Category Archives: iOS

static background in uitableview

July 11, 2014iOSadmin

ref: http://stackoverflow.com/questions/20481118/background-image-uitableview-changes-when-scroll
http://stackoverflow.com/questions/1960603/iphone-fixed-position-uitableview-background

Make the background on a view layer behind the TableView, not on the TableView itself and then set a clear background on the UITableView

or...

Set the tableview.backgroundView not the backgroundColor

Objective-c’s Addresses and Pass by References

June 18, 2014C/C++/Objective-C, iOSadmin

In CPU, a switch is to describe a bit. A bit represent either 0 or 1. You switch on or off. 1 or 0. Thus, its called a switch.

Eight of these bits make up a byte. Each representation of these bits make up a representation. For example, in a byte, we can have:

00000000 (0)
00000001 (1)
00000010 (2)
00000011 (3)
…etc

So as you can see, if we were to make each representation a number, we can have up to
2^8-1 representations. where 8 is the number of bits.
Currently, the example is binary.

Hexadecimal Numbers is a more complex system than using just binary or decimal and is mainly used when dealing with computers and memory address locations.

By dividing a binary number up into groups of 4 bits, each group or set of 4 digits can now have a possible value of between “0000” (0) and “1111” ( 8+4+2+1 = 15 ) giving a total of 16 different number combinations from 0 to 15. Don’t forget that “0” is also a valid digit.

Thus, a 4 bit binary number is a hex digit. If a system has 32 bits, we can say it has 8 hex digits.

If we were to work with hex, each hex digit would have 16 representations: 0123456789abcdef

In computers, data is represented by an address. An address is a hex representation.

The address of a variable is the location in memory where the value for that variable is stored.
To get the variable’s address, you use the & operator:

#include <stdio.h>

int main(int argc, const char * argv[]) {

int i = 17;

printf("i stores its value at %pn", &i); return 0;

}

Notice the %p token. That’s the token you can replace with a memory address. Build and run
the program. You’ll see something like:

i stores its value at 0xbffff738

its in hex which is calculated like this

1	0xbffff738 is b(16^7) f(16^6) f(16^5)+ f(16^4)+ f(16^3) + 7(16^2) + 3(16^1) + 8(16^0)

Storing Addresses in pointers

Declare a new variable named addressOfI that is a pointer to an int. Assign it the address of
i.

int main(int argc, const char * argv[]) {

int i = 17;

int *addressOfI = &i;

printf("i stores its value at %pn", addressOfI); printf("this function starts at %pn", main);

return 0;

}

Getting the data at the address

int main(int argc, const char * argv[]) {

int i = 17;

int *addressOfI = &i;

printf("i stores its value at %pn", addressOfI);

printf("this function starts at %pn", main);

printf("the int stored at addressOfI is %dn", *addressOfI); return 0;

}

Notice that the asterisk is used two different ways The first is in the declaration where you declare the variable addressOfI to be an int *. That is, it is a pointer to a place where an int can be stored.
The second is where you read the int value that is stored at the address stored in addressOfI. (Pointers are also called references. Thus, using the pointer to read data at the address is sometimes called dereferencing the pointer.)
You can also use the * operator on the left-hand side of an assignment to store data at a particular address:

int main(int argc, const char * argv[]) {

int i = 17;

int *addressOfI = &i;

printf("i stores its value at %pn", addressOfI); *addressOfI = 89;

printf("Now i is %dn", i);

return 0;

}

Passing the Reference…by value

This is known as pass-by-reference. That is, you supply an address (also known as “a reference”), and the function puts the data there.

Changes would take place inside method ONLY if you do not move pointer

If you don’t move the parameter pointer, it would work.

For example:

-(void)test3:(int*)ptr

{

DLOG(@"%p", ptr);

*ptr = 6680; //changes outside because we are passing a reference in

//and having our pointer parameter point to it.

}

main(..)

{

int variable = 897;

DLOG(@"%p", &variable);

//here variable would be 897

[self test3:&variable];

//here variable would be 6680

}

In detail, here’s why its pass by value of the reference:

-(void)test4:(int*)ptr

{

DLOG(@"%p", ptr);

*ptr = 6680; //changes outside because we are passing a reference in

//and having our pointer parameter point to it.

ptr = new int;

*ptr = 243;

DLOG(@"%p", ptr);

DLOG(@"%u", *ptr);

}

int variable = 897;

DLOG(@"%p", &variable);

[self test4:&variable];

DLOG(@"variable is: %u", variable);

If you run it, you’ll see that the ptr inside the function points away to another fresh allocated integer. The outside did not move.

