cnicollonline

Custom PHP exception handling

admin — Mon, 23 Aug 2010 19:08:34 +0000

A large project I’ve been working on as of late has many moving parts. It allowed a lot of dynamic edits that utilized AJAX for sending dynamic information to and from a database. When errors occurred it was alright for me, because I could debug them however what it came the client… Well let’s just say they were convinced that with these errors their computer was going to spontaneous combust.

I’ll admit it now that I was a little lazy when developing some of the classes. I went back and modified them so that they would implement exception handling, only I went one step further and used custom exception handling so that I could log any errors that may occur.

Within this posting, im going to create a class that will have errors, and I’ll also create a custom exception class that will catch any of these errors and log them to a file

You can download the complete source here. This class will be a very basic SQL class that will:

Connect to a database
Disconnect from a database
Select from a database

The directory setup after this tutorial should look as follows:

Directory Setup

index.php
/lib/
- SQL.class.php
- SQL.exception.class.php
/sql/
- world.sql
SQLException.log

Make sure you have the world database installed within your database. You can download it here or find it in the download of the completed source.

The SQL class

Before I jump into the mix, this is written for people whom already have a basic grasp on any OOP language, as well as some of the basics of exception handling.

SQL.class.php

username = $u;
		$this->password = $p;
		$this->database = $d;
		$this->connection = false;
	}

	public function connect() {
		if(!$this->connection) {
			// use @ to surpress the error
			if(!@mysql_connect('localhost',$this->username,$this->password)) {
				throw new SQLException('Can\'t connect to the database, either the username or password are wrong');
			}

			// use @ to surpress the error
			if (!@mysql_select_db($this->database)) {
				throw new SQLException('The database '.$this->database.' does not exist.');
			}

			$this->connection = true;
		}
	}

	public function disconnect() {
		if($this->connection) {
			mysql_close();
			$this->connection = false;
		}
	}

	public function getCity($city) {
		$cities = array();

		$query = 'SELECT * FROM City WHERE NAME ='."'$city'";
		$results = @mysql_query($query);
		if ($results) {
			while($row = mysql_fetch_array($results)) {
				$cities[] = $row;
			}

			if (sizeof($cities) > 0) {
				return $cities;
			}
			else {
				throw new SQLException('The following city: '.$city.' was not found',$query);
			}
		}
		else {
			throw new SQLException('Error with query when trying to get a city: ',$query);
		}
	}
}

?>

Theres the SQL class. Theres a few things in here that I should make note of. First, I’ve included the SQLException custom class, we have yet to create that, so hang on for now! Secondly the way that a try catch block works, is that it needs to try to do something and if that something does not work, it will catch that exception to better handle it. In order to catch an exception one must be thrown. We’re throwing the exceptions anytime we feel an error might need to be reported.

Next up the custom exception class

Create a new file within your lib folder called “SQL.exception.class.php”

SQL.exception.class.php

log_file =  $_SERVER['DOCUMENT_ROOT'].'/'.$_SERVER['REQUEST_URI'].'/SQLException.log';

		$code = mysql_errno();
		$sql_error = mysql_error();

		// open the log file for appending
		if ($fp = fopen($this->log_file,'a')) {

			// construct the log message
			$log_msg = date("[Y-m-d H:i:s]") .
				" Code: $code " .
				" || Message: $message".
				" || SQL error: $sql_error \n".
				"Query: $query\n-------\n";

			fwrite($fp, $log_msg);

			fclose($fp);
		}

		// call parent constructor
		parent::__construct($message, $code);
	}

}
?>

All the magic here happens when we extend PHP’s Exception class. Moving down to the class constructor, I’ve set up two parameters. $message takes the message that will be passed into the parent constructor. This message will be shown to the user to better explain whats going. The second parameter $query is meant for the log file. This is passed in so that we as the developers can view the query that may have been botched. Moving into the constructor now, it’s important to provide a path to the logfile, so the first line of code we see does just that. Next the two variables $code and $sql_error grab a little more information for the log file. The las bit of code opens the log file, appends a new entry, saves and closes it. To finish the class off, run the parents constructor.

Finally the index or testing file.

This is the index file that will be within our root directory. It contains sets of variables to help generate exceptions. This file is also where we “try” to complete a statement and if anything goes wrong we “catch” that exception, kill the script and explain why things didn’t work out.

index.php

connect();
	$db->disconnect();
} catch (SQLException $e) {
	$db->disconnect();
	die($e->getMessage());
}

/**
* try catch block
* try to connect to the database
* try to run a select query (note: to get an exception error change the city variable above)
* print the query
* disconnect
* catch any error that may occur.
*/
try {
	$db->connect();
	$r = $db->getCity($city);

	// print the results
	echo '';
		print_r($r);
	echo '';

	$db->disconnect();
} catch (SQLException $e) {
	$db->disconnect();
	die($e->getMessage());
}

?>

Conclusion

Exception handling is a fun subject. The possibilities of being able to recover from errors that might occur create endless possibilities when scripting, just don’t do what I do and leave it all to the bitter end!

