements (ready for the next add), refresh the list of notes so the new one will show up and use a jQTouch function, jQT.goBack() to return to the “home” screen. Since we used “slideup” to show the “addNote” screen, jQTouch is smart enough to slide it down to return to “home”. We then return “false” to the browser, as we don't need it to continue.
We now define the errorHandler() function, which we reuse for all database transactions in the script. It displays an alert box with the error message and returns.
Next is the refreshNotes() function. We use jQuery to find all the <li> elements on the “home” screen and remove them. Then, we execute a database transaction to find all the note records, and use the “home” screen template to create a list item for each note and insert it into the “home” screen. We add a .click function to each list item that will take users to the “editNote” screen when they click on a note title.
The replaceNoteById(), editNoteById() and deleteNoteById() functions are all very similar to addNote(), with the SQL template changed appropriately.
The application can be run from the browser on an iPhone or Android device. As expected from looking at HTML5 features on different phones, Webnotes works fine on the iPhone, iTouch, iPad and Droid. It does not work on the G1, because that phone doesn't support client-side database transactions.
Rick Rogers has been a professional embedded developer for more than 30 years. Now specializing in mobile application software, when Rick isn't writing software for a living, he's writing books and magazine articles like this one.
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