In order to really use a reference (similar to that of C++) to modify the data passed into a method, you need to use a double ptr:

Using pointer of pointer to make changes permanent from inside the method

-(void)ChangePermanently:(int**)dblPtr

{

**dblPtr = *new int(100);

NSLog(@"**dblPtr s: %u", **dblPtr);

NSLog(@"address of the integer is *dblPtr: %p", *dblPtr);

NSLog(@"the address of the pointer pointing to the integer is dblPtr: %p", dblPtr);

}

int * numPtr = new int(2);

NSLog(@"data pointed to by numPtr is *numPtr: %u", *numPtr);

NSLog(@"address pointed to by numPtr is numPtr: %p", numPtr);

[self ChangePermanently:&numPtr];

NSLog(@"data pointed to by numPtr is *numPtr: %u", *numPtr);

NSLog(@"address pointed to by numPtr is numPtr: %p", numPtr);

NSLog(@"the address of the pointer pointing to data numPtr is &numPtr: %p", &numPtr);

Pass by Copy

-(void)test2:(int)passByValue

{

DLOG(@"%p", &passByValue);

passByValue = 43;

}

As you can see, the address of our variable is different outside, than the address of the parameter variable inside test2.

void main()

{

DLOG(@"AppDelegate.m - applicationDidBecomeActive");

int variable = 897;

DLOG(@"%p", &variable);

[self test2:variable];

DLOG(@"variable is: %u", variable);

}

Basically you just copy the value in. The parameter is basically a newly created variable on the stack with a different address, but has the same value as what you pass in.

iPad: add a popover view on Navigation Bar

June 10, 2014iOSadmin

In your app delegate, have property for the current ViewController class:

@class ViewController;

@interface AppDelegate : UIResponder <UIApplicationDelegate>

{

}

@property (strong, nonatomic) UIWindow *window;

@property (strong, nonatomic) ViewController *viewController;

@end

Then in our didFinishLaunchingWithOptions method, we allocate this main ViewController, which we will insert into a newly created UINavigationController variable. We create this new UINavigationController below:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

{

// Override point for customization after application launch

self.viewController = [[ViewController alloc] init];

//1) first, we must create a navigation controller

UINavigationController *navController =

[[UINavigationController alloc] initWithRootViewController:self.viewController];

//2) then, assign it as the root view controller

self.window.rootViewController = navController;

[self.window makeKeyAndVisible];

return YES;

}

This way, our root is this navigation controller. And the navigation controller’s first page is our view controller.

View Controller

ViewController.h

@interface ViewController : UIViewController <ColorPickerDelegate>

{

}

@property (nonatomic, strong) UIPopoverController *popController;

- (void)showPopover:(id)sender;

@end

- (void)viewDidLoad

{

[super viewDidLoad];

// Do any additional setup after loading the view, typically from a nib.

UIBarButtonItem *popoverButton = [[UIBarButtonItem alloc]

initWithBarButtonSystemItem:UIBarButtonSystemItemAdd

target:self

action:@selector(showPopover:)];

self.navigationItem.rightBarButtonItem = popoverButton;

}

- (void)showPopover:(id)sender

{

NSLog(@"show popover ");

if (self.popController.popoverVisible) {

NSLog(@"its visible, let's make it disappear");

[self.popController dismissPopoverAnimated:YES];

return;

}

//create the uiviewcontroller that will sit on top of the popover

UIViewController *contentViewController = [[UIViewController alloc] init];

//background is yellow

contentViewController.view.backgroundColor = [UIColor yellowColor];

UIPopoverController *popController = [[UIPopoverController alloc] initWithContentViewController:contentViewController];

popController.popoverContentSize = CGSizeMake(300.0f, 600.0f);

self.popController = popController;

[self.popController presentPopoverFromBarButtonItem:sender

permittedArrowDirections:UIPopoverArrowDirectionUp

animated:YES];

}

Run the demo and you should have a yellow popover window appear.
Now let’s put a table that has 3 colors to choose from in there instead.

The key is that we create a viewcontroller that extends from UITableViewController. when the table view controller gets a click on a entry, it sends its corresponding UI uiviewcontroller messages via a delegate.