Objective-C images

admin — Fri, 20 Aug 2010 18:46:12 +0000

When programming in any language I find that there are always several things that no matter how hard I try to remember will never stick. One thing as of late has been using images within objective-c and iPhone development.

So many ways!

There are several ways to get images onto your display. The two I find I’m using the most are calling an image from the web, and using an image from your resource directory. Below are two snippets that I find useful to have within your snippet collection.

Snippet 1: Getting an image from the web

The image link I’ll be using in the first example is: http://farm5.static.flickr.com/4098/4911106000_9c3a16bb59.jpg

// ----------------------- .h ------------------------
...
UIImageView *imgHolder;
...
@property(nonatomic, retain) IBOutlet UIImageView *imgHolder;

// ----------------------- .m ------------------------
// PART 1 - update url of path to the image
// PART 2 - update the variable reference to the UIImageView object
// -----------------------------------------------

// ===== PART 1 =====
NSString *imgURLpath = @"http://farm5.static.flickr.com/4098/4911106000_9c3a16bb59.jpg";
UIImage *imgURL = [[UIImage imageWithData: [NSData dataWithContentsOfURL: [NSURL URLWithString: imgURLpath]]] retain];

if (imgURL != nil) { // Image was loaded successfully.
	// ===== PART 2 =====
	[imgHolder setImage:imgURL];
	// ===== PART 2 =====
	[imgHolder setUserInteractionEnabled:NO];
	[imgURL release]; // Release the image now that we have a UIImageView that contains it.
}

Snippet 2: Getting an image from the resource folder

The image I’ll be using is:

The image above will need to be added to your applications resource folder. Note: Don’t forget to check off “Copy items to destination group’s folder. Unless that’s not your style”

	// ----------------------- .h ------------------------
	...
	UIImageView *imgHolder;
	...
	@property(nonatomic, retain) IBOutlet UIImageView *imgHolder;

	// ----------------------- .m ------------------------
	// PART 1 - create an image object
	// PART 2 - update the variable reference to the UIImageView object
	// -----------------------------------------------

	// ===== PART 1 =====
	// note: the image in use should be in your resource folder
	NSString *imgName = @"4911106000_9c3a16bb59.jpg";
	UIImage *myImg = [UIImage imageNamed:imgName];

	if (myImg != nil) { // Image was loaded successfully.
		// ===== PART 2 =====
		[imgHolder setImage:myImg];
		// ===== PART 2 =====
		[imgHolder setUserInteractionEnabled:NO];
		[myImg release]; // Release the image now that we have a UIImageView that contains it.
	}

UITableView Application Tutorial

admin — Mon, 08 Mar 2010 22:29:44 +0000

Learning Objective-C coupled with the Interface Builder, I found that using a UIImageHolder, or UITextLabel, or even the UIScrollBar came more and more simple each time I used them. I had my laptop with a full battery, a fresh piece of paper to scribble on and I was ready to tackle a Navigation-based Application.

Now this wasn’t a hard feat, but it wasn’t an one easy either. I feel I have a good foot in the door with this, but far from a “pro” status.

Why so simple?

I wanted to keep things simple here. The basis for this tutorial is to quickly show how to build a Navigation-based Application that does no more than load a view when clicking on a cell.

I’m not sure if this is the best way to do it, and in more complex projects this may not prove to be resourceful. However for getting started, for me this did the trick!

Step 1

Go ahead and create a new Table View Application within xCode

Step 2

Create a few controller classes for our views to work with. For this tutorial I created three.

SubViewControllerOne
SubViewControllerTwo
SubViewControllerThree

note: that you need both .m and .h files

Next create the nib, or view files to work along with the controllers

SubViewOne.xib
SubViewTwo.xib
SubViewThree.xib

I understand that at the time when creating a controller, you also have the option to create a nib file at the sime time. I choose not to do this because of how Xcode names it’s nibs. for example “SubViewControllerOne” controller would have a nib file called “SubViewControllerOne” which is fine, however because my controller contains the word “controller” that could lead to confusion down the road. It also doesnt stick the nib file in the Resource folder but rather the class folder. There is no right or wrong answer here, just whatever makes you sleep better at night I suppose.

By now your classes and resource folder should look like the following

note: I subgrouped my sub view controllers. Again personal preference.

Step 3

We need to link our nib files to their controllers, so open up each nib file and assign the File Owner to the correct controller

Then ctrl+click on the File Owner delegate and drag the blue line to the view - to link up the view.

While we’re at it we might as well put a label on our view so we know that indeed the view is being loaded.

Step 3

Rinse and repeat step 2 for the other two nib files

Step 4

Alright with everything linked up and ready to go, we can dive into some code! Most of, if not all the programming we’re going to be using will be within the RootViewController class. Go ahead and open RootViewController.h

We’re not going to do a whole lot in here, however to load in and out different views, depending on the cell, I plan to store all this within an NSMutableArray that will hold a NSDictionary object. Let’s declare the NSMutable array within the RootViewController.h file.