ColorPickerDelegate and ColorPickerTableViewController

@protocol ColorPickerDelegate <NSObject>

@required

-(void)selectedColor:(UIColor *)newColor;

@end

@interface ColorPickerTableViewController : UITableViewController

{}

@property (nonatomic, strong) NSMutableArray *colorNames;

@property (nonatomic, weak) id<ColorPickerDelegate> delegate;

@end

- (id)initWithStyle:(UITableViewStyle)style

{

if ([super initWithStyle:style] != nil) {

//Initialize the array

colorNames = [NSMutableArray array];

//Set up the array of colors.

[colorNames addObject:@"Red"];

[colorNames addObject:@"Green"];

[colorNames addObject:@"Blue"];

//Make row selections persist.

self.clearsSelectionOnViewWillAppear = NO;

}

return self;

}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView

{

// Return the number of sections.

return 1;

}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section

{

// Return the number of rows in the section.

return [colorNames count];

}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

{

static NSString *CellIdentifier = @"Cell";

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

if (cell == nil) {

cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];

}

// Configure the cell...

cell.textLabel.text = [colorNames objectAtIndex:indexPath.row];

return cell;

}

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath

{

NSString *selectedColorName = [colorNames objectAtIndex:indexPath.row];

//Create a variable to hold the color, making its default

//color something annoying and obvious so you can see if

//you've missed a case here.

UIColor *color = [UIColor orangeColor];

//Set the color object based on the selected color name.

if ([selectedColorName isEqualToString:@"Red"]) {

color = [UIColor redColor];

} else if ([selectedColorName isEqualToString:@"Green"]){

color = [UIColor greenColor];

} else if ([selectedColorName isEqualToString:@"Blue"]) {

color = [UIColor blueColor];

}

//Notify the delegate if it exists.

if (delegate != nil) {

[delegate selectedColor:color];

}

Go Back to your ViewController and change/add the following methods:

- (void)showPopover:(id)sender

{

NSLog(@"show popover ");

if (self.popController.popoverVisible) {

NSLog(@"its visible, let's make it disappear");

[self.popController dismissPopoverAnimated:YES];

return;

}

//standard

//UIViewController *contentViewController = [[UIViewController alloc] init];

//background is yellow

// contentViewController.view.backgroundColor = [UIColor yellowColor];

//create the uitableViewcontroller

NSLog(@"its NOT visible, let's make it appear");

ColorPickerTableViewController * contentViewController = [[ColorPickerTableViewController alloc] initWithStyle:UITableViewStylePlain];

contentViewController.delegate = self;

UIPopoverController *popController = [[UIPopoverController alloc] initWithContentViewController:contentViewController];

popController.popoverContentSize = CGSizeMake(300.0f, 600.0f);

self.popController = popController;

[self.popController presentPopoverFromBarButtonItem:sender

permittedArrowDirections:UIPopoverArrowDirectionUp

animated:YES];

}

#pragma mark - ColorPickerDelegate method

-(void)selectedColor:(UIColor *)newColor

{

NSLog(@"got it");

if (self.popController.popoverVisible) {

[self.popController dismissPopoverAnimated:YES];

return;

}

Dismiss TextView or TextField

June 3, 2014iOSadmin

1) When clicking ‘Done’

Put protocol UITextViewDelegate and/or UITextFieldDelegate in there…

@interface RegistrationViewController : UIViewController

UITextViewDelegate, UITextFieldDelegate

set up the variable….make sure you add target for the method UIControlEventEditingDidEndOnExit:

//insert uitextfield

UITextField * nameTextField = [[UITextField alloc] initWithFrame:CGRectMake(10.0f, 128.0f, 300.0f, 64.0f)];

nameTextField.tag = UITEXTFIELD_NAME;

[nameTextField setText:@"test"];

nameTextField.borderStyle = UITextBorderStyleRoundedRect;

nameTextField.textColor = [UIColor blackColor];

nameTextField.delegate = self;

[nameTextField addTarget:self action:@selector(textFieldDoneEditing:) forControlEvents:UIControlEventEditingDidEndOnExit ];

nameTextField.font = [UIFont systemFontOfSize:20.0 ];

nameTextField.autocorrectionType = UITextAutocorrectionTypeNo;

nameTextField.keyboardType = UIKeyboardTypeDefault;

nameTextField.returnKeyType = UIReturnKeyDone;

nameTextField.clearButtonMode = UITextFieldViewModeWhileEditing;

[self.view addSubview:nameTextField];

[nameTextField release];

Implement the method:

#pragma mark - responds to Done button pushed on keyboard

- (BOOL)textFieldDoneEditing:(UITextField *)textField

{

DLOG(@"textFieldDoneEditing");

[textField resignFirstResponder];

return YES;

}

2) To dismiss Keyboard on tap of the View:

view controller’s header:

1	@property (nonatomic, assign) id currentResponder;

view controller’s viewDidLoad:

//add tap gesture recognizer for our self.view

UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(resignOnTap:)];

[singleTap setNumberOfTapsRequired:1];

[singleTap setNumberOfTouchesRequired:1];

[self.view addGestureRecognizer:singleTap];

[singleTap release];

view controller:

//our responder takes on whatever textfield is being edited

- (void)textFieldDidBeginEditing:(UITextField *)textField {

DLOG(@"textFieldDidBeginEditing");

self.currentResponder = textField;

}

Finally, follow this link http://rickytsao.com/?p=1299
in order to cancel keyboard by tapping anywhere outside of it.

Set background image to your app

April 21, 2014C/C++/Objective-C, iOSbackground imageadmin

1	self.view.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"wood-ipad-wp.jpg"]];

Apply gradient to UIView

April 15, 2014iOSadmin

Using gradient from one color ro another

UIView* v = [[UIView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 50.0f)];

CAGradientLayer *gradient = [CAGradientLayer layer];

gradient.frame = v.bounds;

gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor whiteColor] CGColor], (id)[[UIColor blackColor] CGColor], nil];

[v.layer insertSublayer:gradient atIndex:0];

Using a sliver of gradient as background

1	weatherView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:gradientImageName]];

Convert hex to UIColor

April 15, 2014iOShex, uicoloradmin

http://scratch.johnnypez.com/hex-to-uicolor/

love the site! 😀

UIViewControllers talk to each other through delegates

April 13, 2014C/C++/Objective-C, iOSdelegate, MVCadmin

The controller manages the communication between the view and the model. It takes the data from the model and communicates it to the view for display.

In the same vein, the controller also takes the changed data (due to user interaction or something else) and communicates it back to the model.

Say SmoothiesViewController and EditRecipeViewController need to communicate with each other.

Declare Protocol and use delegate variable

First declare protocol like this:

EditRecipeViewController.h

@class EditRecipeViewController;

* The delegate for EditRecipeViewController.

@protocol EditRecipeDelegate <NSObject>

- (void)editRecipeDidSave:(EditRecipeViewController*)controller;

@optional

- (void)editRecipeDidCancel:(EditRecipeViewController*)controller;

@end

* The screen that lets you add a new recipe or edit an existing recipe.

@interface EditRecipeViewController : UIViewController

UINavigationControllerDelegate,

UIImagePickerControllerDelegate

{

UIImagePickerController* imagePicker;

}

//@property blah blah

// Our delegate object

@property (nonatomic, assign) id<EditRecipeDelegate> delegate;

//methods blah blah

@end

Once your protocol is set. You declare a delegate:

1	@property (nonatomic, assign) id<EditRecipeDelegate> delegate;

Whoever conforms to that delegate MUST implement the methods in that protocol. Because this class with the delegate, will be calling these methods, and the classes that conform to this protocol, must execute these methods.

In EditRecipeViewController.m it is used like this:

- (IBAction)cancel

{

// Notify the delegate if it implements the optional method

if ([self.delegate respondsToSelector:@selector(editRecipeDidCancel:)])

[self.delegate editRecipeDidCancel:self];

[self.parentViewController dismissModalViewControllerAnimated:YES];

}

First, we check to see if our delegate responds to such method. If it does, then call it. This means that ALLLLL the UIViewControllers that conforms to our EditRecipeDelegate protocol must execute their method of editRecipeDidCancel.

UIViewController conforms to protocol

Say SmoothiesViewController conforms to our EditRecipeDelegate

#import "EditRecipeViewController.h"

@class DataModel;

* This is the view controller that lists all smoothie recipes.

@interface SmoothiesViewController : UITableViewController <EditRecipeDelegate>

{

}

// We have a weak reference to the shared Data Model object

@property (nonatomic, assign) IBOutlet DataModel* dataModel;

- (IBAction)addRecipe;

@end

This means in our SmoothiesViewController.m file, we must implement the required protocol methods:

#pragma mark -

#pragma mark EditRecipeDelegate

- (void)editRecipeDidSave:(EditRecipeViewController*)controller

{

// Create a new Recipe object with the values from the controller

// and add it to the data model

Recipe* recipe = [[Recipe alloc] init];

recipe.name = controller.name;

recipe.instructions = controller.instructions;

recipe.image = controller.image;