Your RootViewController.h should now look like this

RootViewController.h

@interface RootViewController : UITableViewController {

	NSMutableArray *views;
}

@property(nonatomic, retain) IBOutlet NSMutableArray *views;

@end

Next head over to RootViewController.m and let’s add some code. First off it’s important we include all the view controllers we plan to use as well as synthesize the view object

#import "RootViewController.h"
#import "SubViewControllerOne.h"
#import "SubViewControllerTwo.h"
#import "SubViewControllerThree.h"

@implementation RootViewController
@synthesize views;

...

Next we call the

-(void) awakeFromNib {...}

function and start adding our NSDictionary objects to the view. The NSDictionary will hold to properites:

@title - Title you see at the top of the view
@controller - The controller object

-(void) awakeFromNib
{
	views = [[NSMutableArray alloobjc] init];

	// ============================== CELL 1 ==============================

	//init the view
	SubViewControllerOne *viewOne = [[SubViewControllerOne alloobjc] init];

	// value - key pairing
	[views addObject:[NSDictionary dictionaryWithObjectsAndKeys:
					  @"cell 1",	@"title",
					  viewOne,		@"controller",
					  nil]];

	[viewOne release];

	// ============================== CELL 2 ==============================

	//init the view
	SubViewControllerTwo *viewTwo = [[SubViewControllerTwo alloobjc] init];

	// value - key pairing
	[views addObject:[NSDictionary dictionaryWithObjectsAndKeys:
					  @"cell 2",	@"title",
					  viewTwo,		@"controller",
					  nil]];

	[viewTwo release];

	// ============================== CELL 3 ==============================

	//init the view
	SubViewControllerThree *viewThree = [[SubViewControllerThree alloobjc] init];

	// value - key pairing
	[views addObject:[NSDictionary dictionaryWithObjectsAndKeys:
					  @"cell 3",	@"title",
					  viewThree,	@"controller",
					  nil]];

	[viewThree release];
}

Step 4

Ok cool, we’re getting somewhere. We’ve now loaded our views array with Objects that will load a view as well as create a title, next we have to modify how many rows there will be, what the title is, and what view is loaded.

First start off by stating how many rows are within the table. Locate this function and modify it. All that’s going on is that you’re specifying how many objects are in your view array, which should equal the amount of rows needed.

// Customize the number of rows in the table view.
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    [views count];
}

Next let’s get the titles in place. Find this function and modify it

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloobjc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

	// Configure the cell.
	cell.textLabel.text = [[views objectAtIndex:indexPath.row] objectForKey:@"title"]; 

    return cell;
}

And finally, let’s load in the appropriate view depending on the cell being clicked. Modify this function’

// Override to support row selection in the table view.
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

    // Navigation logic may go here -- for example, create and push another view controller.
	// AnotherViewController *anotherViewController = [[AnotherViewController alloobjc] initWithNibName:@"AnotherView" bundle:nil];
	// [self.navigationController pushViewController:anotherViewController animated:YES];
	// [anotherViewController release];

	UIViewController *targetViewController = [[views objectAtIndex:indexPath.row] objectForKey:@"controller"];
	[self.navigationController pushViewController:targetViewController animated:YES];
}

Step 5

We’re almost there! Just one (well 3) minor things. It would be nice for the user to get back home. So let’s create the functionality for that. You will need to do this in all 3 of your viewController classes.

Open up SubViewControllerOne.m and replace the function as well as create the other function seen below

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
	self.navigationItem.rightBarButtonItem = [[[UIBarButtonItem alloobjc] initWithTitle:
	    @"HOME" style:UIBarButtonItemStylePlain
	    target:self
		action:@selector(goHome:)] autorelease]; //auto released memory

    [super viewDidLoad];
}

-(void)goHome:(id)sender{
	NSLog(@"Go Home!");
	[self.navigationController popToRootViewControllerAnimated:YES];
}

Be sure to do this in all three of your ViewControllers

Closing thoughts

By now you should be ready to compile and build, hopefully everything should be up and running. If it’s not I’ve attached my file here.

cnicollonline

Custom PHP exception handling

Directory Setup

The SQL class

SQL.class.php

Next up the custom exception class

SQL.exception.class.php

Finally the index or testing file.

index.php

Conclusion

Objective-C images

So many ways!

Snippet 1: Getting an image from the web

Snippet 2: Getting an image from the resource folder

UITableView Application Tutorial

Why so simple?

Step 1

Step 2

Step 3

Step 3

Step 4

RootViewController.h

Step 4

Step 5

Closing thoughts

Custom Templates within xCode

A Start to Objective-C

Back to the start

The Code

PHP

Java

Objective-C

Conclusion

Class: File Details released

How it works

Demo

File Names Test 2

File Details

Get files of a specific parameter

movie -> batman

Conclusion

Arrays and Loops with php [Level 2]

Multidimensional Arrays

How this can be used

Conclusion

Arrays and Loops with php [Level 1]

What is an array, what is a loop?

Defining an Array

Working with loops

Phone Validation

The Problem

The Solution

Validate Phone

Creating a Java UI Part 1

File Setup

Building the MainFrame (JFrame)

At this point:

Adding a menu bar

At this point:

Adding menu items and key strokes to the menubar

At this point:

Conclusion