[self.dataModel addRecipe:recipe];

[recipe release];

// Refresh the table

[self.tableView reloadData];

}

Data Model (mvc)

April 13, 2014C/C++/Objective-C, iOSMVCadmin

You have your business logic in Recipes:

Recipe.h:

#import "Recipe.h"

@implementation Recipe

@synthesize recipeId, name, instructions, image;

- (void)dealloc

{

[name release];

[instructions release];

[image release];

[super dealloc];

}

- (NSComparisonResult)compareName:(Recipe*)recipe

{

return [self.name localizedCaseInsensitiveCompare:recipe.name];

}

- (NSString*)description

{

return [NSString stringWithFormat:@"%@ ID: %d, Name: %@", [super description], self.recipeId, self.name];

}

@end

Recipe.m

#import "Recipe.h"

@implementation Recipe

@synthesize recipeId, name, instructions, image;

- (void)dealloc

{

[name release];

[instructions release];

[image release];

[super dealloc];

}

- (NSComparisonResult)compareName:(Recipe*)recipe

{

return [self.name localizedCaseInsensitiveCompare:recipe.name];

}

- (NSString*)description

{

return [NSString stringWithFormat:@"%@ ID: %d, Name: %@", [super description], self.recipeId, self.name];

}

@end

We put our business logic into a data structure. Implement some methods that manipulate this business logic. This is called our data model.

DataModel.h:

@class Recipe;

* Notification that is sent when the list of recipes is changed.

extern NSString* const RecipesChangedNotification;

* Notification that is sent when the list of favorites is changed.

extern NSString* const FavoritesChangedNotification;

* The top-level data model object for our app.

@interface DataModel : NSObject

{

int nextId;

NSMutableArray* sortedFavorites;

}

// The favorites as a list of Recipe objects, sorted by name

@property (nonatomic, readonly, retain) NSArray* sortedFavorites;

// Returns how many recipes are in the list.

- (int)recipeCount;

// Returns the Recipe object at the specified position in the list.

- (Recipe*)recipeAtIndex:(int)index;

// Adds a Recipe to the end of the list.

- (void)addRecipe:(Recipe*)recipe;

// Deletes a Recipe object from the list.

- (void)removeRecipeAtIndex:(int)index;

// Call this to send out a notification that the Recipe has changed

- (void)didChangeRecipe:(Recipe*)recipe;

// Returns the number of favorites.

- (int)favoritesCount;

// Determines whether a Recipe is in the list of favorites.

- (BOOL)isFavorite:(Recipe*)recipe;

// Adds a Recipe to the favorites.

- (void)addToFavorites:(Recipe*)recipe;

// Removes a Recipe from the favorites.

- (void)removeFromFavorites:(Recipe*)recipe;

@end

DataModel.m – this is where we manipulate our business logic into a data structure and implement wrapper methods such as add, delete, search, indexOf…etc.

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#import "DataModel.h"

#import "Recipe.h"

static NSString* const FAVORITES_KEY = @"Favorites2";

NSString* const RecipesChangedNotification = @"Smoothies-RecipesChanged";

NSString* const FavoritesChangedNotification = @"Smoothies-FavoritesChanged";

@interface DataModel ()

// The list of Recipe objects

@property (nonatomic, retain) NSMutableArray* recipes;

// The list of favorite Recipe objects

@property (nonatomic, retain) NSMutableArray* favorites;

// We re-declare the property here to make it read-write instead of read-only

@property (nonatomic, retain) NSArray* sortedFavorites;

- (void)loadRecipes;

- (Recipe*)findRecipeWithId:(int)recipeId;

- (void)loadFavorites;

- (void)saveFavorites;

@end

@implementation DataModel

@synthesize recipes, favorites, sortedFavorites;

- (id)init

{

if ((self = [super init]))

{

[self loadRecipes];

[self loadFavorites];

}

return self;

}

- (void)dealloc

{

[recipes release];

[favorites release];

[sortedFavorites release];

[super dealloc];

}

- (void)loadRecipes

{

// Create the recipe list object

recipes = [[NSMutableArray arrayWithCapacity:10] retain];

// And add a few recipes to it

Recipe* recipe = [[Recipe alloc] init];

recipe.recipeId = 1;

recipe.name = @"Banana Shake";

recipe.instructions = @"1 frozen bananan1 fresh bananandollop of coconut milknhalf a glass of waternoptional: pinch of vanilla";

recipe.image = [UIImage imageNamed:@"Banana Shake.png"];

[recipes addObject:recipe];

[recipe release];

recipe = [[Recipe alloc] init];

recipe.recipeId = 2;

recipe.name = @"Green Smoothie";

recipe.instructions = @"2 bananasnhalf a glass of orange juicenhandful of fresh spinach";

recipe.image = [UIImage imageNamed:@"Green Smoothie.png"];

[recipes addObject:recipe];

[recipe release];

recipe = [[Recipe alloc] init];

recipe.recipeId = 3;

recipe.name = @"Raspberry-Blueberry";

recipe.instructions = @"1 bananan125 gr frozen raspberriesn125 gr frozen blueberriesn1 glass soy milknhalf a glass of water";

recipe.image = [UIImage imageNamed:@"Raspberry-Blueberry.png"];

[recipes addObject:recipe];

[recipe release];

// When the user adds a new recipe, this is the ID it will get. It is

// hardcoded here, but if we were actually loading the recipes from a

// file, we would determine what the highest recipeId was and then set

// nextId one higher.

nextId = 4;

}

- (int)recipeCount

{

return self.recipes.count;

}

- (Recipe*)recipeAtIndex:(int)index

{

return [self.recipes objectAtIndex:index];

}

- (void)addRecipe:(Recipe*)recipe

{

recipe.recipeId = nextId++;

[self.recipes addObject:recipe];

}

- (void)removeRecipeAtIndex:(int)index

{

// Also remove the recipe from the list of favorites

Recipe* recipe = [self recipeAtIndex:index];

[self removeFromFavorites:recipe];

[self.recipes removeObjectAtIndex:index];

}

- (void)didChangeRecipe:(Recipe*)recipe

{

[[NSNotificationCenter defaultCenter] postNotificationName:RecipesChangedNotification object:self];

// If the name of the recipe was changed, the sort order of the favorites

// list may be wrong, so we reload the list of favorites as well.

self.sortedFavorites = nil;

[[NSNotificationCenter defaultCenter] postNotificationName:FavoritesChangedNotification object:self];

}

- (Recipe*)findRecipeWithId:(int)recipeId

{

for (Recipe* recipe in self.recipes)

{

if (recipe.recipeId == recipeId)

return recipe;

}

return nil;

}

- (void)loadFavorites

{

// Create the favorites list object

NSArray* array = [[NSUserDefaults standardUserDefaults] objectForKey:FAVORITES_KEY];

self.favorites = [NSMutableArray arrayWithCapacity:array.count];

for (NSNumber* number in array)

{

int recipeId = [number intValue];

if ([self findRecipeWithId:recipeId] != nil)

[self.favorites addObject:number];

}

- (void)saveFavorites

{

[[NSUserDefaults standardUserDefaults] setObject:self.favorites forKey:FAVORITES_KEY];

[[NSUserDefaults standardUserDefaults] synchronize];

}

- (int)favoritesCount

{

return self.sortedFavorites.count;

}

- (NSArray*)sortedFavorites

{

if (sortedFavorites == nil) // lazy loading

{

// Add the Recipe objects to a new list

self.sortedFavorites = [NSMutableArray arrayWithCapacity:favorites.count];

for (NSNumber* number in self.favorites)

{

int recipeId = [number intValue];

Recipe* recipe = [self findRecipeWithId:recipeId];

if (recipe != nil)

{

[sortedFavorites addObject:recipe];

}

// Sort the list by last name

[sortedFavorites sortUsingSelector:@selector(compareName:)];

}

return sortedFavorites;

}

- (BOOL)isFavorite:(Recipe*)recipe

{

return [self.favorites containsObject:[NSNumber numberWithInt:recipe.recipeId]];

}

- (void)addToFavorites:(Recipe*)recipe

{

// Add the recipe's ID to the favorites list

[self.favorites addObject:[NSNumber numberWithInt:recipe.recipeId]];

// Save the favorites to NSUserDefaults

[self saveFavorites];

// We release the old sorted list and set it to nil. The next time anyone

// asks for it, it will be re-created from scratch.

self.sortedFavorites = nil;

// Let any listeners know the list of favorites has changed

[[NSNotificationCenter defaultCenter] postNotificationName:FavoritesChangedNotification object:self];

}

- (void)removeFromFavorites:(Recipe*)recipe

{

[self.favorites removeObject:[NSNumber numberWithInt:recipe.recipeId]];

[self saveFavorites];

self.sortedFavorites = nil;

[[NSNotificationCenter defaultCenter] postNotificationName:FavoritesChangedNotification object:self];

}

@end

Firing events through Notifications

Model — fire events –> Controller

Our Data Model communicates with other UIViewController by firing Notifications like this in our DataModel.m:

- (void)didChangeRecipe:(Recipe*)recipe

{

[[NSNotificationCenter defaultCenter] postNotificationName:RecipesChangedNotification object:self];

// If the name of the recipe was changed, the sort order of the favorites

// list may be wrong, so we reload the list of favorites as well.

self.sortedFavorites = nil;

[[NSNotificationCenter defaultCenter] postNotificationName:FavoritesChangedNotification object:self];

}

Thus, from our DataModel, we fire a notification called FavoritesChangedNotification or RecipesChangedNotification, which are NSStrings defined in our DataModel.h like this:

* Notification that is sent when the list of recipes is changed.

extern NSString* const RecipesChangedNotification;

* Notification that is sent when the list of favorites is changed.

extern NSString* const FavoritesChangedNotification;

Whoever is listening for these notifications will execute their @selector method code.

UIViewControllers listening for Notifications

In our UIViewController we set it up like this:

#import "EditRecipeViewController.h"

@class DataModel;

* This is the view controller that lists all smoothie recipes.

@interface SmoothiesViewController : UITableViewController <EditRecipeDelegate>

{

}

// We have a strong reference to the shared Data Model object

@property (nonatomic, retain) IBOutlet DataModel* dataModel;

- (IBAction)addRecipe;

@end

You can see we have a strong reference to the shared Data Model.

In short: the owner of an object will retain that object and is ultimately responsible for releasing it when it no longer uses that object. When an object is retained, this is called a strong reference. SmoothieViewController has a strong reference to DataModel, because it created that object. SmoothieViewController owns the DataModel for as long as it is alive (which is until this app exits) and will release it in its dealloc.

Whenever we have other UIViewControllers that updates our Data Model like RecipeDetailsViewController, we make it a so-called weak reference like this:

1 2	// We have a weak reference to the shared Data Model object @property (nonatomic, assign) DataModel* dataModel;

note:
RecipeDetailsViewController does not own the object and therefore does not retain it. Because RecipeDetailsViewController is guaranteed that the DataModel instance will be around for at least as long as it is (i.e. until the user exits the app), it has no need to retain it.

In general, if you pass along pointers to objects you should make them weak references (using the “assign” property semantics), to signify that the object you are giving it to does not assume ownership. You only use “retain” or “copy” when you are not guaranteed that the object may stick around, in which case you become responsible for releasing it when the time comes.
end note.

We then have a UITableViewController displaying the data in our dataModel variable.
What happens if our dataModel changes data? Then in our DataModel.m, these methods will fire Notification like this:

1	[[NSNotificationCenter defaultCenter] postNotificationName:FavoritesChangedNotification object:self];

So Data Models post or fire these notifications. We have our UIViewController’s listen for them.

Our UIViewControllers listen up for notifications through [NSNotificationCenter defaultCenter]’s addObserver:

First, make sure the notification strings are set from whichever data models are firing them. In our case its in DataModel.h:

1 2	NSString* const RecipesChangedNotification = @"Smoothies-RecipesChanged"; NSString* const FavoritesChangedNotification = @"Smoothies-FavoritesChanged";

then in your UIViewController’s m file, we set up NSNotificationCenter’s addObservewr:

- (void)viewDidLoad

{

//....etc

// Start listening for notifications

[[NSNotificationCenter defaultCenter] addObserver:self

selector:@selector(recipesChanged:)

name:RecipesChangedNotification

object:nil];

}

Once we set up the observer, we implement the method that will execute whenever we receive such a notification in our UIViewController:

- (void)recipesChanged:(NSNotification*)notification

{

[self.tableView reloadData];

}

What this means is that our UIViewController basically are listening for notifications from our data models. Once there is a notification, we update our view (in our case UITableViewControlelr) accordingly.

Also, remember to remove those observers in your dealloc:

- (void)dealloc

{

// Stop listening for notifications

[[NSNotificationCenter defaultCenter] removeObserver:self

name:RecipesChangedNotification

object:nil];

[super dealloc];

}

Controller updates Model

Controller — updates –> Model

Now in your ViewControllers we also update our DataModel through using the self.dataModel removeRecipeAtIndex method. Our users manipulate our UITableView, and the interaction calls our commitEditingStyle:forRowAtIndexPath, which then manipulates our weak reference dataModel variable. That is how Controllers update our Models.

- (void)tableView:(UITableView*)theTableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath*)indexPath

{

// Remove the Recipe from our data model

[self.dataModel removeRecipeAtIndex:indexPath.row];

// Remove the row from the table with an animation

[theTableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];

}

Working with directories and files in Sandbox

April 10, 2014C/C++/Objective-C, iOSadmin

Home Directory

1	DLOG(@"HOME > %@", NSHomeDirectory());

Naturally, you’d have the documents folder in your home directory as well:

1	NSString * homeDir = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];

which will give you something like this:

homeDir is: /var/mobile/Applications/DF2ACE23-C3D0-444B-9D25-7E56F102595A/Documents

This is where you save your files in your sandbox.

Writing text to a txt file

First, you have to get the name of your path + file. Something like this:

/var/mobile/Applications/DF2ACE23-C3D0-444B-9D25-7E56F102595A/Documents/test.txt

We do this by appending our file name to the home directory. In our case, let’s say self.filename is test.txt:

1	filepath = [self.homeDir stringByAppendingPathComponent:self.filename];

Then you use that path string and use method writeToFile: to write contents to that file:

1	BOOL ok = [textToWrite writeToFile:filepath atomically:YES encoding:NSUnicodeStringEncoding error:&err];

full method:

-(void)WriteToStringFile:(NSMutableString *)textToWrite

{

filepath = [[NSString alloc] init];

NSError *err;

filepath = [self.GetDocumentDirectory stringByAppendingPathComponent:self.filename];

DLOG(@"file path is: %@", filepath);

BOOL ok = [textToWrite writeToFile:filepath atomically:YES encoding:NSUnicodeStringEncoding error:&err];

if (!ok)

{

NSLog(@"Error writing file at %@n%@",

filepath, [err localizedFailureReason]);

}

[filepath release];

}

Reading text from file in sandbox

-(NSString *) readFromFile

{

filepath = [[NSString alloc] init];

NSError *error;

NSString * title = @"uh oh";

filepath = [self.GetDocumentDirectory stringByAppendingPathComponent:self.filename];

DLOG(@"file path is: %@", filepath);

NSString * txtInFile = [[NSString alloc] initWithContentsOfFile:filepath encoding:NSUnicodeStringEncoding error:&error];

if(!txtInFile)

{

UIAlertView *tellErr = [[UIAlertView alloc] initWithTitle:title message:@"Unable to get text from file." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];

[tellErr show];

}

return txtInFile;

}

Writing image to your sandbox

We first create an image. Make sure the image resource exists.
Then we give it a string name and then make sure homeDir is same as we’ve displayed above. Plug in and use like so:

1 2	UIImage * myImage = [UIImage imageNamed:@"refresh.png"]; [myFile saveImage:myImage withFileName:@"refresh" ofType:@"png" inDirectory: myFile.homeDir];

where myFile.homeDir is: /var/mobile/Applications/DF2ACE23-C3D0-444B-9D25-7E56F102595A/Documents

-(void) saveImage:(UIImage *)image

withFileName:(NSString *)imageName

ofType:(NSString *)extension

inDirectory:(NSString *)directoryPath

{

NSString * fullImageName = [NSString stringWithFormat:@"%@.%@", imageName, @"png"];

NSString * fullDirectoryPath = [directoryPath stringByAppendingPathComponent:fullImageName];

if ([[extension lowercaseString] isEqualToString:@"png"])

{

if([UIImagePNGRepresentation(image) writeToFile:fullDirectoryPath options:NSAtomicWrite error:nil])

{

DLOG(@"png written successfully");

}

else if ([[extension lowercaseString] isEqualToString:@"jpg"] || [[extension lowercaseString] isEqualToString:@"jpeg"])

{

if([UIImageJPEGRepresentation(image, 1.0) writeToFile:[directoryPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.%@", imageName, @"jpg"]] options:NSAtomicWrite error:nil])

{

DLOG(@"jpeg written successfully");

}

else

{

DLOG(@"Image Save FailednExtension: (%@) is not recognized, use (PNG/JPG)", extension);

}

Reading images from your sandbox

Used like this:

1	UIImage * tmp = [myFile loadImage:@"refresh.png"];

Implementation:

-(UIImage*)loadImage:(NSString*)imageName

{

NSString * pathComponent = [NSString stringWithFormat:@"Documents/%@", imageName];

NSString *imagePath = [NSHomeDirectory() stringByAppendingPathComponent:pathComponent];

return [UIImage imageWithContentsOfFile:imagePath];

}